1 // Copyright 2014 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/hpack_output_stream.h"
6
7 #include "base/logging.h"
8
9
10 namespace net {
11
12 using base::StringPiece;
13 using std::string;
14
HpackOutputStream()15 HpackOutputStream::HpackOutputStream()
16 : bit_offset_(0) {}
17
~HpackOutputStream()18 HpackOutputStream::~HpackOutputStream() {}
19
AppendBits(uint8 bits,size_t bit_size)20 void HpackOutputStream::AppendBits(uint8 bits, size_t bit_size) {
21 DCHECK_GT(bit_size, 0u);
22 DCHECK_LE(bit_size, 8u);
23 DCHECK_EQ(bits >> bit_size, 0);
24 size_t new_bit_offset = bit_offset_ + bit_size;
25 if (bit_offset_ == 0) {
26 // Buffer ends on a byte boundary.
27 DCHECK_LE(bit_size, 8u);
28 buffer_.append(1, bits << (8 - bit_size));
29 } else if (new_bit_offset <= 8) {
30 // Buffer does not end on a byte boundary but the given bits fit
31 // in the remainder of the last byte.
32 *buffer_.rbegin() |= bits << (8 - new_bit_offset);
33 } else {
34 // Buffer does not end on a byte boundary and the given bits do
35 // not fit in the remainder of the last byte.
36 *buffer_.rbegin() |= bits >> (new_bit_offset - 8);
37 buffer_.append(1, bits << (16 - new_bit_offset));
38 }
39 bit_offset_ = new_bit_offset % 8;
40 }
41
AppendPrefix(HpackPrefix prefix)42 void HpackOutputStream::AppendPrefix(HpackPrefix prefix) {
43 AppendBits(prefix.bits, prefix.bit_size);
44 }
45
AppendBytes(StringPiece buffer)46 void HpackOutputStream::AppendBytes(StringPiece buffer) {
47 DCHECK_EQ(bit_offset_, 0u);
48 buffer_.append(buffer.data(), buffer.size());
49 }
50
AppendUint32(uint32 I)51 void HpackOutputStream::AppendUint32(uint32 I) {
52 // The algorithm below is adapted from the pseudocode in 4.1.1.
53 size_t N = 8 - bit_offset_;
54 uint8 max_first_byte = static_cast<uint8>((1 << N) - 1);
55 if (I < max_first_byte) {
56 AppendBits(static_cast<uint8>(I), N);
57 } else {
58 AppendBits(max_first_byte, N);
59 I -= max_first_byte;
60 while ((I & ~0x7f) != 0) {
61 buffer_.append(1, (I & 0x7f) | 0x80);
62 I >>= 7;
63 }
64 AppendBits(static_cast<uint8>(I), 8);
65 }
66 }
67
TakeString(string * output)68 void HpackOutputStream::TakeString(string* output) {
69 // This must hold, since all public functions cause the buffer to
70 // end on a byte boundary.
71 DCHECK_EQ(bit_offset_, 0u);
72 buffer_.swap(*output);
73 buffer_.clear();
74 bit_offset_ = 0;
75 }
76
77 } // namespace net
78