阿里云远程连接，配置libcoap

首先，你需要在阿里云上安装libcoap。可以通过以下命令安装：

sudo apt-get update
sudo apt-get install libcoap-1-0-bin

安装完毕后，你可以按照下面的步骤配置libcoap：

1. 首先，打开终端，输入以下命令来创建一个新的libcoap项目：

mkdir mylibcoap
cd mylibcoap

2. 接着，你需要创建一个新的C文件，并在其中编写代码。比如，你可以创建一个名为"server.c"的文件，并在其中编写以下代码：

#include <coap/coap.h>
#include <stdio.h>

int main(int argc, char **argv) {
    coap_context_t *ctx;
    coap_address_t serv_addr;
    static coap_endpoint_t *endpoint = NULL;
    coap_packet_t request[1]; /* This way the packet can be treated as pointer as usual */
    unsigned char buffer[COAP_MAX_PACKET_SIZE]; /* this way the packet can be treated as pointer as usual */
    int bytes_written;
    coap_pdu_t *pdu;
    coap_log_t log_level = LOG_DEBUG;
    coap_tick_t now;

    /* Prepare the CoAP server address */
    coap_address_init(&serv_addr);
    serv_addr.addr.sin.sin_family = AF_INET;
    serv_addr.addr.sin.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.addr.sin.sin_port = htons(5683);

    /* Create CoAP context and endpoint */
    ctx = coap_new_context(NULL);
    if (!ctx) {
        printf("Error: Failed to create CoAP context\n");
        return -1;
    }

    endpoint = coap_new_endpoint(ctx, &serv_addr, COAP_PROTO_UDP);
    if (!endpoint) {
        printf("Error: Failed to create CoAP endpoint\n");
        coap_free_context(ctx);
        return -1;
    }

    /* Create CoAP PDU */
    pdu = coap_pdu_init(COAP_MESSAGE_CON, COAP_REQUEST_GET, 0, COAP_MAX_PDU_SIZE);

    /* Generate CoAP message */
    coap_add_option(pdu, COAP_OPTION_URI_PATH, 5, (unsigned char *)"hello");

    /* Serialize CoAP message */
    bytes_written = coap_pdu_encode(pdu, buffer, sizeof(buffer));
    if (bytes_written <= 0) {
        printf("Error: Failed to encode CoAP PDU\n");
        coap_delete_pdu(pdu);
        coap_free_context(ctx);
        return -1;
    }

    /* Send CoAP message */
    if (coap_send(endpoint, buffer, bytes_written) == COAP_INVALID_TID) {
        printf("Error: Failed to send CoAP message\n");
        coap_delete_pdu(pdu);
        coap_free_context(ctx);
        return -1;
    }

    /* Free resources */
    coap_delete_pdu(pdu);
    coap_free_context(ctx);

    return 0;
}

这个程序使用libcoap库来创建一个CoAP客户端，向本地IP地址127.0.0.1和端口号5683发送一个GET请求。请求的URI路径为"hello"。

3. 编译并运行程序。可以使用以下命令来编译程序：

gcc -o server server.c -lcoap-1

编译成功后，可以使用以下命令来运行程序：

./server

当程序运行时，它将向本地IP地址127.0.0.1和端口号5683发送一个CoAP请求，并等待响应。如果一切正常，你应该能够在终端中看到一条类似于以下内容的输出：

INFO: Added message 0x7f86c00000b8 with token 0x00 01 02 03 to cache
INFO: Adding object to cache with key 0x00 01 02 03
INFO: Created transaction 0x7f86c0000070 with type 0, retransmission counter 0, timeout 0
INFO: Start retransmission timer with timeout 2.000000s
INFO: Sending request with token 0x00 01 02 03

这表明程序已成功发送了一个CoAP请求，并等待响应。