Add functions used for building WebSocket frame data.

net/websockets/websocket_frame_builder.cc

+// Copyright (c) 2012 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/websockets/websocket_frame_builder.h"
+
+#include <algorithm>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "base/rand_util.h"
+#include "net/base/big_endian.h"
+#include "net/websockets/websocket_frame.h"
+
+namespace {
+
+const uint8 kFinalBit = 0x80;
+const uint8 kReserved1Bit = 0x40;
+const uint8 kReserved2Bit = 0x20;
+const uint8 kReserved3Bit = 0x10;
+const uint8 kOpCodeMask = 0xF;
+const uint8 kMaskBit = 0x80;
+const uint64 kMaxPayloadLengthWithoutExtendedLengthField = 125;
+const uint64 kPayloadLengthWithTwoByteExtendedLengthField = 126;
+const uint64 kPayloadLengthWithEightByteExtendedLengthField = 127;
+
+}  // Unnamed namespace.
+
+namespace net {
+
+WebSocketFrameBuilder::WebSocketFrameBuilder()
+    : frame_offset_(0),
+      has_pinned_masking_key_for_testing_(false),
+      failed_(false) {
+  std::fill(masking_key_,
+            masking_key_ + WebSocketFrameHeader::kMaskingKeyLength,
+            '\0');
+  std::fill(
+      pinned_masking_key_for_testing_,
+      pinned_masking_key_for_testing_ + WebSocketFrameHeader::kMaskingKeyLength,
+      '\0');
+}
+
+WebSocketFrameBuilder::~WebSocketFrameBuilder() {
+}
+
+bool WebSocketFrameBuilder::Encode(
+    ScopedVector<WebSocketFrameChunk> frame_chunks,
+    std::vector<char>* output) {
+  if (failed_)
+    return false;
+
+  // We DCHECK inconsistency of |frame_chunks| such as payload length mismatch

[mmenke, 2012/05/15 18:36:31]

nit:  Think "We DCHECK on inconsistent |frame_chunks|" or "We DCHECK
|frame_chunks| are consistent" is a little easier to follow.

+  // or missing |header| in the first chunk, because these are programming
+  // errors we want to avoid. When DCHECK isn't functional (i.e. Release and
+  // !DCHECK_ALWAYS_ON), we fail gracefully on these errors.
+  for (ScopedVector<WebSocketFrameChunk>::iterator iter = frame_chunks.begin();
+       iter != frame_chunks.end(); ++iter) {
+    WebSocketFrameChunk* chunk = *iter;
+    if (chunk->header.get()) {  // Beginning of a new frame.
+      DCHECK(!current_frame_header_.get());
+      DCHECK_EQ(0u, frame_offset_);
+      if (current_frame_header_.get() || frame_offset_ != 0u) {
+        Fail();
+        return false;
+      }
+      current_frame_header_ = chunk->header.Pass();
+      if (current_frame_header_->masked)
+        GenerateNewMaskingKey();
+      if (!EncodeFrameHeader(current_frame_header_.get(), output)) {
+        Fail();
+        return false;
+      }
+    }
+
+    DCHECK(current_frame_header_.get());
+    if (!current_frame_header_.get()) {
+      Fail();
+      return false;
+    }
+
+    if (current_frame_header_->masked)

[mmenke, 2012/05/15 18:36:31]

According to specs, it's invalid for this to be false, if we're a client.  Do we
even want to allow it to be false?  Maybe just always set it to true?

+      MaskPayload(&chunk->data);
+    // FIXME(yutak): Remove copy here. Ultimately, we probably need to have
+    // "gather writes" ability (aka vectored I/O) in the Socket interface
+    // so we can send data from multiple local buffers without data copies.
+    output->insert(output->end(), chunk->data.begin(), chunk->data.end());
+    frame_offset_ += chunk->data.size();
+    DCHECK_LE(frame_offset_, current_frame_header_->payload_length);
+    if (frame_offset_ > current_frame_header_->payload_length) {
+      Fail();
+      return false;
+    }
+
+    if (chunk->final_chunk) {
+      // Throw away the information about the current frame to get ready
+      // for the next frame.
+      DCHECK_EQ(frame_offset_, current_frame_header_->payload_length);
+      if (frame_offset_ != current_frame_header_->payload_length) {

[mmenke, 2012/05/15 18:36:31]

I'm a bit worried about the interface complexity and all the failure cases we
have here, and wonder if a slightly simpler interface may be preferable, or at
least a simple wrapper that masks out all the complexity of usage.  What is
going to be generating the chunks and their headers?  WebKit?  Something else in
net?

+        Fail();
+        return false;
+      }
+      current_frame_header_.reset();
+      frame_offset_ = 0;
+    }
+  }
+
+  return true;
+}
+
+bool WebSocketFrameBuilder::EncodeFrameHeader(
+    WebSocketFrameHeader* header,
+    std::vector<char>* output) const {
+  DCHECK(header);
+
+  // header->opcode must fit to kOpCodeMask.
+  DCHECK((header->opcode & kOpCodeMask) == header->opcode);
+
+  uint8 first_byte = 0u;
+  first_byte |= header->final ? kFinalBit : 0u;
+  first_byte |= header->reserved1 ? kReserved1Bit : 0u;
+  first_byte |= header->reserved2 ? kReserved2Bit : 0u;
+  first_byte |= header->reserved3 ? kReserved3Bit : 0u;
+  first_byte |= header->opcode;
+
+  uint8 second_byte = 0;

[mmenke, 2012/05/15 18:36:31]

nit:  0u

+  second_byte |= header->masked ? kMaskBit : 0u;
+  if (header->payload_length <=
+      kMaxPayloadLengthWithoutExtendedLengthField) {
+    second_byte |= header->payload_length;
+  } else if (header->payload_length <= kuint16max) {
+    second_byte |= kPayloadLengthWithTwoByteExtendedLengthField;
+  } else if (header->payload_length <= static_cast<uint64>(kint64max)) {
+    second_byte |= kPayloadLengthWithEightByteExtendedLengthField;
+  } else {
+    // WebSocket protocol specification doesn't allow payload length to
+    // exceed kint64max (0x7FFFFFFFFFFFFFFF).
+    return false;
+  }
+
+  output->push_back(first_byte);
+  output->push_back(second_byte);
+
+  // Writes "extended payload length" field.
+  if (second_byte == kPayloadLengthWithTwoByteExtendedLengthField) {
+    uint16 payload_length_16 = static_cast<uint16>(header->payload_length);
+    char encoded[sizeof(uint16)];
+    WriteBigEndian(encoded, payload_length_16);
+    output->insert(output->end(), encoded, encoded + sizeof(uint16));
+  } else if (second_byte == kPayloadLengthWithEightByteExtendedLengthField) {
+    char encoded[sizeof(uint64)];
+    WriteBigEndian(encoded, header->payload_length);
+    output->insert(output->end(), encoded, encoded + sizeof(uint64));
+  }
+
+  // Writes "masking key" field, if needed.
+  if (header->masked) {
+    output->insert(output->end(), masking_key_,
+                   masking_key_ + WebSocketFrameHeader::kMaskingKeyLength);
+  }
+
+  return true;
+}
+
+void WebSocketFrameBuilder::PinMaskingKeyForTesting(const char masking_key[]) {
+  std::copy(masking_key, masking_key + WebSocketFrameHeader::kMaskingKeyLength,
+            pinned_masking_key_for_testing_);
+  has_pinned_masking_key_for_testing_ = true;
+}
+
+void WebSocketFrameBuilder::GenerateNewMaskingKey() {
+  DCHECK(current_frame_header_->masked);
+
+  static const size_t kMaskingKeyLength =
+      WebSocketFrameHeader::kMaskingKeyLength;
+
+  if (has_pinned_masking_key_for_testing_) {
+    std::copy(pinned_masking_key_for_testing_,
+              pinned_masking_key_for_testing_ + kMaskingKeyLength,
+              masking_key_);
+  } else {
+    // Masking keys should be generated from a cryptographically secure random
+    // number generator, which means web application authors should not be able
+    // to guess the next value of masking key.
+    base::RandBytes(masking_key_, kMaskingKeyLength);
+  }
+}
+
+void WebSocketFrameBuilder::MaskPayload(std::vector<char>* output) {
+  static const size_t kMaskingKeyLength =
+      WebSocketFrameHeader::kMaskingKeyLength;
+
+  // TODO(yutak): Make masking more efficient by XOR'ing every machine word
+  // (4 or 8 bytes), instead of XOR'ing every byte.
+  uint64 masking_key_offset = frame_offset_ % kMaskingKeyLength;
+  for (std::vector<char>::iterator iter = output->begin();
+       iter != output->end(); ++iter) {
+    *iter ^= masking_key_[masking_key_offset++];
+    if (masking_key_offset == kMaskingKeyLength)
+      masking_key_offset = 0;
+  }
+}
+
+void WebSocketFrameBuilder::Fail() {
+  current_frame_header_.reset();
+  frame_offset_ = 0;
+  failed_ = true;
+}
+
+}  // namespace net