text: /*
   * Definitions for tcp compression routines.
   *
   * $Id: vj.h,v 1.7 2010/02/22 17:52:09 goldsimon Exp $
   *
   * Copyright (c) 1989 Regents of the University of California.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms are permitted
   * provided that the above copyright notice and this paragraph are
   * duplicated in all such forms and that any documentation,
   * advertising materials, and other materials related to such
   * distribution and use acknowledge that the software was developed
   * by the University of California, Berkeley.  The name of the
   * University may not be used to endorse or promote products derived
   * from this software without specific prior written permission.
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
   * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
   *
   * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
   * - Initial distribution.
   */
  
  #ifndef VJ_H
  #define VJ_H
  
  #include "lwip/ip.h"
  #include "lwip/tcp_impl.h"
  
  #define MAX_SLOTS 16 /* must be > 2 and < 256 */
  #define MAX_HDR   128
  
  /*
   * Compressed packet format:
   *
   * The first octet contains the packet type (top 3 bits), TCP
   * 'push' bit, and flags that indicate which of the 4 TCP sequence
   * numbers have changed (bottom 5 bits).  The next octet is a
   * conversation number that associates a saved IP/TCP header with
   * the compressed packet.  The next two octets are the TCP checksum
   * from the original datagram.  The next 0 to 15 octets are
   * sequence number changes, one change per bit set in the header
   * (there may be no changes and there are two special cases where
   * the receiver implicitly knows what changed -- see below).
   *
   * There are 5 numbers which can change (they are always inserted
   * in the following order): TCP urgent pointer, window,
   * acknowlegement, sequence number and IP ID.  (The urgent pointer
   * is different from the others in that its value is sent, not the
   * change in value.)  Since typical use of SLIP links is biased
   * toward small packets (see comments on MTU/MSS below), changes
   * use a variable length coding with one octet for numbers in the
   * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
   * range 256 - 65535 or 0.  (If the change in sequence number or
   * ack is more than 65535, an uncompressed packet is sent.)
   */
  
  /*
   * Packet types (must not conflict with IP protocol version)
   *
   * The top nibble of the first octet is the packet type.  There are
   * three possible types: IP (not proto TCP or tcp with one of the
   * control flags set); uncompressed TCP (a normal IP/TCP packet but
   * with the 8-bit protocol field replaced by an 8-bit connection id --
   * this type of packet syncs the sender & receiver); and compressed
   * TCP (described above).
   *
   * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
   * is logically part of the 4-bit "changes" field that follows.  Top
   * three bits are actual packet type.  For backward compatibility
   * and in the interest of conserving bits, numbers are chosen so the
   * IP protocol version number (4) which normally appears in this nibble
   * means "IP packet".
   */
  
  /* packet types */
  #define TYPE_IP               0x40
  #define TYPE_UNCOMPRESSED_TCP 0x70
  #define TYPE_COMPRESSED_TCP   0x80
  #define TYPE_ERROR            0x00
  
  /* Bits in first octet of compressed packet */
  #define NEW_C 0x40 /* flag bits for what changed in a packet */
  #define NEW_I 0x20
  #define NEW_S 0x08
  #define NEW_A 0x04
  #define NEW_W 0x02
  #define NEW_U 0x01
  
  /* reserved, special-case values of above */
  #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
  #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
  #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  
  #define TCP_PUSH_BIT 0x10
  
  
  /*
   * "state" data for each active tcp conversation on the wire.  This is
   * basically a copy of the entire IP/TCP header from the last packet
   * we saw from the conversation together with a small identifier
   * the transmit & receive ends of the line use to locate saved header.
   */
  struct cstate {
      struct cstate *cs_next; /* next most recently used state (xmit only) */
      u_short cs_hlen;        /* size of hdr (receive only) */
      u_char cs_id;           /* connection # associated with this state */
      u_char cs_filler;
      union {
          char csu_hdr[MAX_HDR];
          struct ip_hdr csu_ip;     /* ip/tcp hdr from most recent packet */
      } vjcs_u;
  };
  #define cs_ip vjcs_u.csu_ip
  #define cs_hdr vjcs_u.csu_hdr
  
  
  struct vjstat {
      unsigned long vjs_packets;        /* outbound packets */
      unsigned long vjs_compressed;     /* outbound compressed packets */
      unsigned long vjs_searches;       /* searches for connection state */
      unsigned long vjs_misses;         /* times couldn't find conn. state */
      unsigned long vjs_uncompressedin; /* inbound uncompressed packets */
      unsigned long vjs_compressedin;   /* inbound compressed packets */
      unsigned long vjs_errorin;        /* inbound unknown type packets */
      unsigned long vjs_tossed;         /* inbound packets tossed because of error */
  };
  
  /*
   * all the state data for one serial line (we need one of these per line).
   */
  struct vjcompress {
      struct cstate *last_cs;          /* most recently used tstate */
      u_char last_recv;                /* last rcvd conn. id */
      u_char last_xmit;                /* last sent conn. id */
      u_short flags;
      u_char maxSlotIndex;
      u_char compressSlot;             /* Flag indicating OK to compress slot ID. */
  #if LINK_STATS
      struct vjstat stats;
  #endif
      struct cstate tstate[MAX_SLOTS]; /* xmit connection states */
      struct cstate rstate[MAX_SLOTS]; /* receive connection states */
  };
  
  /* flag values */
  #define VJF_TOSS 1U /* tossing rcvd frames because of input err */
  
  extern void  vj_compress_init    (struct vjcompress *comp);
  extern u_int vj_compress_tcp     (struct vjcompress *comp, struct pbuf *pb);
  extern void  vj_uncompress_err   (struct vjcompress *comp);
  extern int   vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp);
  extern int   vj_uncompress_tcp   (struct pbuf **nb, struct vjcompress *comp);
  
  #endif /* VJ_H */
  