mandoyj / tiny-coap

CoAP client library implementation for constrained embedded devices

CoAP client library for embedded devices in C

Allows to add the CoAP functionality for embedded device.

Features

• very small memory consumption (in the common case it may be about of 200 bytes for rx/tx buffers, you can tune a PDU size)

• implemented CoAP over UDP rfc7252

• implemented CoAP over TCP draft-coap-tcp-tls-07

• retransmition/acknowledgment functionality

• parsing responses. Received data will be return to user via callback.

• helpers for block-wise mode. The block-wise mode is located on higher layer that this implementation. See wiki for example.

How to send CoAP request to server

1. Include tcoap.h in your code.

#include "tcoap.h"

There are several functions in the tcoap.h which declared how external. You should provide it implementation in your code. See wiki for common case of their implementation.

2. Define a tcoap_handle object, e.g.

tcoap_handle tc_handle = {
        .name = "coap_over_gsm",
        .transport = TCOAP_UDP
};

3. Implement a transfer of incoming data from your hardware interface (e.g. serial port) to the tcoap via functions tcoap_rx_byte or tcoap_rx_packet. E.g.

void uart1_rx_irq_handler()
{
    uint8_t byte = UART1_DR;    
    tcoap_rx_byte(&tc_handle, byte);
}

void eth_rx_irq_handler(uint8_t * data, uint32_t len)
{
    tcoap_rx_packet(&tc_handle, data, len);
}

4. Send a coap request and get back response data in the provided callback:

static void data_resource_response_callback(const struct tcoap_request_descriptor * const reqd, const tcoap_result_data * const result)
{
    // ... check response
}


void send_request_to_data_resource(uint32_t *token_etag, uint8_t * data, uint32_t len)
{
    tcoap_error err;
    tcoap_request_descriptor data_request;

    tcoap_option_data opt_etag;
    tcoap_option_data opt_path;
    tcoap_option_data opt_content;

    /* fill options - we should adhere an order of options */
    opt_content.num = TCOAP_CONTENT_FORMAT_OPT;
    opt_content.value = (uint8_t *)"\x2A";  /* 42 = TCOAP_APPLICATION_OCTET_STREAM */
    opt_content.len = 1;
    opt_content.next = NULL;

    opt_path.num = TCOAP_URI_PATH_OPT;
    opt_path.value = (uint8_t *)"data";
    opt_path.len = 4;
    opt_path.next = &opt_content;

    opt_etag.num = TCOAP_ETAG_OPT;
    opt_etag.value = (uint8_t *)token_etag;
    opt_etag.len = 4;
    opt_etag.next = &opt_path;

    /* fill the request descriptor */
    data_request.payload.buf = data;
    data_request.payload.len = len;

    data_request.code = TCOAP_REQ_POST;
    data_request.tkl = 2;
    data_request.type = tc_handle.transport == TCOAP_UDP ? TCOAP_MESSAGE_CON : TCOAP_MESSAGE_NON;
    data_request.options = &opt_etag;
    
    /* define the callback for response data */
    data_request.response_callback = data_resource_response_callback;

    /* enable debug */
    tcoap_debug(&tc_handle, true);
    
    /* send request */
    err = tcoap_send_coap_request(&tc_handle, &data_request);

    if (err != TCOAP_OK) {
        // error handling
    }
}