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// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// The GZipHeader class allows you to parse a gzip header, such as you
// might find at the beginning of a file compressed by gzip (ie, a .gz
// file), or at the beginning of an HTTP response that uses a gzip
// Content-Encoding. See RFC 1952 for the specification for the gzip
// header.
//
// The model is that you call ReadMore() for each chunk of bytes
// you've read from a file or socket.
//
#ifndef NET_FILTER_GZIP_HEADER_H_
#define NET_FILTER_GZIP_HEADER_H_
#include <stddef.h>
#include <stdint.h>
#include "base/containers/span.h"
#include "net/base/net_export.h"
namespace net {
class NET_EXPORT GZipHeader {
public:
enum Status {
INCOMPLETE_HEADER, // don't have all the bits yet...
COMPLETE_HEADER, // complete, valid header
INVALID_HEADER, // found something invalid in the header
};
GZipHeader();
GZipHeader(const GZipHeader&) = delete;
GZipHeader& operator=(const GZipHeader&) = delete;
~GZipHeader();
// Wipe the slate clean and start from scratch.
void Reset();
// Attempt to parse the given buffer as the next installment of
// bytes from a gzip header. If the bytes we've seen so far do not
// yet constitute a complete gzip header, return
// INCOMPLETE_HEADER. If these bytes do not constitute a *valid*
// gzip header, return INVALID_HEADER. When we've seen a complete
// gzip header, return COMPLETE_HEADER and set `header_end` to the offset
// of the first byte beyond the gzip header (i.e., it's the number of bytes of
// `inbuf` the are part of the header).
Status ReadMore(base::span<const uint8_t> inbuf, size_t& header_end);
// Returns true if `inbuf` starts with a gzip header, possibly followed by
// additional bytes.
static bool HasGZipHeader(base::span<const uint8_t> inbuf);
private:
enum { // flags (see RFC)
FLAG_FTEXT = 0x01, // bit 0 set: file probably ascii text
FLAG_FHCRC = 0x02, // bit 1 set: header CRC present
FLAG_FEXTRA = 0x04, // bit 2 set: extra field present
FLAG_FNAME = 0x08, // bit 3 set: original file name present
FLAG_FCOMMENT = 0x10, // bit 4 set: file comment present
FLAG_RESERVED = 0xE0, // bits 5..7: reserved
};
enum State {
// The first 10 bytes are the fixed-size header:
IN_HEADER_ID1,
IN_HEADER_ID2,
IN_HEADER_CM,
IN_HEADER_FLG,
IN_HEADER_MTIME_BYTE_0,
IN_HEADER_MTIME_BYTE_1,
IN_HEADER_MTIME_BYTE_2,
IN_HEADER_MTIME_BYTE_3,
IN_HEADER_XFL,
IN_HEADER_OS,
IN_XLEN_BYTE_0,
IN_XLEN_BYTE_1,
IN_FEXTRA,
IN_FNAME,
IN_FCOMMENT,
IN_FHCRC_BYTE_0,
IN_FHCRC_BYTE_1,
IN_DONE,
};
int state_; // our current State in the parsing FSM: an int so we can ++
uint8_t flags_; // the flags byte of the header ("FLG" in the RFC)
uint16_t extra_length_; // how much of the "extra field" we have yet to read
};
} // namespace net
#endif // NET_FILTER_GZIP_HEADER_H_
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