okhttp源码解析--五种内部拦截器

Okhttpclient流程图.png

okhttp中的拦截器：

1. RetryAndFollowUpInterceptor源码以及作用

 private static final int MAX_FOLLOW_UPS = 20;
@Override public Response intercept(Chain chain) throws IOException {
    Request request = chain.request();

    streamAllocation = new StreamAllocation(
        client.connectionPool(), createAddress(request.url()), callStackTrace);

    Response priorResponse = null;
    while (true) {
      if (canceled) {
        streamAllocation.release();
        throw new IOException("Canceled");
      }

      Response response = null;
      boolean releaseConnection = true;
      try {
        response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);
        releaseConnection = false;
      }  finally {
        // We're throwing an unchecked exception. Release any resources.
        if (releaseConnection) {
          streamAllocation.streamFailed(null);
          streamAllocation.release();
        }
      }
      
      if (++followUpCount > MAX_FOLLOW_UPS) {
        streamAllocation.release();
        throw new ProtocolException("Too many follow-up requests: " + followUpCount);
      }
    }
  }

由于源码比较多这里做了很大段的删减，这里主要体现了RetryAndFollowUpInterceptor的作用就是重连，重连次数是MAX_FOLLOW_UPS（20次）

总结
1.创建streamAllocation对象（里面包含我们所有对http请求对组件）
2.调用(RealInterceptorChain)proceed进行网络请求
3.根据异常结果或者响应结果判断是否需要重新请求
4.调用下一个拦截器，对response进行处理，返回给上一个拦截器

2. BridgeInterceptor源码以及作用

/**
 * Bridges from application code to network code. First it builds a network request from a user
 * request. Then it proceeds to call the network. Finally it builds a user response from the network
 * response.
 */
public final class BridgeInterceptor implements Interceptor {
  private final CookieJar cookieJar;

  public BridgeInterceptor(CookieJar cookieJar) {
    this.cookieJar = cookieJar;
  }

  @Override public Response intercept(Chain chain) throws IOException {
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();

    RequestBody body = userRequest.body();
    if (body != null) {
      MediaType contentType = body.contentType();
      if (contentType != null) {
        requestBuilder.header("Content-Type", contentType.toString());
      }

      long contentLength = body.contentLength();
      if (contentLength != -1) {
        requestBuilder.header("Content-Length", Long.toString(contentLength));
        requestBuilder.removeHeader("Transfer-Encoding");
      } else {
        requestBuilder.header("Transfer-Encoding", "chunked");
        requestBuilder.removeHeader("Content-Length");
      }
    }

    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", hostHeader(userRequest.url(), false));
    }

    if (userRequest.header("Connection") == null) {
      requestBuilder.header("Connection", "Keep-Alive");
    }

    // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
    // the transfer stream.
    boolean transparentGzip = false;
    if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
      transparentGzip = true;
      requestBuilder.header("Accept-Encoding", "gzip");
    }

    List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
    if (!cookies.isEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies));
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", Version.userAgent());
    }

    Response networkResponse = chain.proceed(requestBuilder.build());

    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

    Response.Builder responseBuilder = networkResponse.newBuilder()
        .request(userRequest);

    if (transparentGzip
        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
        && HttpHeaders.hasBody(networkResponse)) {
      GzipSource responseBody = new GzipSource(networkResponse.body().source());
      Headers strippedHeaders = networkResponse.headers().newBuilder()
          .removeAll("Content-Encoding")
          .removeAll("Content-Length")
          .build();
      responseBuilder.headers(strippedHeaders);
      responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
    }

    return responseBuilder.build();
  }

  /** Returns a 'Cookie' HTTP request header with all cookies, like {@code a=b; c=d}. */
  private String cookieHeader(List<Cookie> cookies) {
    StringBuilder cookieHeader = new StringBuilder();
    for (int i = 0, size = cookies.size(); i < size; i++) {
      if (i > 0) {
        cookieHeader.append("; ");
      }
      Cookie cookie = cookies.get(i);
      cookieHeader.append(cookie.name()).append('=').append(cookie.value());
    }
    return cookieHeader.toString();
  }
}

从各种header中可以很好的看出BridgeInterceptor主要是对请求体Request的设置

 if (transparentGzip
        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
        && HttpHeaders.hasBody(networkResponse)) {
      GzipSource responseBody = new GzipSource(networkResponse.body().source());
      Headers strippedHeaders = networkResponse.headers().newBuilder()
          .removeAll("Content-Encoding")
          .removeAll("Content-Length")
          .build();
      responseBuilder.headers(strippedHeaders);
      responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
    }

对gzip的支持使我们直接获取到解压后的response

总结：
1.将用户构建Request请求转化为能够进行网络访问的请求
2.将这个符合网络请求的Request进行网络请求
3.将网络请求回来的响应Respond转化为用户可用的response（包括gzip解压）

3. CacheInterceptor源码以及作用

okhttp的缓存使用非常简单，只需要OkHttpClient创建的时候设置cache就可以了

new OkHttpClient().newBuilder().cache(new Cache(new File("cache"),1024*1024*10)).connectTimeout(5,TimeUnit.SECONDS).build();

@Override public Response intercept(Chain chain) throws IOException {
1   Response cacheCandidate = cache != null
        ? cache.get(chain.request())
        : null;

    long now = System.currentTimeMillis();

2   CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
    Request networkRequest = strategy.networkRequest;
    Response cacheResponse = strategy.cacheResponse;

    if (cache != null) {
3     cache.trackResponse(strategy);
    }

    if (cacheCandidate != null && cacheResponse == null) {
      closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
    }

    // If we're forbidden from using the network and the cache is insufficient, fail.
4   if (networkRequest == null && cacheResponse == null) {
      return new Response.Builder()
          .request(chain.request())
          .protocol(Protocol.HTTP_1_1)
          .code(504)
          .message("Unsatisfiable Request (only-if-cached)")
          .body(Util.EMPTY_RESPONSE)
          .sentRequestAtMillis(-1L)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build();
    }

    // If we don't need the network, we're done.
5   if (networkRequest == null) {
      return cacheResponse.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build();
    }

    Response networkResponse = null;
    try {
      networkResponse = chain.proceed(networkRequest);
    } finally {
      // If we're crashing on I/O or otherwise, don't leak the cache body.
      if (networkResponse == null && cacheCandidate != null) {
        closeQuietly(cacheCandidate.body());
      }
    }

    // If we have a cache response too, then we're doing a conditional get.
6  if (cacheResponse != null) {
      if (networkResponse.code() == HTTP_NOT_MODIFIED) {
        Response response = cacheResponse.newBuilder()
            .headers(combine(cacheResponse.headers(), networkResponse.headers()))
            .sentRequestAtMillis(networkResponse.sentRequestAtMillis())
            .receivedResponseAtMillis(networkResponse.receivedResponseAtMillis())
            .cacheResponse(stripBody(cacheResponse))
            .networkResponse(stripBody(networkResponse))
            .build();
        networkResponse.body().close();

        // Update the cache after combining headers but before stripping the
        // Content-Encoding header (as performed by initContentStream()).
        cache.trackConditionalCacheHit();
        cache.update(cacheResponse, response);
        return response;
      } else {
        closeQuietly(cacheResponse.body());
      }
    }

    Response response = networkResponse.newBuilder()
        .cacheResponse(stripBody(cacheResponse))
        .networkResponse(stripBody(networkResponse))
        .build();

7  if (cache != null) {
      if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
        // Offer this request to the cache.
        CacheRequest cacheRequest = cache.put(response);
        return cacheWritingResponse(cacheRequest, response);
      }

      if (HttpMethod.invalidatesCache(networkRequest.method())) {
        try {
          cache.remove(networkRequest);
        } catch (IOException ignored) {
          // The cache cannot be written.
        }
      }
    }

    return response;
  }

• 1.cache不为空苁中获取cacheCandidate
• 2.通过FacheStrategy.Factory获取到缓存策略，获取网络请求与响应缓存
• 3.调用cache的同步方法trackResponse，保证请求一致性

  synchronized void trackResponse(CacheStrategy cacheStrategy) {
    requestCount++;

    if (cacheStrategy.networkRequest != null) {
      // If this is a conditional request, we'll increment hitCount if/when it hits.
      networkCount++;
    } else if (cacheStrategy.cacheResponse != null) {
      // This response uses the cache and not the network. That's a cache hit.
      hitCount++;
    }
  }

• 4.没网和没缓存的请求下直接返回一个504错误响应
• 5.没网的情况下直接通过响应缓存创建Response并返回
• 6.有响应缓存(cacheResponse != null)并且响应码为304时(networkResponse.code() == HTTP_NOT_MODIFIED)--该响应码意思直接使用缓存。通过cacheResponse创建Response并返回。
• 7.cache不为空，有请求头和缓存策略时，通过cache的put方法进行缓存。

CacheInterceptor拦截器中获取了cache和CacheStrategy，然后一系列的判网络情况和缓存体的情况来对Response进行处理,代码较多但比较简单就不做过多解释,如果想要深入了解建议从cache类入手

4. ConnectInterceptor源码以及作用

/** Opens a connection to the target server and proceeds to the next interceptor. */
public final class ConnectInterceptor implements Interceptor {
  public final OkHttpClient client;

  public ConnectInterceptor(OkHttpClient client) {
    this.client = client;
  }

  @Override public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    Request request = realChain.request();
    StreamAllocation streamAllocation = realChain.streamAllocation();

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    boolean doExtensiveHealthChecks = !request.method().equals("GET");
    HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);
    RealConnection connection = streamAllocation.connection();

    return realChain.proceed(request, streamAllocation, httpCodec, connection);
  }
}

    StreamAllocation streamAllocation = realChain.streamAllocation();

从拦截器链获取到了StreamAllocation对象，这里的StreamAllocation是在RetryAndFollowUpInterceptor初始化完成的而且设置了链接池、url路径等。

 public HttpCodec newStream(OkHttpClient client, boolean doExtensiveHealthChecks) {
    int connectTimeout = client.connectTimeoutMillis();
    int readTimeout = client.readTimeoutMillis();
    int writeTimeout = client.writeTimeoutMillis();
    boolean connectionRetryEnabled = client.retryOnConnectionFailure();

    try {
      RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
          writeTimeout, connectionRetryEnabled, doExtensiveHealthChecks);

      HttpCodec resultCodec;
      if (resultConnection.http2Connection != null) {
        resultCodec = new Http2Codec(client, this, resultConnection.http2Connection);
      } else {
        resultConnection.socket().setSoTimeout(readTimeout);
        resultConnection.source.timeout().timeout(readTimeout, MILLISECONDS);
        resultConnection.sink.timeout().timeout(writeTimeout, MILLISECONDS);
        resultCodec = new Http1Codec(
            client, this, resultConnection.source, resultConnection.sink);
      }

      synchronized (connectionPool) {
        codec = resultCodec;
        return resultCodec;
      }
    } catch (IOException e) {
      throw new RouteException(e);
    }
  }

• findHealthyConnection()最终从连接池ConnectionPool获得可用连接resultConnection并为
• 创建并返回HttpCodec(http中所有流对象都封装到了HttpCodec实现类中)

总结
1.ConnectInterceptor获取intercepter传过来的StreamAllocation，treamAllocation.connection()获得连接RealConnection
2.将刚才创建的用于网络io的RealConnection对象，以及对于与服务器交换最为关键的HttpCodec对象传递给后面的拦截器

3. CallServerInterceptor源码以及作用

作用：

• 1.发起真正的网络请求
• 2.介绍服务器返回的响应

public final class CallServerInterceptor implements Interceptor {
  private final boolean forWebSocket;

  public CallServerInterceptor(boolean forWebSocket) {
    this.forWebSocket = forWebSocket;
  }

  @Override public Response intercept(Chain chain) throws IOException {
1   HttpCodec httpCodec = ((RealInterceptorChain) chain).httpStream();
    StreamAllocation streamAllocation = ((RealInterceptorChain) chain).streamAllocation();
    Request request = chain.request();

    long sentRequestMillis = System.currentTimeMillis();
2   httpCodec.writeRequestHeaders(request);

3   if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
      Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
      BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
      request.body().writeTo(bufferedRequestBody);
      bufferedRequestBody.close();
    }

4   httpCodec.finishRequest();

    Response response = httpCodec.readResponseHeaders()
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    int code = response.code();
    if (forWebSocket && code == 101) {
      // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
      response = response.newBuilder()
          .body(Util.EMPTY_RESPONSE)
          .build();
    } else {
5     response = response.newBuilder()
          .body(httpCodec.openResponseBody(response))
          .build();
    }

6   if ("close".equalsIgnoreCase(response.request().header("Connection"))
        || "close".equalsIgnoreCase(response.header("Connection"))) {
      streamAllocation.noNewStreams();
    }

    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
      throw new ProtocolException(
          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
    }

    return response;
  }
}

• 1.HttpCodec(http中所有流对象都封装到了HttpCodec实现类中),可以简单的理解为它能编码request和解码response
• 2.可以看到证实了上面说的HttpCodec写入了请求的头部信息
• 3.想socket写入请求体
• 4.表明完成了http请求request的写入工作
• 5.读取响应的body信息
• 6.关闭连接

这样一个网络请求的发起于接受就在这个拦截器中真正的完成了