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package javax.net.ssl;

import java.nio.ByteBuffer;
import java.nio.ReadOnlyBufferException;
import java.util.List;
import java.util.function.BiFunction;


A class which enables secure communications using protocols such as
the Secure Sockets Layer (SSL) or
 IETF RFC 2246 "Transport
Layer Security" (TLS)  protocols, but is transport independent.

The secure communications modes include: 

     
 Integrity Protection.  SSL/TLS/DTLS protects against
     modification of messages by an active wiretapper.
     
 Authentication.  In most modes, SSL/TLS/DTLS provides
     peer authentication.  Servers are usually authenticated, and
     clients may be authenticated as requested by servers.
     
 Confidentiality (Privacy Protection).  In most
     modes, SSL/TLS/DTLS encrypts data being sent between client and
     server.  This protects the confidentiality of data, so that
     passive wiretappers won't see sensitive data such as financial
     information or personal information of many kinds.
     
These kinds of protection are specified by a "cipher suite", which
is a combination of cryptographic algorithms used by a given SSL
connection.  During the negotiation process, the two endpoints must
agree on a cipher suite that is available in both environments.  If
there is no such suite in common, no SSL connection can be
established, and no data can be exchanged.
 The cipher suite used is established by a negotiation process called "handshaking". The goal of this process is to create or rejoin a "session", which may protect many connections over time. After handshaking has completed, you can access session attributes by using the getSession() method. 
 The SSLSocket class provides much of the same security functionality, but all of the inbound and outbound data is automatically transported using the underlying Socket, which by design uses a blocking model. While this is appropriate for many applications, this model does not provide the scalability required by large servers. 
 The primary distinction of an SSLEngine is that it operates on inbound and outbound byte streams, independent of the transport mechanism. It is the responsibility of the SSLEngine user to arrange for reliable I/O transport to the peer. By separating the SSL/TLS/DTLS abstraction from the I/O transport mechanism, the SSLEngine can be used for a wide variety of I/O types, such as 
non-blocking I/O (polling), 
selectable non-blocking I/O, Socket and the traditional Input/OutputStreams, local 
ByteBuffers or byte arrays,  future asynchronous
I/O models , and so on.
 At a high level, the SSLEngine appears thus: 
                  app data
               |           ^
               |     |     |
               v     |     |
          +----+-----|-----+----+
          |          |          |
          |       SSL|Engine    |
  wrap()  |          |          |  unwrap()
          | OUTBOUND | INBOUND  |
          |          |          |
          +----+-----|-----+----+
               |     |     ^
               |     |     |
               v           |
                  net data

Application data (also known as plaintext or cleartext) is data which
is produced or consumed by an application.  Its counterpart is
network data, which consists of either handshaking and/or ciphertext
(encrypted) data, and destined to be transported via an I/O
mechanism.  Inbound data is data which has been received from the
peer, and outbound data is destined for the peer.
 (In the context of an SSLEngine, the term "handshake data" is taken to mean any data exchanged to establish and control a secure connection. Handshake data includes the SSL/TLS/DTLS messages "alert", "change_cipher_spec," and "handshake.") 
 There are five distinct phases to an SSLEngine. 

    
 Creation - The SSLEngine has been created and initialized, but has not yet been used. During this phase, an application may set any SSLEngine-specific settings (enabled cipher suites, whether the SSLEngine should handshake in client or server mode, and so on). Once handshaking has begun, though, any new settings (except client/server mode, see below) will be used for the next handshake. 
 Initial Handshake - The initial handshake is a procedure by
    which the two peers exchange communication parameters until an
    SSLSession is established.  Application data can not be sent during
    this phase.
    
 Application Data - Once the communication parameters have been established and the handshake is complete, application data may flow through the SSLEngine. Outbound application messages are encrypted and integrity protected, and inbound messages reverse the process. 
 Rehandshaking - Either side may request a renegotiation of the session at any time during the Application Data phase. New handshaking data can be intermixed among the application data. Before starting the rehandshake phase, the application may reset the SSL/TLS/DTLS communication parameters such as the list of enabled ciphersuites and whether to use client authentication, but can not change between client/server modes. As before, once handshaking has begun, any new SSLEngine configuration settings will not be used until the next handshake. 
 Closure - When the connection is no longer needed, the client and the server applications should each close both sides of their respective connections. For SSLEngine objects, an application should call closeOutbound() and send any remaining messages to the peer. Likewise, an application should receive any remaining messages from the peer before calling closeInbound(). The underlying transport mechanism can then be closed after both sides of the SSLEngine have been closed. If the connection is not closed in an orderly manner (for example closeInbound() is called before the peer's write closure notification has been received), exceptions will be raised to indicate that an error has occurred. Once an engine is closed, it is not reusable: a new SSLEngine must be created. 
 An SSLEngine is created by calling SSLContext.createSSLEngine() from an initialized SSLContext. Any configuration parameters should be set before making the first call to wrap(), unwrap(), or beginHandshake(). These methods all trigger the initial handshake. 
 Data moves through the engine by calling wrap() or 
unwrap() on outbound or inbound data, respectively. Depending on the state of the SSLEngine, a wrap() call may consume application data from the source buffer and may produce network data in the destination buffer. The outbound data may contain application and/or handshake data. A call to unwrap() will examine the source buffer and may advance the handshake if the data is handshaking information, or may place application data in the destination buffer if the data is application. The state of the underlying SSL/TLS/DTLS algorithm will determine when data is consumed and produced. 
 Calls to wrap() and unwrap() return an SSLEngineResult which indicates the status of the operation, and (optionally) how to interact with the engine to make progress. 
 The SSLEngine produces/consumes complete SSL/TLS/DTLS packets only, and does not store application data internally between calls to wrap()/unwrap(). Thus input and output ByteBuffers must be sized appropriately to hold the maximum record that can be produced. Calls to SSLSession.getPacketBufferSize() and SSLSession.getApplicationBufferSize() should be used to determine the appropriate buffer sizes. The size of the outbound application data buffer generally does not matter. If buffer conditions do not allow for the proper consumption/production of data, the application must determine (via SSLEngineResult) and correct the problem, and then try the call again. 
 For example, unwrap() will return a Status.BUFFER_OVERFLOW result if the engine determines that there is not enough destination buffer space available. Applications should call SSLSession.getApplicationBufferSize() and compare that value with the space available in the destination buffer, enlarging the buffer if necessary. Similarly, if unwrap() were to return a Status.BUFFER_UNDERFLOW, the application should call SSLSession.getPacketBufferSize() to ensure that the source buffer has enough room to hold a record (enlarging if necessary), and then obtain more inbound data. 

  SSLEngineResult r = engine.unwrap(src, dst);
  switch (r.getStatus()) {
  BUFFER_OVERFLOW:
      // Could attempt to drain the dst buffer of any already obtained
      // data, but we'll just increase it to the size needed.
      int appSize = engine.getSession().getApplicationBufferSize();
      ByteBuffer b = ByteBuffer.allocate(appSize + dst.position());
      dst.flip();
      b.put(dst);
      dst = b;
      // retry the operation.
      break;
  BUFFER_UNDERFLOW:
      int netSize = engine.getSession().getPacketBufferSize();
      // Resize buffer if needed.
      if (netSize > src.capacity()) {
          ByteBuffer b = ByteBuffer.allocate(netSize);
          src.flip();
          b.put(src);
          src = b;
      }
      // Obtain more inbound network data for src,
      // then retry the operation.
      break;
  // other cases: CLOSED, OK.
  }

 Unlike SSLSocket, all methods of SSLEngine are non-blocking. SSLEngine implementations may require the results of tasks that may take an extended period of time to complete, or may even block. For example, a TrustManager may need to connect to a remote certificate validation service, or a KeyManager might need to prompt a user to determine which certificate to use as part of client authentication. Additionally, creating cryptographic signatures and verifying them can be slow, seemingly blocking. 
 For any operation which may potentially block, the SSLEngine will create a Runnable delegated task. When SSLEngineResult indicates that a delegated task result is needed, the application must call getDelegatedTask() to obtain an outstanding delegated task and call its run() method (possibly using a different thread depending on the compute strategy). The application should continue obtaining delegated tasks until no more exist, and try the original operation again. 
 At the end of a communication session, applications should properly close the SSL/TLS/DTLS link. The SSL/TLS/DTLS protocols have closure handshake messages, and these messages should be communicated to the peer before releasing the SSLEngine and closing the underlying transport mechanism. A close can be initiated by one of: an SSLException, an inbound closure handshake message, or one of the close methods. In all cases, closure handshake messages are generated by the engine, and wrap() should be repeatedly called until the resulting SSLEngineResult's status returns "CLOSED", or isOutboundDone() returns true. All data obtained from the wrap() method should be sent to the peer. 
 closeOutbound() is used to signal the engine that the application will not be sending any more data. 
 A peer will signal its intent to close by sending its own closure handshake message. After this message has been received and processed by the local SSLEngine's unwrap() call, the application can detect the close by calling unwrap() and looking for a SSLEngineResult with status "CLOSED", or if isInboundDone() returns true. If for some reason the peer closes the communication link without sending the proper SSL/TLS/DTLS closure message, the application can detect the end-of-stream and can signal the engine via closeInbound() that there will no more inbound messages to process. Some applications might choose to require orderly shutdown messages from a peer, in which case they can check that the closure was generated by a handshake message and not by an end-of-stream condition. 

There are two groups of cipher suites which you will need to know
about when managing cipher suites:

     
 Supported cipher suites: all the suites which are supported by the SSL implementation. This list is reported using getSupportedCipherSuites(). 
 Enabled cipher suites, which may be fewer than the full set of supported suites. This group is set using the setEnabledCipherSuites(String[]) method, and queried using the getEnabledCipherSuites() method. Initially, a default set of cipher suites will be enabled on a new engine that represents the minimum suggested configuration. 
Implementation defaults require that only cipher suites which
authenticate servers and provide confidentiality be enabled by
default.  Only if both sides explicitly agree to unauthenticated
and/or non-private (unencrypted) communications will such a
cipher suite be selected.
 Each SSL/TLS/DTLS connection must have one client and one server, thus each endpoint must decide which role to assume. This choice determines who begins the handshaking process as well as which type of messages should be sent by each party. The method setUseClientMode(boolean) configures the mode. Note that the default mode for a new SSLEngine is provider-specific. Applications should set the mode explicitly before invoking other methods of the SSLEngine. Once the initial handshaking has started, an SSLEngine can not switch between client and server modes, even when performing renegotiations. 
 The ApplicationProtocol String values returned by the methods in this class are in the network byte representation sent by the peer. The bytes could be directly compared, or converted to its Unicode {code String} format for comparison. 
 String networkString = sslEngine.getHandshakeApplicationProtocol(); byte[] bytes = networkString.getBytes(StandardCharsets.ISO_8859_1); // // Match using bytes: // // "http/1.1" (7-bit ASCII values same in UTF-8) // MEETEI MAYEK LETTERS "HUK UN I" (Unicode 0xabcd->0xabcf) // String HTTP1_1 = "http/1.1"; byte[] HTTP1_1_BYTES = HTTP1_1.getBytes(StandardCharsets.UTF_8); byte[] HUK_UN_I_BYTES = new byte[] { (byte) 0xab, (byte) 0xcd, (byte) 0xab, (byte) 0xce, (byte) 0xab, (byte) 0xcf}; if ((Arrays.compare(bytes, HTTP1_1_BYTES) == 0 ) || Arrays.compare(bytes, HUK_UN_I_BYTES) == 0) { ... } // // Alternatively match using string.equals() if we know the ALPN value // was encoded from a String using a certain character set, // for example UTF-8. The ALPN value must first be properly // decoded to a Unicode String before use. // String unicodeString = new String(bytes, StandardCharsets.UTF_8); if (unicodeString.equals(HTTP1_1) || unicodeString.equals("\u005cuabcd\u005cuabce\u005cuabcf")) { ... } 
 Applications might choose to process delegated tasks in different threads. When an SSLEngine is created, the current AccessControlContext is saved. All future delegated tasks will be processed using this context: that is, all access control decisions will be made using the context captured at engine creation. 

Concurrency Notes:
There are two concurrency issues to be aware of:

     
The wrap() and unwrap() methods may execute concurrently of each other. 
 The SSL/TLS/DTLS protocols employ ordered packets.
     Applications must take care to ensure that generated packets
     are delivered in sequence.  If packets arrive
     out-of-order, unexpected or fatal results may occur.

     For example:
     
             synchronized (outboundLock) {
                 sslEngine.wrap(src, dst);
                 outboundQueue.put(dst);
             }
     
 As a corollary, two threads must not attempt to call the same method (either wrap() or unwrap()) concurrently, because there is no way to guarantee the eventual packet ordering. 
Author:
Brad R. Wetmore
See Also:
SSLContext
SSLSocket
SSLServerSocket
SSLSession
Socket
Since:
1.5/**
 * A class which enables secure communications using protocols such as
 * the Secure Sockets Layer (SSL) or
 * <A HREF="http://www.ietf.org/rfc/rfc2246.txt"> IETF RFC 2246 "Transport
 * Layer Security" (TLS) </A> protocols, but is transport independent.
 * <P>
 * The secure communications modes include: <UL>
 *
 *      <LI> <em>Integrity Protection</em>.  SSL/TLS/DTLS protects against
 *      modification of messages by an active wiretapper.
 *
 *      <LI> <em>Authentication</em>.  In most modes, SSL/TLS/DTLS provides
 *      peer authentication.  Servers are usually authenticated, and
 *      clients may be authenticated as requested by servers.
 *
 *      <LI> <em>Confidentiality (Privacy Protection)</em>.  In most
 *      modes, SSL/TLS/DTLS encrypts data being sent between client and
 *      server.  This protects the confidentiality of data, so that
 *      passive wiretappers won't see sensitive data such as financial
 *      information or personal information of many kinds.
 *
 *      </UL>
 *
 * These kinds of protection are specified by a "cipher suite", which
 * is a combination of cryptographic algorithms used by a given SSL
 * connection.  During the negotiation process, the two endpoints must
 * agree on a cipher suite that is available in both environments.  If
 * there is no such suite in common, no SSL connection can be
 * established, and no data can be exchanged.
 * <P>
 * The cipher suite used is established by a negotiation process called
 * "handshaking".  The goal of this process is to create or rejoin a
 * "session", which may protect many connections over time.  After
 * handshaking has completed, you can access session attributes by
 * using the {@link #getSession()} method.
 * <P>
 * The {@code SSLSocket} class provides much of the same security
 * functionality, but all of the inbound and outbound data is
 * automatically transported using the underlying {@link
 * java.net.Socket Socket}, which by design uses a blocking model.
 * While this is appropriate for many applications, this model does not
 * provide the scalability required by large servers.
 * <P>
 * The primary distinction of an {@code SSLEngine} is that it
 * operates on inbound and outbound byte streams, independent of the
 * transport mechanism.  It is the responsibility of the
 * {@code SSLEngine} user to arrange for reliable I/O transport to
 * the peer.  By separating the SSL/TLS/DTLS abstraction from the I/O
 * transport mechanism, the {@code SSLEngine} can be used for a
 * wide variety of I/O types, such as {@link
 * java.nio.channels.spi.AbstractSelectableChannel#configureBlocking(boolean)
 * non-blocking I/O (polling)}, {@link java.nio.channels.Selector
 * selectable non-blocking I/O}, {@link java.net.Socket Socket} and the
 * traditional Input/OutputStreams, local {@link java.nio.ByteBuffer
 * ByteBuffers} or byte arrays, <A
 * HREF="http://www.jcp.org/en/jsr/detail?id=203"> future asynchronous
 * I/O models </A>, and so on.
 * <P>
 * At a high level, the {@code SSLEngine} appears thus:
 *
 * <pre>
 *                   app data
 *
 *                |           ^
 *                |     |     |
 *                v     |     |
 *           +----+-----|-----+----+
 *           |          |          |
 *           |       SSL|Engine    |
 *   wrap()  |          |          |  unwrap()
 *           | OUTBOUND | INBOUND  |
 *           |          |          |
 *           +----+-----|-----+----+
 *                |     |     ^
 *                |     |     |
 *                v           |
 *
 *                   net data
 * </pre>
 * Application data (also known as plaintext or cleartext) is data which
 * is produced or consumed by an application.  Its counterpart is
 * network data, which consists of either handshaking and/or ciphertext
 * (encrypted) data, and destined to be transported via an I/O
 * mechanism.  Inbound data is data which has been received from the
 * peer, and outbound data is destined for the peer.
 * <P>
 * (In the context of an {@code SSLEngine}, the term "handshake
 * data" is taken to mean any data exchanged to establish and control a
 * secure connection.  Handshake data includes the SSL/TLS/DTLS messages
 * "alert", "change_cipher_spec," and "handshake.")
 * <P>
 * There are five distinct phases to an {@code SSLEngine}.
 *
 * <OL>
 *     <li> Creation - The {@code SSLEngine} has been created and
 *     initialized, but has not yet been used.  During this phase, an
 *     application may set any {@code SSLEngine}-specific settings
 *     (enabled cipher suites, whether the {@code SSLEngine} should
 *     handshake in client or server mode, and so on).  Once
 *     handshaking has begun, though, any new settings (except
 *     client/server mode, see below) will be used for
 *     the next handshake.
 *
 *     <li> Initial Handshake - The initial handshake is a procedure by
 *     which the two peers exchange communication parameters until an
 *     SSLSession is established.  Application data can not be sent during
 *     this phase.
 *
 *     <li> Application Data - Once the communication parameters have
 *     been established and the handshake is complete, application data
 *     may flow through the {@code SSLEngine}.  Outbound
 *     application messages are encrypted and integrity protected,
 *     and inbound messages reverse the process.
 *
 *     <li> Rehandshaking - Either side may request a renegotiation of
 *     the session at any time during the Application Data phase.  New
 *     handshaking data can be intermixed among the application data.
 *     Before starting the rehandshake phase, the application may
 *     reset the SSL/TLS/DTLS communication parameters such as the list of
 *     enabled ciphersuites and whether to use client authentication,
 *     but can not change between client/server modes.  As before, once
 *     handshaking has begun, any new {@code SSLEngine}
 *     configuration settings will not be used until the next
 *     handshake.
 *
 *     <li> Closure - When the connection is no longer needed, the client
 *     and the server applications should each close both sides of their
 *     respective connections.  For {@code SSLEngine} objects, an
 *     application should call {@link SSLEngine#closeOutbound()} and
 *     send any remaining messages to the peer.  Likewise, an application
 *     should receive any remaining messages from the peer before calling
 *     {@link SSLEngine#closeInbound()}.  The underlying transport mechanism
 *     can then be closed after both sides of the {@code SSLEngine} have
 *     been closed.  If the connection is not closed in an orderly manner
 *     (for example {@link SSLEngine#closeInbound()} is called before the
 *     peer's write closure notification has been received), exceptions
 *     will be raised to indicate that an error has occurred.  Once an
 *     engine is closed, it is not reusable: a new {@code SSLEngine}
 *     must be created.
 * </OL>
 * An {@code SSLEngine} is created by calling {@link
 * SSLContext#createSSLEngine()} from an initialized
 * {@code SSLContext}.  Any configuration
 * parameters should be set before making the first call to
 * {@code wrap()}, {@code unwrap()}, or
 * {@code beginHandshake()}.  These methods all trigger the
 * initial handshake.
 * <P>
 * Data moves through the engine by calling {@link #wrap(ByteBuffer,
 * ByteBuffer) wrap()} or {@link #unwrap(ByteBuffer, ByteBuffer)
 * unwrap()} on outbound or inbound data, respectively.  Depending on
 * the state of the {@code SSLEngine}, a {@code wrap()} call
 * may consume application data from the source buffer and may produce
 * network data in the destination buffer.  The outbound data
 * may contain application and/or handshake data.  A call to
 * {@code unwrap()} will examine the source buffer and may
 * advance the handshake if the data is handshaking information, or
 * may place application data in the destination buffer if the data
 * is application.  The state of the underlying SSL/TLS/DTLS algorithm
 * will determine when data is consumed and produced.
 * <P>
 * Calls to {@code wrap()} and {@code unwrap()} return an
 * {@code SSLEngineResult} which indicates the status of the
 * operation, and (optionally) how to interact with the engine to make
 * progress.
 * <P>
 * The {@code SSLEngine} produces/consumes complete SSL/TLS/DTLS
 * packets only, and does not store application data internally between
 * calls to {@code wrap()/unwrap()}.  Thus input and output
 * {@code ByteBuffer}s must be sized appropriately to hold the
 * maximum record that can be produced.  Calls to {@link
 * SSLSession#getPacketBufferSize()} and {@link
 * SSLSession#getApplicationBufferSize()} should be used to determine
 * the appropriate buffer sizes.  The size of the outbound application
 * data buffer generally does not matter.  If buffer conditions do not
 * allow for the proper consumption/production of data, the application
 * must determine (via {@link SSLEngineResult}) and correct the
 * problem, and then try the call again.
 * <P>
 * For example, {@code unwrap()} will return a {@link
 * SSLEngineResult.Status#BUFFER_OVERFLOW} result if the engine
 * determines that there is not enough destination buffer space available.
 * Applications should call {@link SSLSession#getApplicationBufferSize()}
 * and compare that value with the space available in the destination buffer,
 * enlarging the buffer if necessary.  Similarly, if {@code unwrap()}
 * were to return a {@link SSLEngineResult.Status#BUFFER_UNDERFLOW}, the
 * application should call {@link SSLSession#getPacketBufferSize()} to ensure
 * that the source buffer has enough room to hold a record (enlarging if
 * necessary), and then obtain more inbound data.
 *
 * <pre>{@code
 *   SSLEngineResult r = engine.unwrap(src, dst);
 *   switch (r.getStatus()) {
 *   BUFFER_OVERFLOW:
 *       // Could attempt to drain the dst buffer of any already obtained
 *       // data, but we'll just increase it to the size needed.
 *       int appSize = engine.getSession().getApplicationBufferSize();
 *       ByteBuffer b = ByteBuffer.allocate(appSize + dst.position());
 *       dst.flip();
 *       b.put(dst);
 *       dst = b;
 *       // retry the operation.
 *       break;
 *   BUFFER_UNDERFLOW:
 *       int netSize = engine.getSession().getPacketBufferSize();
 *       // Resize buffer if needed.
 *       if (netSize > src.capacity()) {
 *           ByteBuffer b = ByteBuffer.allocate(netSize);
 *           src.flip();
 *           b.put(src);
 *           src = b;
 *       }
 *       // Obtain more inbound network data for src,
 *       // then retry the operation.
 *       break;
 *   // other cases: CLOSED, OK.
 *   }
 * }</pre>
 *
 * <P>
 * Unlike {@code SSLSocket}, all methods of SSLEngine are
 * non-blocking.  {@code SSLEngine} implementations may
 * require the results of tasks that may take an extended period of
 * time to complete, or may even block.  For example, a TrustManager
 * may need to connect to a remote certificate validation service,
 * or a KeyManager might need to prompt a user to determine which
 * certificate to use as part of client authentication.  Additionally,
 * creating cryptographic signatures and verifying them can be slow,
 * seemingly blocking.
 * <P>
 * For any operation which may potentially block, the
 * {@code SSLEngine} will create a {@link java.lang.Runnable}
 * delegated task.  When {@code SSLEngineResult} indicates that a
 * delegated task result is needed, the application must call {@link
 * #getDelegatedTask()} to obtain an outstanding delegated task and
 * call its {@link java.lang.Runnable#run() run()} method (possibly using
 * a different thread depending on the compute strategy).  The
 * application should continue obtaining delegated tasks until no more
 * exist, and try the original operation again.
 * <P>
 * At the end of a communication session, applications should properly
 * close the SSL/TLS/DTLS link.  The SSL/TLS/DTLS protocols have closure
 * handshake messages, and these messages should be communicated to the
 * peer before releasing the {@code SSLEngine} and closing the
 * underlying transport mechanism.  A close can be initiated by one of:
 * an SSLException, an inbound closure handshake message, or one of the
 * close methods.  In all cases, closure handshake messages are
 * generated by the engine, and {@code wrap()} should be repeatedly
 * called until the resulting {@code SSLEngineResult}'s status
 * returns "CLOSED", or {@link #isOutboundDone()} returns true.  All
 * data obtained from the {@code wrap()} method should be sent to the
 * peer.
 * <P>
 * {@link #closeOutbound()} is used to signal the engine that the
 * application will not be sending any more data.
 * <P>
 * A peer will signal its intent to close by sending its own closure
 * handshake message.  After this message has been received and
 * processed by the local {@code SSLEngine}'s {@code unwrap()}
 * call, the application can detect the close by calling
 * {@code unwrap()} and looking for a {@code SSLEngineResult}
 * with status "CLOSED", or if {@link #isInboundDone()} returns true.
 * If for some reason the peer closes the communication link without
 * sending the proper SSL/TLS/DTLS closure message, the application can
 * detect the end-of-stream and can signal the engine via {@link
 * #closeInbound()} that there will no more inbound messages to
 * process.  Some applications might choose to require orderly shutdown
 * messages from a peer, in which case they can check that the closure
 * was generated by a handshake message and not by an end-of-stream
 * condition.
 * <P>
 * There are two groups of cipher suites which you will need to know
 * about when managing cipher suites:
 *
 * <UL>
 *      <LI> <em>Supported</em> cipher suites:  all the suites which are
 *      supported by the SSL implementation.  This list is reported
 *      using {@link #getSupportedCipherSuites()}.
 *
 *      <LI> <em>Enabled</em> cipher suites, which may be fewer than
 *      the full set of supported suites.  This group is set using the
 *      {@link #setEnabledCipherSuites(String [])} method, and
 *      queried using the {@link #getEnabledCipherSuites()} method.
 *      Initially, a default set of cipher suites will be enabled on a
 *      new engine that represents the minimum suggested
 *      configuration.
 * </UL>
 *
 * Implementation defaults require that only cipher suites which
 * authenticate servers and provide confidentiality be enabled by
 * default.  Only if both sides explicitly agree to unauthenticated
 * and/or non-private (unencrypted) communications will such a
 * cipher suite be selected.
 * <P>
 * Each SSL/TLS/DTLS connection must have one client and one server, thus
 * each endpoint must decide which role to assume.  This choice determines
 * who begins the handshaking process as well as which type of messages
 * should be sent by each party.  The method {@link
 * #setUseClientMode(boolean)} configures the mode.  Note that the
 * default mode for a new {@code SSLEngine} is provider-specific.
 * Applications should set the mode explicitly before invoking other
 * methods of the {@code SSLEngine}.  Once the initial handshaking has
 * started, an {@code SSLEngine} can not switch between client and server
 * modes, even when performing renegotiations.
 * <P>
 * The ApplicationProtocol {@code String} values returned by the methods
 * in this class are in the network byte representation sent by the peer.
 * The bytes could be directly compared, or converted to its Unicode
 * {code String} format for comparison.
 *
 * <blockquote><pre>
 *     String networkString = sslEngine.getHandshakeApplicationProtocol();
 *     byte[] bytes = networkString.getBytes(StandardCharsets.ISO_8859_1);
 *
 *     //
 *     // Match using bytes:
 *     //
 *     //   "http/1.1"                       (7-bit ASCII values same in UTF-8)
 *     //   MEETEI MAYEK LETTERS "HUK UN I"  (Unicode 0xabcd->0xabcf)
 *     //
 *     String HTTP1_1 = "http/1.1";
 *     byte[] HTTP1_1_BYTES = HTTP1_1.getBytes(StandardCharsets.UTF_8);
 *
 *     byte[] HUK_UN_I_BYTES = new byte[] {
 *         (byte) 0xab, (byte) 0xcd,
 *         (byte) 0xab, (byte) 0xce,
 *         (byte) 0xab, (byte) 0xcf};
 *
 *     if ((Arrays.compare(bytes, HTTP1_1_BYTES) == 0 )
 *             || Arrays.compare(bytes, HUK_UN_I_BYTES) == 0) {
 *        ...
 *     }
 *
 *     //
 *     // Alternatively match using string.equals() if we know the ALPN value
 *     // was encoded from a {@code String} using a certain character set,
 *     // for example {@code UTF-8}.  The ALPN value must first be properly
 *     // decoded to a Unicode {@code String} before use.
 *     //
 *     String unicodeString = new String(bytes, StandardCharsets.UTF_8);
 *     if (unicodeString.equals(HTTP1_1)
 *             || unicodeString.equals("\u005cuabcd\u005cuabce\u005cuabcf")) {
 *         ...
 *     }
 * </pre></blockquote>
 *
 * <P>
 * Applications might choose to process delegated tasks in different
 * threads.  When an {@code SSLEngine}
 * is created, the current {@link java.security.AccessControlContext}
 * is saved.  All future delegated tasks will be processed using this
 * context:  that is, all access control decisions will be made using the
 * context captured at engine creation.
 *
 * <HR>
 *
 * <B>Concurrency Notes</B>:
 * There are two concurrency issues to be aware of:
 *
 * <OL>
 *      <li>The {@code wrap()} and {@code unwrap()} methods
 *      may execute concurrently of each other.
 *
 *      <li> The SSL/TLS/DTLS protocols employ ordered packets.
 *      Applications must take care to ensure that generated packets
 *      are delivered in sequence.  If packets arrive
 *      out-of-order, unexpected or fatal results may occur.
 * <P>
 *      For example:
 *
 *      <pre>
 *              synchronized (outboundLock) {
 *                  sslEngine.wrap(src, dst);
 *                  outboundQueue.put(dst);
 *              }
 *      </pre>
 *
 *      As a corollary, two threads must not attempt to call the same method
 *      (either {@code wrap()} or {@code unwrap()}) concurrently,
 *      because there is no way to guarantee the eventual packet ordering.
 * </OL>
 *
 * @see SSLContext
 * @see SSLSocket
 * @see SSLServerSocket
 * @see SSLSession
 * @see java.net.Socket
 *
 * @since 1.5
 * @author Brad R. Wetmore
 */

public abstract class SSLEngine {

    private String peerHost = null;
    private int peerPort = -1;

    
Constructor for an SSLEngine providing no hints for an internal session reuse strategy. 
See Also:
SSLContext.createSSLEngine()
SSLSessionContext/**
     * Constructor for an {@code SSLEngine} providing no hints
     * for an internal session reuse strategy.
     *
     * @see     SSLContext#createSSLEngine()
     * @see     SSLSessionContext
     */
    protected SSLEngine() {
    }

    
Constructor for an SSLEngine. 
 SSLEngine implementations may use the peerHost and peerPort parameters as hints for their internal session reuse strategy. 

Some cipher suites (such as Kerberos) require remote hostname
information. Implementations of this class should use this
constructor to use Kerberos.
 The parameters are not authenticated by the SSLEngine. 
Params:
peerHost – the name of the peer host
peerPort – the port number of the peer
See Also:
SSLContext.createSSLEngine(String, int)
SSLSessionContext/**
     * Constructor for an {@code SSLEngine}.
     * <P>
     * {@code SSLEngine} implementations may use the
     * {@code peerHost} and {@code peerPort} parameters as hints
     * for their internal session reuse strategy.
     * <P>
     * Some cipher suites (such as Kerberos) require remote hostname
     * information. Implementations of this class should use this
     * constructor to use Kerberos.
     * <P>
     * The parameters are not authenticated by the
     * {@code SSLEngine}.
     *
     * @param   peerHost the name of the peer host
     * @param   peerPort the port number of the peer
     * @see     SSLContext#createSSLEngine(String, int)
     * @see     SSLSessionContext
     */
    protected SSLEngine(String peerHost, int peerPort) {
        this.peerHost = peerHost;
        this.peerPort = peerPort;
    }

    
Returns the host name of the peer.

Note that the value is not authenticated, and should not be
relied upon.
Returns:
 the host name of the peer, or null if nothing is
         available./**
     * Returns the host name of the peer.
     * <P>
     * Note that the value is not authenticated, and should not be
     * relied upon.
     *
     * @return  the host name of the peer, or null if nothing is
     *          available.
     */
    public String getPeerHost() {
        return peerHost;
    }

    
Returns the port number of the peer.

Note that the value is not authenticated, and should not be
relied upon.
Returns:
 the port number of the peer, or -1 if nothing is
         available./**
     * Returns the port number of the peer.
     * <P>
     * Note that the value is not authenticated, and should not be
     * relied upon.
     *
     * @return  the port number of the peer, or -1 if nothing is
     *          available.
     */
    public int getPeerPort() {
        return peerPort;
    }

    
Attempts to encode a buffer of plaintext application data into
SSL/TLS/DTLS network data.

An invocation of this method behaves in exactly the same manner
as the invocation:
wrap(ByteBuffer[], int, int, ByteBuffer) engine.wrap(new ByteBuffer [] src }, 0, 1, dst);} 
Params:
src –  a ByteBuffer containing outbound application data
dst –  a ByteBuffer to hold outbound network data
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
ReadOnlyBufferException –  if the dst buffer is read-only.
IllegalArgumentException –  if either src or dst is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
wrap(ByteBuffer[], int, int, ByteBuffer)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to encode a buffer of plaintext application data into
     * SSL/TLS/DTLS network data.
     * <P>
     * An invocation of this method behaves in exactly the same manner
     * as the invocation:
     * <blockquote><pre>
     * {@link #wrap(ByteBuffer [], int, int, ByteBuffer)
     *     engine.wrap(new ByteBuffer [] { src }, 0, 1, dst);}
     * </pre></blockquote>
     *
     * @param   src
     *          a {@code ByteBuffer} containing outbound application data
     * @param   dst
     *          a {@code ByteBuffer} to hold outbound network data
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  ReadOnlyBufferException
     *          if the {@code dst} buffer is read-only.
     * @throws  IllegalArgumentException
     *          if either {@code src} or {@code dst}
     *          is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     #wrap(ByteBuffer [], int, int, ByteBuffer)
     */
    public SSLEngineResult wrap(ByteBuffer src,
            ByteBuffer dst) throws SSLException {
        return wrap(new ByteBuffer [] { src }, 0, 1, dst);
    }

    
Attempts to encode plaintext bytes from a sequence of data
buffers into SSL/TLS/DTLS network data.

An invocation of this method behaves in exactly the same manner
as the invocation:

    engine.wrap(srcs, 0, srcs.length, dst); 
Params:
srcs –  an array of ByteBuffers containing the outbound application data
dst –  a ByteBuffer to hold outbound network data
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
ReadOnlyBufferException –  if the dst buffer is read-only.
IllegalArgumentException –  if either srcs or dst is null, or if any element in srcs is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
wrap(ByteBuffer[], int, int, ByteBuffer)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to encode plaintext bytes from a sequence of data
     * buffers into SSL/TLS/DTLS network data.
     * <P>
     * An invocation of this method behaves in exactly the same manner
     * as the invocation:
     * <blockquote><pre>
     * {@link #wrap(ByteBuffer [], int, int, ByteBuffer)
     *     engine.wrap(srcs, 0, srcs.length, dst);}
     * </pre></blockquote>
     *
     * @param   srcs
     *          an array of {@code ByteBuffers} containing the
     *          outbound application data
     * @param   dst
     *          a {@code ByteBuffer} to hold outbound network data
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  ReadOnlyBufferException
     *          if the {@code dst} buffer is read-only.
     * @throws  IllegalArgumentException
     *          if either {@code srcs} or {@code dst}
     *          is null, or if any element in {@code srcs} is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     #wrap(ByteBuffer [], int, int, ByteBuffer)
     */
    public SSLEngineResult wrap(ByteBuffer [] srcs,
            ByteBuffer dst) throws SSLException {
        if (srcs == null) {
            throw new IllegalArgumentException("src == null");
        }
        return wrap(srcs, 0, srcs.length, dst);
    }


    
Attempts to encode plaintext bytes from a subsequence of data
buffers into SSL/TLS/DTLS network data.  This "gathering" operation encodes, in a single invocation, a sequence of bytes from one or more of a given sequence of buffers. Gathering wraps are often useful when implementing network protocols or file formats that, for example, group data into segments consisting of one or more fixed-length headers followed by a variable-length body. See GatheringByteChannel for more information on gathering, and GatheringByteChannel.write(ByteBuffer[], int, int) for more information on the subsequence behavior. 

Depending on the state of the SSLEngine, this method may produce
network data without consuming any application data (for example,
it may generate handshake data.)

The application is responsible for reliably transporting the
network data to the peer, and for ensuring that data created by
multiple calls to wrap() is transported in the same order in which
it was generated.  The application must properly synchronize
multiple calls to this method.
 If this SSLEngine has not yet started its initial handshake, this method will automatically start the handshake. 
 This method will attempt to produce SSL/TLS/DTLS records, and will consume as much source data as possible, but will never consume more than the sum of the bytes remaining in each buffer. Each ByteBuffer's position is updated to reflect the amount of data consumed or produced. The limits remain the same. 
 The underlying memory used by the srcs and dst ByteBuffers must not be the same. 

See the class description for more information on engine closure.
Params:
srcs –  an array of ByteBuffers containing the outbound application data
offset –  The offset within the buffer array of the first buffer from which bytes are to be retrieved; it must be non-negative and no larger than srcs.length
length –  The maximum number of buffers to be accessed; it must be non-negative and no larger than srcs.length - offset
dst –  a ByteBuffer to hold outbound network data
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
IndexOutOfBoundsException –  if the preconditions on the offset and length parameters do not hold.
ReadOnlyBufferException –  if the dst buffer is read-only.
IllegalArgumentException –  if either srcs or dst is null, or if any element in the srcs subsequence specified is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
GatheringByteChannel
GatheringByteChannel.write(ByteBuffer[], int, int)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to encode plaintext bytes from a subsequence of data
     * buffers into SSL/TLS/DTLS network data.  This <i>"gathering"</i>
     * operation encodes, in a single invocation, a sequence of bytes
     * from one or more of a given sequence of buffers.  Gathering
     * wraps are often useful when implementing network protocols or
     * file formats that, for example, group data into segments
     * consisting of one or more fixed-length headers followed by a
     * variable-length body.  See
     * {@link java.nio.channels.GatheringByteChannel} for more
     * information on gathering, and {@link
     * java.nio.channels.GatheringByteChannel#write(ByteBuffer[],
     * int, int)} for more information on the subsequence
     * behavior.
     * <P>
     * Depending on the state of the SSLEngine, this method may produce
     * network data without consuming any application data (for example,
     * it may generate handshake data.)
     * <P>
     * The application is responsible for reliably transporting the
     * network data to the peer, and for ensuring that data created by
     * multiple calls to wrap() is transported in the same order in which
     * it was generated.  The application must properly synchronize
     * multiple calls to this method.
     * <P>
     * If this {@code SSLEngine} has not yet started its initial
     * handshake, this method will automatically start the handshake.
     * <P>
     * This method will attempt to produce SSL/TLS/DTLS records, and will
     * consume as much source data as possible, but will never consume
     * more than the sum of the bytes remaining in each buffer.  Each
     * {@code ByteBuffer}'s position is updated to reflect the
     * amount of data consumed or produced.  The limits remain the
     * same.
     * <P>
     * The underlying memory used by the {@code srcs} and
     * {@code dst ByteBuffer}s must not be the same.
     * <P>
     * See the class description for more information on engine closure.
     *
     * @param   srcs
     *          an array of {@code ByteBuffers} containing the
     *          outbound application data
     * @param   offset
     *          The offset within the buffer array of the first buffer from
     *          which bytes are to be retrieved; it must be non-negative
     *          and no larger than {@code srcs.length}
     * @param   length
     *          The maximum number of buffers to be accessed; it must be
     *          non-negative and no larger than
     *          {@code srcs.length}&nbsp;-&nbsp;{@code offset}
     * @param   dst
     *          a {@code ByteBuffer} to hold outbound network data
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  IndexOutOfBoundsException
     *          if the preconditions on the {@code offset} and
     *          {@code length} parameters do not hold.
     * @throws  ReadOnlyBufferException
     *          if the {@code dst} buffer is read-only.
     * @throws  IllegalArgumentException
     *          if either {@code srcs} or {@code dst}
     *          is null, or if any element in the {@code srcs}
     *          subsequence specified is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     java.nio.channels.GatheringByteChannel
     * @see     java.nio.channels.GatheringByteChannel#write(
     *              ByteBuffer[], int, int)
     */
    public abstract SSLEngineResult wrap(ByteBuffer [] srcs, int offset,
            int length, ByteBuffer dst) throws SSLException;

    
Attempts to decode SSL/TLS/DTLS network data into a plaintext
application data buffer.

An invocation of this method behaves in exactly the same manner
as the invocation:
unwrap(ByteBuffer, ByteBuffer[], int, int) engine.unwrap(src, new ByteBuffer [] dst }, 0, 1);} 
Params:
src –  a ByteBuffer containing inbound network data.
dst –  a ByteBuffer to hold inbound application data.
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
ReadOnlyBufferException –  if the dst buffer is read-only.
IllegalArgumentException –  if either src or dst is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
unwrap(ByteBuffer, ByteBuffer[], int, int)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to decode SSL/TLS/DTLS network data into a plaintext
     * application data buffer.
     * <P>
     * An invocation of this method behaves in exactly the same manner
     * as the invocation:
     * <blockquote><pre>
     * {@link #unwrap(ByteBuffer, ByteBuffer [], int, int)
     *     engine.unwrap(src, new ByteBuffer [] { dst }, 0, 1);}
     * </pre></blockquote>
     *
     * @param   src
     *          a {@code ByteBuffer} containing inbound network data.
     * @param   dst
     *          a {@code ByteBuffer} to hold inbound application data.
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  ReadOnlyBufferException
     *          if the {@code dst} buffer is read-only.
     * @throws  IllegalArgumentException
     *          if either {@code src} or {@code dst}
     *          is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     #unwrap(ByteBuffer, ByteBuffer [], int, int)
     */
    public SSLEngineResult unwrap(ByteBuffer src,
            ByteBuffer dst) throws SSLException {
        return unwrap(src, new ByteBuffer [] { dst }, 0, 1);
    }

    
Attempts to decode SSL/TLS/DTLS network data into a sequence of plaintext
application data buffers.

An invocation of this method behaves in exactly the same manner
as the invocation:

    engine.unwrap(src, dsts, 0, dsts.length); 
Params:
src –  a ByteBuffer containing inbound network data.
dsts –  an array of ByteBuffers to hold inbound application data.
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
ReadOnlyBufferException –  if any of the dst buffers are read-only.
IllegalArgumentException –  if either src or dsts is null, or if any element in dsts is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
unwrap(ByteBuffer, ByteBuffer[], int, int)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to decode SSL/TLS/DTLS network data into a sequence of plaintext
     * application data buffers.
     * <P>
     * An invocation of this method behaves in exactly the same manner
     * as the invocation:
     * <blockquote><pre>
     * {@link #unwrap(ByteBuffer, ByteBuffer [], int, int)
     *     engine.unwrap(src, dsts, 0, dsts.length);}
     * </pre></blockquote>
     *
     * @param   src
     *          a {@code ByteBuffer} containing inbound network data.
     * @param   dsts
     *          an array of {@code ByteBuffer}s to hold inbound
     *          application data.
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  ReadOnlyBufferException
     *          if any of the {@code dst} buffers are read-only.
     * @throws  IllegalArgumentException
     *          if either {@code src} or {@code dsts}
     *          is null, or if any element in {@code dsts} is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     #unwrap(ByteBuffer, ByteBuffer [], int, int)
     */
    public SSLEngineResult unwrap(ByteBuffer src,
            ByteBuffer [] dsts) throws SSLException {
        if (dsts == null) {
            throw new IllegalArgumentException("dsts == null");
        }
        return unwrap(src, dsts, 0, dsts.length);
    }

    
Attempts to decode SSL/TLS/DTLS network data into a subsequence of
plaintext application data buffers.  This "scattering" operation decodes, in a single invocation, a sequence of bytes into one or more of a given sequence of buffers. Scattering unwraps are often useful when implementing network protocols or file formats that, for example, group data into segments consisting of one or more fixed-length headers followed by a variable-length body. See ScatteringByteChannel for more information on scattering, and ScatteringByteChannel.read(ByteBuffer[], int, int) for more information on the subsequence behavior. 

Depending on the state of the SSLEngine, this method may consume
network data without producing any application data (for example,
it may consume handshake data.)

The application is responsible for reliably obtaining the network
data from the peer, and for invoking unwrap() on the data in the
order it was received.  The application must properly synchronize
multiple calls to this method.
 If this SSLEngine has not yet started its initial handshake, this method will automatically start the handshake. 
 This method will attempt to consume one complete SSL/TLS/DTLS network packet, but will never consume more than the sum of the bytes remaining in the buffers. Each ByteBuffer's position is updated to reflect the amount of data consumed or produced. The limits remain the same. 
 The underlying memory used by the src and dsts ByteBuffers must not be the same. 

The inbound network buffer may be modified as a result of this
call:  therefore if the network data packet is required for some
secondary purpose, the data should be duplicated before calling this
method.  Note:  the network data will not be useful to a second
SSLEngine, as each SSLEngine contains unique random state which
influences the SSL/TLS/DTLS messages.

See the class description for more information on engine closure.
Params:
src –  a ByteBuffer containing inbound network data.
dsts –  an array of ByteBuffers to hold inbound application data.
offset –  The offset within the buffer array of the first buffer from which bytes are to be transferred; it must be non-negative and no larger than dsts.length.
length –  The maximum number of buffers to be accessed; it must be non-negative and no larger than dsts.length - offset.
Throws:
SSLException –  A problem was encountered while processing the data that caused the SSLEngine to abort. See the class description for more information on engine closure.
IndexOutOfBoundsException –  If the preconditions on the offset and length parameters do not hold.
ReadOnlyBufferException –  if any of the dst buffers are read-only.
IllegalArgumentException –  if either src or dsts is null, or if any element in the dsts subsequence specified is null.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
ScatteringByteChannel
ScatteringByteChannel.read(ByteBuffer[], int, int)
Returns:
 an SSLEngineResult describing the result of this operation./**
     * Attempts to decode SSL/TLS/DTLS network data into a subsequence of
     * plaintext application data buffers.  This <i>"scattering"</i>
     * operation decodes, in a single invocation, a sequence of bytes
     * into one or more of a given sequence of buffers.  Scattering
     * unwraps are often useful when implementing network protocols or
     * file formats that, for example, group data into segments
     * consisting of one or more fixed-length headers followed by a
     * variable-length body.  See
     * {@link java.nio.channels.ScatteringByteChannel} for more
     * information on scattering, and {@link
     * java.nio.channels.ScatteringByteChannel#read(ByteBuffer[],
     * int, int)} for more information on the subsequence
     * behavior.
     * <P>
     * Depending on the state of the SSLEngine, this method may consume
     * network data without producing any application data (for example,
     * it may consume handshake data.)
     * <P>
     * The application is responsible for reliably obtaining the network
     * data from the peer, and for invoking unwrap() on the data in the
     * order it was received.  The application must properly synchronize
     * multiple calls to this method.
     * <P>
     * If this {@code SSLEngine} has not yet started its initial
     * handshake, this method will automatically start the handshake.
     * <P>
     * This method will attempt to consume one complete SSL/TLS/DTLS network
     * packet, but will never consume more than the sum of the bytes
     * remaining in the buffers.  Each {@code ByteBuffer}'s
     * position is updated to reflect the amount of data consumed or
     * produced.  The limits remain the same.
     * <P>
     * The underlying memory used by the {@code src} and
     * {@code dsts ByteBuffer}s must not be the same.
     * <P>
     * The inbound network buffer may be modified as a result of this
     * call:  therefore if the network data packet is required for some
     * secondary purpose, the data should be duplicated before calling this
     * method.  Note:  the network data will not be useful to a second
     * SSLEngine, as each SSLEngine contains unique random state which
     * influences the SSL/TLS/DTLS messages.
     * <P>
     * See the class description for more information on engine closure.
     *
     * @param   src
     *          a {@code ByteBuffer} containing inbound network data.
     * @param   dsts
     *          an array of {@code ByteBuffer}s to hold inbound
     *          application data.
     * @param   offset
     *          The offset within the buffer array of the first buffer from
     *          which bytes are to be transferred; it must be non-negative
     *          and no larger than {@code dsts.length}.
     * @param   length
     *          The maximum number of buffers to be accessed; it must be
     *          non-negative and no larger than
     *          {@code dsts.length}&nbsp;-&nbsp;{@code offset}.
     * @return  an {@code SSLEngineResult} describing the result
     *          of this operation.
     * @throws  SSLException
     *          A problem was encountered while processing the
     *          data that caused the {@code SSLEngine} to abort.
     *          See the class description for more information on
     *          engine closure.
     * @throws  IndexOutOfBoundsException
     *          If the preconditions on the {@code offset} and
     *          {@code length} parameters do not hold.
     * @throws  ReadOnlyBufferException
     *          if any of the {@code dst} buffers are read-only.
     * @throws  IllegalArgumentException
     *          if either {@code src} or {@code dsts}
     *          is null, or if any element in the {@code dsts}
     *          subsequence specified is null.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     java.nio.channels.ScatteringByteChannel
     * @see     java.nio.channels.ScatteringByteChannel#read(
     *              ByteBuffer[], int, int)
     */
    public abstract SSLEngineResult unwrap(ByteBuffer src,
            ByteBuffer [] dsts, int offset, int length) throws SSLException;


    
Returns a delegated Runnable task for this SSLEngine. 
 SSLEngine operations may require the results of operations that block, or may take an extended period of time to complete. This method is used to obtain an outstanding Runnable operation (task). Each task must be assigned a thread (possibly the current) to perform the run operation. Once the run method returns, the Runnable object is no longer needed and may be discarded. 
 Delegated tasks run in the AccessControlContext in place when this object was created. 

A call to this method will return each outstanding task
exactly once.

Multiple delegated tasks can be run in parallel.
Returns:
 a delegated Runnable task, or null if none are available./**
     * Returns a delegated {@code Runnable} task for
     * this {@code SSLEngine}.
     * <P>
     * {@code SSLEngine} operations may require the results of
     * operations that block, or may take an extended period of time to
     * complete.  This method is used to obtain an outstanding {@link
     * java.lang.Runnable} operation (task).  Each task must be assigned
     * a thread (possibly the current) to perform the {@link
     * java.lang.Runnable#run() run} operation.  Once the
     * {@code run} method returns, the {@code Runnable} object
     * is no longer needed and may be discarded.
     * <P>
     * Delegated tasks run in the {@code AccessControlContext}
     * in place when this object was created.
     * <P>
     * A call to this method will return each outstanding task
     * exactly once.
     * <P>
     * Multiple delegated tasks can be run in parallel.
     *
     * @return  a delegated {@code Runnable} task, or null
     *          if none are available.
     */
    public abstract Runnable getDelegatedTask();


    
Signals that no more inbound network data will be sent to this SSLEngine. 
 If the application initiated the closing process by calling closeOutbound(), under some circumstances it is not required that the initiator wait for the peer's corresponding close message. (See section 7.2.1 of the TLS specification (RFC 2246) for more
information on waiting for closure alerts.)  In such cases, this
method need not be called.

But if the application did not initiate the closure process, or
if the circumstances above do not apply, this method should be
called whenever the end of the SSL/TLS/DTLS data stream is reached.
This ensures closure of the inbound side, and checks that the
peer followed the SSL/TLS/DTLS close procedure properly, thus
detecting possible truncation attacks.

This method is idempotent:  if the inbound side has already
been closed, this method does not do anything.
 wrap() should be called to flush any remaining handshake data. 
Throws:
SSLException – 
         if this engine has not received the proper SSL/TLS/DTLS close
         notification message from the peer.
See Also:
isInboundDone()
isOutboundDone()/**
     * Signals that no more inbound network data will be sent
     * to this {@code SSLEngine}.
     * <P>
     * If the application initiated the closing process by calling
     * {@link #closeOutbound()}, under some circumstances it is not
     * required that the initiator wait for the peer's corresponding
     * close message.  (See section 7.2.1 of the TLS specification (<A
     * HREF="http://www.ietf.org/rfc/rfc2246.txt">RFC 2246</A>) for more
     * information on waiting for closure alerts.)  In such cases, this
     * method need not be called.
     * <P>
     * But if the application did not initiate the closure process, or
     * if the circumstances above do not apply, this method should be
     * called whenever the end of the SSL/TLS/DTLS data stream is reached.
     * This ensures closure of the inbound side, and checks that the
     * peer followed the SSL/TLS/DTLS close procedure properly, thus
     * detecting possible truncation attacks.
     * <P>
     * This method is idempotent:  if the inbound side has already
     * been closed, this method does not do anything.
     * <P>
     * {@link #wrap(ByteBuffer, ByteBuffer) wrap()} should be
     * called to flush any remaining handshake data.
     *
     * @throws  SSLException
     *          if this engine has not received the proper SSL/TLS/DTLS close
     *          notification message from the peer.
     *
     * @see     #isInboundDone()
     * @see     #isOutboundDone()
     */
    public abstract void closeInbound() throws SSLException;


    
Returns whether unwrap(ByteBuffer, ByteBuffer) will accept any more inbound data messages. 
See Also:
closeInbound()
Returns:
 true if the SSLEngine will not consume anymore network data (and by implication, will not produce any more application data.)/**
     * Returns whether {@link #unwrap(ByteBuffer, ByteBuffer)} will
     * accept any more inbound data messages.
     *
     * @return  true if the {@code SSLEngine} will not
     *          consume anymore network data (and by implication,
     *          will not produce any more application data.)
     * @see     #closeInbound()
     */
    public abstract boolean isInboundDone();


    
Signals that no more outbound application data will be sent on this SSLEngine. 

This method is idempotent:  if the outbound side has already
been closed, this method does not do anything.
 wrap(ByteBuffer, ByteBuffer) should be called to flush any remaining handshake data. 
See Also:
isOutboundDone()/**
     * Signals that no more outbound application data will be sent
     * on this {@code SSLEngine}.
     * <P>
     * This method is idempotent:  if the outbound side has already
     * been closed, this method does not do anything.
     * <P>
     * {@link #wrap(ByteBuffer, ByteBuffer)} should be
     * called to flush any remaining handshake data.
     *
     * @see     #isOutboundDone()
     */
    public abstract void closeOutbound();


    
Returns whether wrap(ByteBuffer, ByteBuffer) will produce any more outbound data messages. 
 Note that during the closure phase, a SSLEngine may generate handshake closure data that must be sent to the peer. wrap() must be called to generate this data. When this method returns true, no more outbound data will be created. 
See Also:
closeOutbound()
closeInbound()
Returns:
 true if the SSLEngine will not produce any more network data/**
     * Returns whether {@link #wrap(ByteBuffer, ByteBuffer)} will
     * produce any more outbound data messages.
     * <P>
     * Note that during the closure phase, a {@code SSLEngine} may
     * generate handshake closure data that must be sent to the peer.
     * {@code wrap()} must be called to generate this data.  When
     * this method returns true, no more outbound data will be created.
     *
     * @return  true if the {@code SSLEngine} will not produce
     *          any more network data
     *
     * @see     #closeOutbound()
     * @see     #closeInbound()
     */
    public abstract boolean isOutboundDone();


    
Returns the names of the cipher suites which could be enabled for use
on this engine.  Normally, only a subset of these will actually
be enabled by default, since this list may include cipher suites which
do not meet quality of service requirements for those defaults.  Such
cipher suites might be useful in specialized applications.

The returned array includes cipher suites from the list of standard
cipher suite names in the 
JSSE Cipher Suite Names section of the Java Cryptography
Architecture Standard Algorithm Name Documentation, and may also
include other cipher suites that the provider supports.
See Also:
getEnabledCipherSuites()
setEnabledCipherSuites(String[])
Returns:
 an array of cipher suite names/**
     * Returns the names of the cipher suites which could be enabled for use
     * on this engine.  Normally, only a subset of these will actually
     * be enabled by default, since this list may include cipher suites which
     * do not meet quality of service requirements for those defaults.  Such
     * cipher suites might be useful in specialized applications.
     * <P>
     * The returned array includes cipher suites from the list of standard
     * cipher suite names in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#jsse-cipher-suite-names">
     * JSSE Cipher Suite Names</a> section of the Java Cryptography
     * Architecture Standard Algorithm Name Documentation, and may also
     * include other cipher suites that the provider supports.
     *
     * @return  an array of cipher suite names
     * @see     #getEnabledCipherSuites()
     * @see     #setEnabledCipherSuites(String [])
     */
    public abstract String [] getSupportedCipherSuites();


    
Returns the names of the SSL cipher suites which are currently
enabled for use on this engine.  When an SSLEngine is first
created, all enabled cipher suites support a minimum quality of
service.  Thus, in some environments this value might be empty.

Note that even if a suite is enabled, it may never be used. This
can occur if the peer does not support it, or its use is restricted,
or the requisite certificates (and private keys) for the suite are
not available, or an anonymous suite is enabled but authentication
is required.

The returned array includes cipher suites from the list of standard
cipher suite names in the 
JSSE Cipher Suite Names section of the Java Cryptography
Architecture Standard Algorithm Name Documentation, and may also
include other cipher suites that the provider supports.
See Also:
getSupportedCipherSuites()
setEnabledCipherSuites(String[])
Returns:
 an array of cipher suite names/**
     * Returns the names of the SSL cipher suites which are currently
     * enabled for use on this engine.  When an SSLEngine is first
     * created, all enabled cipher suites support a minimum quality of
     * service.  Thus, in some environments this value might be empty.
     * <P>
     * Note that even if a suite is enabled, it may never be used. This
     * can occur if the peer does not support it, or its use is restricted,
     * or the requisite certificates (and private keys) for the suite are
     * not available, or an anonymous suite is enabled but authentication
     * is required.
     * <P>
     * The returned array includes cipher suites from the list of standard
     * cipher suite names in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#jsse-cipher-suite-names">
     * JSSE Cipher Suite Names</a> section of the Java Cryptography
     * Architecture Standard Algorithm Name Documentation, and may also
     * include other cipher suites that the provider supports.
     *
     * @return  an array of cipher suite names
     * @see     #getSupportedCipherSuites()
     * @see     #setEnabledCipherSuites(String [])
     */
    public abstract String [] getEnabledCipherSuites();


    
Sets the cipher suites enabled for use on this engine.
 Each cipher suite in the suites parameter must have been listed by getSupportedCipherSuites(), or the method will fail. Following a successful call to this method, only suites listed in the suites parameter are enabled for use. 

Note that the standard list of cipher suite names may be found in the

JSSE Cipher Suite Names section of the Java Cryptography
Architecture Standard Algorithm Name Documentation.  Providers
may support cipher suite names not found in this list or might not
use the recommended name for a certain cipher suite.
 See getEnabledCipherSuites() for more information on why a specific cipher suite may never be used on a engine. 
Params:
suites – Names of all the cipher suites to enable
Throws:
IllegalArgumentException – when one or more of the ciphers
         named by the parameter is not supported, or when the
         parameter is null.
See Also:
getSupportedCipherSuites()
getEnabledCipherSuites()/**
     * Sets the cipher suites enabled for use on this engine.
     * <P>
     * Each cipher suite in the {@code suites} parameter must have
     * been listed by getSupportedCipherSuites(), or the method will
     * fail.  Following a successful call to this method, only suites
     * listed in the {@code suites} parameter are enabled for use.
     * <P>
     * Note that the standard list of cipher suite names may be found in the
     * <a href=
     * "{@docRoot}/../specs/security/standard-names.html#jsse-cipher-suite-names">
     * JSSE Cipher Suite Names</a> section of the Java Cryptography
     * Architecture Standard Algorithm Name Documentation.  Providers
     * may support cipher suite names not found in this list or might not
     * use the recommended name for a certain cipher suite.
     * <P>
     * See {@link #getEnabledCipherSuites()} for more information
     * on why a specific cipher suite may never be used on a engine.
     *
     * @param   suites Names of all the cipher suites to enable
     * @throws  IllegalArgumentException when one or more of the ciphers
     *          named by the parameter is not supported, or when the
     *          parameter is null.
     * @see     #getSupportedCipherSuites()
     * @see     #getEnabledCipherSuites()
     */
    public abstract void setEnabledCipherSuites(String suites []);


    
Returns the names of the protocols which could be enabled for use with this SSLEngine. 
Returns:
 an array of protocols supported/**
     * Returns the names of the protocols which could be enabled for use
     * with this {@code SSLEngine}.
     *
     * @return  an array of protocols supported
     */
    public abstract String [] getSupportedProtocols();


    
Returns the names of the protocol versions which are currently enabled for use with this SSLEngine. 

Note that even if a protocol is enabled, it may never be used.
This can occur if the peer does not support the protocol, or its
use is restricted, or there are no enabled cipher suites supported
by the protocol.
See Also:
setEnabledProtocols(String[])
Returns:
 an array of protocols/**
     * Returns the names of the protocol versions which are currently
     * enabled for use with this {@code SSLEngine}.
     * <P>
     * Note that even if a protocol is enabled, it may never be used.
     * This can occur if the peer does not support the protocol, or its
     * use is restricted, or there are no enabled cipher suites supported
     * by the protocol.
     *
     * @return  an array of protocols
     * @see     #setEnabledProtocols(String [])
     */
    public abstract String [] getEnabledProtocols();


    
Set the protocol versions enabled for use on this engine.
 The protocols must have been listed by getSupportedProtocols() as being supported. Following a successful call to this method, only protocols listed in the protocols parameter are enabled for use. 
Params:
protocols – Names of all the protocols to enable.
Throws:
IllegalArgumentException – when one or more of
         the protocols named by the parameter is not supported or
         when the protocols parameter is null.
See Also:
getEnabledProtocols()/**
     * Set the protocol versions enabled for use on this engine.
     * <P>
     * The protocols must have been listed by getSupportedProtocols()
     * as being supported.  Following a successful call to this method,
     * only protocols listed in the {@code protocols} parameter
     * are enabled for use.
     *
     * @param   protocols Names of all the protocols to enable.
     * @throws  IllegalArgumentException when one or more of
     *          the protocols named by the parameter is not supported or
     *          when the protocols parameter is null.
     * @see     #getEnabledProtocols()
     */
    public abstract void setEnabledProtocols(String protocols[]);


    
Returns the SSLSession in use in this SSLEngine. 

These can be long lived, and frequently correspond to an entire
login session for some user.  The session specifies a particular
cipher suite which is being actively used by all connections in
that session, as well as the identities of the session's client
and server.
 Unlike SSLSocket.getSession() this method does not block until handshaking is complete. 

Until the initial handshake has completed, this method returns
a session object which reports an invalid cipher suite of
"SSL_NULL_WITH_NULL_NULL".
See Also:
SSLSession
Returns:
 the SSLSession for this SSLEngine/**
     * Returns the {@code SSLSession} in use in this
     * {@code SSLEngine}.
     * <P>
     * These can be long lived, and frequently correspond to an entire
     * login session for some user.  The session specifies a particular
     * cipher suite which is being actively used by all connections in
     * that session, as well as the identities of the session's client
     * and server.
     * <P>
     * Unlike {@link SSLSocket#getSession()}
     * this method does not block until handshaking is complete.
     * <P>
     * Until the initial handshake has completed, this method returns
     * a session object which reports an invalid cipher suite of
     * "SSL_NULL_WITH_NULL_NULL".
     *
     * @return  the {@code SSLSession} for this {@code SSLEngine}
     * @see     SSLSession
     */
    public abstract SSLSession getSession();


    
Returns the SSLSession being constructed during a SSL/TLS/DTLS handshake. 
 TLS/DTLS protocols may negotiate parameters that are needed when using an instance of this class, but before the SSLSession has been completely initialized and made available via getSession. For example, the list of valid signature algorithms may restrict the type of certificates that can be used during TrustManager decisions, or the maximum TLS/DTLS fragment packet sizes can be resized to better support the network environment. 
 This method provides early access to the SSLSession being constructed. Depending on how far the handshake has progressed, some data may not yet be available for use. For example, if a remote server will be sending a Certificate chain, but that chain has yet not been processed, the getPeerCertificates method of SSLSession will throw a SSLPeerUnverifiedException. Once that chain has been processed, getPeerCertificates will return the proper value. 
Throws:
UnsupportedOperationException – if the underlying provider
        does not implement the operation.
See Also:
SSLSocket
SSLSession
ExtendedSSLSession
X509ExtendedKeyManager
X509ExtendedTrustManager
Returns:
null if this instance is not currently handshaking, or if the current handshake has not progressed far enough to create a basic SSLSession. Otherwise, this method returns the SSLSession currently being negotiated.
Since:
1.7/**
     * Returns the {@code SSLSession} being constructed during a SSL/TLS/DTLS
     * handshake.
     * <p>
     * TLS/DTLS protocols may negotiate parameters that are needed when using
     * an instance of this class, but before the {@code SSLSession} has
     * been completely initialized and made available via {@code getSession}.
     * For example, the list of valid signature algorithms may restrict
     * the type of certificates that can be used during TrustManager
     * decisions, or the maximum TLS/DTLS fragment packet sizes can be
     * resized to better support the network environment.
     * <p>
     * This method provides early access to the {@code SSLSession} being
     * constructed.  Depending on how far the handshake has progressed,
     * some data may not yet be available for use.  For example, if a
     * remote server will be sending a Certificate chain, but that chain
     * has yet not been processed, the {@code getPeerCertificates}
     * method of {@code SSLSession} will throw a
     * SSLPeerUnverifiedException.  Once that chain has been processed,
     * {@code getPeerCertificates} will return the proper value.
     *
     * @see SSLSocket
     * @see SSLSession
     * @see ExtendedSSLSession
     * @see X509ExtendedKeyManager
     * @see X509ExtendedTrustManager
     *
     * @return null if this instance is not currently handshaking, or
     *         if the current handshake has not progressed far enough to
     *         create a basic SSLSession.  Otherwise, this method returns the
     *         {@code SSLSession} currently being negotiated.
     * @throws UnsupportedOperationException if the underlying provider
     *         does not implement the operation.
     *
     * @since 1.7
     */
    public SSLSession getHandshakeSession() {
        throw new UnsupportedOperationException();
    }


    
Initiates handshaking (initial or renegotiation) on this SSLEngine.
 This method is not needed for the initial handshake, as the wrap() and unwrap() methods will implicitly call this method if handshaking has not already begun. 
 Note that the peer may also request a session renegotiation with this SSLEngine by sending the appropriate session renegotiate handshake message. 
 Unlike the 
SSLSocket#startHandshake() method, this method does not block until handshaking is completed. 

To force a complete SSL/TLS/DTLS session renegotiation, the current
session should be invalidated prior to calling this method.
 Some protocols may not support multiple handshakes on an existing engine and may throw an SSLException. 
Throws:
SSLException –  if a problem was encountered while signaling the SSLEngine to begin a new handshake. See the class description for more information on engine closure.
IllegalStateException – if the client/server mode
         has not yet been set.
See Also:
SSLSession.invalidate()/**
     * Initiates handshaking (initial or renegotiation) on this SSLEngine.
     * <P>
     * This method is not needed for the initial handshake, as the
     * {@code wrap()} and {@code unwrap()} methods will
     * implicitly call this method if handshaking has not already begun.
     * <P>
     * Note that the peer may also request a session renegotiation with
     * this {@code SSLEngine} by sending the appropriate
     * session renegotiate handshake message.
     * <P>
     * Unlike the {@link SSLSocket#startHandshake()
     * SSLSocket#startHandshake()} method, this method does not block
     * until handshaking is completed.
     * <P>
     * To force a complete SSL/TLS/DTLS session renegotiation, the current
     * session should be invalidated prior to calling this method.
     * <P>
     * Some protocols may not support multiple handshakes on an existing
     * engine and may throw an {@code SSLException}.
     *
     * @throws  SSLException
     *          if a problem was encountered while signaling the
     *          {@code SSLEngine} to begin a new handshake.
     *          See the class description for more information on
     *          engine closure.
     * @throws  IllegalStateException if the client/server mode
     *          has not yet been set.
     * @see     SSLSession#invalidate()
     */
    public abstract void beginHandshake() throws SSLException;


    
Returns the current handshake status for this SSLEngine. 
Returns:
 the current SSLEngineResult.HandshakeStatus./**
     * Returns the current handshake status for this {@code SSLEngine}.
     *
     * @return  the current {@code SSLEngineResult.HandshakeStatus}.
     */
    public abstract SSLEngineResult.HandshakeStatus getHandshakeStatus();


    
Configures the engine to use client (or server) mode when
handshaking.

This method must be called before any handshaking occurs.
Once handshaking has begun, the mode can not be reset for the
life of this engine.

Servers normally authenticate themselves, and clients
are not required to do so.
Params:
mode – true if the engine should start its handshaking
         in "client" mode
Throws:
IllegalArgumentException – if a mode change is attempted
         after the initial handshake has begun.
See Also:
getUseClientMode()
Implementation Note:

The JDK SunJSSE provider implementation default for this mode is false./**
     * Configures the engine to use client (or server) mode when
     * handshaking.
     * <P>
     * This method must be called before any handshaking occurs.
     * Once handshaking has begun, the mode can not be reset for the
     * life of this engine.
     * <P>
     * Servers normally authenticate themselves, and clients
     * are not required to do so.
     *
     * @implNote
     * The JDK SunJSSE provider implementation default for this mode is false.
     *
     * @param   mode true if the engine should start its handshaking
     *          in "client" mode
     * @throws  IllegalArgumentException if a mode change is attempted
     *          after the initial handshake has begun.
     * @see     #getUseClientMode()
     */
    public abstract void setUseClientMode(boolean mode);


    
Returns true if the engine is set to use client mode when
handshaking.
See Also:
setUseClientMode(boolean)
Implementation Note:
 The JDK SunJSSE provider implementation returns false unless setUseClientMode(boolean) is used to change the mode to true.
Returns:
 true if the engine should do handshaking
         in "client" mode/**
     * Returns true if the engine is set to use client mode when
     * handshaking.
     *
     * @implNote
     * The JDK SunJSSE provider implementation returns false unless
     * {@link setUseClientMode(boolean)} is used to change the mode to true.
     *
     * @return  true if the engine should do handshaking
     *          in "client" mode
     * @see     #setUseClientMode(boolean)
     */
    public abstract boolean getUseClientMode();


    
Configures the engine to require client authentication.  This
option is only useful for engines in the server mode.

An engine's client authentication setting is one of the following:

 client authentication required
 client authentication requested
 no client authentication desired

 Unlike setWantClientAuth(boolean), if this option is set and the client chooses not to provide authentication information about itself, the negotiations will stop and the engine will
begin its closure procedure.
 Calling this method overrides any previous setting made by this method or setWantClientAuth(boolean). 
Params:
need – set to true if client authentication is required,
         or false if no client authentication is desired.
See Also:
getNeedClientAuth()
setWantClientAuth(boolean)
getWantClientAuth()
setUseClientMode(boolean)/**
     * Configures the engine to <i>require</i> client authentication.  This
     * option is only useful for engines in the server mode.
     * <P>
     * An engine's client authentication setting is one of the following:
     * <ul>
     * <li> client authentication required
     * <li> client authentication requested
     * <li> no client authentication desired
     * </ul>
     * <P>
     * Unlike {@link #setWantClientAuth(boolean)}, if this option is set and
     * the client chooses not to provide authentication information
     * about itself, <i>the negotiations will stop and the engine will
     * begin its closure procedure</i>.
     * <P>
     * Calling this method overrides any previous setting made by
     * this method or {@link #setWantClientAuth(boolean)}.
     *
     * @param   need set to true if client authentication is required,
     *          or false if no client authentication is desired.
     * @see     #getNeedClientAuth()
     * @see     #setWantClientAuth(boolean)
     * @see     #getWantClientAuth()
     * @see     #setUseClientMode(boolean)
     */
    public abstract void setNeedClientAuth(boolean need);


    
Returns true if the engine will require client authentication.
This option is only useful to engines in the server mode.
See Also:
setNeedClientAuth(boolean)
setWantClientAuth(boolean)
getWantClientAuth()
setUseClientMode(boolean)
Returns:
 true if client authentication is required,
         or false if no client authentication is desired./**
     * Returns true if the engine will <i>require</i> client authentication.
     * This option is only useful to engines in the server mode.
     *
     * @return  true if client authentication is required,
     *          or false if no client authentication is desired.
     * @see     #setNeedClientAuth(boolean)
     * @see     #setWantClientAuth(boolean)
     * @see     #getWantClientAuth()
     * @see     #setUseClientMode(boolean)
     */
    public abstract boolean getNeedClientAuth();


    
Configures the engine to request client authentication.
This option is only useful for engines in the server mode.

An engine's client authentication setting is one of the following:

 client authentication required
 client authentication requested
 no client authentication desired

 Unlike setNeedClientAuth(boolean), if this option is set and the client chooses not to provide authentication information about itself, the negotiations will continue.
 Calling this method overrides any previous setting made by this method or setNeedClientAuth(boolean). 
Params:
want – set to true if client authentication is requested,
         or false if no client authentication is desired.
See Also:
getWantClientAuth()
setNeedClientAuth(boolean)
getNeedClientAuth()
setUseClientMode(boolean)/**
     * Configures the engine to <i>request</i> client authentication.
     * This option is only useful for engines in the server mode.
     * <P>
     * An engine's client authentication setting is one of the following:
     * <ul>
     * <li> client authentication required
     * <li> client authentication requested
     * <li> no client authentication desired
     * </ul>
     * <P>
     * Unlike {@link #setNeedClientAuth(boolean)}, if this option is set and
     * the client chooses not to provide authentication information
     * about itself, <i>the negotiations will continue</i>.
     * <P>
     * Calling this method overrides any previous setting made by
     * this method or {@link #setNeedClientAuth(boolean)}.
     *
     * @param   want set to true if client authentication is requested,
     *          or false if no client authentication is desired.
     * @see     #getWantClientAuth()
     * @see     #setNeedClientAuth(boolean)
     * @see     #getNeedClientAuth()
     * @see     #setUseClientMode(boolean)
     */
    public abstract void setWantClientAuth(boolean want);


    
Returns true if the engine will request client authentication.
This option is only useful for engines in the server mode.
See Also:
setNeedClientAuth(boolean)
getNeedClientAuth()
setWantClientAuth(boolean)
setUseClientMode(boolean)
Returns:
 true if client authentication is requested,
         or false if no client authentication is desired./**
     * Returns true if the engine will <i>request</i> client authentication.
     * This option is only useful for engines in the server mode.
     *
     * @return  true if client authentication is requested,
     *          or false if no client authentication is desired.
     * @see     #setNeedClientAuth(boolean)
     * @see     #getNeedClientAuth()
     * @see     #setWantClientAuth(boolean)
     * @see     #setUseClientMode(boolean)
     */
    public abstract boolean getWantClientAuth();


    
Controls whether new SSL sessions may be established by this engine.
If session creations are not allowed, and there are no
existing sessions to resume, there will be no successful
handshaking.
Params:
flag – true indicates that sessions may be created; this
         is the default.  false indicates that an existing session
         must be resumed
See Also:
getEnableSessionCreation()/**
     * Controls whether new SSL sessions may be established by this engine.
     * If session creations are not allowed, and there are no
     * existing sessions to resume, there will be no successful
     * handshaking.
     *
     * @param   flag true indicates that sessions may be created; this
     *          is the default.  false indicates that an existing session
     *          must be resumed
     * @see     #getEnableSessionCreation()
     */
    public abstract void setEnableSessionCreation(boolean flag);


    
Returns true if new SSL sessions may be established by this engine.
See Also:
setEnableSessionCreation(boolean)
Returns:
 true indicates that sessions may be created; this
         is the default.  false indicates that an existing session
         must be resumed/**
     * Returns true if new SSL sessions may be established by this engine.
     *
     * @return  true indicates that sessions may be created; this
     *          is the default.  false indicates that an existing session
     *          must be resumed
     * @see     #setEnableSessionCreation(boolean)
     */
    public abstract boolean getEnableSessionCreation();

    
Returns the SSLParameters in effect for this SSLEngine.
The ciphersuites and protocols of the returned SSLParameters
are always non-null.
Returns:
the SSLParameters in effect for this SSLEngine.
Since:
1.6/**
     * Returns the SSLParameters in effect for this SSLEngine.
     * The ciphersuites and protocols of the returned SSLParameters
     * are always non-null.
     *
     * @return the SSLParameters in effect for this SSLEngine.
     * @since 1.6
     */
    public SSLParameters getSSLParameters() {
        SSLParameters params = new SSLParameters();
        params.setCipherSuites(getEnabledCipherSuites());
        params.setProtocols(getEnabledProtocols());
        if (getNeedClientAuth()) {
            params.setNeedClientAuth(true);
        } else if (getWantClientAuth()) {
            params.setWantClientAuth(true);
        }
        return params;
    }

    
Applies SSLParameters to this engine.
This means:

If params.getCipherSuites() is non-null, setEnabledCipherSuites() is called with that value.
If params.getProtocols() is non-null, setEnabledProtocols() is called with that value.
If params.getNeedClientAuth() or params.getWantClientAuth() return true, setNeedClientAuth(true) and setWantClientAuth(true) are called, respectively; otherwise setWantClientAuth(false) is called.
If params.getServerNames() is non-null, the engine will configure its server names with that value.
If params.getSNIMatchers() is non-null, the engine will configure its SNI matchers with that value.

Params:
params – the parameters
Throws:
IllegalArgumentException – if the setEnabledCipherSuites() or
   the setEnabledProtocols() call fails
Since:
1.6/**
     * Applies SSLParameters to this engine.
     *
     * <p>This means:
     * <ul>
     * <li>If {@code params.getCipherSuites()} is non-null,
     *   {@code setEnabledCipherSuites()} is called with that value.</li>
     * <li>If {@code params.getProtocols()} is non-null,
     *   {@code setEnabledProtocols()} is called with that value.</li>
     * <li>If {@code params.getNeedClientAuth()} or
     *   {@code params.getWantClientAuth()} return {@code true},
     *   {@code setNeedClientAuth(true)} and
     *   {@code setWantClientAuth(true)} are called, respectively;
     *   otherwise {@code setWantClientAuth(false)} is called.</li>
     * <li>If {@code params.getServerNames()} is non-null, the engine will
     *   configure its server names with that value.</li>
     * <li>If {@code params.getSNIMatchers()} is non-null, the engine will
     *   configure its SNI matchers with that value.</li>
     * </ul>
     *
     * @param params the parameters
     * @throws IllegalArgumentException if the setEnabledCipherSuites() or
     *    the setEnabledProtocols() call fails
     * @since 1.6
     */
    public void setSSLParameters(SSLParameters params) {
        String[] s;
        s = params.getCipherSuites();
        if (s != null) {
            setEnabledCipherSuites(s);
        }
        s = params.getProtocols();
        if (s != null) {
            setEnabledProtocols(s);
        }
        if (params.getNeedClientAuth()) {
            setNeedClientAuth(true);
        } else if (params.getWantClientAuth()) {
            setWantClientAuth(true);
        } else {
            setWantClientAuth(false);
        }
    }

    
Returns the most recent application protocol value negotiated for this
connection.

If supported by the underlying SSL/TLS/DTLS implementation,
application name negotiation mechanisms such as  RFC 7301 , the
Application-Layer Protocol Negotiation (ALPN), can negotiate
application-level values between peers.
Throws:
UnsupportedOperationException – if the underlying provider
        does not implement the operation.
Implementation Requirements:
 The implementation in this class throws UnsupportedOperationException and performs no other action.
Returns:
null if it has not yet been determined if application protocols might be used for this connection, an empty String if application protocols values will not be used, or a non-empty application protocol String if a value was successfully negotiated.
Since:
9/**
     * Returns the most recent application protocol value negotiated for this
     * connection.
     * <p>
     * If supported by the underlying SSL/TLS/DTLS implementation,
     * application name negotiation mechanisms such as <a
     * href="http://www.ietf.org/rfc/rfc7301.txt"> RFC 7301 </a>, the
     * Application-Layer Protocol Negotiation (ALPN), can negotiate
     * application-level values between peers.
     *
     * @implSpec
     * The implementation in this class throws
     * {@code UnsupportedOperationException} and performs no other action.
     *
     * @return null if it has not yet been determined if application
     *         protocols might be used for this connection, an empty
     *         {@code String} if application protocols values will not
     *         be used, or a non-empty application protocol {@code String}
     *         if a value was successfully negotiated.
     * @throws UnsupportedOperationException if the underlying provider
     *         does not implement the operation.
     * @since 9
     */
    public String getApplicationProtocol() {
        throw new UnsupportedOperationException();
    }

    
Returns the application protocol value negotiated on a SSL/TLS
handshake currently in progress.
 Like getHandshakeSession(), a connection may be in the middle of a handshake. The application protocol may or may not yet be available. 
Throws:
UnsupportedOperationException – if the underlying provider
        does not implement the operation.
Implementation Requirements:
 The implementation in this class throws UnsupportedOperationException and performs no other action.
Returns:
null if it has not yet been determined if application protocols might be used for this handshake, an empty String if application protocols values will not be used, or a non-empty application protocol String if a value was successfully negotiated.
Since:
9/**
     * Returns the application protocol value negotiated on a SSL/TLS
     * handshake currently in progress.
     * <p>
     * Like {@link #getHandshakeSession()},
     * a connection may be in the middle of a handshake. The
     * application protocol may or may not yet be available.
     *
     * @implSpec
     * The implementation in this class throws
     * {@code UnsupportedOperationException} and performs no other action.
     *
     * @return null if it has not yet been determined if application
     *         protocols might be used for this handshake, an empty
     *         {@code String} if application protocols values will not
     *         be used, or a non-empty application protocol {@code String}
     *         if a value was successfully negotiated.
     * @throws UnsupportedOperationException if the underlying provider
     *         does not implement the operation.
     * @since 9
     */
    public String getHandshakeApplicationProtocol() {
        throw new UnsupportedOperationException();
    }

    
Registers a callback function that selects an application protocol value for a SSL/TLS/DTLS handshake. The function overrides any values supplied using 
SSLParameters.setApplicationProtocols and it supports the following type parameters: 


 SSLEngine 
 The function's first argument allows the current SSLEngine to be inspected, including the handshake session and configuration settings. 
 List<String> 
 The function's second argument lists the application protocol names
     advertised by the TLS peer.
 String 
 The function's result is an application protocol name, or null to indicate that none of the advertised names are acceptable. If the return value is an empty String then application protocol indications will not be used. If the return value is null (no value chosen) or is a value that was not advertised by the peer, the underlying protocol will determine what action to take. (For example, ALPN will send a "no_application_protocol" alert and terminate the connection.) 

For example, the following call registers a callback function that
examines the TLS handshake parameters and selects an application protocol
name:

    serverEngine.setHandshakeApplicationProtocolSelector(
        (serverEngine, clientProtocols) -> {
            SSLSession session = serverEngine.getHandshakeSession();
            return chooseApplicationProtocol(
                serverEngine,
                clientProtocols,
                session.getProtocol(),
                session.getCipherSuite());
        });

Params:
selector – the callback function, or null to disable the callback
        functionality.
Throws:
UnsupportedOperationException – if the underlying provider
        does not implement the operation.
API Note:
 This method should be called by TLS server applications before the TLS handshake begins. Also, this SSLEngine should be configured with parameters that are compatible with the application protocol selected by the callback function. For example, enabling a poor choice of cipher suites could result in no suitable application protocol. See SSLParameters.
Implementation Requirements:
 The implementation in this class throws UnsupportedOperationException and performs no other action.
Since:
9/**
     * Registers a callback function that selects an application protocol
     * value for a SSL/TLS/DTLS handshake.
     * The function overrides any values supplied using
     * {@link SSLParameters#setApplicationProtocols
     * SSLParameters.setApplicationProtocols} and it supports the following
     * type parameters:
     * <blockquote>
     * <dl>
     * <dt> {@code SSLEngine}
     * <dd> The function's first argument allows the current {@code SSLEngine}
     *      to be inspected, including the handshake session and configuration
     *      settings.
     * <dt> {@code List<String>}
     * <dd> The function's second argument lists the application protocol names
     *      advertised by the TLS peer.
     * <dt> {@code String}
     * <dd> The function's result is an application protocol name, or null to
     *      indicate that none of the advertised names are acceptable.
     *      If the return value is an empty {@code String} then application
     *      protocol indications will not be used.
     *      If the return value is null (no value chosen) or is a value that
     *      was not advertised by the peer, the underlying protocol will
     *      determine what action to take. (For example, ALPN will send a
     *      "no_application_protocol" alert and terminate the connection.)
     * </dl>
     * </blockquote>
     *
     * For example, the following call registers a callback function that
     * examines the TLS handshake parameters and selects an application protocol
     * name:
     * <pre>{@code
     *     serverEngine.setHandshakeApplicationProtocolSelector(
     *         (serverEngine, clientProtocols) -> {
     *             SSLSession session = serverEngine.getHandshakeSession();
     *             return chooseApplicationProtocol(
     *                 serverEngine,
     *                 clientProtocols,
     *                 session.getProtocol(),
     *                 session.getCipherSuite());
     *         });
     * }</pre>
     *
     * @apiNote
     * This method should be called by TLS server applications before the TLS
     * handshake begins. Also, this {@code SSLEngine} should be configured with
     * parameters that are compatible with the application protocol selected by
     * the callback function. For example, enabling a poor choice of cipher
     * suites could result in no suitable application protocol.
     * See {@link SSLParameters}.
     *
     * @implSpec
     * The implementation in this class throws
     * {@code UnsupportedOperationException} and performs no other action.
     *
     * @param selector the callback function, or null to disable the callback
     *         functionality.
     * @throws UnsupportedOperationException if the underlying provider
     *         does not implement the operation.
     * @since 9
     */
    public void setHandshakeApplicationProtocolSelector(
            BiFunction<SSLEngine, List<String>, String> selector) {
        throw new UnsupportedOperationException();
    }

    
Retrieves the callback function that selects an application protocol value during a SSL/TLS/DTLS handshake. See 
setHandshakeApplicationProtocolSelector for the function's type parameters. 
Throws:
UnsupportedOperationException – if the underlying provider
        does not implement the operation.
Implementation Requirements:
 The implementation in this class throws UnsupportedOperationException and performs no other action.
Returns:
the callback function, or null if none has been set.
Since:
9/**
     * Retrieves the callback function that selects an application protocol
     * value during a SSL/TLS/DTLS handshake.
     * See {@link #setHandshakeApplicationProtocolSelector
     * setHandshakeApplicationProtocolSelector}
     * for the function's type parameters.
     *
     * @implSpec
     * The implementation in this class throws
     * {@code UnsupportedOperationException} and performs no other action.
     *
     * @return the callback function, or null if none has been set.
     * @throws UnsupportedOperationException if the underlying provider
     *         does not implement the operation.
     * @since 9
     */
    public BiFunction<SSLEngine, List<String>, String>
            getHandshakeApplicationProtocolSelector() {
        throw new UnsupportedOperationException();
    }
}