[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 "base/bind.h"
+#include "base/bit_cast.h"
+#include "net/filter/block_buffer.h"
+#include "net/filter/gzip_stream_source.h"
+#include "third_party/zlib/zlib.h"
+
+namespace net {
+
+GzipStreamSource::GzipStreamSource(scoped_ptr<StreamSource> previous)
+    : buffer_(new BlockBuffer()),
+      previous_(std::move(previous)),
+      zlib_eof_(false),
+      zlib_header_added_(false),
+      gzip_header_unchecked_(false),
+      gzip_footer_bytes_left_(0),
+      total_bytes_output_(0) {}
+
+GzipStreamSource::~GzipStreamSource() {
+  if (zlib_stream_)
+    inflateEnd(zlib_stream_.get());
+}
+
+bool GzipStreamSource::Init(GzipStreamSourceMode mode, bool gzip_fallback) {
+  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) {
+    gzip_header_unchecked_ = true;
+    gzip_fallback_unchecked_ = gzip_fallback;
+    if (inflateInit2(zlib_stream_.get(), -MAX_WBITS) != Z_OK)
+      return false;
+  } else {
+    if (inflateInit(zlib_stream_.get()) != Z_OK)
+      return false;
+  }
+
+  return true;
+}
+
+Error GzipStreamSource::Read(IOBuffer* dest_buffer,
+                             size_t buffer_size,
+                             size_t* bytes_read,
+                             const OnReadCompleteCallback& callback) {
+  *bytes_read = 0;
+
+  // Loop on reading the previous source until either:
+  // * Decompress() returns some data, in which case this method completes
+  //   synchronously, or
+  // * Read() does not complete synchronously, in which case OnReadComplete() is
+  //   responsible for finishing the decompression.
+  Error error;
+  do {
+    // If this stream is not really gzipped as detected by
+    // ShouldFallbackToPlain, pretend the zlib stream already ended.
+    if (ShouldFallbackToPlain()) {
+      zlib_eof_ = true;
+      gzip_header_unchecked_ = false;
+      gzip_fallback_unchecked_ = false;
+    }
+
+    // Require a valid gzip header when decompressing a gzip stream.
+    if (gzip_header_unchecked_ && 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) {
+      total_bytes_output_ += *bytes_read;
+      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());
+
+    // Dispatch a read to refill the input buffer.
+    size_t previous_bytes_read;

[Randy Smith (Not in Mondays), 2016/02/08 23:28:42]

nit: Initialize to zero.

[xunjieli, 2016/03/03 23:00:08]

Done.

+    error = previous_->Read(
+        buffer_->buffer(), buffer_->size(), &previous_bytes_read,
+        base::Bind(&GzipStreamSource::OnReadComplete, base::Unretained(this),
+                   callback, base::Unretained(dest_buffer), buffer_size));
+
+    // OK with 0 bytes read means EOF. Since the buffer is already empty, and
+    // Decompress already failed to return any more data, this source is also
+    // at EOF. Just return that synchronously.
+    if (error == OK && previous_bytes_read == 0)
+      return OK;
+
+    // If the underlying read completed synchronously, mark the buffer as
+    // refilled and try again.
+    if (error == OK)
+      buffer_->WasRefilled(previous_bytes_read);
+  } while (error == OK);
+
+  if (error == ERR_IO_PENDING)
+    pending_read_buffer_ = dest_buffer;
+
+  return error;
+}
+
+// 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(buffer_size != 0);
+
+  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);
+
+  LOG(ERROR) << "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;
+}
+
+void GzipStreamSource::OnReadComplete(const OnReadCompleteCallback& callback,
+                                      IOBuffer* dest_buffer,
+                                      size_t dest_buffer_size,
+                                      Error error,
+                                      size_t bytes_read) {
+  DCHECK(!buffer_->HasMoreBytes());
+  DCHECK_EQ(dest_buffer, pending_read_buffer_.get());
+
+  // Take a ref for the lifetime of this function.
+  scoped_refptr<IOBuffer> dest_ref(dest_buffer);
+  pending_read_buffer_ = nullptr;
+
+  // If the underlying read failed, fail this read directly.
+  if (error != OK) {
+    callback.Run(error, bytes_read);
+    return;
+  }
+
+  if (bytes_read == 0) {
+    // EOF. Since the buffer is empty, there is no more data to decompress (any
+    // internally buffered data would have been drained already before calling
+    // the previous stream's Read). Return EOF to our caller.
+    callback.Run(OK, 0);
+    return;
+  }
+
+  // Mark the buffer as refilled and try decompressing.
+  buffer_->WasRefilled(bytes_read);
+
+  // Recurse. If this Read completes synchronously, this method runs the
+  // callback; if it does not, Read will have posted an asynchronous read that
+  // will later re-invoke OnReadComplete to run the callback.
+  error = Read(dest_buffer, dest_buffer_size, &bytes_read, callback);
+  if (error != ERR_IO_PENDING) {
+    if (error == OK)
+      total_bytes_output_ += bytes_read;
+    callback.Run(error, bytes_read);
+  }
+}
+
+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;
+  }
+
+  gzip_header_unchecked_ = 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 (!gzip_header_unchecked_ || !gzip_fallback_unchecked_)
+    return false;
+  if (!buffer_->HasMoreBytes())
+    return false;
+  char d = buffer_->bytes()[0];
+  return d != kGzipFirstByte;
+}
+
+size_t GzipStreamSource::GetBytesOutput() const {
+  return total_bytes_output_;
+}
+
+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