Update zlib to 1.2.11

net/websockets/websocket_deflater.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/websockets/websocket_deflater.h"
 
 #include <string.h>
 #include <algorithm>
 #include <deque>
 #include <vector>
@@ skipping 13 matching lines @@
     stream_.reset(NULL);
   }
 }
 
 bool WebSocketDeflater::Initialize(int window_bits) {
   DCHECK(!stream_);
   stream_.reset(new z_stream);
 
   DCHECK_LE(8, window_bits);
   DCHECK_GE(15, window_bits);
+
+  // Use a negative value to compress a raw deflate stream.
+  //
+  // Upgrade window_bits = 8 to 9 because zlib is unable to compress at
+  // window_bits = 8. Historically, zlib has silently increased the window size
+  // during compression in this case, although this is no longer done for raw
+  // deflate streams since zlib 1.2.9.
+  //
+  // Because of a zlib deflate quirk, back-references will not use the entire
+  // range of 1 << window_bits, but will instead use a restricted range of (1 <<
+  // window_bits) - 262. With an increased window_bits = 9, back-references will
+  // be within a range of 250. These can still be decompressed with window_bits
+  // = 8 and the 256-byte window used there.
+  //
+  // Both the requirement to do this upgrade and the ability to compress with
+  // window_bits = 9 while expecting a decompressor to function with window_bits
+  // = 8 are quite specific to zlib's particular deflate implementation, but not
+  // specific to any particular inflate implementation.
+  //
+  // See https://crbug.com/691074
+  window_bits = -std::max(window_bits, 9);
+
   memset(stream_.get(), 0, sizeof(*stream_));
   int result = deflateInit2(stream_.get(),
                             Z_DEFAULT_COMPRESSION,
                             Z_DEFLATED,
-                            -window_bits,  // Negative value for raw deflate
+                            window_bits,
                             8,  // default mem level
                             Z_DEFAULT_STRATEGY);
   if (result != Z_OK) {
     deflateEnd(stream_.get());
     stream_.reset();
     return false;
   }
   const size_t kFixedBufferSize = 4096;
   fixed_buffer_.resize(kFixedBufferSize);
   return true;
@@ skipping 70 matching lines @@
     stream_->next_out = reinterpret_cast<Bytef*>(&fixed_buffer_[0]);
     stream_->avail_out = fixed_buffer_.size();
     result = deflate(stream_.get(), flush);
     size_t size = fixed_buffer_.size() - stream_->avail_out;
     buffer_.insert(buffer_.end(), &fixed_buffer_[0], &fixed_buffer_[0] + size);
   } while (result == Z_OK);
   return result;
 }
 
 }  // namespace net