OkHttp 源码分析

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implementation "com.squareup.okhttp3:okhttp:4.9.0"

基本用法

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// 创建一个 OkHttpClient 
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.build();
// 创建一个请求体 Request
Request request = new Request.Builder()
.url("http://wwww.baidu.com")
.get()
.build();
// 网络请求 Call
Call call = okHttpClient.newCall(request);
call.enqueue(new Callback() {
@Override
public void onFailure(@NotNull Call call, @NotNull IOException e) {
// 请求失败回调
}

@Override
public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
// 请求成功回调
}
});

// call.execute()

核心处理流程图

来自:开源库—OkHttp 源码解析

172b3a24e88d0981

OkHttpClient 的创建

OkHttpClient 实例通过建造者模式创建。

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internal var dispatcher: Dispatcher = Dispatcher()
internal var connectionPool: ConnectionPool = ConnectionPool()
internal val interceptors: MutableList<Interceptor> = mutableListOf()
internal val networkInterceptors: MutableList<Interceptor> = mutableListOf()
internal var eventListenerFactory: EventListener.Factory = EventListener.NONE.asFactory()
internal var retryOnConnectionFailure = true
internal var authenticator: Authenticator = Authenticator.NONE
internal var followRedirects = true
internal var followSslRedirects = true
internal var cookieJar: CookieJar = CookieJar.NO_COOKIES
internal var cache: Cache? = null
internal var dns: Dns = Dns.SYSTEM
internal var proxy: Proxy? = null
internal var proxySelector: ProxySelector? = null
internal var proxyAuthenticator: Authenticator = Authenticator.NONE
internal var socketFactory: SocketFactory = SocketFactory.getDefault()
internal var sslSocketFactoryOrNull: SSLSocketFactory? = null
internal var x509TrustManagerOrNull: X509TrustManager? = null
internal var connectionSpecs: List<ConnectionSpec> = DEFAULT_CONNECTION_SPECS
internal var protocols: List<Protocol> = DEFAULT_PROTOCOLS
internal var hostnameVerifier: HostnameVerifier = OkHostnameVerifier
internal var certificatePinner: CertificatePinner = CertificatePinner.DEFAULT
internal var certificateChainCleaner: CertificateChainCleaner? = null
internal var callTimeout = 0
internal var connectTimeout = 10_000
internal var readTimeout = 10_000
internal var writeTimeout = 10_000
internal var pingInterval = 0
internal var minWebSocketMessageToCompress = RealWebSocket.DEFAULT_MINIMUM_DEFLATE_SIZE
internal var routeDatabase: RouteDatabase? = null

Request 创建

Request 同样通过建造者模式创建。

Call 创建

将 Request 实例传入 OkHttpClient 对象的 newCall 方法中创建 Call 对象。

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/** Prepares the [request] to be executed at some point in the future. */
override fun newCall(request: Request): Call = RealCall(this, request, forWebSocket = false)

Call 是一个接口,这里创建的是 Call 的实现类 RealCall。

RealCall

execute 同步

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override fun execute(): Response {
check(executed.compareAndSet(false, true)) { "Already Executed" }

timeout.enter()
callStart()
try {
client.dispatcher.executed(this)
return getResponseWithInterceptorChain()
} finally {
client.dispatcher.finished(this)
}
}

首先检查 AtomBoolean 类的变量 executed 是否已经执行,已经执行过会抛出异常。

超时计时。

调用 OkHttpClient 的 Dispatcher 的 executed 方法执行 Call,调用 getResponseWithInterceptorChain 获得 Response。

最后关闭 Call。

enqueue 异步

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override fun enqueue(responseCallback: Callback) {
check(executed.compareAndSet(false, true)) { "Already Executed" }

callStart()
client.dispatcher.enqueue(AsyncCall(responseCallback))
}

将 Callback 封装为一个 AsyncCall。

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internal fun enqueue(call: AsyncCall) {
synchronized(this) {
readyAsyncCalls.add(call)

// Mutate the AsyncCall so that it shares the AtomicInteger of an existing running call to
// the same host.
if (!call.call.forWebSocket) {
val existingCall = findExistingCallWithHost(call.host)
if (existingCall != null) call.reuseCallsPerHostFrom(existingCall)
}
}
promoteAndExecute()
}
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/**
* Promotes eligible calls from [readyAsyncCalls] to [runningAsyncCalls] and runs them on the
* executor service. Must not be called with synchronization because executing calls can call
* into user code.
*
* @return true if the dispatcher is currently running calls.
*/
private fun promoteAndExecute(): Boolean {
this.assertThreadDoesntHoldLock()

val executableCalls = mutableListOf<AsyncCall>()
val isRunning: Boolean
synchronized(this) {
val i = readyAsyncCalls.iterator()
while (i.hasNext()) {
val asyncCall = i.next()

if (runningAsyncCalls.size >= this.maxRequests) break // Max capacity.
if (asyncCall.callsPerHost.get() >= this.maxRequestsPerHost) continue // Host max capacity.

i.remove()
asyncCall.callsPerHost.incrementAndGet()
executableCalls.add(asyncCall)
runningAsyncCalls.add(asyncCall)
}
isRunning = runningCallsCount() > 0
}

for (i in 0 until executableCalls.size) {
val asyncCall = executableCalls[i]
asyncCall.executeOn(executorService)
}

return isRunning
}
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/**
* Attempt to enqueue this async call on [executorService]. This will attempt to clean up
* if the executor has been shut down by reporting the call as failed.
*/
fun executeOn(executorService: ExecutorService) {
client.dispatcher.assertThreadDoesntHoldLock()

var success = false
try {
executorService.execute(this)
success = true
} catch (e: RejectedExecutionException) {
val ioException = InterruptedIOException("executor rejected")
ioException.initCause(e)
noMoreExchanges(ioException)
responseCallback.onFailure(this@RealCall, ioException)
} finally {
if (!success) {
client.dispatcher.finished(this) // This call is no longer running!
}
}
}
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override fun run() {
threadName("OkHttp ${redactedUrl()}") {
var signalledCallback = false
timeout.enter()
try {
val response = getResponseWithInterceptorChain()
signalledCallback = true
responseCallback.onResponse(this@RealCall, response)
} catch (e: IOException) {
if (signalledCallback) {
// Do not signal the callback twice!
Platform.get().log("Callback failure for ${toLoggableString()}", Platform.INFO, e)
} else {
responseCallback.onFailure(this@RealCall, e)
}
} catch (t: Throwable) {
cancel()
if (!signalledCallback) {
val canceledException = IOException("canceled due to $t")
canceledException.addSuppressed(t)
responseCallback.onFailure(this@RealCall, canceledException)
}
throw t
} finally {
client.dispatcher.finished(this)
}
}
}

调用 getResponseWithInterceptorChain() 获得 Response。

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@Throws(IOException::class)
internal fun getResponseWithInterceptorChain(): Response {
// Build a full stack of interceptors.
val interceptors = mutableListOf<Interceptor>()
interceptors += client.interceptors
interceptors += RetryAndFollowUpInterceptor(client)
interceptors += BridgeInterceptor(client.cookieJar)
interceptors += CacheInterceptor(client.cache)
interceptors += ConnectInterceptor
if (!forWebSocket) {
interceptors += client.networkInterceptors
}
interceptors += CallServerInterceptor(forWebSocket)

val chain = RealInterceptorChain(
call = this,
interceptors = interceptors,
index = 0,
exchange = null,
request = originalRequest,
connectTimeoutMillis = client.connectTimeoutMillis,
readTimeoutMillis = client.readTimeoutMillis,
writeTimeoutMillis = client.writeTimeoutMillis
)

var calledNoMoreExchanges = false
try {
val response = chain.proceed(originalRequest)
if (isCanceled()) {
response.closeQuietly()
throw IOException("Canceled")
}
return response
} catch (e: IOException) {
calledNoMoreExchanges = true
throw noMoreExchanges(e) as Throwable
} finally {
if (!calledNoMoreExchanges) {
noMoreExchanges(null)
}
}
}

这里先初始化 interceptor,再根据这些 interceptor 创建 RealInterceptorChain,调用 proceed 处理请求:

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@Throws(IOException::class)
override fun proceed(request: Request): Response {
check(index < interceptors.size)

calls++

if (exchange != null) {
check(exchange.finder.sameHostAndPort(request.url)) {
"network interceptor ${interceptors[index - 1]} must retain the same host and port"
}
check(calls == 1) {
"network interceptor ${interceptors[index - 1]} must call proceed() exactly once"
}
}

// Call the next interceptor in the chain.
val next = copy(index = index + 1, request = request)
val interceptor = interceptors[index]

@Suppress("USELESS_ELVIS")
val response = interceptor.intercept(next) ?: throw NullPointerException(
"interceptor $interceptor returned null")

if (exchange != null) {
check(index + 1 >= interceptors.size || next.calls == 1) {
"network interceptor $interceptor must call proceed() exactly once"
}
}

check(response.body != null) { "interceptor $interceptor returned a response with no body" }

return response
}

调用 copy 函数,获得一个 index = index + 1 的 RealInterceptorChain,接着获得 list 中 index 位置的 interceptor,接着调用 interceptor.intercept 得到 Response。

RetryAndFollowUpInterceptor

除了用户通过 OkHttpClient 设置的 interceptor,第一个加到列表中的就是 RetryAndFollowUpInterceptor,TA 的 intercept:

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@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val realChain = chain as RealInterceptorChain
var request = chain.request
val call = realChain.call
var followUpCount = 0
var priorResponse: Response? = null
var newExchangeFinder = true
var recoveredFailures = listOf<IOException>()
while (true) {
call.enterNetworkInterceptorExchange(request, newExchangeFinder)

var response: Response
var closeActiveExchange = true
try {
if (call.isCanceled()) {
throw IOException("Canceled")
}

try {
response = realChain.proceed(request)
newExchangeFinder = true
} catch (e: RouteException) {
// The attempt to connect via a route failed. The request will not have been sent.
if (!recover(e.lastConnectException, call, request, requestSendStarted = false)) {
throw e.firstConnectException.withSuppressed(recoveredFailures)
} else {
recoveredFailures += e.firstConnectException
}
newExchangeFinder = false
continue
} catch (e: IOException) {
// An attempt to communicate with a server failed. The request may have been sent.
if (!recover(e, call, request, requestSendStarted = e !is ConnectionShutdownException)) {
throw e.withSuppressed(recoveredFailures)
} else {
recoveredFailures += e
}
newExchangeFinder = false
continue
}

// Attach the prior response if it exists. Such responses never have a body.
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build()
}

val exchange = call.interceptorScopedExchange
val followUp = followUpRequest(response, exchange)

if (followUp == null) {
if (exchange != null && exchange.isDuplex) {
call.timeoutEarlyExit()
}
closeActiveExchange = false
return response
}

val followUpBody = followUp.body
if (followUpBody != null && followUpBody.isOneShot()) {
closeActiveExchange = false
return response
}

response.body?.closeQuietly()

if (++followUpCount > MAX_FOLLOW_UPS) {
throw ProtocolException("Too many follow-up requests: $followUpCount")
}

request = followUp
priorResponse = response
} finally {
call.exitNetworkInterceptorExchange(closeActiveExchange)
}
}
}

可以看到这里调用了下一个 interceptor 的 proceed 方法。其它的 interceptor 也是这样,直到 list 中的最后一个 CallServerInterceptor:

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@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val realChain = chain as RealInterceptorChain
val exchange = realChain.exchange!!
val request = realChain.request
val requestBody = request.body
val sentRequestMillis = System.currentTimeMillis()

exchange.writeRequestHeaders(request)

var invokeStartEvent = true
var responseBuilder: Response.Builder? = null
if (HttpMethod.permitsRequestBody(request.method) && requestBody != null) {
// If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
// Continue" response before transmitting the request body. If we don't get that, return
// what we did get (such as a 4xx response) without ever transmitting the request body.
if ("100-continue".equals(request.header("Expect"), ignoreCase = true)) {
exchange.flushRequest()
responseBuilder = exchange.readResponseHeaders(expectContinue = true)
exchange.responseHeadersStart()
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 {
// Write the request body if the "Expect: 100-continue" expectation was met.
val bufferedRequestBody = exchange.createRequestBody(request, false).buffer()
requestBody.writeTo(bufferedRequestBody)
bufferedRequestBody.close()
}
} else {
exchange.noRequestBody()
if (!exchange.connection.isMultiplexed) {
// If the "Expect: 100-continue" expectation wasn't met, prevent the HTTP/1 connection
// from being reused. Otherwise we're still obligated to transmit the request body to
// leave the connection in a consistent state.
exchange.noNewExchangesOnConnection()
}
}
} else {
exchange.noRequestBody()
}

if (requestBody == null || !requestBody.isDuplex()) {
exchange.finishRequest()
}
if (responseBuilder == null) {
responseBuilder = exchange.readResponseHeaders(expectContinue = false)!!
if (invokeStartEvent) {
exchange.responseHeadersStart()
invokeStartEvent = false
}
}
var response = responseBuilder
.request(request)
.handshake(exchange.connection.handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build()
var code = response.code
if (code == 100) {
// Server sent a 100-continue even though we did not request one. Try again to read the actual
// response status.
responseBuilder = exchange.readResponseHeaders(expectContinue = false)!!
if (invokeStartEvent) {
exchange.responseHeadersStart()
}
response = responseBuilder
.request(request)
.handshake(exchange.connection.handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build()
code = response.code
}

exchange.responseHeadersEnd(response)

response = if (forWebSocket && code == 101) {
// Connection is upgrading, but we need to ensure interceptors see a non-null response body.
response.newBuilder()
.body(EMPTY_RESPONSE)
.build()
} else {
response.newBuilder()
.body(exchange.openResponseBody(response))
.build()
}
if ("close".equals(response.request.header("Connection"), ignoreCase = true) ||
"close".equals(response.header("Connection"), ignoreCase = true)) {
exchange.noNewExchangesOnConnection()
}
if ((code == 204 || code == 205) && response.body?.contentLength() ?: -1L > 0L) {
throw ProtocolException(
"HTTP $code had non-zero Content-Length: ${response.body?.contentLength()}")
}
return response
}

是 chain 中的最后一个 interceptor,向 server 进行网络请求。这一个 interceptor 结束后,return Response,前面的 interceptor 再进行处理。

RetryAndFollowUpInterceptor

BridgeInterceptor

CacheInterceptor

ConnectInterceptor

CallServerInterceptor