Decode gzip body if not handled by okhttp (#21187)

Summary:
When looking at enabling gzip content encoding on Android I stumbled on this old issue where the body content is not decoded. It happens because okhttp only handles gzip decoding if the user does NOT provide an accept-encoding header. This is pretty confusing because on iOS we need to pass the header manually if we want to receive a gzipped response. I think it makes sense to handle the decoding no matter what.

See the comment in code for more details.

Fixed #5297
Pull Request resolved: #21187

Differential Revision: D9978889

Pulled By: hramos

fbshipit-source-id: b86791fb7d3157f325a0904225d2f63d166080d5

ReactAndroid/src/main/java/com/facebook/react/modules/network/NetworkingModule.java

@@ -47,6 +47,8 @@
 import okhttp3.Response;
 import okhttp3.ResponseBody;
 import okio.ByteString;
+import okio.GzipSource;
+import okio.Okio;
 
 /**
  * Implements the XMLHttpRequest JavaScript interface.
@@ -454,8 +456,26 @@ public void onResponse(Call call, Response response) throws IOException {
               translateHeaders(response.headers()),
               response.request().url().toString());
 
-            ResponseBody responseBody = response.body();
             try {
+              // OkHttp implements something called transparent gzip, which mean that it will
+              // automatically add the Accept-Encoding gzip header and handle decoding internally.
+              // The issue is that it won't handle decoding if the user provides a Accept-Encoding
+              // header. This is also undesirable considering that iOS does handle the decoding even
+              // when the header is provided. To make sure this works in all cases, handle gzip body
+              // here also. This works fine since OKHttp will remove the Content-Encoding header if
+              // it used transparent gzip.
+              // See https://github.com/square/okhttp/blob/5b37cda9e00626f43acf354df145fd452c3031f1/okhttp/src/main/java/okhttp3/internal/http/BridgeInterceptor.java#L76-L111
+              ResponseBody responseBody = response.body();
+              if ("gzip".equalsIgnoreCase(response.header("Content-Encoding")) &&
+                  responseBody != null) {
+                GzipSource gzipSource = new GzipSource(responseBody.source());
+                String contentType = response.header("Content-Type");
+                responseBody = ResponseBody.create(
+                    contentType != null ? MediaType.parse(contentType) : null,
+                    -1L,
+                    Okio.buffer(gzipSource));
+              }
+
               // Check if a handler is registered
               for (ResponseHandler handler : mResponseHandlers) {
                 if (handler.supports(responseType)) {