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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package jdk.internal.net.http;

import java.io.IOException;
import java.net.http.HttpResponse;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executor;

import jdk.internal.net.http.common.Logger;
import jdk.internal.net.http.common.MinimalFuture;
import jdk.internal.net.http.common.Utils;

import static java.net.http.HttpClient.Version.HTTP_1_1;

Splits request so that headers and body can be sent separately with optional
(multiple) responses in between (e.g. 100 Continue). Also request and
response always sent/received in different calls.
Synchronous and asynchronous versions of each method are provided.
Separate implementations of this class exist for HTTP/1.1 and HTTP/2
     Http1Exchange   (HTTP/1.1)
     Stream          (HTTP/2)
These implementation classes are where work is allocated to threads.
/**
 * Splits request so that headers and body can be sent separately with optional
 * (multiple) responses in between (e.g. 100 Continue). Also request and
 * response always sent/received in different calls.
 *
 * Synchronous and asynchronous versions of each method are provided.
 *
 * Separate implementations of this class exist for HTTP/1.1 and HTTP/2
 *      Http1Exchange   (HTTP/1.1)
 *      Stream          (HTTP/2)
 *
 * These implementation classes are where work is allocated to threads.
 */
abstract class ExchangeImpl<T> {

    private static final Logger debug =
            Utils.getDebugLogger("ExchangeImpl"::toString, Utils.DEBUG);

    final Exchange<T> exchange;

    ExchangeImpl(Exchange<T> e) {
        // e == null means a http/2 pushed stream
        this.exchange = e;
    }

    final Exchange<T> getExchange() {
        return exchange;
    }


    
Returns the HttpConnection instance to which this exchange is assigned. /**
     * Returns the {@link HttpConnection} instance to which this exchange is
     * assigned.
     */
    abstract HttpConnection connection();

    
Initiates a new exchange and assigns it to a connection if one exists
already. connection usually null.
/**
     * Initiates a new exchange and assigns it to a connection if one exists
     * already. connection usually null.
     */
    static <U> CompletableFuture<? extends ExchangeImpl<U>>
    get(Exchange<U> exchange, HttpConnection connection)
    {
        if (exchange.version() == HTTP_1_1) {
            if (debug.on())
                debug.log("get: HTTP/1.1: new Http1Exchange");
            return createHttp1Exchange(exchange, connection);
        } else {
            Http2ClientImpl c2 = exchange.client().client2(); // #### improve
            HttpRequestImpl request = exchange.request();
            CompletableFuture<Http2Connection> c2f = c2.getConnectionFor(request, exchange);
            if (debug.on())
                debug.log("get: Trying to get HTTP/2 connection");
            // local variable required here; see JDK-8223553
            CompletableFuture<CompletableFuture<? extends ExchangeImpl<U>>> fxi =
                c2f.handle((h2c, t) -> createExchangeImpl(h2c, t, exchange, connection));
            return fxi.thenCompose(x->x);
        }
    }

    private static <U> CompletableFuture<? extends ExchangeImpl<U>>
    createExchangeImpl(Http2Connection c,
                       Throwable t,
                       Exchange<U> exchange,
                       HttpConnection connection)
    {
        if (debug.on())
            debug.log("handling HTTP/2 connection creation result");
        boolean secure = exchange.request().secure();
        if (t != null) {
            if (debug.on())
                debug.log("handling HTTP/2 connection creation failed: %s",
                                 (Object)t);
            t = Utils.getCompletionCause(t);
            if (t instanceof Http2Connection.ALPNException) {
                Http2Connection.ALPNException ee = (Http2Connection.ALPNException)t;
                AbstractAsyncSSLConnection as = ee.getConnection();
                if (debug.on())
                    debug.log("downgrading to HTTP/1.1 with: %s", as);
                CompletableFuture<? extends ExchangeImpl<U>> ex =
                        createHttp1Exchange(exchange, as);
                return ex;
            } else {
                if (debug.on())
                    debug.log("HTTP/2 connection creation failed "
                                     + "with unexpected exception: %s", (Object)t);
                return MinimalFuture.failedFuture(t);
            }
        }
        if (secure && c== null) {
            if (debug.on())
                debug.log("downgrading to HTTP/1.1 ");
            CompletableFuture<? extends ExchangeImpl<U>> ex =
                    createHttp1Exchange(exchange, null);
            return ex;
        }
        if (c == null) {
            // no existing connection. Send request with HTTP 1 and then
            // upgrade if successful
            if (debug.on())
                debug.log("new Http1Exchange, try to upgrade");
            return createHttp1Exchange(exchange, connection)
                    .thenApply((e) -> {
                        exchange.h2Upgrade();
                        return e;
                    });
        } else {
            if (debug.on()) debug.log("creating HTTP/2 streams");
            Stream<U> s = c.createStream(exchange);
            CompletableFuture<? extends ExchangeImpl<U>> ex = MinimalFuture.completedFuture(s);
            return ex;
        }
    }

    private static <T> CompletableFuture<Http1Exchange<T>>
    createHttp1Exchange(Exchange<T> ex, HttpConnection as)
    {
        try {
            return MinimalFuture.completedFuture(new Http1Exchange<>(ex, as));
        } catch (Throwable e) {
            return MinimalFuture.failedFuture(e);
        }
    }

    // Called for 204 response - when no body is permitted
    void nullBody(HttpResponse<T> resp, Throwable t) {
        // Needed for HTTP/1.1 to close the connection or return it to the pool
        // Needed for HTTP/2 to subscribe a dummy subscriber and close the stream
    }

    /* The following methods have separate HTTP/1.1 and HTTP/2 implementations */

    abstract CompletableFuture<ExchangeImpl<T>> sendHeadersAsync();

    
Sends a request body, after request headers have been sent. /** Sends a request body, after request headers have been sent. */
    abstract CompletableFuture<ExchangeImpl<T>> sendBodyAsync();

    abstract CompletableFuture<T> readBodyAsync(HttpResponse.BodyHandler<T> handler,
                                                boolean returnConnectionToPool,
                                                Executor executor);

    
Ignore/consume the body.
/**
     * Ignore/consume the body.
     */
    abstract CompletableFuture<Void> ignoreBody();


    
Gets the response headers. Completes before body is read. /** Gets the response headers. Completes before body is read. */
    abstract CompletableFuture<Response> getResponseAsync(Executor executor);


    
Cancels a request.  Not currently exposed through API. /** Cancels a request.  Not currently exposed through API. */
    abstract void cancel();

    
Cancels a request with a cause.  Not currently exposed through API.
/**
     * Cancels a request with a cause.  Not currently exposed through API.
     */
    abstract void cancel(IOException cause);

    
Called when the exchange is released, so that cleanup actions may be
performed - such as deregistering callbacks.
Typically released is called during upgrade, when an HTTP/2 stream
takes over from an Http1Exchange, or when a new exchange is created
during a multi exchange before the final response body was received.
/**
     * Called when the exchange is released, so that cleanup actions may be
     * performed - such as deregistering callbacks.
     * Typically released is called during upgrade, when an HTTP/2 stream
     * takes over from an Http1Exchange, or when a new exchange is created
     * during a multi exchange before the final response body was received.
     */
    abstract void released();

    
Called when the exchange is completed, so that cleanup actions may be
performed - such as deregistering callbacks.
Typically, completed is called at the end of the exchange, when the
final response body has been received (or an error has caused the
completion of the exchange).
/**
     * Called when the exchange is completed, so that cleanup actions may be
     * performed - such as deregistering callbacks.
     * Typically, completed is called at the end of the exchange, when the
     * final response body has been received (or an error has caused the
     * completion of the exchange).
     */
    abstract void completed();

    
Returns true if this exchange was canceled.
Returns:
true if this exchange was canceled./**
     * Returns true if this exchange was canceled.
     * @return true if this exchange was canceled.
     */
    abstract boolean isCanceled();

    
Returns the cause for which this exchange was canceled, if available.
Returns:
the cause for which this exchange was canceled, if available./**
     * Returns the cause for which this exchange was canceled, if available.
     * @return the cause for which this exchange was canceled, if available.
     */
    abstract Throwable getCancelCause();
}