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)
36    : buffer_(new char[size]),
37      capacity_(size),
38      length_(0) {
39}
40
41SpdyFrameBuilder::~SpdyFrameBuilder() {
42}
43
44char* SpdyFrameBuilder::GetWritableBuffer(size_t length) {
45  if (!CanWrite(length)) {
46    return NULL;
47  }
48  return buffer_.get() + length_;
49}
50
51bool SpdyFrameBuilder::Seek(size_t length) {
52  if (!CanWrite(length)) {
53    return false;
54  }
55
56  length_ += length;
57  return true;
58}
59
60bool SpdyFrameBuilder::WriteControlFrameHeader(const SpdyFramer& framer,
61                                               SpdyFrameType type,
62                                               uint8 flags) {
63  DCHECK_GE(type, FIRST_CONTROL_TYPE);
64  DCHECK_LE(type, LAST_CONTROL_TYPE);
65  DCHECK_GT(4, framer.protocol_version());
66  bool success = true;
67  FlagsAndLength flags_length = CreateFlagsAndLength(
68      flags, capacity_ - framer.GetControlFrameHeaderSize());
69  success &= WriteUInt16(kControlFlagMask | framer.protocol_version());
70  success &= WriteUInt16(type);
71  success &= WriteBytes(&flags_length, sizeof(flags_length));
72  DCHECK_EQ(framer.GetControlFrameHeaderSize(), length());
73  return success;
74}
75
76bool SpdyFrameBuilder::WriteDataFrameHeader(const SpdyFramer& framer,
77                                            SpdyStreamId stream_id,
78                                            SpdyDataFlags flags) {
79  if (framer.protocol_version() >= 4) {
80    return WriteFramePrefix(framer, DATA, flags, stream_id);
81  }
82  DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
83  bool success = true;
84  success &= WriteUInt32(stream_id);
85  size_t length_field = capacity_ - framer.GetDataFrameMinimumSize();
86  DCHECK_EQ(0u, length_field & ~static_cast<size_t>(kLengthMask));
87  FlagsAndLength flags_length;
88  flags_length.length_ = htonl(length_field);
89  DCHECK_EQ(0, flags & ~kDataFlagsMask);
90  flags_length.flags_[0] = flags;
91  success &= WriteBytes(&flags_length, sizeof(flags_length));
92  DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
93  return success;
94}
95
96bool SpdyFrameBuilder::WriteFramePrefix(const SpdyFramer& framer,
97                                        SpdyFrameType type,
98                                        uint8 flags,
99                                        SpdyStreamId stream_id) {
100  DCHECK_LE(DATA, type);
101  DCHECK_GE(LAST_CONTROL_TYPE, type);
102  DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
103  DCHECK_LE(4, framer.protocol_version());
104  bool success = true;
105  DCHECK_GT(1u<<16, capacity_);  // Make sure length fits in 2B.
106  success &= WriteUInt16(capacity_);
107  success &= WriteUInt8(type);
108  success &= WriteUInt8(flags);
109  success &= WriteUInt32(stream_id);
110  DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
111  return success;
112}
113
114bool SpdyFrameBuilder::WriteString(const std::string& value) {
115  if (value.size() > 0xffff) {
116    DCHECK(false) << "Tried to write string with length > 16bit.";
117    return false;
118  }
119
120  if (!WriteUInt16(static_cast<int>(value.size())))
121    return false;
122
123  return WriteBytes(value.data(), static_cast<uint16>(value.size()));
124}
125
126bool SpdyFrameBuilder::WriteStringPiece32(const base::StringPiece& value) {
127  if (!WriteUInt32(value.size())) {
128    return false;
129  }
130
131  return WriteBytes(value.data(), value.size());
132}
133
134bool SpdyFrameBuilder::WriteBytes(const void* data, uint32 data_len) {
135  if (!CanWrite(data_len)) {
136    return false;
137  }
138
139  char* dest = GetWritableBuffer(data_len);
140  memcpy(dest, data, data_len);
141  Seek(data_len);
142  return true;
143}
144
145bool SpdyFrameBuilder::RewriteLength(const SpdyFramer& framer) {
146  if (framer.protocol_version() < 4) {
147    return OverwriteLength(framer,
148                           length_ - framer.GetControlFrameHeaderSize());
149  } else {
150    return OverwriteLength(framer, length_);
151  }
152}
153
154bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
155                                       size_t length) {
156  bool success = false;
157  const size_t old_length = length_;
158
159  if (framer.protocol_version() < 4) {
160    FlagsAndLength flags_length = CreateFlagsAndLength(
161        0,  // We're not writing over the flags value anyway.
162        length);
163
164    // Write into the correct location by temporarily faking the offset.
165    length_ = 5;  // Offset at which the length field occurs.
166    success = WriteBytes(reinterpret_cast<char*>(&flags_length) + 1,
167                         sizeof(flags_length) - 1);
168  } else {
169    length_ = 0;
170    success = WriteUInt16(length);
171  }
172
173  length_ = old_length;
174  return success;
175}
176
177bool SpdyFrameBuilder::CanWrite(size_t length) const {
178  if (length > kLengthMask) {
179    DCHECK(false);
180    return false;
181  }
182
183  if (length_ + length > capacity_) {
184    DCHECK(false);
185    return false;
186  }
187
188  return true;
189}
190
191}  // namespace net
192