Blimp: add padding for zlib framing to buffer preallocation calculations.

blimp/net/compressed_packet_writer.cc

 // Copyright 2016 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 "blimp/net/compressed_packet_writer.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/sys_byteorder.h"
 #include "blimp/net/common.h"
 #include "net/base/io_buffer.h"
 #include "third_party/zlib/zlib.h"
 
 namespace blimp {
 namespace {
 
 // Allocate the maxmimum amount of memory to deflate (512KB) for higher
 // compression. (See zconf.h for details on memLevel semantics.)
 const int kZlibMemoryLevel = 9;
 
+// Byte count of the zlib end-of-block marker (0x00, 0x00, 0xFF, 0xFF).
+// Used for buffer preallocation.
+const size_t kZlibBlockFooterLength = 4;

[Wez, 2016/04/12 23:54:34]

nit: You call it a marker but name it "footer" - be consistent. :)

Similarly, don't we use "size" to refer to a number-of-bytes, normally, rather
than length?

[Kevin M, 2016/04/13 00:53:34]

Done, done.

+
 }  // namespace
 
 CompressedPacketWriter::CompressedPacketWriter(
     std::unique_ptr<PacketWriter> sink)
     : sink_(std::move(sink)), compressed_buf_(new net::GrowableIOBuffer) {
   DCHECK(sink_);
 
   memset(&zlib_stream_, 0, sizeof(z_stream));
 
   // MAX_WBITS means we are using the maximal window size for decompression;
@@ skipping 48 matching lines @@
            << compress_result << " out.";
   DVLOG(3) << "deflate total: " << uncompressed_size_total_ << " in, "
            << compressed_size_total_ << " out.";
 }
 
 int CompressedPacketWriter::Compress(
     const scoped_refptr<net::DrainableIOBuffer>& src_buf,
     const scoped_refptr<net::GrowableIOBuffer>& dest_buf) {
   DCHECK_EQ(0, dest_buf->offset());
 
+  // Preallocate a buffer that's large enough to fit the compressed contents of
+  // src_buf, plus some overhead for zlib.
   const int zlib_output_ubound =
-      deflateBound(&zlib_stream_, src_buf->BytesRemaining());
+      deflateBound(&zlib_stream_, src_buf->BytesRemaining()) +
+      kZlibBlockFooterLength;

[Wez, 2016/04/12 23:54:34]

Indentation looks wrong - git cl format this?

[Kevin M, 2016/04/13 00:53:35]

Already formatted.

   if (dest_buf->capacity() < zlib_output_ubound) {
     dest_buf->SetCapacity(zlib_output_ubound);
   }
 
   zlib_stream_.next_in = reinterpret_cast<uint8_t*>(src_buf->data());
   zlib_stream_.avail_in = static_cast<unsigned>(src_buf->BytesRemaining());
   zlib_stream_.next_out = reinterpret_cast<uint8_t*>(dest_buf->data());
   zlib_stream_.avail_out = static_cast<unsigned>(zlib_output_ubound);
   int deflate_error = deflate(&zlib_stream_, Z_SYNC_FLUSH);
 
   if (deflate_error != Z_OK) {
     DLOG(FATAL) << "Unexpected deflate() return value: " << deflate_error;
     return net::ERR_UNEXPECTED;
   }
   if (zlib_stream_.avail_in > 0) {
     DLOG(ERROR) << "deflate() did not consume all data, remainder: "
                 << zlib_stream_.avail_in << " bytes.";
     return net::ERR_UNEXPECTED;
   }
 
   return zlib_output_ubound - zlib_stream_.avail_out;
 }
 
 }  // namespace blimp