import okio.BufferedSource
import okio.ForwardingTimeout
import okio.Sink
import okio.Source
import okio.Timeout

/**
 * A socket connection that can be used to send HTTP/1.1 messages. This class strictly enforces the
 * following lifecycle:
 *
 *  1. [Send request headers][writeRequest].
 *  2. Open a sink to write the request body. Either [known][newKnownLengthSink] or
 *     [chunked][newChunkedSink].

  object DisconnectDuringResponseBody : SocketPolicy

  /**
   * Process the response without even attempting to reading the request body. For HTTP/2 this will
   * send [http2ErrorCode] after the response body or trailers. For HTTP/1 this will close the
   * socket after the response body or trailers.
   */
  class DoNotReadRequestBody(
    val http2ErrorCode: Int = 0,
  ) : SocketPolicy

    const val DEFAULT_INITIAL_WINDOW_SIZE = 65535

    /** HTTP/2: Size in bytes of the table used to decode the sender's header blocks. */
    const val HEADER_TABLE_SIZE = 1

    /** HTTP/2: The peer must not send a PUSH_PROMISE frame when this is 0. */
    const val ENABLE_PUSH = 2

    /** Sender's maximum number of concurrent streams. */
    const val MAX_CONCURRENT_STREAMS = 4

===========

This document describes the concurrency considerations for http/2 connections and the connection pool within OkHttp.

## HTTP/2 Connections

The HttpURLConnection API is a blocking API. You make a blocking write to send a request, and a blocking read to receive the response.

#### Blocking APIs

 *    cache.
 *
 * Sometimes a request will result in a conditional cache hit. If the cache contains a stale copy of
 * the response, the client will issue a conditional `GET`. The server will then send either
 * the updated response if it has changed, or a short 'not modified' response if the client's copy
 * is still valid. Such responses increment both the network count and hit count.
 *

    taskFaker.runTasks()
    client.listener.assertFailure(IOException::class.java, "source is closed")
    assertThat(client.webSocket!!.send("Hello!")).isFalse()
  }

  @Test
  fun socketClosedDuringMessageKillsWebSocket() {
    client2Server.source.close()
    assertThat(client.webSocket!!.send("Hello!")).isTrue()
    taskFaker.runTasks()
    client.listener.assertFailure(IOException::class.java, "source is closed")

    server.send(message3)
    clientListener.assertTextMessage(message3)

    // Empty client to server message.
    val message4 = ""
    client.send(message4)
    serverListener.assertTextMessage(message4)

    // Server to client message that shares context with message1.
    val message5 = message1 + message1
    server.send(message5)
    clientListener.assertTextMessage(message5)

  @Throws(IOException::class)
  fun connectionPreface() {
    this.withLock {
      if (closed) throw IOException("closed")
      if (!client) return // Nothing to write; servers don't send connection headers!
      if (logger.isLoggable(FINE)) {
        logger.fine(format(">> CONNECTION ${CONNECTION_PREFACE.hex()}"))
      }
      sink.write(CONNECTION_PREFACE)
      sink.flush()
    }
  }

          invokeStartEvent = false
        }
        if (responseBuilder == null) {
          if (requestBody.isDuplex()) {
            // Prepare a duplex body so that the application can send a request body later.
            exchange.flushRequest()
            val bufferedRequestBody = exchange.createRequestBody(request, true).buffer()
            requestBody.writeTo(bufferedRequestBody)
          } else {

### Conditional Cache Hit
 
When cache flags require checking the cache results are still valid an early cacheConditionalHit event is
received followed by a cache hit or miss.  Critically in the cache hit scenario the server won’t send the response body.

The response will have non-null `cacheResponse` and `networkResponse`. The cacheResponse will be used as the top level
response only if the response code is HTTP/1.1 304 Not Modified.
 
 - CallStart