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

blimp/net/compressed_packet_unittest.cc

Index: blimp/net/compressed_packet_unittest.cc
diff --git a/blimp/net/compressed_packet_unittest.cc b/blimp/net/compressed_packet_unittest.cc
index 61e39b88bb8779645626e61e92ee60387937f4bc..d462689544632ad4a86e7208e065d89c2ab81183 100644
--- a/blimp/net/compressed_packet_unittest.cc
+++ b/blimp/net/compressed_packet_unittest.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <stdlib.h>
+
 #include "base/memory/ptr_util.h"
 #include "base/sys_byteorder.h"
 #include "blimp/net/common.h"
@@ -153,6 +155,26 @@ TEST_F(CompressedPacketTest, LargeInput) {
   EXPECT_TRUE(CheckRoundTrip(big_str));
 }
 
+TEST_F(CompressedPacketTest, LowCompressionRatio) {
+  // This size (2338) was found "in the wild" to repro an issue with output
+  // buffer overflows.
+  std::vector<uint8_t> source_data(2338);
+  unsigned int rand_seed = 0;
+
+  // Write two incompressible (high entropy) blocks.

[Wez, 2016/04/13 01:11:02]

nit: Why two?

+  for (size_t i = 0; i < source_data.size(); ++i) {
+    source_data[i] = rand_r(&rand_seed);
+  }
+  EXPECT_TRUE(
+      CheckRoundTrip(std::string(source_data.begin(), source_data.end())));
+
+  for (size_t i = 0; i < source_data.size(); ++i) {
+    source_data[i] = rand_r(&rand_seed);
+  }
+  EXPECT_TRUE(
+      CheckRoundTrip(std::string(source_data.begin(), source_data.end())));
+}
+
 TEST_F(CompressedPacketTest, DecompressIllegallyLargePayload) {
   // We can't use the compressor to compress an illegally sized payload, however
   // we can concatenate the output of smaller payloads to form an uber-payload.