der_encoder.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 <errno.h>

static ssize_t der_write_TL(ber_tlv_tag_t tag, ber_tlv_len_t len,
    asn_app_consume_bytes_f *cb, void *app_key, int constructed);

/*
 * The DER encoder of any type.
 */
asn_enc_rval_t
der_encode(asn_TYPE_descriptor_t *type_descriptor, void *struct_ptr,
    asn_app_consume_bytes_f *consume_bytes, void *app_key) {

    ASN_DEBUG("DER encoder invoked for %s",
        type_descriptor->name);

    /*
     * Invoke type-specific encoder.
     */
    return type_descriptor->der_encoder(type_descriptor,
        struct_ptr, /* Pointer to the destination structure */
        0, 0,
        consume_bytes, app_key);
}

/*
 * Argument type and callback necessary for der_encode_to_buffer().
 */
typedef struct enc_to_buf_arg {
    void *buffer;
    size_t left;
} enc_to_buf_arg;
static int encode_to_buffer_cb(const void *buffer, size_t size, void *key) {
    enc_to_buf_arg *arg = (enc_to_buf_arg *)key;

    if(arg->left < size)
        return -1;  /* Data exceeds the available buffer size */

    memcpy(arg->buffer, buffer, size);
    arg->buffer = ((char *)arg->buffer) + size;
    arg->left -= size;

    return 0;
}

/*
 * A variant of the der_encode() which encodes the data into the provided buffer
 */
asn_enc_rval_t
der_encode_to_buffer(asn_TYPE_descriptor_t *type_descriptor, void *struct_ptr,
    void *buffer, size_t buffer_size) {
    enc_to_buf_arg arg;
    asn_enc_rval_t ec;

    arg.buffer = buffer;
    arg.left = buffer_size;

    ec = type_descriptor->der_encoder(type_descriptor,
        struct_ptr, /* Pointer to the destination structure */
        0, 0, encode_to_buffer_cb, &arg);
    if(ec.encoded != -1) {
        assert(ec.encoded == (ssize_t)(buffer_size - arg.left));
        /* Return the encoded contents size */
    }
    return ec;
}


/*
 * Write out leading TL[v] sequence according to the type definition.
 */
ssize_t
der_write_tags(asn_TYPE_descriptor_t *sd,
        size_t struct_length,
        int tag_mode, int last_tag_form,
        ber_tlv_tag_t tag,  /* EXPLICIT or IMPLICIT tag */
        asn_app_consume_bytes_f *cb,
        void *app_key) {
    ber_tlv_tag_t *tags;    /* Copy of tags stream */
    int tags_count;     /* Number of tags */
    size_t overall_length;
    ssize_t *lens;
    int i;

    ASN_DEBUG("Writing tags (%s, tm=%d, tc=%d, tag=%s, mtc=%d)",
        sd->name, tag_mode, sd->tags_count,
        ber_tlv_tag_string(tag),
        tag_mode
            ?(sd->tags_count+1
                -((tag_mode == -1) && sd->tags_count))
            :sd->tags_count
    );

    if(tag_mode) {
        /*
         * Instead of doing shaman dance like we do in ber_check_tags(),
         * allocate a small array on the stack
         * and initialize it appropriately.
         */
        int stag_offset;
        tags = (ber_tlv_tag_t *)alloca((sd->tags_count + 1) * sizeof(ber_tlv_tag_t));
        if(!tags) { /* Can fail on !x86 */
            errno = ENOMEM;
            return -1;
        }
        tags_count = sd->tags_count
            + 1 /* EXPLICIT or IMPLICIT tag is given */
            - ((tag_mode == -1) && sd->tags_count);
        /* Copy tags over */
        tags[0] = tag;
        stag_offset = -1 + ((tag_mode == -1) && sd->tags_count);
        for(i = 1; i < tags_count; i++)
            tags[i] = sd->tags[i + stag_offset];
    } else {
        tags = sd->tags;
        tags_count = sd->tags_count;
    }

    /* No tags to write */
    if(tags_count == 0)
        return 0;

    lens = (ssize_t *)alloca(tags_count * sizeof(lens[0]));
    if(!lens) {
        errno = ENOMEM;
        return -1;
    }

    /*
     * Array of tags is initialized.
     * Now, compute the size of the TLV pairs, from right to left.
     */
    overall_length = struct_length;
    for(i = tags_count - 1; i >= 0; --i) {
        lens[i] = der_write_TL(tags[i], overall_length, 0, 0, 0);
        if(lens[i] == -1) return -1;
        overall_length += lens[i];
        lens[i] = overall_length - lens[i];
    }

    if(!cb) return overall_length - struct_length;

    ASN_DEBUG("%s %s TL sequence (%d elements)",
        cb?"Encoding":"Estimating", sd->name, tags_count);

    /*
     * Encode the TL sequence for real.
     */
    for(i = 0; i < tags_count; i++) {
        ssize_t len;
        int _constr;

        /* Check if this tag happens to be constructed */
        _constr = (last_tag_form || i < (tags_count - 1));

        len = der_write_TL(tags[i], lens[i], cb, app_key, _constr);
        if(len == -1) return -1;
    }

    return overall_length - struct_length;
}

static ssize_t
der_write_TL(ber_tlv_tag_t tag, ber_tlv_len_t len,
        asn_app_consume_bytes_f *cb, void *app_key,
        int constructed) {
    uint8_t buf[32];
    size_t size = 0;
    int buf_size = cb?sizeof(buf):0;
    ssize_t tmp;

    /* Serialize tag (T from TLV) into possibly zero-length buffer */
    tmp = ber_tlv_tag_serialize(tag, buf, buf_size);
    if(tmp == -1 || tmp > (ssize_t)sizeof(buf)) return -1;
    size += tmp;

    /* Serialize length (L from TLV) into possibly zero-length buffer */
    tmp = der_tlv_length_serialize(len, buf+size, buf_size?buf_size-size:0);
    if(tmp == -1) return -1;
    size += tmp;

    if(size > sizeof(buf))
        return -1;

    /*
     * If callback is specified, invoke it, and check its return value.
     */
    if(cb) {
        if(constructed) *buf |= 0x20;
        if(cb(buf, size, app_key) < 0)
            return -1;
    }

    return size;
}