coap协议C语言实现

CoAP（Constrained Application Protocol）是一种轻量级的应用层协议，用于在受限的网络环境中传输数据。以下是一个简单的CoAP协议C语言实现的示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <arpa/inet.h>

#define COAP_VERSION 1
#define COAP_HEADER_LENGTH 4

typedef struct {
    uint8_t version;
    uint8_t type;
    uint8_t token_length;
    uint8_t code;
    uint16_t message_id;
} coap_header_t;

typedef struct {
    uint8_t *token;
    uint16_t token_length;
    uint8_t *payload;
    uint16_t payload_length;
} coap_message_t;

typedef struct {
    int socket_fd;
    struct sockaddr_in address;
} coap_endpoint_t;

typedef struct {
    uint8_t *data;
    uint16_t length;
} coap_buffer_t;

coap_header_t *coap_create_header(uint8_t type, uint8_t code, uint16_t message_id) {
    coap_header_t *header = calloc(1, sizeof(coap_header_t));
    header->version = COAP_VERSION;
    header->type = type;
    header->token_length = 0;
    header->code = code;
    header->message_id = htons(message_id);
    return header;
}

void coap_free_header(coap_header_t *header) {
    free(header);
}

coap_message_t *coap_create_message(uint8_t type, uint8_t code, uint16_t message_id) {
    coap_message_t *message = calloc(1, sizeof(coap_message_t));
    message->token = NULL;
    message->token_length = 0;
    message->payload = NULL;
    message->payload_length = 0;
    coap_header_t *header = coap_create_header(type, code, message_id);
    message->payload_length += COAP_HEADER_LENGTH;
    message->payload = calloc(1, message->payload_length);
    memcpy(message->payload, header, COAP_HEADER_LENGTH);
    coap_free_header(header);
    return message;
}

void coap_free_message(coap_message_t *message) {
    free(message->token);
    free(message->payload);
    free(message);
}

coap_endpoint_t *coap_create_endpoint(char *ip, int port) {
    coap_endpoint_t *endpoint = calloc(1, sizeof(coap_endpoint_t));
    endpoint->socket_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    memset(&endpoint->address, 0, sizeof(endpoint->address));
    endpoint->address.sin_family = AF_INET;
    endpoint->address.sin_addr.s_addr = inet_addr(ip);
    endpoint->address.sin_port = htons(port);
    return endpoint;
}

void coap_free_endpoint(coap_endpoint_t *endpoint) {
    close(endpoint->socket_fd);
    free(endpoint);
}

coap_buffer_t *coap_receive(coap_endpoint_t *endpoint) {
    coap_buffer_t *buffer = calloc(1, sizeof(coap_buffer_t));
    socklen_t address_length = sizeof(endpoint->address);
    int length = recvfrom(endpoint->socket_fd, buffer->data, buffer->length, 0, (struct sockaddr *) &endpoint->address, &address_length);
    buffer->length = length;
    return buffer;
}

void coap_send(coap_endpoint_t *endpoint, coap_message_t *message) {
    sendto(endpoint->socket_fd, message->payload, message->payload_length, 0, (struct sockaddr *) &endpoint->address, sizeof(endpoint->address));
}

int main() {
    coap_endpoint_t *endpoint = coap_create_endpoint("127.0.0.1", 5683);
    coap_message_t *message = coap_create_message(0, 1, 1);
    coap_send(endpoint, message);
    coap_buffer_t *buffer = coap_receive(endpoint);
    printf("Received %d bytes: %.*s\n", buffer->length, buffer->length, buffer->data);
    coap_free_message(message);
    coap_free_endpoint(endpoint);
    free(buffer);
    return 0;
}

这个示例实现了CoAP协议的基本功能，包括创建和发送CoAP消息，以及接收和处理CoAP消息。在这个示例中，我们使用了标准的C语言库函数和一些网络相关的函数来实现CoAP协议的功能。如果您想要了解更多关于CoAP协议的信息，请参考CoAP协议的官方网站。