Correctly handle (and log) receipt of gzip response to SDCH encode proposal

When the only response to a SDCH encoding proposal (including a statement of
an Avail-Dict) is a gzip response, the filtering infrastructure needs to
add in a missing "sdch" sniffing filter.  This filter should enter into
pass-through mode if the content does not have a valid SDCH header.  This
functionality is critical to the latency experiment, which will signal
the fact that a session is in the control group by doing exactly the
above pattern (only using gzip, despite the dictionary).

This is a blocker for the Chrome SDCH latency experiment.


bug = 1520081
reviewers= huanr,openvcdiff,kmixter
Review URL: http://codereview.chromium.org/12964

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@6415 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 29 insertions, 2 deletions

diff --git a/net/base/filter.cc b/net/base/filter.cc
index 3069880..6bf48d1 100644
--- a/net/base/filter.cc
+++ b/net/base/filter.cc
@@ -89,7 +89,6 @@ void Filter::FixupEncodingTypes(
       // .gz files.  We match Firefox's nsHttpChannel::ProcessNormal and ignore
       // the Content-Encoding here.
       encoding_types->clear();
-    return;
   }
 
   if (!is_sdch_response) {
diff --git a/net/base/gzip_filter_unittest.cc b/net/base/gzip_filter_unittest.cc
index 7b2f73d..1fe4ee4 100644
--- a/net/base/gzip_filter_unittest.cc
+++ b/net/base/gzip_filter_unittest.cc
@@ -263,6 +263,30 @@ TEST_F(GZipUnitTest, DecodeGZip) {
   EXPECT_EQ(memcmp(source_buffer(), gzip_decode_buffer, source_len()), 0);
 }
 
+// SDCH scenario: decoding gzip data when content type says sdch,gzip.
+// This tests that sdch will degrade to pass through, and is what allows robust
+// handling when the response *might* be sdch,gzip by simply adding in the
+// tentative sdch decode.
+// All test code is otherwise modeled after the "basic" scenario above.
+TEST_F(GZipUnitTest, DecodeGZipWithMistakenSdch) {
+  // Decode the compressed data with filter
+  std::vector<Filter::FilterType> filter_types;
+  filter_types.push_back(Filter::FILTER_TYPE_SDCH);
+  filter_types.push_back(Filter::FILTER_TYPE_GZIP);
+  scoped_ptr<Filter> filter(Filter::Factory(filter_types, kDefaultBufferSize));
+  ASSERT_TRUE(filter.get());
+  memcpy(filter->stream_buffer(), gzip_encode_buffer_, gzip_encode_len_);
+  filter->FlushStreamBuffer(gzip_encode_len_);
+
+  char gzip_decode_buffer[kDefaultBufferSize];
+  int gzip_decode_size = kDefaultBufferSize;
+  filter->ReadData(gzip_decode_buffer, &gzip_decode_size);
+
+  // Compare the decoding result with source data
+  EXPECT_TRUE(gzip_decode_size == source_len());
+  EXPECT_EQ(memcmp(source_buffer(), gzip_decode_buffer, source_len()), 0);
+}
+
 // Tests we can call filter repeatedly to get all the data decoded.
 // To do that, we create a filter with a small buffer that can not hold all
 // the input data.
diff --git a/net/base/sdch_filter.cc b/net/base/sdch_filter.cc
index ae4d5ac..4b9cf70 100644
--- a/net/base/sdch_filter.cc
+++ b/net/base/sdch_filter.cc
@@ -144,7 +144,11 @@ Filter::FilterStatus SdchFilter::ReadFilteredData(char* dest_buffer,
       return FILTER_NEED_MORE_DATA;
     }
     if (PASS_THROUGH == decoding_status_) {
-      return CopyOut(dest_buffer, dest_len);
+      // We must pass in available_space, but it will be changed to bytes_used.
+      FilterStatus result = CopyOut(dest_buffer, &available_space);
+      // Accumulate the returned count of bytes_used (a.k.a., available_space).
+      *dest_len += available_space;
+      return result;
     }
     DCHECK(false);
     decoding_status_ = DECODING_ERROR;