slip_common.h

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#ifndef __UM_SLIP_COMMON_H
#define __UM_SLIP_COMMON_H

#define BUF_SIZE 1500
 /* two bytes each for a (pathological) max packet of escaped chars +  *
  * terminating END char + initial END char                            */
#define ENC_BUF_SIZE (2 * BUF_SIZE + 2)

/* SLIP protocol characters. */
#define SLIP_END             0300   /* indicates end of frame   */
#define SLIP_ESC             0333   /* indicates byte stuffing  */
#define SLIP_ESC_END         0334   /* ESC ESC_END means END 'data' */
#define SLIP_ESC_ESC         0335   /* ESC ESC_ESC means ESC 'data' */

static inline int slip_unesc(unsigned char c, unsigned char *buf, int *pos,
                             int *esc)
{
    int ret;

    switch(c){
    case SLIP_END:
        *esc = 0;
        ret=*pos;
        *pos=0;
        return(ret);
    case SLIP_ESC:
        *esc = 1;
        return(0);
    case SLIP_ESC_ESC:
        if(*esc){
            *esc = 0;
            c = SLIP_ESC;
        }
        break;
    case SLIP_ESC_END:
        if(*esc){
            *esc = 0;
            c = SLIP_END;
        }
        break;
    }
    buf[(*pos)++] = c;
    return(0);
}

static inline int slip_esc(unsigned char *s, unsigned char *d, int len)
{
    unsigned char *ptr = d;
    unsigned char c;

    /*
     * Send an initial END character to flush out any
     * data that may have accumulated in the receiver
     * due to line noise.
     */

    *ptr++ = SLIP_END;

    /*
     * For each byte in the packet, send the appropriate
     * character sequence, according to the SLIP protocol.
     */

    while (len-- > 0) {
        switch(c = *s++) {
        case SLIP_END:
            *ptr++ = SLIP_ESC;
            *ptr++ = SLIP_ESC_END;
            break;
        case SLIP_ESC:
            *ptr++ = SLIP_ESC;
            *ptr++ = SLIP_ESC_ESC;
            break;
        default:
            *ptr++ = c;
            break;
        }
    }
    *ptr++ = SLIP_END;
    return (ptr - d);
}

struct slip_proto {
    unsigned char ibuf[ENC_BUF_SIZE];
    unsigned char obuf[ENC_BUF_SIZE];
    int more; /* more data: do not read fd until ibuf has been drained */
    int pos;
    int esc;
};

static inline void slip_proto_init(struct slip_proto * slip)
{
    memset(slip->ibuf, 0, sizeof(slip->ibuf));
    memset(slip->obuf, 0, sizeof(slip->obuf));
    slip->more = 0;
    slip->pos = 0;
    slip->esc = 0;
}

extern int slip_proto_read(int fd, void *buf, int len,
               struct slip_proto *slip);
extern int slip_proto_write(int fd, void *buf, int len,
                struct slip_proto *slip);

#endif