Add functions used for building WebSocket frame data.

net/websockets/websocket_frame.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.h"
 
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/rand_util.h"
+#include "net/base/big_endian.h"
+#include "net/base/net_errors.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 {
 
 // Definitions for in-struct constants.
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodeContinuation =
     0x0;
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodeText = 0x1;
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodeBinary = 0x2;
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodeClose = 0x8;
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodePing = 0x9;
 const WebSocketFrameHeader::OpCode WebSocketFrameHeader::kOpCodePong = 0xA;
 
 WebSocketFrameChunk::WebSocketFrameChunk() : final_chunk(false) {
 }
 
 WebSocketFrameChunk::~WebSocketFrameChunk() {
 }
 
+int WriteWebSocketFrameHeader(const WebSocketFrameHeader& header,
+                              const WebSocketMaskingKey* masking_key,
+                              char* buffer,
+                              int buffer_size) {
+  DCHECK((header.opcode & kOpCodeMask) == header.opcode)
+      << "header.opcode must fit to kOpCodeMask.";
+  DCHECK(header.payload_length <= static_cast<uint64>(kint64max))
+      << "WebSocket specification doesn't allow a frame longer than "
+      << "kint64max (0x7FFFFFFFFFFFFFFF) bytes.";
+  DCHECK_GE(buffer_size, 0);
+
+  // WebSocket frame format is as follows:
+  // - Common header (2 bytes)
+  // - Optional extended payload length
+  //   (2 or 8 bytes, present if actual payload length is more than 125 bytes)
+  // - Optional masking key (4 bytes, present if MASK bit is on)
+  // - Actual payload (XOR masked with masking key if MASK bit is on)
+  //
+  // This function constructs frame header (the first three in the list
+  // above).
+
+  size_t extended_length_size = 0;
+  if (header.payload_length > kMaxPayloadLengthWithoutExtendedLengthField &&
+      header.payload_length <= kuint16max) {
+    extended_length_size = 2;
+  } else if (header.payload_length > kuint16max) {
+    extended_length_size = 8;
+  }
+  int header_size =
+      WebSocketFrameHeader::kBaseHeaderSize +
+      extended_length_size +
+      (header.masked ? WebSocketFrameHeader::kMaskingKeyLength : 0);
+  if (header_size > buffer_size)
+    return ERR_INVALID_ARGUMENT;
+
+  int buffer_index = 0;
+
+  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;

[mmenke, 2012/06/08 16:00:03]

May want to use header.opcode & kOpCodeMask here, out of paranoia.

[Yuta Kitamura, 2012/06/11 15:56:01]

Done.

+  buffer[buffer_index++] = first_byte;
+
+  uint8 second_byte = 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 {
+    second_byte |= kPayloadLengthWithEightByteExtendedLengthField;
+  }
+  buffer[buffer_index++] = second_byte;
+
+  // Writes "extended payload length" field.
+  if (extended_length_size == 2u) {
+    uint16 payload_length_16 = static_cast<uint16>(header.payload_length);
+    WriteBigEndian(buffer + buffer_index, payload_length_16);
+    buffer_index += sizeof(uint16);
+  } else if (extended_length_size == 8u) {
+    WriteBigEndian(buffer + buffer_index, header.payload_length);
+    buffer_index += sizeof(uint64);
+  }
+
+  // Writes "masking key" field, if needed.
+  if (header.masked) {
+    DCHECK(masking_key);
+    std::copy(masking_key->key,
+              masking_key->key + WebSocketFrameHeader::kMaskingKeyLength,
+              buffer + buffer_index);
+    buffer_index += WebSocketFrameHeader::kMaskingKeyLength;
+  } else {
+    DCHECK(!masking_key);
+  }
+
+  DCHECK_EQ(header_size, buffer_index);
+  return header_size;
+}
+
+WebSocketMaskingKey GenerateWebSocketMaskingKey() {
+  // 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.
+  WebSocketMaskingKey masking_key;
+  base::RandBytes(masking_key.key, WebSocketFrameHeader::kMaskingKeyLength);
+  return masking_key;
+}
+
+void MaskWebSocketFramePayload(const WebSocketMaskingKey& masking_key,
+                               uint64 frame_offset,
+                               char* data,
+                               int data_size) {
+  static const size_t kMaskingKeyLength =
+      WebSocketFrameHeader::kMaskingKeyLength;
+
+  DCHECK_GE(data_size, 0);
+
+  // TODO(yutak): Make masking more efficient by XOR'ing every machine word
+  // (4 or 8 bytes), instead of XOR'ing every byte.
+  size_t masking_key_offset = frame_offset % kMaskingKeyLength;
+  for (int i = 0; i < data_size; ++i) {
+    data[i] ^= masking_key.key[masking_key_offset++];
+    if (masking_key_offset == kMaskingKeyLength)
+      masking_key_offset = 0;
+  }
+}
+
 }  // namespace net