fix: Correctly handling chunked response streams with gzip (#990)

Previous implementation doesn't properly cleanup the last chunk of a chunked response when the response is also gzipped. This in turns prevents proper connection reuse.

Fixes #367

google-http-client/src/main/java/com/google/api/client/http/HttpResponse.java

@@ -353,8 +353,13 @@ public InputStream getContent() throws IOException {
           if (!returnRawInputStream && this.contentEncoding != null) {
             String oontentencoding = this.contentEncoding.trim().toLowerCase(Locale.ENGLISH);
             if (CONTENT_ENCODING_GZIP.equals(oontentencoding) || CONTENT_ENCODING_XGZIP.equals(oontentencoding)) {
+              // Wrap the original stream in a ConsumingInputStream before passing it to
+              // GZIPInputStream. The GZIPInputStream leaves content unconsumed in the original
+              // stream (it almost always leaves the last chunk unconsumed in chunked responses).
+              // ConsumingInputStream ensures that any unconsumed bytes are read at close.
+              // GZIPInputStream.close() --> ConsumingInputStream.close() --> exhaust(ConsumingInputStream)
               lowLevelResponseContent =
-                  new ConsumingInputStream(new GZIPInputStream(lowLevelResponseContent));
+                  new GZIPInputStream(new ConsumingInputStream(lowLevelResponseContent));
             }
           }
           // logging (wrap content with LoggingInputStream)

google-http-client/src/test/java/com/google/api/client/http/HttpResponseTest.java

@@ -567,6 +567,12 @@ private void do_testGetContent_gzipEncoding_finishReading(String contentEncoding
     ) {
       zipStream.write(dataToCompress);
       zipStream.close();
+
+      // GZIPInputStream uses a default buffer of 512B. Add enough content to exceed this
+      // limit, so that some content will be left in the connection.
+      for (int i = 0; i < 1024; i++) {
+        byteStream.write('7');
+      }
       mockBytes = byteStream.toByteArray();
     }
     final MockLowLevelHttpResponse mockResponse = new MockLowLevelHttpResponse();
@@ -594,6 +600,8 @@ public LowLevelHttpResponse execute() throws IOException {
       assertFalse(output.isClosed());
       assertEquals("abcd", response.parseAsString());
       assertTrue(output.isClosed());
+      // The underlying stream should be fully consumed, even if gzip only returns some of it.
+      assertEquals(-1, output.read());
     }
   }