*/
interface Connection {
  /** Returns the route used by this connection. */
  fun route(): Route

  /**
   * Returns the socket that this connection is using. Returns an
   * [SSL socket][javax.net.ssl.SSLSocket] if this connection is HTTPS. If this is an HTTP/2
   * connection the socket may be shared by multiple concurrent calls.
   */
  fun socket(): Socket

      }
    }
    return null
  }

  fun put(connection: RealConnection) {
    connection.lock.assertHeld()

    connections.add(connection)
//    connection.queueEvent { connectionListener.connectEnd(connection) }
    scheduleCloser()
  }

  /**
   * Notify this pool that [connection] has become idle. Returns true if the connection has been
   * removed from the pool and should be closed.

    return null
  }

  override fun connectionReleased(connection: Connection) {
  }

  override fun connectionConnectionAcquired(connection: RealConnection) {
  }

  override fun connectionConnectionReleased(connection: RealConnection) {
  }

  override fun connectionConnectionClosed(connection: RealConnection) {
  }

  override fun noNewExchanges(connection: RealConnection) {
  }

address may also share the same underlying TCP socket connection. Sharing a connection has substantial performance benefits: lower latency, higher throughput (due to [TCP slow start](https://www.igvita.com/2011/10/20/faster-web-vs-tcp-slow-start/)) and conserved battery. OkHttp uses a [ConnectionPool](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-connection-pool/) that automatically reuses HTTP/1.x connections and multiplexes HTTP/2 connections.

In OkHttp some fields of the address come...

A **Manager** is used to manage all incoming and outgoing connections to a server.

On startup all remote servers must be specified. 
From that individual connections will be spawned to each remote server, 
or incoming requests will be hooked up to the appropriate connection.

To get a connection to a specific server, use `Manager.Connection(host)` to get a connection to the specified host.
From this connection individual requests can be made.

    override val connection: Connection,
    val call: Call,
  ) : ConnectionEvent()

  data class ConnectionReleased(
    override val timestampNs: Long,
    override val connection: Connection,
    val call: Call,
  ) : ConnectionEvent() {
    override fun closes(event: ConnectionEvent): Boolean =
      event is ConnectionAcquired && connection == event.connection && call == event.call
  }

  }

  /**
   * Invoked after a connection has been acquired for the `call`.
   *
   * This can be invoked more than 1 time for a single [Call]. For example, if the response
   * to the [Call.request] is a redirect to a different address.
   */
  open fun connectionAcquired(
    call: Call,
    connection: Connection,
  ) {
  }

  /**
   * Invoked after a connection has been released for the `call`.
   *

    // flow-control window is fully depleted.
    if (!flushHeaders) {
      this.withLock {
        flushHeaders = (connection.writeBytesTotal >= connection.writeBytesMaximum)
      }
    }

    connection.writeHeaders(id, outFinished, responseHeaders)

    if (flushHeaders) {
      connection.flush()
    }
  }

        val http2SocketHandler = Http2SocketHandler(socket, protocol)
        val connection =
          Http2Connection.Builder(false, taskRunner)
            .socket(socket)
            .listener(http2SocketHandler)
            .build()
        connection.start()
        openConnections.add(connection)
        openClientSockets.remove(socket)
        return
      } else if (protocol !== Protocol.HTTP_1_1) {

After this, the client and the server have an **encrypted TCP connection**, this is what TLS provides. And then they can use that connection to start the actual **HTTP communication**.

And that's what **HTTPS** is, it's just plain **HTTP** inside a **secure TLS connection** instead of a pure (unencrypted) TCP connection.

!!! tip