feat: wrap GZIPInputStream for connection reuse

If a connection is closed and there are some bytes that have not
been read that connection can't be reused. Now GZIPInputStream
will have all of its bytes read on close automatically to promote
connection reuse.

Cherry-picked: googleapis#749
Fixes: googleapis#367

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

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.api.client.http;
+
+import com.google.api.client.util.Preconditions;
+import com.google.common.io.ByteStreams;
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * This class in meant to wrap an {@link InputStream} so that all bytes in the steam are read and
+ * discarded on {@link InputStream#close()}. This ensures that the underlying connection has the
+ * option to be reused.
+ */
+final class ConsumingInputStream extends InputStream {
+  private InputStream inputStream;
+  private boolean closed = false;
+
+  ConsumingInputStream(InputStream inputStream) {
+    this.inputStream = Preconditions.checkNotNull(inputStream);
+  }
+
+  @Override
+  public int read() throws IOException {
+    return inputStream.read();
+  }
+
+  @Override
+  public int read(byte[] b, int off, int len) throws IOException {
+    return inputStream.read(b, off, len);
+  }
+
+  @Override
+  public void close() throws IOException {
+    if (!closed && inputStream != null) {
+      try {
+        ByteStreams.exhaust(this);
+        inputStream.close();
+      } finally {
+        this.closed = true;
+      }
+    }
+  }
+}

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

@@ -331,8 +331,8 @@ public InputStream getContent() throws IOException {
           if (!returnRawInputStream
               && contentEncoding != null
               && contentEncoding.contains("gzip")) {
-            lowLevelResponseContent = new ConsumingInputStream(
-                new GZIPInputStream(lowLevelResponseContent));
+            lowLevelResponseContent =
+                new ConsumingInputStream(new GZIPInputStream(lowLevelResponseContent));
           }
           // logging (wrap content with LoggingInputStream)
           Logger logger = HttpTransport.LOGGER;
@@ -357,44 +357,6 @@ public InputStream getContent() throws IOException {
     return content;
   }
 
-  static class ConsumingInputStream extends InputStream {
-    private InputStream inputStream;
-    private boolean closed = false;
-
-    private ConsumingInputStream(InputStream inputStream) {
-      this.inputStream = Preconditions.checkNotNull(inputStream);
-    }
-
-    @Override
-    public int read() throws IOException {
-      return inputStream.read();
-    }
-
-    @Override
-    public int read(byte[] b, int off, int len) throws IOException {
-      return inputStream.read(b, off, len);
-    }
-
-    @Override
-    public void close() throws IOException {
-      if (!closed && inputStream != null) {
-        try {
-          drainInputStream(this);
-          inputStream.close();
-        } finally {
-          this.closed = true;
-        }
-      }
-    }
-
-    static void drainInputStream(final InputStream inputStream) throws IOException {
-      byte buffer[] = new byte[1024];
-      while (inputStream.read(buffer) >= 0) {
-        // do nothing
-      }
-    }
-  }
-
   /**
    * Writes the content of the HTTP response into the given destination output stream.
    *

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

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.api.client.http;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.io.InputStream;
+import org.junit.Test;
+
+public class ConsumingInputStreamTest {
+
+  @Test
+  public void testClose_drainsBytesOnClose() throws IOException {
+    MockInputStream mockInputStream = new MockInputStream("abc123".getBytes());
+    InputStream consumingInputStream = new ConsumingInputStream(mockInputStream);
+
+    assertEquals(6, mockInputStream.getBytesToRead());
+
+    // read one byte
+    consumingInputStream.read();
+    assertEquals(5, mockInputStream.getBytesToRead());
+
+    // closing the stream should read the remaining bytes
+    consumingInputStream.close();
+    assertEquals(0, mockInputStream.getBytesToRead());
+  }
+
+  private class MockInputStream extends InputStream {
+    private int bytesToRead;
+
+    MockInputStream(byte[] data) {
+      this.bytesToRead = data.length;
+    }
+
+    @Override
+    public int read() throws IOException {
+      if (bytesToRead == 0) {
+        return -1;
+      }
+      bytesToRead--;
+      return 1;
+    }
+
+    int getBytesToRead() {
+      return bytesToRead;
+    }
+  }
+}

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

@@ -33,7 +33,6 @@
 import java.util.zip.GZIPInputStream;
 import java.util.zip.GZIPOutputStream;
 import junit.framework.TestCase;
-import sun.net.www.http.ChunkedInputStream;
 
 /**
  * Tests {@link HttpResponse}.