AU: Beginnings of delta support

src/platform/update_engine/decompressing_file_writer.cc

 // Copyright (c) 2009 The Chromium OS 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 "update_engine/decompressing_file_writer.h"
 
 namespace chromeos_update_engine {
 
 //  typedef struct z_stream_s {
 //      Bytef    *next_in;  /* next input byte */
@@ skipping 19 matching lines @@
 int GzipDecompressingFileWriter::Write(const void* bytes, size_t count) {
   // Steps:
   // put the data on next_in
   // call inflate until it returns nothing, each time writing what we get
   // check that next_in has no data left.
 
   // It seems that zlib can keep internal buffers in the stream object,
   // so not all data we get fed to us this time will necessarily
   // be written out this time (in decompressed form).
 
-  CHECK_EQ(0, stream_.avail_in);
+  if (stream_.avail_in) {
+    LOG(ERROR) << "Have data already. Bailing";
+    return -1;
+  }
   char buf[1024];
 
   buffer_.reserve(count);
   buffer_.clear();
   CHECK_GE(buffer_.capacity(), count);
   const char* char_bytes = reinterpret_cast<const char*>(bytes);
   buffer_.insert(buffer_.end(), char_bytes, char_bytes + count);
 
   stream_.next_in = reinterpret_cast<Bytef*>(&buffer_[0]);
   stream_.avail_in = count;
@@ skipping 17 matching lines @@
       // Inflate returned no data; we're done for now. Make sure no
       // input data remain.
       CHECK_EQ(0, stream_.avail_in);
       break;
     }
   }
   return count;
 }
 
 }  // namespace chromeos_update_engine