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/spdy/spdy_frame_builder.h"
6
7#include <limits>
8
9#include "base/logging.h"
10#include "net/spdy/spdy_framer.h"
11#include "net/spdy/spdy_protocol.h"
12
13namespace net {
14
15namespace {
16
17// A special structure for the 8 bit flags and 24 bit length fields.
18union FlagsAndLength {
19  uint8 flags[4];  // 8 bits
20  uint32 length;   // 24 bits
21};
22
23// Creates a FlagsAndLength.
24FlagsAndLength CreateFlagsAndLength(uint8 flags, size_t length) {
25  DCHECK_EQ(0u, length & ~static_cast<size_t>(kLengthMask));
26  FlagsAndLength flags_length;
27  flags_length.length = htonl(static_cast<uint32>(length));
28  DCHECK_EQ(0, flags & ~kControlFlagsMask);
29  flags_length.flags[0] = flags;
30  return flags_length;
31}
32
33}  // namespace
34
35SpdyFrameBuilder::SpdyFrameBuilder(size_t size, SpdyMajorVersion version)
36    : buffer_(new char[size]),
37      capacity_(size),
38      length_(0),
39      offset_(0),
40      version_(version) {
41}
42
43SpdyFrameBuilder::~SpdyFrameBuilder() {
44}
45
46char* SpdyFrameBuilder::GetWritableBuffer(size_t length) {
47  if (!CanWrite(length)) {
48    return NULL;
49  }
50  return buffer_.get() + offset_ + length_;
51}
52
53bool SpdyFrameBuilder::Seek(size_t length) {
54  if (!CanWrite(length)) {
55    return false;
56  }
57
58  length_ += length;
59  return true;
60}
61
62bool SpdyFrameBuilder::WriteControlFrameHeader(const SpdyFramer& framer,
63                                               SpdyFrameType type,
64                                               uint8 flags) {
65  DCHECK_GE(SPDY3, version_);
66  DCHECK_NE(-1,
67            SpdyConstants::SerializeFrameType(version_, type));
68  bool success = true;
69  FlagsAndLength flags_length = CreateFlagsAndLength(
70      flags, capacity_ - framer.GetControlFrameHeaderSize());
71  success &= WriteUInt16(kControlFlagMask |
72                         SpdyConstants::SerializeMajorVersion(version_));
73  success &= WriteUInt16(
74      SpdyConstants::SerializeFrameType(framer.protocol_version(), type));
75  success &= WriteBytes(&flags_length, sizeof(flags_length));
76  DCHECK_EQ(framer.GetControlFrameHeaderSize(), length());
77  return success;
78}
79
80bool SpdyFrameBuilder::WriteDataFrameHeader(const SpdyFramer& framer,
81                                            SpdyStreamId stream_id,
82                                            uint8 flags) {
83  if (version_ > SPDY3) {
84    return BeginNewFrame(framer, DATA, flags, stream_id);
85  }
86  DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
87  bool success = true;
88  success &= WriteUInt32(stream_id);
89  size_t length_field = capacity_ - framer.GetDataFrameMinimumSize();
90  DCHECK_EQ(0u, length_field & ~static_cast<size_t>(kLengthMask));
91  FlagsAndLength flags_length;
92  flags_length.length = htonl(length_field);
93  DCHECK_EQ(0, flags & ~kDataFlagsMask);
94  flags_length.flags[0] = flags;
95  success &= WriteBytes(&flags_length, sizeof(flags_length));
96  DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
97  return success;
98}
99
100bool SpdyFrameBuilder::BeginNewFrame(const SpdyFramer& framer,
101                                     SpdyFrameType type,
102                                     uint8 flags,
103                                     SpdyStreamId stream_id) {
104  DCHECK(SpdyConstants::IsValidFrameType(version_,
105      SpdyConstants::SerializeFrameType(version_, type)));
106  DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
107  DCHECK_LT(SPDY3, framer.protocol_version());
108  bool success = true;
109  if (length_ > 0) {
110    // Update length field for previous frame.
111    OverwriteLength(framer, length_ - framer.GetPrefixLength(type));
112    DLOG_IF(DFATAL, SpdyConstants::GetFrameMaximumSize(version_) < length_)
113        << "Frame length  " << length_
114        << " is longer than the maximum allowed length.";
115  }
116
117  offset_ += length_;
118  length_ = 0;
119
120  // Assume all remaining capacity will be used for this frame. If not,
121  // the length will get overwritten when we begin the next frame.
122  // Don't check for length limits here because this may be larger than the
123  // actual frame length.
124  success &= WriteUInt24(capacity_ - offset_ - framer.GetPrefixLength(type));
125  success &= WriteUInt8(
126      SpdyConstants::SerializeFrameType(version_, type));
127  success &= WriteUInt8(flags);
128  success &= WriteUInt32(stream_id);
129  DCHECK_EQ(framer.GetDataFrameMinimumSize(), length_);
130  return success;
131}
132
133bool SpdyFrameBuilder::WriteString(const std::string& value) {
134  if (value.size() > 0xffff) {
135    DCHECK(false) << "Tried to write string with length > 16bit.";
136    return false;
137  }
138
139  if (!WriteUInt16(static_cast<int>(value.size())))
140    return false;
141
142  return WriteBytes(value.data(), static_cast<uint16>(value.size()));
143}
144
145bool SpdyFrameBuilder::WriteStringPiece32(const base::StringPiece& value) {
146  if (!WriteUInt32(value.size())) {
147    return false;
148  }
149
150  return WriteBytes(value.data(), value.size());
151}
152
153bool SpdyFrameBuilder::WriteBytes(const void* data, uint32 data_len) {
154  if (!CanWrite(data_len)) {
155    return false;
156  }
157
158  char* dest = GetWritableBuffer(data_len);
159  memcpy(dest, data, data_len);
160  Seek(data_len);
161  return true;
162}
163
164bool SpdyFrameBuilder::RewriteLength(const SpdyFramer& framer) {
165  return OverwriteLength(framer,
166                         length_ - framer.GetControlFrameHeaderSize());
167}
168
169bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
170                                       size_t length) {
171  if (version_ <= SPDY3) {
172    DCHECK_GE(SpdyConstants::GetFrameMaximumSize(version_) -
173              framer.GetFrameMinimumSize(),
174              length);
175  } else {
176    DCHECK_GE(SpdyConstants::GetFrameMaximumSize(version_), length);
177  }
178  bool success = false;
179  const size_t old_length = length_;
180
181  if (version_ <= SPDY3) {
182    FlagsAndLength flags_length = CreateFlagsAndLength(
183        0,  // We're not writing over the flags value anyway.
184        length);
185
186    // Write into the correct location by temporarily faking the offset.
187    length_ = 5;  // Offset at which the length field occurs.
188    success = WriteBytes(reinterpret_cast<char*>(&flags_length) + 1,
189                         sizeof(flags_length) - 1);
190  } else {
191    length_ = 0;
192    success = WriteUInt24(length);
193  }
194
195  length_ = old_length;
196  return success;
197}
198
199bool SpdyFrameBuilder::OverwriteFlags(const SpdyFramer& framer,
200                                      uint8 flags) {
201  DCHECK_LT(SPDY3, framer.protocol_version());
202  bool success = false;
203  const size_t old_length = length_;
204  // Flags are the fifth octet in the frame prefix.
205  length_ = 4;
206  success = WriteUInt8(flags);
207  length_ = old_length;
208  return success;
209}
210
211bool SpdyFrameBuilder::CanWrite(size_t length) const {
212  if (length > kLengthMask) {
213    DCHECK(false);
214    return false;
215  }
216
217  if (offset_ + length_ + length > capacity_) {
218    DCHECK(false);
219    return false;
220  }
221
222  return true;
223}
224
225}  // namespace net
226