Add brotli content-encoding filter.

net/filter/brotli_filter.cc

Index: net/filter/brotli_filter.cc
diff --git a/net/filter/brotli_filter.cc b/net/filter/brotli_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e5ef5c30aaaaa3c348024e266369fc0b754341fd
--- /dev/null
+++ b/net/filter/brotli_filter.cc
@@ -0,0 +1,107 @@
+// Copyright 2015 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/filter/brotli_filter.h"
+
+#include "base/macros.h"
+#include "base/numerics/safe_conversions.h"
+#include "third_party/brotli/dec/decode.h"
+
+namespace net {
+
+// BrotliFilter applies Brotli content decoding to a data stream.
+// Brotli format specification: http://www.ietf.org/id/draft-alakuijala-brotli
+//
+// BrotliFilter is a subclass of Filter. See the latter's header file filter.h
+// for sample usage.
+class BrotliFilter : public Filter {
+ public:
+  BrotliFilter(FilterType type)
+      : Filter(type), decoding_status_(DECODING_IN_PROGRESS) {
+    BrotliStateInit(&brotli_state_);
+  }
+
+  ~BrotliFilter() override { BrotliStateCleanup(&brotli_state_); }
+
+  // Decodes the pre-filter data and writes the output into the |dest_buffer|
+  // passed in.
+  // The function returns FilterStatus. See filter.h for its description.
+  //
+  // Upon entry, |*dest_len| is the total size (in number of chars) of the
+  // destination buffer. Upon exit, |*dest_len| is the actual number of chars
+  // written into the destination buffer.
+  //
+  // This function will fail if there is no pre-filter data in the
+  // |stream_buffer_|. On the other hand, |*dest_len| can be 0 upon successful
+  // return. For example, decompressor may process some pre-filter data
+  // but not produce output yet.
+  FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override {
+    if (!dest_buffer || !dest_len)
+      return Filter::FILTER_ERROR;
+
+    if (!base::IsValueInRangeForNumericType<size_t>(*dest_len))
+      return Filter::FILTER_ERROR;

[Ryan Sleevi, 2015/12/29 20:59:11]

If this ever happens, isn't it a programmer error? That seems like a CHECK() is
fine, meaning

size_t output_buffer_size = base::checked_cast<size_t>(*dest_len);

should be safe

[eustas, 2015/12/30 11:38:35]

Surely.

+    size_t output_buffer_size = static_cast<size_t>(*dest_len);
+
+    if (decoding_status_ == DECODING_DONE) {
+      *dest_len = 0;
+      return Filter::FILTER_DONE;
+    }
+
+    if (decoding_status_ != DECODING_IN_PROGRESS)
+      return Filter::FILTER_ERROR;
+
+    size_t available_in = stream_data_len_;
+    const uint8_t* next_in = bit_cast<uint8_t*>(next_stream_data_);
+    size_t available_out = output_buffer_size;
+    uint8_t* next_out = bit_cast<uint8_t*>(dest_buffer);
+    size_t total_out = 0;
+    BrotliResult result =
+        BrotliDecompressStream(&available_in, &next_in, &available_out,
+                               &next_out, &total_out, &brotli_state_);
+    int bytes_written =
+        base::checked_cast<int>(output_buffer_size - available_out);

[Ryan Sleevi, 2015/12/29 20:59:11]

So this isn't actually safe (or at least, jschuh agreed it looked
wrong/dangerous)

You could do
size_t safe_bytes_written = base::CheckedNumeric<size_t>(output_buffer_size);
safe_bytes_written -= available_out;
int bytes_written = base::checked_cast<int>(safe_bytes_written.ValueOrDie());


That will cover the case where available_out > output_buffer_size (a range
underflow), as well as downcasting to int (a range overflow)

[eustas, 2015/12/30 11:38:34]

Done.
I've also added explicit decompressor contract checks (that available_in/out
could only decrease) and checked_cast for stream_data_len_ assignment (because
it is also int).

+
+    switch (result) {
+      case BROTLI_RESULT_NEEDS_MORE_OUTPUT:
+      // Fall through.
+      case BROTLI_RESULT_SUCCESS:
+        *dest_len = bytes_written;
+        stream_data_len_ = available_in;
+        next_stream_data_ = bit_cast<char*>(next_in);
+        if (result == BROTLI_RESULT_SUCCESS) {
+          decoding_status_ = DECODING_DONE;
+          return Filter::FILTER_DONE;
+        }
+        return Filter::FILTER_OK;
+
+      case BROTLI_RESULT_NEEDS_MORE_INPUT:
+        *dest_len = bytes_written;
+        stream_data_len_ = 0;
+        next_stream_data_ = nullptr;
+        return Filter::FILTER_NEED_MORE_DATA;
+
+      default:
+        decoding_status_ = DECODING_ERROR;
+        return Filter::FILTER_ERROR;
+    }
+  }
+
+ private:
+  enum DecodingStatus { DECODING_IN_PROGRESS, DECODING_DONE, DECODING_ERROR };
+
+  // Tracks the status of decoding.
+  // This variable is updated only by ReadFilteredData.
+  DecodingStatus decoding_status_;
+
+  BrotliState brotli_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(BrotliFilter);
+};
+
+Filter* CreateBrotliFilter(Filter::FilterType type_id) {
+  return new BrotliFilter(type_id);
+}
+
+}  // namespace net