Fix throwIfFalseEOF if skip method was called before read (googleapis#447)

* Fix throwIfFalseEOF when using skip method

throwIfFalseEOF method don't take into account bytes read/skipped in skip method and throws IOException when legit EOF was reached.

* Fix variables naming

* Fix variable type

* Remove '-1' check - `skip` method never returns it

* Add test

Author: medb

google-http-client/src/main/java/com/google/api/client/http/javanet/NetHttpResponse.java

@@ -186,6 +186,13 @@ public int read() throws IOException {
       return n;
     }
 
+    @Override
+    public long skip(long len) throws IOException {
+      long n = in.skip(len);
+      bytesRead += n;
+      return n;
+    }
+
     // Throws an IOException if gets an EOF in the middle of a response.
     private void throwIfFalseEOF() throws IOException {
       long contentLength = getContentLength();

google-http-client/src/test/java/com/google/api/client/http/javanet/NetHttpResponseTest.java

@@ -94,4 +94,18 @@ public void subtestGetContentWithShortRead(int responseCode) throws IOException
       assertEquals(ERROR_RESPONSE, new String(buf, 0, bytes, Charset.forName("UTF-8")));
     }
   }
+
+  public void testSkippingBytes() throws IOException {
+    MockHttpURLConnection connection = new MockHttpURLConnection(null)
+        .setResponseCode(200)
+        .setInputStream(new ByteArrayInputStream(StringUtils.getBytesUtf8("0123456789")))
+        .addHeader("Content-Length", "10");
+    NetHttpResponse response = new NetHttpResponse(connection);
+    InputStream is = response.getContent();
+    // read 1 byte, then skip 9 (to EOF)
+    assertEquals('0', is.read());
+    assertEquals(9, is.skip(9));
+    // expect EOF, not an exception
+    assertEquals(-1, is.read());
+  }
 }