ber_tlv_tag.c

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/*-
 * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
 * Redistribution and modifications are permitted subject to BSD license.
 */
#include <asn_internal.h>
#include <ber_tlv_tag.h>
#include <errno.h>

ssize_t
ber_fetch_tag(const void *ptr, size_t size, ber_tlv_tag_t *tag_r) {
    ber_tlv_tag_t val;
    ber_tlv_tag_t tclass;
    size_t skipped;

    if(size == 0)
        return 0;

    val = *(const uint8_t *)ptr;
    tclass = (val >> 6);
    if((val &= 0x1F) != 0x1F) {
        /*
         * Simple form: everything encoded in a single octet.
         * Tag Class is encoded using two least significant bits.
         */
        *tag_r = (val << 2) | tclass;
        return 1;
    }

    /*
     * Each octet contains 7 bits of useful information.
     * The MSB is 0 if it is the last octet of the tag.
     */
    for(val = 0, ptr = ((const char *)ptr) + 1, skipped = 2;
            skipped <= size;
                ptr = ((const char *)ptr) + 1, skipped++) {
        unsigned int oct = *(const uint8_t *)ptr;
        if(oct & 0x80) {
            val = (val << 7) | (oct & 0x7F);
            /*
             * Make sure there are at least 9 bits spare
             * at the MS side of a value.
             */
            if(val >> ((8 * sizeof(val)) - 9)) {
                /*
                 * We would not be able to accomodate
                 * any more tag bits.
                 */
                return -1;
            }
        } else {
            val = (val << 7) | oct;
            *tag_r = (val << 2) | tclass;
            return skipped;
        }
    }

    return 0;   /* Want more */
}


ssize_t
ber_tlv_tag_fwrite(ber_tlv_tag_t tag, FILE *f) {
    char buf[sizeof("[APPLICATION ]") + 32];
    ssize_t ret;

    ret = ber_tlv_tag_snprint(tag, buf, sizeof(buf));
    if(ret >= (ssize_t)sizeof(buf) || ret < 2) {
        errno = EPERM;
        return -1;
    }

    return fwrite(buf, 1, ret, f);
}

ssize_t
ber_tlv_tag_snprint(ber_tlv_tag_t tag, char *buf, size_t size) {
    char *type = 0;
    int ret;

    switch(tag & 0x3) {
    case ASN_TAG_CLASS_UNIVERSAL:   type = "UNIVERSAL ";    break;
    case ASN_TAG_CLASS_APPLICATION: type = "APPLICATION ";  break;
    case ASN_TAG_CLASS_CONTEXT: type = "";      break;
    case ASN_TAG_CLASS_PRIVATE: type = "PRIVATE ";  break;
    }

    ret = snprintf(buf, size, "[%s%u]", type, ((unsigned)tag) >> 2);
    if(ret <= 0 && size) buf[0] = '\0'; /* against broken libc's */

    return ret;
}

char *
ber_tlv_tag_string(ber_tlv_tag_t tag) {
    static char buf[sizeof("[APPLICATION ]") + 32];

    (void)ber_tlv_tag_snprint(tag, buf, sizeof(buf));

    return buf;
}


size_t
ber_tlv_tag_serialize(ber_tlv_tag_t tag, void *bufp, size_t size) {
    int tclass = BER_TAG_CLASS(tag);
    ber_tlv_tag_t tval = BER_TAG_VALUE(tag);
    uint8_t *buf = (uint8_t *)bufp;
    uint8_t *end;
    size_t required_size;
    size_t i;

    if(tval <= 30) {
        /* Encoded in 1 octet */
        if(size) buf[0] = (tclass << 6) | tval;
        return 1;
    } else if(size) {
        *buf++ = (tclass << 6) | 0x1F;
        size--;
    }

    /*
     * Compute the size of the subsequent bytes.
     */
    for(required_size = 1, i = 7; i < 8 * sizeof(tval); i += 7) {
        if(tval >> i)
            required_size++;
        else
            break;
    }

    if(size < required_size)
        return required_size + 1;

    /*
     * Fill in the buffer, space permitting.
     */
    end = buf + required_size - 1;
    for(i -= 7; buf < end; i -= 7, buf++)
        *buf = 0x80 | ((tval >> i) & 0x7F);
    *buf = (tval & 0x7F);   /* Last octet without high bit */

    return required_size + 1;
}