[ON HOLD] Implement pull-based design for content decoding

net/filter/gzip_stream_source.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 "net/filter/gzip_stream_source.h"
+
+#include "base/bind.h"
+#include "base/bit_cast.h"
+#include "base/logging.h"
+#include "net/filter/block_buffer.h"
+#include "third_party/zlib/zlib.h"
+
+namespace net {
+
+GzipStreamSource::GzipStreamSource(std::unique_ptr<StreamSource> previous,
+                                   GzipStreamSourceMode mode)
+    : FilterStreamSource(StreamSource::TYPE_GZIP, std::move(previous)),
+      mode_(mode),
+      zlib_eof_(false),
+      zlib_header_added_(false),
+      should_check_gzip_header_(true),
+      gzip_footer_bytes_left_(0) {}
+
+GzipStreamSource::~GzipStreamSource() {
+  if (zlib_stream_)
+    inflateEnd(zlib_stream_.get());
+}
+
+bool GzipStreamSource::Init() {
+  zlib_stream_.reset(new z_stream);
+  if (!zlib_stream_)
+    return false;
+  memset(zlib_stream_.get(), 0, sizeof(z_stream));
+
+  if (mode_ == GZIP_STREAM_SOURCE_GZIP ||
+      mode_ == GZIP_STREAM_SOURCE_GZIP_WITH_FALLBACK) {
+    if (inflateInit2(zlib_stream_.get(), -MAX_WBITS) != Z_OK)
+      return false;
+  } else {
+    should_check_gzip_header_ = false;
+    if (inflateInit(zlib_stream_.get()) != Z_OK)
+      return false;
+  }
+  return true;
+}
+
+Error GzipStreamSource::ReadInternal(IOBuffer* dest_buffer,
+                                     size_t buffer_size,
+                                     size_t* bytes_read) {
+  // If this stream is not really gzipped as detected by
+  // ShouldFallbackToPlain, pretend the zlib stream already ended.
+  if (ShouldFallbackToPlain()) {
+    zlib_eof_ = true;
+    should_check_gzip_header_ = false;
+  }
+
+  // Require a valid gzip header when decompressing a gzip stream.
+  if (should_check_gzip_header_ && IsGzipHeaderInvalid())
+    return ERR_CONTENT_DECODING_FAILED;
+
+  GzipStreamState state = Decompress(dest_buffer, buffer_size, bytes_read);
+
+  // If the decompressor threw an error, fail synchronously.
+  if (state == GZIP_STREAM_ERROR)
+    return ERR_CONTENT_DECODING_FAILED;
+
+  // Awkward special case: if Decompress returns with data still left in the
+  // input buffer, ordinarily that would imply needing more output space.
+  // However, for compatibility reasons, it is permissible to include trailing
+  // uncompressed data after the zlib stream ends. That data is copied through
+  // here by Passthrough.
+  if (*bytes_read == 0 && zlib_eof_ && buffer_->HasMoreBytes()) {
+    state = Passthrough(dest_buffer, buffer_size, bytes_read);
+  }
+
+  // If there was already some data buffered internally in |buffer_|,
+  // or some output buffered internally in zlib, |Decompress| can succeed
+  // synchronously. If this happens, return right here.
+  if (*bytes_read > 0)
+    return OK;
+
+  // GZIP_STREAM_MORE_OUTPUT_SPACE implies |*bytes_read| > 0, since Decompress
+  // will fill all available output buffer space first and the output buffer
+  // is empty coming into |Read|. Since GZIP_STREAM_ERROR is handled above,
+  // this is the only other case.
+  DCHECK_EQ(GZIP_STREAM_MORE_INPUT, state);
+
+  // Since Decompress needs more input, it has consumed all existing input.
+  DCHECK(!buffer_->HasMoreBytes());
+
+  return OK;
+}
+
+// Private helpers.
+
+// Synchronous decompressor. This function consumes bytes from |buffer_| and
+// decompresses them into |dest_buffer| until either:
+//   a) |buffer_| is empty, and it returns MORE_INPUT;
+//   b) |dest_buffer| is full, and it returns MORE_OUTPUT_SPACE;
+// This decompressor will decompress a zlib stream (either gzip or deflate)
+// until the zlib EOF, then will pass any further input through untouched.
+GzipStreamSource::GzipStreamState GzipStreamSource::Decompress(
+    IOBuffer* dest_buffer,
+    size_t buffer_size,
+    size_t* bytes_output) {
+  DCHECK(dest_buffer);
+  DCHECK_NE(0u, buffer_size);
+
+  if (!buffer_->HasMoreBytes()) {
+    return GZIP_STREAM_MORE_INPUT;
+  }
+
+  // If the zlib stream has already ended, pass any further data through.
+  if (zlib_eof_)
+    return Passthrough(dest_buffer, buffer_size, bytes_output);
+
+  zlib_stream_.get()->next_in = bit_cast<Bytef*>(buffer_->bytes());
+  zlib_stream_.get()->avail_in = buffer_->bytes_left();
+  zlib_stream_.get()->next_out = bit_cast<Bytef*>(dest_buffer->data());
+  zlib_stream_.get()->avail_out = buffer_size;
+
+  int ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+
+  DVLOG(1) << "inflate " << ret << " " << zlib_stream_.get()->avail_in << " "
+           << zlib_stream_.get()->avail_out;
+
+  // Sometime misconfigured servers omit the zlib header, relying on clients to
+  // splice it back in.
+  if (ret < 0 && !zlib_header_added_) {
+    zlib_header_added_ = true;
+    if (!InsertZlibHeader())
+      return GZIP_STREAM_ERROR;
+
+    zlib_stream_.get()->next_in = bit_cast<Bytef*>(buffer_->bytes());
+    zlib_stream_.get()->avail_in = buffer_->bytes_left();
+    zlib_stream_.get()->next_out = bit_cast<Bytef*>(dest_buffer->data());
+    zlib_stream_.get()->avail_out = buffer_size;
+
+    ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+    // TODO(ellyjones): add a histogram to see how often this happens. The
+    // original bug for this behavior was ancient and maybe it doesn't happen in
+    // the wild any more?
+  }
+
+  size_t bytes_used = buffer_->bytes_left() - zlib_stream_.get()->avail_in;
+  size_t bytes_out = buffer_size - zlib_stream_.get()->avail_out;
+
+  buffer_->WasDrained(bytes_used);
+  *bytes_output = bytes_out;
+
+  if (ret != Z_STREAM_END && ret != Z_OK)
+    return GZIP_STREAM_ERROR;
+
+  // The zlib stream can end before the input stream ends. If this happens,
+  // |Decompress| will pass any further data on untouched.
+  if (ret == Z_STREAM_END)
+    zlib_eof_ = true;
+
+  if (!buffer_->HasMoreBytes())
+    return GZIP_STREAM_MORE_INPUT;
+  else
+    return GZIP_STREAM_MORE_OUTPUT_SPACE;
+}
+
+GzipStreamSource::GzipStreamState GzipStreamSource::Passthrough(
+    IOBuffer* dest_buffer,
+    size_t buffer_size,
+    size_t* bytes_read) {
+  SkipGzipFooterIfNeeded();
+  size_t to_copy = buffer_->bytes_left();
+  if (to_copy > buffer_size)
+    to_copy = buffer_size;
+  memcpy(dest_buffer->data(), buffer_->bytes(), to_copy);
+  buffer_->WasDrained(to_copy);
+  *bytes_read = to_copy;
+  if (!buffer_->HasMoreBytes())
+    return GZIP_STREAM_MORE_INPUT;
+  else
+    return GZIP_STREAM_MORE_OUTPUT_SPACE;
+}
+
+bool GzipStreamSource::InsertZlibHeader() {
+  char dummy_header[] = {0x78, 0x01};
+  char dummy_output[4];
+
+  inflateReset(zlib_stream_.get());
+  zlib_stream_.get()->next_in = bit_cast<Bytef*>(&dummy_header[0]);
+  zlib_stream_.get()->avail_in = sizeof(dummy_header);
+  zlib_stream_.get()->next_out = bit_cast<Bytef*>(&dummy_output[0]);
+  zlib_stream_.get()->avail_out = sizeof(dummy_output);
+
+  int ret = inflate(zlib_stream_.get(), Z_NO_FLUSH);
+  return ret == Z_OK;
+}
+
+bool GzipStreamSource::IsGzipHeaderInvalid() {
+  const size_t kGzipFooterBytes = 8;
+  const char* end = nullptr;
+  GZipHeader::Status status =
+      gzip_header_.ReadMore(buffer_->bytes(), buffer_->bytes_left(), &end);
+  if (status == GZipHeader::INCOMPLETE_HEADER) {
+    buffer_->WasDrained(buffer_->bytes_left());
+    return false;
+  }
+
+  should_check_gzip_header_ = false;
+  if (status == GZipHeader::COMPLETE_HEADER) {
+    // If there is a valid header, there should also be a valid footer.
+    gzip_footer_bytes_left_ = kGzipFooterBytes;
+    buffer_->WasDrained(end - buffer_->bytes());
+  }
+
+  return status == GZipHeader::INVALID_HEADER;
+}
+
+// Dumb heuristic. Gzip files always start with a two-byte magic value per RFC
+// 1952 2.3.1, so if the first byte isn't the first byte of the gzip magic, and
+// this filter is checking whether it should fallback, then fallback.
+bool GzipStreamSource::ShouldFallbackToPlain() {
+  static const char kGzipFirstByte = 0x1f;
+  if (mode_ != GZIP_STREAM_SOURCE_GZIP_WITH_FALLBACK)
+    return false;
+  if (!should_check_gzip_header_)
+    return false;
+  if (!buffer_->HasMoreBytes())
+    return false;
+  char d = buffer_->bytes()[0];
+  return d != kGzipFirstByte;
+}
+
+void GzipStreamSource::SkipGzipFooterIfNeeded() {
+  if (gzip_footer_bytes_left_ == 0)
+    return;
+  size_t to_read = gzip_footer_bytes_left_;
+  if (to_read > buffer_->bytes_left())
+    to_read = buffer_->bytes_left();
+  buffer_->WasDrained(to_read);
+}
+
+}  // namespace net