CoAP协议学习——CoAP基础

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。