skeletons/oer_decoder.c

/*
 * Copyright (c) 2017 Lev Walkin <vlm@lionet.info>. All rights reserved.
 * Redistribution and modifications are permitted subject to BSD license.
 */
#include <asn_internal.h>

/*
 * The OER decoder of any type.
 */
asn_dec_rval_t
oer_decode(const asn_codec_ctx_t *opt_codec_ctx,
	asn_TYPE_descriptor_t *type_descriptor,
	void **struct_ptr, const void *ptr, size_t size) {
	asn_codec_ctx_t s_codec_ctx;

	/*
	 * Stack checker requires that the codec context
	 * must be allocated on the stack.
	 */
	if(opt_codec_ctx) {
		if(opt_codec_ctx->max_stack_size) {
			s_codec_ctx = *opt_codec_ctx;
			opt_codec_ctx = &s_codec_ctx;
		}
	} else {
		/* If context is not given, be security-conscious anyway */
		memset(&s_codec_ctx, 0, sizeof(s_codec_ctx));
		s_codec_ctx.max_stack_size = ASN__DEFAULT_STACK_MAX;
		opt_codec_ctx = &s_codec_ctx;
	}

	/*
	 * Invoke type-specific decoder.
	 */
	return type_descriptor->op->oer_decoder(opt_codec_ctx, type_descriptor, 0,
		struct_ptr,	/* Pointer to the destination structure */
		ptr, size	/* Buffer and its size */
		);
}

/*
 * Open Type is encoded as a length (#8.6) followed by that number of bytes.
 * Since we're just skipping, reading the length would be enough.
 */
ssize_t
oer_open_type_skip(const void *bufptr, size_t size) {
    size_t len = 0;
    return oer_fetch_length(bufptr, size, &len);
}

/*
 * Read the Open Type (X.696 (08/2015), #30).
 * RETURN VALUES:
 *       0:     More data expected than bufptr contains.
 *      -1:     Fatal error deciphering length.
 *      >0:     Number of bytes used from bufptr.
 */
ssize_t
oer_open_type_get(const asn_codec_ctx_t *opt_codec_ctx,
                  struct asn_TYPE_descriptor_s *td,
                  const asn_oer_constraints_t *constraints, void **struct_ptr,
                  const void *bufptr, size_t size) {
    asn_dec_rval_t dr;
    size_t container_len = 0;
    ssize_t len_len;

    /* Get the size of a length determinant */
    len_len = oer_fetch_length(bufptr, size, &container_len);
    if(len_len <= 0) {
        return len_len; /* Error or more data expected */
    }

    /*
     * len_len can't be bigger than size, but size without len_len
     * should be bigger or equal to container length
     */
    if(size - len_len < container_len) {
        /* More data is expected */
        return 0;
    }

    dr = td->op->oer_decoder(opt_codec_ctx, td, constraints, struct_ptr,
                         (const uint8_t *)bufptr + len_len, container_len);
    if(dr.code == RC_OK) {
        return len_len + container_len;
    } else {
        /* Even if RC_WMORE, we can't get more data into a closed container. */
        ASN_STRUCT_FREE(*td, *struct_ptr);
        *struct_ptr = 0;
        return -1;
    }
}