[Sync] Finch Experiment : Enable compression between sync client and server

sync/internal_api/http_bridge.cc

Index: sync/internal_api/http_bridge.cc
diff --git a/sync/internal_api/http_bridge.cc b/sync/internal_api/http_bridge.cc
index c64822d5836d2e729d6f7bca00069e5eebbd7c80..e5729f2dcf26f66552ee1fc02262a4d7dcc6258b 100644
--- a/sync/internal_api/http_bridge.cc
+++ b/sync/internal_api/http_bridge.cc
@@ -5,8 +5,10 @@
 #include "sync/internal_api/public/http_bridge.h"
 
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
@@ -20,6 +22,7 @@
 #include "net/url_request/url_request_job_factory_impl.h"
 #include "net/url_request/url_request_status.h"
 #include "sync/internal_api/public/base/cancelation_signal.h"
+#include "third_party/zlib/zlib.h"
 
 namespace syncer {
 
@@ -35,6 +38,109 @@ void LogTimeout(bool timed_out) {
   UMA_HISTOGRAM_BOOLEAN("Sync.URLFetchTimedOut", timed_out);
 }
 
+bool IsSyncHttpContentCompressionEnabled() {
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("SyncHttpContentCompression");
+  return StartsWith(group_name, "Enabled", base::CompareCase::SENSITIVE);
+}
+
+void RecordSyncRequestContentLengthHistograms(int64 compressed_content_length,
+                                              int64 original_content_length) {
+  UMA_HISTOGRAM_COUNTS("Sync.RequestContentLength.Compressed",
+                       compressed_content_length);
+  UMA_HISTOGRAM_COUNTS("Sync.RequestContentLength.Original",
+                       original_content_length);
+}
+
+void RecordSyncResponseContentLengthHistograms(int64 compressed_content_length,
+                                               int64 original_content_length) {
+  UMA_HISTOGRAM_COUNTS("Sync.ResponseContentLength.Compressed",
+                       compressed_content_length);
+  UMA_HISTOGRAM_COUNTS("Sync.ResponseContentLength.Original",
+                       original_content_length);
+}
+
+// -----------------------------------------------------------------------------
+// The rest of the code in the anon namespace is copied from
+// components/metrics/compression_utils.cc
+// TODO(gangwu): crbug.com/515695. The following code is copied from
+// components/metrics/compression_utils.cc. We copied them because if we
+// reference them, we will get cycle dependency warning. Once the functions
+// have been moved from //component to //base, we can remove the following
+// functions.
+//------------------------------------------------------------------------------
+// The difference in bytes between a zlib header and a gzip header.
+const size_t kGzipZlibHeaderDifferenceBytes = 16;
+
+// Pass an integer greater than the following get a gzip header instead of a
+// zlib header when calling deflateInit2() and inflateInit2().
+const int kWindowBitsToGetGzipHeader = 16;
+
+// This describes the amount of memory zlib uses to compress data. It can go
+// from 1 to 9, with 8 being the default. For details, see:
+// http://www.zlib.net/manual.html (search for memLevel).
+const int kZlibMemoryLevel = 8;
+
+// This code is taken almost verbatim from third_party/zlib/compress.c. The only
+// difference is deflateInit2() is called which sets the window bits to be > 16.
+// That causes a gzip header to be emitted rather than a zlib header.
+int GzipCompressHelper(Bytef* dest,
+                       uLongf* dest_length,
+                       const Bytef* source,
+                       uLong source_length) {
+  z_stream stream;
+
+  stream.next_in = bit_cast<Bytef*>(source);
+  stream.avail_in = static_cast<uInt>(source_length);
+  stream.next_out = dest;
+  stream.avail_out = static_cast<uInt>(*dest_length);
+  if (static_cast<uLong>(stream.avail_out) != *dest_length)
+    return Z_BUF_ERROR;
+
+  stream.zalloc = static_cast<alloc_func>(0);
+  stream.zfree = static_cast<free_func>(0);
+  stream.opaque = static_cast<voidpf>(0);
+
+  gz_header gzip_header;
+  memset(&gzip_header, 0, sizeof(gzip_header));
+  int err = deflateInit2(&stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
+                         MAX_WBITS + kWindowBitsToGetGzipHeader,
+                         kZlibMemoryLevel, Z_DEFAULT_STRATEGY);
+  if (err != Z_OK)
+    return err;
+
+  err = deflateSetHeader(&stream, &gzip_header);
+  if (err != Z_OK)
+    return err;
+
+  err = deflate(&stream, Z_FINISH);
+  if (err != Z_STREAM_END) {
+    deflateEnd(&stream);
+    return err == Z_OK ? Z_BUF_ERROR : err;
+  }
+  *dest_length = stream.total_out;
+
+  err = deflateEnd(&stream);
+  return err;
+}
+
+bool GzipCompress(const std::string& input, std::string* output) {
+  const uLongf input_size = static_cast<uLongf>(input.size());
+  std::vector<Bytef> compressed_data(kGzipZlibHeaderDifferenceBytes +
+                                     compressBound(input_size));
+
+  uLongf compressed_size = static_cast<uLongf>(compressed_data.size());
+  if (GzipCompressHelper(&compressed_data.front(), &compressed_size,
+                         bit_cast<const Bytef*>(input.data()),
+                         input_size) != Z_OK) {
+    return false;
+  }
+
+  compressed_data.resize(compressed_size);
+  output->assign(compressed_data.begin(), compressed_data.end());
+  return true;
+}
+
 }  // namespace
 
 HttpBridgeFactory::HttpBridgeFactory(
@@ -203,19 +309,36 @@ void HttpBridge::MakeAsynchronousPost() {
       base::Bind(&HttpBridge::OnURLFetchTimedOut, this));
 
   DCHECK(request_context_getter_.get());
+  fetch_state_.start_time = base::Time::Now();
   fetch_state_.url_poster =
       net::URLFetcher::Create(url_for_request_, net::URLFetcher::POST, this)
           .release();
   fetch_state_.url_poster->SetRequestContext(request_context_getter_.get());
-  fetch_state_.url_poster->SetUploadData(content_type_, request_content_);
   fetch_state_.url_poster->SetExtraRequestHeaders(extra_headers_);
+
+  int64 compressed_content_size = 0;
+  if (IsSyncHttpContentCompressionEnabled()) {
+    std::string compressed_request_content;
+    GzipCompress(request_content_, &compressed_request_content);
+    compressed_content_size = compressed_request_content.size();
+    fetch_state_.url_poster->SetUploadData(content_type_,
+                                           compressed_request_content);
+    fetch_state_.url_poster->AddExtraRequestHeader("Content-Encoding: gzip");
+  } else {
+    fetch_state_.url_poster->SetUploadData(content_type_, request_content_);
+    fetch_state_.url_poster->AddExtraRequestHeader(base::StringPrintf(
+        "%s: %s", net::HttpRequestHeaders::kAcceptEncoding, "deflate"));
+  }
+
+  RecordSyncRequestContentLengthHistograms(compressed_content_size,
+                                           request_content_.size());
+
   fetch_state_.url_poster->AddExtraRequestHeader(base::StringPrintf(
       "%s: %s", net::HttpRequestHeaders::kUserAgent, user_agent_.c_str()));
   fetch_state_.url_poster->SetLoadFlags(net::LOAD_BYPASS_CACHE |
                                         net::LOAD_DISABLE_CACHE |
                                         net::LOAD_DO_NOT_SAVE_COOKIES |
                                         net::LOAD_DO_NOT_SEND_COOKIES);
-  fetch_state_.start_time = base::Time::Now();
 
   fetch_state_.url_poster->Start();
 }
@@ -315,6 +438,17 @@ void HttpBridge::OnURLFetchComplete(const net::URLFetcher* source) {
   fetch_state_.response_headers = source->GetResponseHeaders();
   UpdateNetworkTime();
 
+  int64 compressed_content_length = fetch_state_.response_content.size();
+  int64 original_content_length = compressed_content_length;
+  if (fetch_state_.response_headers &&
+      fetch_state_.response_headers->HasHeaderValue("content-encoding",
+                                                    "gzip")) {
+    compressed_content_length =
+        fetch_state_.response_headers->GetContentLength();
+  }
+  RecordSyncResponseContentLengthHistograms(compressed_content_length,
+                                            original_content_length);
+
   // End of the line for url_poster_. It lives only on the IO loop.
   // We defer deletion because we're inside a callback from a component of the
   // URLFetcher, so it seems most natural / "polite" to let the stack unwind.