net/base/gzip_header.h

   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
  21 namespace net {
  22
  23 class 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_