GH-934: Update Default Client to wrap GZIP Responses correctly

This change updates the Input Stream handling when using the Default
client implementation to detect when a response is `gzipped` and
wrap it in a `GZipInputStream`.

This addresses any issues related to compression when using the
default client.

core/src/main/java/feign/Client.java

@@ -35,6 +35,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.zip.DeflaterOutputStream;
+import java.util.zip.GZIPInputStream;
 import java.util.zip.GZIPOutputStream;
 import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.HttpsURLConnection;
@@ -129,7 +130,11 @@ Response convertResponse(HttpURLConnection connection, Request request) throws I
       if (status >= 400) {
         stream = connection.getErrorStream();
       } else {
-        stream = connection.getInputStream();
+        if (this.isGzip(connection)) {
+          stream = new GZIPInputStream(connection.getInputStream());
+        } else {
+          stream = connection.getInputStream();
+        }
       }
       return Response.builder()
           .status(status)
@@ -216,6 +221,14 @@ HttpURLConnection convertAndSend(Request request, Options options) throws IOExce
       }
       return connection;
     }
+
+    private boolean isGzip(HttpURLConnection connection) {
+      String contentEncoding = connection.getHeaderField("Content-Encoding");
+      if (Util.isNotBlank(contentEncoding)) {
+        return contentEncoding.equalsIgnoreCase("gzip");
+      }
+      return false;
+    }
   }
 
   /**

core/src/test/java/feign/client/DefaultClientTest.java

@@ -16,6 +16,8 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.hamcrest.core.Is.isA;
 import static org.junit.Assert.assertEquals;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.net.HttpURLConnection;
 import java.net.InetSocketAddress;
@@ -24,8 +26,11 @@
 import java.net.Proxy.Type;
 import java.net.SocketAddress;
 import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.zip.GZIPOutputStream;
 import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.SSLSession;
+import okio.Buffer;
 import org.junit.Test;
 import feign.Client;
 import feign.Client.Proxied;
@@ -144,4 +149,33 @@ public void canCreateWithExplicitCredentials() throws Exception {
     assertThat(connection).isNotNull().isInstanceOf(HttpURLConnection.class);
   }
 
+
+  @Test
+  public void canSupportGzip() throws Exception {
+    /* enqueue a zipped response */
+    final String responseData = "Compressed Data";
+    server.enqueue(new MockResponse()
+        .addHeader("Content-Encoding", "gzip")
+        .setBody(new Buffer().write(compress(responseData))));
+
+    TestInterface api = newBuilder()
+        .target(TestInterface.class, "http://localhost:" + server.getPort());
+
+    String result = api.get();
+
+    /* verify that the response is unzipped */
+    assertThat(result).isNotNull()
+        .isEqualToIgnoringCase(responseData);
+
+  }
+
+  private byte[] compress(String data) throws Exception {
+    try (ByteArrayOutputStream bos = new ByteArrayOutputStream(data.length())) {
+      GZIPOutputStream gzipOutputStream = new GZIPOutputStream(bos);
+      gzipOutputStream.write(data.getBytes(StandardCharsets.UTF_8), 0, data.length());
+      gzipOutputStream.close();
+      return bos.toByteArray();
+    }
+
+  }
 }