/*
 * Copyright (C) 2014 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3;

import java.util.Arrays;
import java.util.List;
import javax.annotation.Nullable;
import javax.net.ssl.SSLSocket;
import okhttp3.internal.Util;

import static okhttp3.internal.Util.concat;
import static okhttp3.internal.Util.indexOf;
import static okhttp3.internal.Util.intersect;
import static okhttp3.internal.Util.nonEmptyIntersection;

Specifies configuration for the socket connection that HTTP traffic travels through. For 
https: URLs, this includes the TLS version and cipher suites to use when negotiating a secure connection. 
The TLS versions configured in a connection spec are only be used if they are also enabled in
the SSL socket. For example, if an SSL socket does not have TLS 1.3 enabled, it will not be used
even if it is present on the connection spec. The same policy also applies to cipher suites.
Use Builder.allEnabledTlsVersions() and Builder.allEnabledCipherSuites to defer all feature selection to the underlying SSL socket. /**
 * Specifies configuration for the socket connection that HTTP traffic travels through. For {@code
 * https:} URLs, this includes the TLS version and cipher suites to use when negotiating a secure
 * connection.
 *
 * <p>The TLS versions configured in a connection spec are only be used if they are also enabled in
 * the SSL socket. For example, if an SSL socket does not have TLS 1.3 enabled, it will not be used
 * even if it is present on the connection spec. The same policy also applies to cipher suites.
 *
 * <p>Use {@link Builder#allEnabledTlsVersions()} and {@link Builder#allEnabledCipherSuites} to
 * defer all feature selection to the underlying SSL socket.
 */
public final class ConnectionSpec {

  // Most secure but generally supported list.
  private static final CipherSuite[] RESTRICTED_CIPHER_SUITES = new CipherSuite[] {
      // TLSv1.3
      CipherSuite.TLS_AES_128_GCM_SHA256,
      CipherSuite.TLS_AES_256_GCM_SHA384,
      CipherSuite.TLS_CHACHA20_POLY1305_SHA256,
      CipherSuite.TLS_AES_128_CCM_SHA256,
      CipherSuite.TLS_AES_256_CCM_8_SHA256,

      CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
      CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
      CipherSuite.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
      CipherSuite.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
  };

  // This is nearly equal to the cipher suites supported in Chrome 51, current as of 2016-05-25.
  // All of these suites are available on Android 7.0; earlier releases support a subset of these
  // suites. https://github.com/square/okhttp/issues/1972
  private static final CipherSuite[] APPROVED_CIPHER_SUITES = new CipherSuite[] {
      // TLSv1.3
      CipherSuite.TLS_AES_128_GCM_SHA256,
      CipherSuite.TLS_AES_256_GCM_SHA384,
      CipherSuite.TLS_CHACHA20_POLY1305_SHA256,
      CipherSuite.TLS_AES_128_CCM_SHA256,
      CipherSuite.TLS_AES_256_CCM_8_SHA256,

      CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
      CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
      CipherSuite.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
      CipherSuite.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,

      // Note that the following cipher suites are all on HTTP/2's bad cipher suites list. We'll
      // continue to include them until better suites are commonly available. For example, none
      // of the better cipher suites listed above shipped with Android 4.4 or Java 7.
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
      CipherSuite.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
      CipherSuite.TLS_RSA_WITH_AES_128_GCM_SHA256,
      CipherSuite.TLS_RSA_WITH_AES_256_GCM_SHA384,
      CipherSuite.TLS_RSA_WITH_AES_128_CBC_SHA,
      CipherSuite.TLS_RSA_WITH_AES_256_CBC_SHA,
      CipherSuite.TLS_RSA_WITH_3DES_EDE_CBC_SHA,
  };

  
A secure TLS connection assuming a modern client platform and server. /** A secure TLS connection assuming a modern client platform and server. */
  public static final ConnectionSpec RESTRICTED_TLS = new Builder(true)
      .cipherSuites(RESTRICTED_CIPHER_SUITES)
      .tlsVersions(TlsVersion.TLS_1_3, TlsVersion.TLS_1_2)
      .supportsTlsExtensions(true)
      .build();

  
A modern TLS connection with extensions like SNI and ALPN available. /** A modern TLS connection with extensions like SNI and ALPN available. */
  public static final ConnectionSpec MODERN_TLS = new Builder(true)
      .cipherSuites(APPROVED_CIPHER_SUITES)
      .tlsVersions(TlsVersion.TLS_1_3, TlsVersion.TLS_1_2, TlsVersion.TLS_1_1, TlsVersion.TLS_1_0)
      .supportsTlsExtensions(true)
      .build();

  
A backwards-compatible fallback connection for interop with obsolete servers. /** A backwards-compatible fallback connection for interop with obsolete servers. */
  public static final ConnectionSpec COMPATIBLE_TLS = new Builder(true)
      .cipherSuites(APPROVED_CIPHER_SUITES)
      .tlsVersions(TlsVersion.TLS_1_0)
      .supportsTlsExtensions(true)
      .build();

  
Unencrypted, unauthenticated connections for http: URLs. /** Unencrypted, unauthenticated connections for {@code http:} URLs. */
  public static final ConnectionSpec CLEARTEXT = new Builder(false).build();

  final boolean tls;
  final boolean supportsTlsExtensions;
  final @Nullable String[] cipherSuites;
  final @Nullable String[] tlsVersions;

  ConnectionSpec(Builder builder) {
    this.tls = builder.tls;
    this.cipherSuites = builder.cipherSuites;
    this.tlsVersions = builder.tlsVersions;
    this.supportsTlsExtensions = builder.supportsTlsExtensions;
  }

  public boolean isTls() {
    return tls;
  }

  
Returns the cipher suites to use for a connection. Returns null if all of the SSL socket's
enabled cipher suites should be used.
/**
   * Returns the cipher suites to use for a connection. Returns null if all of the SSL socket's
   * enabled cipher suites should be used.
   */
  public @Nullable List<CipherSuite> cipherSuites() {
    return cipherSuites != null ? CipherSuite.forJavaNames(cipherSuites) : null;
  }

  
Returns the TLS versions to use when negotiating a connection. Returns null if all of the SSL
socket's enabled TLS versions should be used.
/**
   * Returns the TLS versions to use when negotiating a connection. Returns null if all of the SSL
   * socket's enabled TLS versions should be used.
   */
  public @Nullable List<TlsVersion> tlsVersions() {
    return tlsVersions != null ? TlsVersion.forJavaNames(tlsVersions) : null;
  }

  public boolean supportsTlsExtensions() {
    return supportsTlsExtensions;
  }

  
Applies this spec to sslSocket. /** Applies this spec to {@code sslSocket}. */
  void apply(SSLSocket sslSocket, boolean isFallback) {
    ConnectionSpec specToApply = supportedSpec(sslSocket, isFallback);

    if (specToApply.tlsVersions != null) {
      sslSocket.setEnabledProtocols(specToApply.tlsVersions);
    }
    if (specToApply.cipherSuites != null) {
      sslSocket.setEnabledCipherSuites(specToApply.cipherSuites);
    }
  }

  
Returns a copy of this that omits cipher suites and TLS versions not enabled by 
sslSocket. /**
   * Returns a copy of this that omits cipher suites and TLS versions not enabled by {@code
   * sslSocket}.
   */
  private ConnectionSpec supportedSpec(SSLSocket sslSocket, boolean isFallback) {
    String[] cipherSuitesIntersection = cipherSuites != null
        ? intersect(CipherSuite.ORDER_BY_NAME, sslSocket.getEnabledCipherSuites(), cipherSuites)
        : sslSocket.getEnabledCipherSuites();
    String[] tlsVersionsIntersection = tlsVersions != null
        ? intersect(Util.NATURAL_ORDER, sslSocket.getEnabledProtocols(), tlsVersions)
        : sslSocket.getEnabledProtocols();

    // In accordance with https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00
    // the SCSV cipher is added to signal that a protocol fallback has taken place.
    String[] supportedCipherSuites = sslSocket.getSupportedCipherSuites();
    int indexOfFallbackScsv = indexOf(
        CipherSuite.ORDER_BY_NAME, supportedCipherSuites, "TLS_FALLBACK_SCSV");
    if (isFallback && indexOfFallbackScsv != -1) {
      cipherSuitesIntersection = concat(
          cipherSuitesIntersection, supportedCipherSuites[indexOfFallbackScsv]);
    }

    return new Builder(this)
        .cipherSuites(cipherSuitesIntersection)
        .tlsVersions(tlsVersionsIntersection)
        .build();
  }

  
Returns true if the socket, as currently configured, supports this connection spec. In order for a socket to be compatible the enabled cipher suites and protocols must intersect. 
For cipher suites, at least one of the required cipher suites must match the socket's enabled cipher suites. If there are no required cipher suites the socket must have at least one cipher suite enabled. 
For protocols, at least one of the required protocols must match the socket's enabled protocols. /**
   * Returns {@code true} if the socket, as currently configured, supports this connection spec. In
   * order for a socket to be compatible the enabled cipher suites and protocols must intersect.
   *
   * <p>For cipher suites, at least one of the {@link #cipherSuites() required cipher suites} must
   * match the socket's enabled cipher suites. If there are no required cipher suites the socket
   * must have at least one cipher suite enabled.
   *
   * <p>For protocols, at least one of the {@link #tlsVersions() required protocols} must match the
   * socket's enabled protocols.
   */
  public boolean isCompatible(SSLSocket socket) {
    if (!tls) {
      return false;
    }

    if (tlsVersions != null && !nonEmptyIntersection(
        Util.NATURAL_ORDER, tlsVersions, socket.getEnabledProtocols())) {
      return false;
    }

    if (cipherSuites != null && !nonEmptyIntersection(
        CipherSuite.ORDER_BY_NAME, cipherSuites, socket.getEnabledCipherSuites())) {
      return false;
    }

    return true;
  }

  @Override public boolean equals(@Nullable Object other) {
    if (!(other instanceof ConnectionSpec)) return false;
    if (other == this) return true;

    ConnectionSpec that = (ConnectionSpec) other;
    if (this.tls != that.tls) return false;

    if (tls) {
      if (!Arrays.equals(this.cipherSuites, that.cipherSuites)) return false;
      if (!Arrays.equals(this.tlsVersions, that.tlsVersions)) return false;
      if (this.supportsTlsExtensions != that.supportsTlsExtensions) return false;
    }

    return true;
  }

  @Override public int hashCode() {
    int result = 17;
    if (tls) {
      result = 31 * result + Arrays.hashCode(cipherSuites);
      result = 31 * result + Arrays.hashCode(tlsVersions);
      result = 31 * result + (supportsTlsExtensions ? 0 : 1);
    }
    return result;
  }

  @Override public String toString() {
    if (!tls) {
      return "ConnectionSpec()";
    }

    String cipherSuitesString = cipherSuites != null ? cipherSuites().toString() : "[all enabled]";
    String tlsVersionsString = tlsVersions != null ? tlsVersions().toString() : "[all enabled]";
    return "ConnectionSpec("
        + "cipherSuites=" + cipherSuitesString
        + ", tlsVersions=" + tlsVersionsString
        + ", supportsTlsExtensions=" + supportsTlsExtensions
        + ")";
  }

  public static final class Builder {
    boolean tls;
    @Nullable String[] cipherSuites;
    @Nullable String[] tlsVersions;
    boolean supportsTlsExtensions;

    Builder(boolean tls) {
      this.tls = tls;
    }

    public Builder(ConnectionSpec connectionSpec) {
      this.tls = connectionSpec.tls;
      this.cipherSuites = connectionSpec.cipherSuites;
      this.tlsVersions = connectionSpec.tlsVersions;
      this.supportsTlsExtensions = connectionSpec.supportsTlsExtensions;
    }

    public Builder allEnabledCipherSuites() {
      if (!tls) throw new IllegalStateException("no cipher suites for cleartext connections");
      this.cipherSuites = null;
      return this;
    }

    public Builder cipherSuites(CipherSuite... cipherSuites) {
      if (!tls) throw new IllegalStateException("no cipher suites for cleartext connections");

      String[] strings = new String[cipherSuites.length];
      for (int i = 0; i < cipherSuites.length; i++) {
        strings[i] = cipherSuites[i].javaName;
      }
      return cipherSuites(strings);
    }

    public Builder cipherSuites(String... cipherSuites) {
      if (!tls) throw new IllegalStateException("no cipher suites for cleartext connections");

      if (cipherSuites.length == 0) {
        throw new IllegalArgumentException("At least one cipher suite is required");
      }

      this.cipherSuites = cipherSuites.clone(); // Defensive copy.
      return this;
    }

    public Builder allEnabledTlsVersions() {
      if (!tls) throw new IllegalStateException("no TLS versions for cleartext connections");
      this.tlsVersions = null;
      return this;
    }

    public Builder tlsVersions(TlsVersion... tlsVersions) {
      if (!tls) throw new IllegalStateException("no TLS versions for cleartext connections");

      String[] strings = new String[tlsVersions.length];
      for (int i = 0; i < tlsVersions.length; i++) {
        strings[i] = tlsVersions[i].javaName;
      }

      return tlsVersions(strings);
    }

    public Builder tlsVersions(String... tlsVersions) {
      if (!tls) throw new IllegalStateException("no TLS versions for cleartext connections");

      if (tlsVersions.length == 0) {
        throw new IllegalArgumentException("At least one TLS version is required");
      }

      this.tlsVersions = tlsVersions.clone(); // Defensive copy.
      return this;
    }

    public Builder supportsTlsExtensions(boolean supportsTlsExtensions) {
      if (!tls) throw new IllegalStateException("no TLS extensions for cleartext connections");
      this.supportsTlsExtensions = supportsTlsExtensions;
      return this;
    }

    public ConnectionSpec build() {
      return new ConnectionSpec(this);
    }
  }
}