Decoding

Another way to decode data using libcbor is to specify a callbacks that will be invoked when upon finding certain items in the input. This service is provided by

struct cbor_decoder_result cbor_stream_decode(cbor_data buffer, size_t buffer_size, const struct cbor_callbacks *callbacks, void *context)

Stateless decoder.

Will try parsing the buffer and will invoke the appropriate callback on success. Decodes one item at a time. No memory allocations occur.

Parameters
  • buffer: Input buffer
  • buffer_size: Length of the buffer
  • callbacks: The callback bundle
  • context: An arbitrary pointer to allow for maintaining context.

To get started, you might want to have a look at the simple streaming example:

#include "cbor.h"
#include <stdio.h>
#include <string.h>

/*
 * Illustrates how one might skim through a map (which is assumed to have
 * string keys and values only), looking for the value of a specific key
 *
 * Use the examples/data/map.cbor input to test this.
 */

const char * key = "a secret key";
bool key_found = false;

void find_string(void * _ctx, cbor_data buffer, size_t len)
{
    if (key_found) {
        printf("Found the value: %*s\n", (int) len, buffer);
        key_found = false;
    } else if (len == strlen(key)) {
        key_found = (memcmp(key, buffer, len) == 0);
    }
}

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    struct cbor_callbacks callbacks = cbor_empty_callbacks;
    struct cbor_decoder_result decode_result;
    size_t bytes_read = 0;
    callbacks.string = find_string;
    while (bytes_read < length) {
        decode_result = cbor_stream_decode(buffer + bytes_read,
                                           length - bytes_read,
                                           &callbacks, NULL);
        bytes_read += decode_result.read;
    }

    free(buffer);
    fclose(f);
}

The callbacks are defined by

struct

Callback bundle passed to the decoder.

Public Members

cbor_int8_callback cbor_callbacks::uint8

Unsigned int.

cbor_int16_callback cbor_callbacks::uint16

Unsigned int.

cbor_int32_callback cbor_callbacks::uint32

Unsigned int.

cbor_int64_callback cbor_callbacks::uint64

Unsigned int.

cbor_int64_callback cbor_callbacks::negint64

Negative int.

cbor_int32_callback cbor_callbacks::negint32

Negative int.

cbor_int16_callback cbor_callbacks::negint16

Negative int.

cbor_int8_callback cbor_callbacks::negint8

Negative int.

cbor_simple_callback cbor_callbacks::byte_string_start

Definite byte string.

cbor_string_callback cbor_callbacks::byte_string

Indefinite byte string start.

cbor_string_callback cbor_callbacks::string

Definite string.

cbor_simple_callback cbor_callbacks::string_start

Indefinite string start.

cbor_simple_callback cbor_callbacks::indef_array_start

Definite array.

cbor_collection_callback cbor_callbacks::array_start

Indefinite array.

cbor_simple_callback cbor_callbacks::indef_map_start

Definite map.

cbor_collection_callback cbor_callbacks::map_start

Indefinite map.

cbor_int64_callback cbor_callbacks::tag

Tags.

cbor_float_callback cbor_callbacks::float2

Half float.

cbor_float_callback cbor_callbacks::float4

Single float.

cbor_double_callback cbor_callbacks::float8

Double float.

cbor_simple_callback cbor_callbacks::undefined

Undef.

cbor_simple_callback cbor_callbacks::null

Null.

cbor_bool_callback cbor_callbacks::boolean

Bool.

cbor_simple_callback cbor_callbacks::indef_break

Indefinite item break.

When building custom sets of callbacks, feel free to start from

const struct cbor_callbacks cbor_empty_callbacks

Dummy callback bundle - does nothing.

Callback types definition

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.

typedef

Callback prototype.