HttpClient默认重试策略不处理SocketTimeoutException

摘要: # 背景
与公司外服务采用http交互，使用httpClient 4.5.2版本的默认重试策略DefaultHttpRequestRetryHandler，发现对方接口连接超时（3秒）后， **并不会重试** 而是直接抛出```ConnectTimeoutException```，不符合预期。
# 结论先行
httpClient默认重试策略DefaultHttpRequestRetryHandler针对连接超时和获取数据超时并不会重试，需要自定义重试策略。

背景

与公司外服务采用http交互，使用httpClient 4.5.2版本的默认重试策略DefaultHttpRequestRetryHandler，发现对方接口连接超时（3秒）后， 并不会重试 而是直接抛出

ConnectTimeoutException

，不符合预期。

结论先行

httpClient默认重试策略DefaultHttpRequestRetryHandler针对连接超时和获取数据超时并不会重试，需要自定义重试策略。

问题分析

详细场景

采用HttpClient 4.5.2发起http请求，代码如下，使用方式正常

//http设置，retryHandler采用组件提供默认的重试策略DefaultHttpRequestRetryHandler，重试次数为3
return HttpClients.custom()
.setConnectionManager(****)
.setDefaultRequestConfig(****)
.setRetryHandler(new DefaultHttpRequestRetryHandler())
.build();

//请求发起主要代码
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs, UTF_8));
CloseableHttpResponse response = httpClient.execute(request);
HttpEntity entity = response.getEntity();
……其他关闭资源代码

请求后过了超时时间3s得到ConnectTimeoutException异常，且log中没有重试日志，堆栈如下：

Caused by: org.apache.http.conn.ConnectTimeoutException: Connect to www.XXX.com:443 [www.XXX.com/XX.1.XX.12] failed: connect timed out
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:150)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:353)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:380)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)
at com.sankuai.meituan.resv.platform.utils.HttpUtil.getResult(HttpUtil.java:124)
... 36 more
Caused by: java.net.SocketTimeoutException: connect timed out
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at org.apache.http.conn.ssl.SSLConnectionSocketFactory.connectSocket(SSLConnectionSocketFactory.java:337)
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:141)
... 46 more

原因分析

出现这个问题，只好看默认重试策略的代码了，DefaultHttpRequestRetryHandler实现了HttpRequestRetryHandler，其中有这么一个方法

public boolean retryRequest(final IOException exception,final int executionCount,final HttpContext context)

，判断是否需要重试。

那么我们试图请求facebook（实验机器访问不了）来复现连接超时的情况，并进行断点调试，看这个方法的返回值。抛出的异常符合预期，即为ConnectTimeoutException，断点情况如下：



该方法的确返回了false，即不会重试。

代码分析

实例化DefaultHttpRequestRetryHandler时会初始化nonRetriableClasses，结果如上图圈红出所示，然后发现这个继承关系

public class ConnectTimeoutException extends InterruptedIOException {

，所以进入if分支返回false。

举一反三读取数据超时

连接超时不会重试，那读取数据超时是否会重试呢，根据继承关系

public class SocketTimeoutException extends java.io.InterruptedIOException

判断是不会重试的。我们通过测试来复现下。

复现方式：http请求本地某个服务，设置SocketTimeout为3s，在服务端打上断点，让client调用超时。
结果的确没有重试，异常堆栈如下，

Caused by: java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:137)
at org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:153)
at org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:282)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:140)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57)
at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:167)
at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:271)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)

解决方案

自定义重试策略，某些异常时让它返回true重试就好。

private class MyHttpRequestRetryHandler implements HttpRequestRetryHandler{

@Override
public boolean retryRequest(IOException exception, int executionCount, HttpContext context) {
if (executionCount > retryTimes){
return false;
}
if (exception instanceof InterruptedIOException
|| exception instanceof NoHttpResponseException) {
// Timeout or 服务端断开连接
return true;
}
// Unknown host
if (exception instanceof UnknownHostException) {
return false;
}
// SSL handshake exception
if (exception instanceof SSLException) {
return false;
}

final HttpClientContext clientContext = HttpClientContext.adapt(context);
final HttpRequest request = clientContext.getRequest();
boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
if (idempotent) {
// Retry if the request is considered idempotent
return true;
}
return false;
}
}

几个超时时间设置参数

/** 从连接池获取连接超时时间 **/
private int connectionRequestTimeout = 500;

/** 连接一个url的连接等待时间,建立socket连接时间 **/
private int connectTimeout = 3000;

/** 传输数据等待返回的超时时间 **/
private int socketTimeout = 3000;

反思总结

coding时认为默认重试策略遇到连接超时是会重试的，但实际没有进行这种异常case的测试，也没有看默认策略的代码实现，所以线上出现超时并没有重试的情况。

总结 ：为异常流程开发的处理方式，测试的时候虽然会麻烦些，但应该覆盖到，保证线上真正出现异常时恢复流程能正常work。