Okhttp心跳策略研究

摘要： Android元件化架構 我是蒼王，以下是我這個系列的相關文章，有興趣可以參考一下，可以給個喜歡或者關注我的文章。 [Android]如何做一個崩潰率少於千分之三噶應用app--章節列表 這一張非常經典的心跳策略圖示 ...

這一張非常經典的心跳策略圖示

現在一般的心跳策略，都是從客戶端傳送一個ping訊號給伺服器，告訴伺服器是長連線存活。

伺服器會返回一個pong訊號給客戶端，讓其更新心跳執行緒時間。如果超時沒有接收到訊號，那麼客戶端考慮重連機制。

這裡說一下okhttp有提供了WebSocket的封裝，我們的應用也是使用了WebSocket，那就直接看一下WebSocket對pingpong的封裝

public Builder() {
……
//這裡預設的ping的時間間隔為0，因為okhttp也可以有如http短連線
pingInterval = 0;
}

Builder(OkHttpClient okHttpClient) {
……
//builder函式提供封裝
this.pingInterval = okHttpClient.pingInterval;
}
//設定間隔
public Builder pingInterval(long interval, TimeUnit unit) {
pingInterval = checkDuration("interval", interval, unit);
return this;
}

在RealWebSocket中啟動迴圈傳送ping訊號

public void initReaderAndWriter(String name, Streams streams) throws IOException {
synchronized (this) {
this.streams = streams;
this.writer = new WebSocketWriter(streams.client, streams.sink, random);
this.executor = new ScheduledThreadPoolExecutor(1, Util.threadFactory(name, false));
if (pingIntervalMillis != 0) {
//迴圈定時任務
executor.scheduleAtFixedRate(
new PingRunnable(), pingIntervalMillis, pingIntervalMillis, MILLISECONDS);
}
if (!messageAndCloseQueue.isEmpty()) {
runWriter(); // Send messages that were enqueued before we were connected.
}
}

reader = new WebSocketReader(streams.client, streams.source, this);
}


private final class PingRunnable implements Runnable {
PingRunnable() {
}

@Override public void run() {
//寫入ping訊號
writePingFrame();
}
}

void writePingFrame() {
WebSocketWriter writer;
int failedPing;
synchronized (this) {
if (failed) return;
writer = this.writer;
//是否等待pong訊號
failedPing = awaitingPong ? sentPingCount : -1;
//等待ping計數
sentPingCount++;
//等待pong
awaitingPong = true;
}

//ping失敗，長連線失效
if (failedPing != -1) {
failWebSocket(new SocketTimeoutException("sent ping but didn't receive pong within "
+ pingIntervalMillis + "ms (after " + (failedPing - 1) + " successful ping/pongs)"),
null);
return;
}

try {
//寫入空支付到websocket頭部
writer.writePing(ByteString.EMPTY);
} catch (IOException e) {
failWebSocket(e, null);
}
}

在RealWebSocket的call中執行loopReader監聽讀取接收到的資訊

/** Receive frames until there are no more. Invoked only by the reader thread. */
public void loopReader() throws IOException {
//監聽資訊
while (receivedCloseCode == -1) {
// This method call results in one or more onRead* methods being called on this thread.
reader.processNextFrame();
}
}

void processNextFrame() throws IOException {
//讀取頭部
readHeader();
if (isControlFrame) {
//讀取頭部資訊體
readControlFrame();
} else {
readMessageFrame();
}
}

讀取到是頂部資訊

private void readControlFrame() throws IOException {
if (frameLength > 0) {
source.readFully(controlFrameBuffer, frameLength);

if (!isClient) {
controlFrameBuffer.readAndWriteUnsafe(maskCursor);
maskCursor.seek(0);
toggleMask(maskCursor, maskKey);
maskCursor.close();
}
}

switch (opcode) {
//讀取ping訊號
case OPCODE_CONTROL_PING:
frameCallback.onReadPing(controlFrameBuffer.readByteString());
break;
//讀取pong訊號
case OPCODE_CONTROL_PONG:
frameCallback.onReadPong(controlFrameBuffer.readByteString());
break;
//讀取到關閉連線訊號
case OPCODE_CONTROL_CLOSE:
int code = CLOSE_NO_STATUS_CODE;
String reason = "";
long bufferSize = controlFrameBuffer.size();
if (bufferSize == 1) {
throw new ProtocolException("Malformed close payload length of 1.");
} else if (bufferSize != 0) {
code = controlFrameBuffer.readShort();
reason = controlFrameBuffer.readUtf8();
String codeExceptionMessage = WebSocketProtocol.closeCodeExceptionMessage(code);
if (codeExceptionMessage != null) throw new ProtocolException(codeExceptionMessage);
}
frameCallback.onReadClose(code, reason);
closed = true;
break;
default:
throw new ProtocolException("Unknown control opcode: " + toHexString(opcode));
}
}

讀取到pong訊號，等待pong置為false

@Override public synchronized void onReadPong(ByteString buffer) {
// This API doesn't expose pings.
receivedPongCount++;
awaitingPong = false;
}

這邊做IM的應用的，說一下這邊方案，僅供參考。

手機進入後臺後十秒後主動關閉長連線，通過推送來維護訊息，這裡有個問題就是國內的Umeng推送可達率大家懂的，小米和華為還好點，如果是其他山寨機，到8.0後後臺很難保活了。如果是國外FCM送達率是非常高的，如果是最推國外平臺，直接依靠推送也非常可靠。