net/filter/gzip_header.h

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