slcompress.h 5.7 KB

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  1. /*
  2. * Definitions for tcp compression routines.
  3. *
  4. * $Id: slcompress.h,v 1.1 2001/01/16 10:03:48 andersen Exp $
  5. *
  6. * Copyright (c) 1989 Regents of the University of California.
  7. * All rights reserved.
  8. *
  9. * Redistribution and use in source and binary forms are permitted
  10. * provided that the above copyright notice and this paragraph are
  11. * duplicated in all such forms and that any documentation,
  12. * advertising materials, and other materials related to such
  13. * distribution and use acknowledge that the software was developed
  14. * by the University of California, Berkeley. The name of the
  15. * University may not be used to endorse or promote products derived
  16. * from this software without specific prior written permission.
  17. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  18. * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  19. * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20. *
  21. * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
  22. * - Initial distribution.
  23. */
  24. #ifndef _SLCOMPRESS_H_
  25. #define _SLCOMPRESS_H_
  26. #define MAX_STATES 16 /* must be > 2 and < 256 */
  27. #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */
  28. /*
  29. * Compressed packet format:
  30. *
  31. * The first octet contains the packet type (top 3 bits), TCP
  32. * 'push' bit, and flags that indicate which of the 4 TCP sequence
  33. * numbers have changed (bottom 5 bits). The next octet is a
  34. * conversation number that associates a saved IP/TCP header with
  35. * the compressed packet. The next two octets are the TCP checksum
  36. * from the original datagram. The next 0 to 15 octets are
  37. * sequence number changes, one change per bit set in the header
  38. * (there may be no changes and there are two special cases where
  39. * the receiver implicitly knows what changed -- see below).
  40. *
  41. * There are 5 numbers which can change (they are always inserted
  42. * in the following order): TCP urgent pointer, window,
  43. * acknowlegement, sequence number and IP ID. (The urgent pointer
  44. * is different from the others in that its value is sent, not the
  45. * change in value.) Since typical use of SLIP links is biased
  46. * toward small packets (see comments on MTU/MSS below), changes
  47. * use a variable length coding with one octet for numbers in the
  48. * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
  49. * range 256 - 65535 or 0. (If the change in sequence number or
  50. * ack is more than 65535, an uncompressed packet is sent.)
  51. */
  52. /*
  53. * Packet types (must not conflict with IP protocol version)
  54. *
  55. * The top nibble of the first octet is the packet type. There are
  56. * three possible types: IP (not proto TCP or tcp with one of the
  57. * control flags set); uncompressed TCP (a normal IP/TCP packet but
  58. * with the 8-bit protocol field replaced by an 8-bit connection id --
  59. * this type of packet syncs the sender & receiver); and compressed
  60. * TCP (described above).
  61. *
  62. * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
  63. * is logically part of the 4-bit "changes" field that follows. Top
  64. * three bits are actual packet type. For backward compatibility
  65. * and in the interest of conserving bits, numbers are chosen so the
  66. * IP protocol version number (4) which normally appears in this nibble
  67. * means "IP packet".
  68. */
  69. /* packet types */
  70. #define TYPE_IP 0x40
  71. #define TYPE_UNCOMPRESSED_TCP 0x70
  72. #define TYPE_COMPRESSED_TCP 0x80
  73. #define TYPE_ERROR 0x00
  74. /* Bits in first octet of compressed packet */
  75. #define NEW_C 0x40 /* flag bits for what changed in a packet */
  76. #define NEW_I 0x20
  77. #define NEW_S 0x08
  78. #define NEW_A 0x04
  79. #define NEW_W 0x02
  80. #define NEW_U 0x01
  81. /* reserved, special-case values of above */
  82. #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
  83. #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
  84. #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  85. #define TCP_PUSH_BIT 0x10
  86. /*
  87. * "state" data for each active tcp conversation on the wire. This is
  88. * basically a copy of the entire IP/TCP header from the last packet
  89. * we saw from the conversation together with a small identifier
  90. * the transmit & receive ends of the line use to locate saved header.
  91. */
  92. struct cstate {
  93. struct cstate *cs_next; /* next most recently used cstate (xmit only) */
  94. u_short cs_hlen; /* size of hdr (receive only) */
  95. u_char cs_id; /* connection # associated with this state */
  96. u_char cs_filler;
  97. union {
  98. char csu_hdr[MAX_HDR];
  99. struct ip csu_ip; /* ip/tcp hdr from most recent packet */
  100. } slcs_u;
  101. };
  102. #define cs_ip slcs_u.csu_ip
  103. #define cs_hdr slcs_u.csu_hdr
  104. /*
  105. * all the state data for one serial line (we need one of these
  106. * per line).
  107. */
  108. struct slcompress {
  109. struct cstate *last_cs; /* most recently used tstate */
  110. u_char last_recv; /* last rcvd conn. id */
  111. u_char last_xmit; /* last sent conn. id */
  112. u_short flags;
  113. #ifndef SL_NO_STATS
  114. int sls_packets; /* outbound packets */
  115. int sls_compressed; /* outbound compressed packets */
  116. int sls_searches; /* searches for connection state */
  117. int sls_misses; /* times couldn't find conn. state */
  118. int sls_uncompressedin; /* inbound uncompressed packets */
  119. int sls_compressedin; /* inbound compressed packets */
  120. int sls_errorin; /* inbound unknown type packets */
  121. int sls_tossed; /* inbound packets tossed because of error */
  122. #endif
  123. struct cstate tstate[MAX_STATES]; /* xmit connection states */
  124. struct cstate rstate[MAX_STATES]; /* receive connection states */
  125. };
  126. /* flag values */
  127. #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
  128. void sl_compress_init __P((struct slcompress *));
  129. void sl_compress_setup __P((struct slcompress *, int));
  130. u_int sl_compress_tcp __P((struct mbuf *,
  131. struct ip *, struct slcompress *, int));
  132. int sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
  133. int sl_uncompress_tcp_core __P((u_char *, int, int, u_int,
  134. struct slcompress *, u_char **, u_int *));
  135. #endif /* _SLCOMPRESS_H_ */