net/websockets/websocket_frame.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/websockets/websocket_frame.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/basictypes.h"
  10 #include "base/big_endian.h"
  11 #include "base/logging.h"
  12 #include "base/rand_util.h"
  13 #include "net/base/io_buffer.h"
  14 #include "net/base/net_errors.h"
  15
  16 namespace net {
  17
  18 namespace {
  19
  20 const uint8 kFinalBit = 0x80;
  21 const uint8 kReserved1Bit = 0x40;
  22 const uint8 kReserved2Bit = 0x20;
  23 const uint8 kReserved3Bit = 0x10;
  24 const uint8 kOpCodeMask = 0xF;
  25 const uint8 kMaskBit = 0x80;
  26 const uint64 kMaxPayloadLengthWithoutExtendedLengthField = 125;
  27 const uint64 kPayloadLengthWithTwoByteExtendedLengthField = 126;
  28 const uint64 kPayloadLengthWithEightByteExtendedLengthField = 127;
  29
  30 inline void MaskWebSocketFramePayloadByBytes(
  31     const WebSocketMaskingKey& masking_key,
  32     size_t masking_key_offset,
  33     char* const begin,
  34     char* const end) {
  35   for (char* masked = begin; masked != end; ++masked) {
  36     *masked ^= masking_key.key[masking_key_offset++];
  37     if (masking_key_offset == WebSocketFrameHeader::kMaskingKeyLength)
  38       masking_key_offset = 0;
  39   }
  40 }
  41
  42 }  // namespace
  43
  44 scoped_ptr<WebSocketFrameHeader> WebSocketFrameHeader::Clone() const {
  45   scoped_ptr<WebSocketFrameHeader> ret(new WebSocketFrameHeader(opcode));
  46   ret->CopyFrom(*this);
  47   return ret.Pass();
  48 }
  49
  50 void WebSocketFrameHeader::CopyFrom(const WebSocketFrameHeader& source) {
  51   final = source.final;
  52   reserved1 = source.reserved1;
  53   reserved2 = source.reserved2;
  54   reserved3 = source.reserved3;
  55   opcode = source.opcode;
  56   masked = source.masked;
  57   payload_length = source.payload_length;
  58 }
  59
  60 WebSocketFrame::WebSocketFrame(WebSocketFrameHeader::OpCode opcode)
  61     : header(opcode) {}
  62
  63 WebSocketFrame::~WebSocketFrame() {}
  64
  65 WebSocketFrameChunk::WebSocketFrameChunk() : final_chunk(false) {}
  66
  67 WebSocketFrameChunk::~WebSocketFrameChunk() {}
  68
  69 int GetWebSocketFrameHeaderSize(const WebSocketFrameHeader& header) {
  70   int extended_length_size = 0;
  71   if (header.payload_length > kMaxPayloadLengthWithoutExtendedLengthField &&
  72       header.payload_length <= kuint16max) {
  73     extended_length_size = 2;
  74   } else if (header.payload_length > kuint16max) {
  75     extended_length_size = 8;
  76   }
  77
  78   return (WebSocketFrameHeader::kBaseHeaderSize + extended_length_size +
  79           (header.masked ? WebSocketFrameHeader::kMaskingKeyLength : 0));
  80 }
  81
  82 int WriteWebSocketFrameHeader(const WebSocketFrameHeader& header,
  83                               const WebSocketMaskingKey* masking_key,
  84                               char* buffer,
  85                               int buffer_size) {
  86   DCHECK((header.opcode & kOpCodeMask) == header.opcode)
  87       << "header.opcode must fit to kOpCodeMask.";
  88   DCHECK(header.payload_length <= static_cast<uint64>(kint64max))
  89       << "WebSocket specification doesn't allow a frame longer than "
  90       << "kint64max (0x7FFFFFFFFFFFFFFF) bytes.";
  91   DCHECK_GE(buffer_size, 0);
  92
  93   // WebSocket frame format is as follows:
  94   // - Common header (2 bytes)
  95   // - Optional extended payload length
  96   //   (2 or 8 bytes, present if actual payload length is more than 125 bytes)
  97   // - Optional masking key (4 bytes, present if MASK bit is on)
  98   // - Actual payload (XOR masked with masking key if MASK bit is on)
  99   //
 100   // This function constructs frame header (the first three in the list
 101   // above).
 102
 103   int header_size = GetWebSocketFrameHeaderSize(header);
 104   if (header_size > buffer_size)
 105     return ERR_INVALID_ARGUMENT;
 106
 107   int buffer_index = 0;
 108
 109   uint8 first_byte = 0u;
 110   first_byte |= header.final ? kFinalBit : 0u;
 111   first_byte |= header.reserved1 ? kReserved1Bit : 0u;
 112   first_byte |= header.reserved2 ? kReserved2Bit : 0u;
 113   first_byte |= header.reserved3 ? kReserved3Bit : 0u;
 114   first_byte |= header.opcode & kOpCodeMask;
 115   buffer[buffer_index++] = first_byte;
 116
 117   int extended_length_size = 0;
 118   uint8 second_byte = 0u;
 119   second_byte |= header.masked ? kMaskBit : 0u;
 120   if (header.payload_length <= kMaxPayloadLengthWithoutExtendedLengthField) {
 121     second_byte |= header.payload_length;
 122   } else if (header.payload_length <= kuint16max) {
 123     second_byte |= kPayloadLengthWithTwoByteExtendedLengthField;
 124     extended_length_size = 2;
 125   } else {
 126     second_byte |= kPayloadLengthWithEightByteExtendedLengthField;
 127     extended_length_size = 8;
 128   }
 129   buffer[buffer_index++] = second_byte;
 130
 131   // Writes "extended payload length" field.
 132   if (extended_length_size == 2) {
 133     uint16 payload_length_16 = static_cast<uint16>(header.payload_length);
 134     base::WriteBigEndian(buffer + buffer_index, payload_length_16);
 135     buffer_index += sizeof(payload_length_16);
 136   } else if (extended_length_size == 8) {
 137     base::WriteBigEndian(buffer + buffer_index, header.payload_length);
 138     buffer_index += sizeof(header.payload_length);
 139   }
 140
 141   // Writes "masking key" field, if needed.
 142   if (header.masked) {
 143     DCHECK(masking_key);
 144     std::copy(masking_key->key,
 145               masking_key->key + WebSocketFrameHeader::kMaskingKeyLength,
 146               buffer + buffer_index);
 147     buffer_index += WebSocketFrameHeader::kMaskingKeyLength;
 148   } else {
 149     DCHECK(!masking_key);
 150   }
 151
 152   DCHECK_EQ(header_size, buffer_index);
 153   return header_size;
 154 }
 155
 156 WebSocketMaskingKey GenerateWebSocketMaskingKey() {
 157   // Masking keys should be generated from a cryptographically secure random
 158   // number generator, which means web application authors should not be able
 159   // to guess the next value of masking key.
 160   WebSocketMaskingKey masking_key;
 161   base::RandBytes(masking_key.key, WebSocketFrameHeader::kMaskingKeyLength);
 162   return masking_key;
 163 }
 164
 165 void MaskWebSocketFramePayload(const WebSocketMaskingKey& masking_key,
 166                                uint64 frame_offset,
 167                                char* const data,
 168                                int data_size) {
 169   static const size_t kMaskingKeyLength =
 170       WebSocketFrameHeader::kMaskingKeyLength;
 171
 172   DCHECK_GE(data_size, 0);
 173
 174   // Most of the masking is done one word at a time, except for the beginning
 175   // and the end of the buffer which may be unaligned. We use size_t to get the
 176   // word size for this architecture. We require it be a multiple of
 177   // kMaskingKeyLength in size.
 178   typedef size_t PackedMaskType;
 179   PackedMaskType packed_mask_key = 0;
 180   static const size_t kPackedMaskKeySize = sizeof(packed_mask_key);
 181   static_assert((kPackedMaskKeySize >= kMaskingKeyLength &&
 182                  kPackedMaskKeySize % kMaskingKeyLength == 0),
 183                 "word size is not a multiple of mask length");
 184   char* const end = data + data_size;
 185   // If the buffer is too small for the vectorised version to be useful, revert
 186   // to the byte-at-a-time implementation early.
 187   if (data_size <= static_cast<int>(kPackedMaskKeySize * 2)) {
 188     MaskWebSocketFramePayloadByBytes(
 189         masking_key, frame_offset % kMaskingKeyLength, data, end);
 190     return;
 191   }
 192   const size_t data_modulus =
 193       reinterpret_cast<size_t>(data) % kPackedMaskKeySize;
 194   char* const aligned_begin =
 195       data_modulus == 0 ? data : (data + kPackedMaskKeySize - data_modulus);
 196   // Guaranteed by the above check for small data_size.
 197   DCHECK(aligned_begin < end);
 198   MaskWebSocketFramePayloadByBytes(
 199       masking_key, frame_offset % kMaskingKeyLength, data, aligned_begin);
 200   const size_t end_modulus = reinterpret_cast<size_t>(end) % kPackedMaskKeySize;
 201   char* const aligned_end = end - end_modulus;
 202   // Guaranteed by the above check for small data_size.
 203   DCHECK(aligned_end > aligned_begin);
 204   // Create a version of the mask which is rotated by the appropriate offset
 205   // for our alignment. The "trick" here is that 0 XORed with the mask will
 206   // give the value of the mask for the appropriate byte.
 207   char realigned_mask[kMaskingKeyLength] = {};
 208   MaskWebSocketFramePayloadByBytes(
 209       masking_key,
 210       (frame_offset + aligned_begin - data) % kMaskingKeyLength,
 211       realigned_mask,
 212       realigned_mask + kMaskingKeyLength);
 213
 214   for (size_t i = 0; i < kPackedMaskKeySize; i += kMaskingKeyLength) {
 215     // memcpy() is allegedly blessed by the C++ standard for type-punning.
 216     memcpy(reinterpret_cast<char*>(&packed_mask_key) + i,
 217            realigned_mask,
 218            kMaskingKeyLength);
 219   }
 220
 221   // The main loop.
 222   for (char* merged = aligned_begin; merged != aligned_end;
 223        merged += kPackedMaskKeySize) {
 224     // This is not quite standard-compliant C++. However, the standard-compliant
 225     // equivalent (using memcpy()) compiles to slower code using g++. In
 226     // practice, this will work for the compilers and architectures currently
 227     // supported by Chromium, and the tests are extremely unlikely to pass if a
 228     // future compiler/architecture breaks it.
 229     *reinterpret_cast<PackedMaskType*>(merged) ^= packed_mask_key;
 230   }
 231
 232   MaskWebSocketFramePayloadByBytes(
 233       masking_key,
 234       (frame_offset + (aligned_end - data)) % kMaskingKeyLength,
 235       aligned_end,
 236       end);
 237 }
 238
 239 }  // namespace net