OkHttp如何移除User-Agent，Accept-Encoding等框架自動新增的請求頭引數

RaoMeng發表於2018-12-06
HTTPEncoding框架

使用OkHttp網路框架在進行網路請求時會發現，傳到後臺的請求頭中會比我們自己新增的引數多出幾個額外引數。檢視原始碼會發現

 private Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!retryAndFollowUpInterceptor.isForWebSocket()) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(
        retryAndFollowUpInterceptor.isForWebSocket()));

    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }
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OkHttp會預設新增一個橋接攔截器BridgeInterceptor，檢視BridgeInterceptor的原始碼

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) {
      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());
    }
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在BridgeInterceptor中會預設新增User-Agent，Accept-Encoding等請求頭引數。有時候我們並不需要這些預設新增的引數，那麼我們如何才能做到移除它們呢？

通過上面第一段的部分原始碼

    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!retryAndFollowUpInterceptor.isForWebSocket()) {
      interceptors.addAll(client.networkInterceptors());
    }
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可以看到OkHttp內部在新增完BridgeInterceptor後，才開始新增networkInterceptors，所以我們需要藉助網路攔截器來重新攔截請求頭，並操作頭部引數。

首先我們要自定義一個攔截器，在攔截器中移除我們不需要的引數。

public class NetInterceptorimplements Interceptor {

    private HttpClient builder;

    public NetInterceptor() {
        super();
    }

    public NetInterceptor(HttpClient builder) {
        this.builder = builder;
    }

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        //移除頭部引數
        request = request.newBuilder()
                    .removeHeader("User-Agent")
                    .removeHeader("Accept-Encoding")
                    .build();
        Response response = chain.proceed(request);
        if (response.body() != null && response.body().contentType() != null) {
            MediaType mediaType = response.body().contentType();
            String content = response.body().string();
            ResponseBody responseBody = ResponseBody.create(mediaType, content);
            return response.newBuilder().body(responseBody).build();
        } else {
            return response;
        }
    }

}
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然後再將自定義的攔截器設定為網路攔截器

  mOkBuilder = new Builder()
                .connectTimeout(mbuilder.getConnectTimeout(), TimeUnit.SECONDS)
                .readTimeout(mbuilder.getReadTimeout(), TimeUnit.SECONDS)
                .writeTimeout(mbuilder.getWriteTimeout(), TimeUnit.SECONDS)
                .sslSocketFactory(createSSLSocketFactory(), new TrustAllCerts())// 信任所有證書
                .hostnameVerifier(new TrustAllHostnameVerifier())
                .cookieJar(new CookieJar() {
                    private final HashMap<String, List<Cookie>> cookieStore = new HashMap<>();

                    @Override
                    public void saveFromResponse(HttpUrl httpUrl, List<Cookie> list) {
                        cookieStore.put(httpUrl.host(), list);
                    }

                    @Override
                    public List<Cookie> loadForRequest(HttpUrl httpUrl) {
                        List<Cookie> cookies = cookieStore.get(httpUrl.host());
                        return cookies != null ? cookies : new ArrayList<Cookie>();
                    }
                });

  NetInterceptor netInterceptor = new NetInterceptor(mbuilder);
  //mOkBuilder.addNetworkInterceptor(netInterceptor);//設定應用攔截器無效，因為BridgeInterceptor是在應用攔截器之後新增的
  mOkBuilder.addNetworkInterceptor(netInterceptor);
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這樣就能達到移除BridgeInterceptor自動新增的請求頭引數的目的了。

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