func()

in http2/server.go [814:939]
102 lines of code
31 McCabe index (conditional complexity)

func (sc *serverConn) serve() {
	sc.serveG.check()
	defer sc.notePanic()
	defer sc.conn.Close()
	defer sc.closeAllStreamsOnConnClose()
	defer sc.stopShutdownTimer()
	defer close(sc.doneServing) // unblocks handlers trying to send

	if VerboseLogs {
		sc.vlogf("http2: server connection from %v on %p", sc.conn.RemoteAddr(), sc.hs)
	}

	sc.writeFrame(FrameWriteRequest{
		write: writeSettings{
			{SettingMaxFrameSize, sc.srv.maxReadFrameSize()},
			{SettingMaxConcurrentStreams, sc.advMaxStreams},
			{SettingMaxHeaderListSize, sc.maxHeaderListSize()},
			{SettingInitialWindowSize, uint32(sc.srv.initialStreamRecvWindowSize())},
		},
	})
	sc.unackedSettings++

	// Each connection starts with initialWindowSize inflow tokens.
	// If a higher value is configured, we add more tokens.
	if diff := sc.srv.initialConnRecvWindowSize() - initialWindowSize; diff > 0 {
		sc.sendWindowUpdate(nil, int(diff))
	}

	if err := sc.readPreface(); err != nil {
		sc.condlogf(err, "http2: server: error reading preface from client %v: %v", sc.conn.RemoteAddr(), err)
		return
	}
	// Now that we've got the preface, get us out of the
	// "StateNew" state. We can't go directly to idle, though.
	// Active means we read some data and anticipate a request. We'll
	// do another Active when we get a HEADERS frame.
	sc.setConnState(http.StateActive)
	sc.setConnState(http.StateIdle)

	if sc.srv.IdleTimeout != 0 {
		sc.idleTimer = time.AfterFunc(sc.srv.IdleTimeout, sc.onIdleTimer)
		defer sc.idleTimer.Stop()
	}

	go sc.readFrames() // closed by defer sc.conn.Close above

	settingsTimer := time.AfterFunc(firstSettingsTimeout, sc.onSettingsTimer)
	defer settingsTimer.Stop()

	loopNum := 0
	for {
		loopNum++
		select {
		case wr := <-sc.wantWriteFrameCh:
			if se, ok := wr.write.(StreamError); ok {
				sc.resetStream(se)
				break
			}
			sc.writeFrame(wr)
		case res := <-sc.wroteFrameCh:
			sc.wroteFrame(res)
		case res := <-sc.readFrameCh:
			// Process any written frames before reading new frames from the client since a
			// written frame could have triggered a new stream to be started.
			if sc.writingFrameAsync {
				select {
				case wroteRes := <-sc.wroteFrameCh:
					sc.wroteFrame(wroteRes)
				default:
				}
			}
			if !sc.processFrameFromReader(res) {
				return
			}
			res.readMore()
			if settingsTimer != nil {
				settingsTimer.Stop()
				settingsTimer = nil
			}
		case m := <-sc.bodyReadCh:
			sc.noteBodyRead(m.st, m.n)
		case msg := <-sc.serveMsgCh:
			switch v := msg.(type) {
			case func(int):
				v(loopNum) // for testing
			case *serverMessage:
				switch v {
				case settingsTimerMsg:
					sc.logf("timeout waiting for SETTINGS frames from %v", sc.conn.RemoteAddr())
					return
				case idleTimerMsg:
					sc.vlogf("connection is idle")
					sc.goAway(ErrCodeNo)
				case shutdownTimerMsg:
					sc.vlogf("GOAWAY close timer fired; closing conn from %v", sc.conn.RemoteAddr())
					return
				case gracefulShutdownMsg:
					sc.startGracefulShutdownInternal()
				default:
					panic("unknown timer")
				}
			case *startPushRequest:
				sc.startPush(v)
			default:
				panic(fmt.Sprintf("unexpected type %T", v))
			}
		}

		// If the peer is causing us to generate a lot of control frames,
		// but not reading them from us, assume they are trying to make us
		// run out of memory.
		if sc.queuedControlFrames > sc.srv.maxQueuedControlFrames() {
			sc.vlogf("http2: too many control frames in send queue, closing connection")
			return
		}

		// Start the shutdown timer after sending a GOAWAY. When sending GOAWAY
		// with no error code (graceful shutdown), don't start the timer until
		// all open streams have been completed.
		sentGoAway := sc.inGoAway && !sc.needToSendGoAway && !sc.writingFrame
		gracefulShutdownComplete := sc.goAwayCode == ErrCodeNo && sc.curOpenStreams() == 0
		if sentGoAway && sc.shutdownTimer == nil && (sc.goAwayCode != ErrCodeNo || gracefulShutdownComplete) {
			sc.shutDownIn(goAwayTimeout)
		}
	}
}