1// Copyright (c) 2011 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// The GZipHeader class allows you to parse a gzip header, such as you
6// might find at the beginning of a file compressed by gzip (ie, a .gz
7// file), or at the beginning of an HTTP response that uses a gzip
8// Content-Encoding. See RFC 1952 for the specification for the gzip
9// header.
10//
11// The model is that you call ReadMore() for each chunk of bytes
12// you've read from a file or socket.
13//
14
15#ifndef NET_BASE_GZIP_HEADER_H_
16#define NET_BASE_GZIP_HEADER_H_
17#pragma once
18
19#include "base/basictypes.h"
20
21namespace net {
22
23class GZipHeader {
24 public:
25  enum Status {
26    INCOMPLETE_HEADER,    // don't have all the bits yet...
27    COMPLETE_HEADER,      // complete, valid header
28    INVALID_HEADER,       // found something invalid in the header
29  };
30
31  GZipHeader();
32  ~GZipHeader();
33
34  // Wipe the slate clean and start from scratch.
35  void Reset();
36
37  // Attempt to parse the given buffer as the next installment of
38  // bytes from a gzip header. If the bytes we've seen so far do not
39  // yet constitute a complete gzip header, return
40  // INCOMPLETE_HEADER. If these bytes do not constitute a *valid*
41  // gzip header, return INVALID_HEADER. When we've seen a complete
42  // gzip header, return COMPLETE_HEADER and set the pointer pointed
43  // to by header_end to the first byte beyond the gzip header.
44  Status ReadMore(const char* inbuf,
45                  int inbuf_len,
46                  const char** header_end);
47 private:
48  enum {                       // flags (see RFC)
49    FLAG_FTEXT        = 0x01,  // bit 0 set: file probably ascii text
50    FLAG_FHCRC        = 0x02,  // bit 1 set: header CRC present
51    FLAG_FEXTRA       = 0x04,  // bit 2 set: extra field present
52    FLAG_FNAME        = 0x08,  // bit 3 set: original file name present
53    FLAG_FCOMMENT     = 0x10,  // bit 4 set: file comment present
54    FLAG_RESERVED     = 0xE0,  // bits 5..7: reserved
55  };
56
57  enum State {
58    // The first 10 bytes are the fixed-size header:
59    IN_HEADER_ID1,
60    IN_HEADER_ID2,
61    IN_HEADER_CM,
62    IN_HEADER_FLG,
63    IN_HEADER_MTIME_BYTE_0,
64    IN_HEADER_MTIME_BYTE_1,
65    IN_HEADER_MTIME_BYTE_2,
66    IN_HEADER_MTIME_BYTE_3,
67    IN_HEADER_XFL,
68    IN_HEADER_OS,
69
70    IN_XLEN_BYTE_0,
71    IN_XLEN_BYTE_1,
72    IN_FEXTRA,
73
74    IN_FNAME,
75
76    IN_FCOMMENT,
77
78    IN_FHCRC_BYTE_0,
79    IN_FHCRC_BYTE_1,
80
81    IN_DONE,
82  };
83
84  static const uint8 magic[];  // gzip magic header
85
86  int    state_;  // our current State in the parsing FSM: an int so we can ++
87  uint8  flags_;         // the flags byte of the header ("FLG" in the RFC)
88  uint16 extra_length_;  // how much of the "extra field" we have yet to read
89
90  DISALLOW_COPY_AND_ASSIGN(GZipHeader);
91};
92
93}  // namespace net
94
95#endif  // NET_BASE_GZIP_HEADER_H_
96