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

net/filter/filter_source_stream.cc

Index: net/filter/filter_source_stream.cc
diff --git a/net/filter/filter_source_stream.cc b/net/filter/filter_source_stream.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5fb229e9716f46c87fea0e0a4091babd5ee239a8
--- /dev/null
+++ b/net/filter/filter_source_stream.cc
@@ -0,0 +1,160 @@
+// 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/filter_source_stream.h"
+
+#include "base/bind.h"
+#include "base/callback_helpers.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/numerics/safe_conversions.h"
+#include "base/strings/string_util.h"
+
+namespace net {
+
+namespace {
+
+const size_t kBufferSize = 32 * 1024;
+
+}  // namespace
+
+FilterSourceStream::FilterSourceStream(SourceType type,
+                                       std::unique_ptr<SourceStream> next)
+    : SourceStream(type),
+      next_(std::move(next)),
+      next_state_(STATE_NONE),
+      output_buffer_size_(0),
+      next_end_reached_(false) {
+  DCHECK(next_);
+}
+
+FilterSourceStream::~FilterSourceStream() {}
+
+int FilterSourceStream::Read(IOBuffer* read_buffer,
+                             size_t read_buffer_size,
+                             const CompletionCallback& callback) {
+  // Allocate a BlockBuffer during first Read().
+  if (!input_buffer_) {
+    input_buffer_ = new IOBufferWithSize(kBufferSize);
+  }

[mmenke, 2016/08/01 21:55:30]

nit:  Remove braces.

[xunjieli, 2016/08/02 13:44:31]

Done.

+  // Start with filtering data, which tells us whether it needs input data.
+  next_state_ = STATE_FILTER_DATA;
+
+  output_buffer_ = read_buffer;
+  output_buffer_size_ = read_buffer_size;
+  int rv = DoLoop(OK);
+  if (rv > OK) {
+    return rv;
+  } else if (rv == ERR_IO_PENDING) {
+    callback_ = callback;
+  }
+  return static_cast<Error>(rv);

[mmenke, 2016/08/01 21:55:30]

cast not needed.

[xunjieli, 2016/08/02 13:44:31]

Done.

+}
+
+std::string FilterSourceStream::OrderedTypeStringList() const {
+  std::string next_type_string = next_->OrderedTypeStringList();
+  if (next_type_string.empty()) {
+    return GetTypeAsString();
+  }

[mmenke, 2016/08/01 21:55:30]

nit:  Remove braces

[xunjieli, 2016/08/02 13:44:31]

Done.

+  return next_type_string + "," + GetTypeAsString();
+}
+
+int FilterSourceStream::DoLoop(int result) {
+  DCHECK(this);
+  DCHECK_NE(STATE_NONE, next_state_);
+  int rv = result;
+  do {
+    State state = next_state_;
+    next_state_ = STATE_NONE;
+    switch (state) {
+      case STATE_READ_DATA:
+        rv = DoReadData();
+        break;
+      case STATE_READ_DATA_COMPLETE:
+        rv = DoReadDataComplete(rv);
+        break;
+      case STATE_FILTER_DATA:
+        rv = DoFilterData(rv);
+        break;
+      default:
+        NOTREACHED() << "bad state: " << state;
+        rv = ERR_UNEXPECTED;
+        break;
+    }
+  } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);
+  return rv;
+}
+
+int FilterSourceStream::DoReadData() {
+  // Read more data means subclasses have consumed all input or this is the
+  // first read in which case the |drainable_input_buffer_| is not initialized.
+  DCHECK(drainable_input_buffer_ == nullptr ||
+         0 == drainable_input_buffer_->BytesRemaining());
+  // Use base::Unretained here is safe because |this| owns |next_|.
+  int rv = next_->Read(input_buffer_.get(), kBufferSize,
+                       base::Bind(&FilterSourceStream::OnNextReadCompleted,
+                                  base::Unretained(this)));
+
+  if (rv != ERR_IO_PENDING)
+    next_state_ = STATE_READ_DATA_COMPLETE;
+  return rv;
+}
+
+int FilterSourceStream::DoReadDataComplete(int result) {
+  DCHECK_NE(ERR_IO_PENDING, result);
+
+  if (result > OK) {
+    drainable_input_buffer_ = new DrainableIOBuffer(
+        input_buffer_.get(), base::checked_cast<size_t>(result));

[mmenke, 2016/08/01 21:55:30]

static_cast (We have the > OK check just above, so the checked_cast seems
redundant)

[xunjieli, 2016/08/02 13:44:31]

Done.

+    next_state_ = STATE_FILTER_DATA;
+  } else {
+    next_end_reached_ = true;
+  }
+  return result;
+}
+
+void FilterSourceStream::OnNextReadCompleted(int result) {
+  next_state_ = STATE_READ_DATA_COMPLETE;
+  int rv = DoLoop(result);
+  if (rv != ERR_IO_PENDING)
+    DoCallback(rv);
+}
+
+int FilterSourceStream::DoFilterData(int result) {
+  DCHECK(output_buffer_);
+  DCHECK_LE(0, result);
+
+  // This is first Read(), short circuit it and go straight to read data from
+  // |next_|.
+  if (drainable_input_buffer_ == nullptr) {
+    next_state_ = STATE_READ_DATA;
+    return OK;
+  }
+
+  int bytes_output = FilterData(output_buffer_.get(), output_buffer_size_,
+                                drainable_input_buffer_.get());
+  if (bytes_output == ERR_CONTENT_DECODING_FAILED) {
+    UMA_HISTOGRAM_ENUMERATION("Net.ContentDecodingFailed.FilterType", type(),
+                              TYPE_MAX);
+  }
+  // FilterData() is not allowed to return ERR_IO_PENDING.
+  DCHECK_NE(ERR_IO_PENDING, bytes_output);
+
+  // If can still read data from |next_| and filter did not return any data,
+  // it is likely that the filter needs more input.
+  if (bytes_output == OK && !next_end_reached_)
+    next_state_ = STATE_READ_DATA;
+  return bytes_output;
+}
+
+void FilterSourceStream::DoCallback(int result) {
+  DCHECK_NE(ERR_IO_PENDING, result);
+
+  output_buffer_ = nullptr;
+  output_buffer_size_ = 0;
+
+  DCHECK(!callback_.is_null());

[mmenke, 2016/08/01 21:55:30]

Suggest putting this up next to DCHECK_NE(ERR_IO_PENDING, result); - it's one of
the prerequisites on the state machine when calling this method.  Up to you,
though.  Largely a matter of personal preference.

[xunjieli, 2016/08/02 13:44:31]

Done.

+  base::ResetAndReturn(&callback_).Run(result);
+}
+
+}  // namespace net