在libcoap coap服务器获取响应处理程序中，如何访问对URI的查询添加？

Question

我正在使用Raspbian下的libcoap-dev-1库和一个Raspberry Pi，使用这个库和一个简单的客户机和简单的服务器来实现CoAP协议。我有一个正常工作的客户机和一个正常工作的服务器，现在正在尝试修改服务器，以便它可以接受包含查询字符串的URI，然后我可以获取该URI的查询字符串。

我目前正在测试的URI是coap://127.0.0.1/hello?item=1，它有一个查询参数，即?之后的item=1。

服务器中的请求处理程序是以下函数，它是一个存根，用于测试将录制的响应以JSON文本形式发送回客户端。这可以很好地工作，客户端接收JSON文本，并能够使用Fast JSON库来解析它。

// header for the libcoap library. it should be in /usr/include/coap
#include <coap/coap.h>

/*
 * The resource handler which the libcoap library will invoke when the registered
 * URI is specified.
 */
static void
hello_handler(coap_context_t *ctx, struct coap_resource_t *resource,
              const coap_endpoint_t *local_interface, coap_address_t *peer,
              coap_pdu_t *request, str *token, coap_pdu_t *response)
{
        static  int iCount = 0;
        unsigned char buf[3];
        const char* response_data     = "{\"device\": \"DEV-01-123\", \"item\" : %d }";
        char response_buf[256] = {0};

        response->hdr->code           = COAP_RESPONSE_CODE(205);
        coap_add_option(response, COAP_OPTION_CONTENT_TYPE, coap_encode_var_bytes(buf, COAP_MEDIATYPE_TEXT_PLAIN), buf);

        sprintf (response_buf, response_data, iCount);
        coap_add_data  (response, strlen(response_buf), (unsigned char *)response_buf);
        iCount++;

        printf (" request %s\n", resource->uri.s);
}

函数末尾的printf()打印不带查询部分的URI。所以打印的是hello而不是hello?item=1。

我的问题是，如何访问客户端发送的URI的查询部分？

Answer 1

作为格式化URI和从CoAP请求中检索URI和URI查询信息的一部分，用于创建服务器和客户机的libcoap函数还需要几个步骤。

完整的示例应用程序client.c和server.c在我位于https://github.com/RichardChambers/raspberrypi/tree/master/coap的GitHub存储库中。

在服务器端，消息处理程序将使用一个选项迭代器(一个coap_opt_iterator_t结构对象)来迭代coap_pdu_t结构请求对象的选项。在迭代时，服务器将查找COAP_OPTION_URI_QUERY类型的选项，该选项将包含查询参数，通常是关键字相等值对。

因此，可以使用助手函数重写发布的问题的函数hello_handler()，以获得URI查询项的列表，如下所示：

/*
 * The following helper function, printQueryOption(), is used to
 * iterate over the list of options looking for query type options
 * to the base URI. This is analogous to a web URL that contains
 * a question mark followed by options such as:
 *    http://www.server.com/hello?type=1,id=2345
 *
 * We will return a value of 1 (true) if we found something or a value
 * of 0 (false) if we do not.
*/
static int
printQueryOption (coap_pdu_t *request, coap_opt_iterator_t * popt_iter )
{
        int  iRet = 0;
        coap_opt_t *option;

        // iterate over the options looking for queries. If we find one
        // then print it and return a value of 1, true, to indicate we
        // found one. If we don't find any then return the default value
        // of 0, false.
        while (option = coap_option_next(popt_iter)) {
                // found an option, is it a query option or not.
                if (popt_iter->type != COAP_OPTION_URI_QUERY) continue;
                // it is a query option so print out the query text.
                char xBuff[128] = {0};
                strncpy (xBuff, COAP_OPT_VALUE(option), COAP_OPT_LENGTH(option));
                printf ("    option  len %d\n         %s \n", COAP_OPT_LENGTH(option), xBuff);

                // indicate that we found a query option.
                iRet = 1;
                break;
        }

        return iRet;
}

/*
 * The resource handler which the libcoap library will invoke when the registered
 * URI is specified. This is a simple request handler which will just display some
 * of the information from the request.
 */
static void
hello_handler(coap_context_t *ctx, struct coap_resource_t *resource,
              const coap_endpoint_t *local_interface, coap_address_t *peer,
              coap_pdu_t *request, str *token, coap_pdu_t *response)
{
        static  int iCount = 0;   // a simple count to provide some kind of response data.
        unsigned char buf[3];
        const char* response_data     = "{\"device\": \"DEV-01-123\", \"item\" : %d }";
        char response_buf[256] = {0};

        // generate a response to this request. we have a hard coded JSON text that
        // we are using as a stub for testing.
        response->hdr->code           = COAP_RESPONSE_CODE(205);
        coap_add_option(response, COAP_OPTION_CONTENT_TYPE, coap_encode_var_bytes(buf, COAP_MEDIATYPE_TEXT_PLAIN), buf);

        sprintf (response_buf, response_data, iCount);
        coap_add_data  (response, strlen(response_buf), (unsigned char *)response_buf);
        iCount++;    // this count is some type of varying data so that we can see things are working.

        if (request != NULL) {
                // there is a request URI so lets print out the base URI and then
                // iterate over the options looking for the Query type options.
                coap_opt_iterator_t  opt_iter;

                printf (" request %s\n", resource->uri.s);
                coap_option_iterator_init (request, &opt_iter, COAP_OPT_ALL);

                // iterate over the options of the request printing out any
                // query text that may exist.
                while (printQueryOption (request, &opt_iter));
        } else {
                printf (" request - NONE\n");
        }
}

在客户端，我们将构建我们的请求，添加我们想要包含在请求中的查询，并通过一系列函数coap_add_option()调用，如下所示：

coap_split_uri(server_uri, strlen(server_uri), &uri);
request            = coap_new_pdu();
request->hdr->type = COAP_MESSAGE_CON;
request->hdr->id   = coap_new_message_id(ctx);
request->hdr->code = get_method;

printf (" Request URI: path %d %s\n", uri.path.length, uri.path.s);

coap_add_option(request, COAP_OPTION_URI_PATH, uri.path.length, uri.path.s);
sprintf (server_query, "item=%d", iItem);
coap_add_option(request, COAP_OPTION_URI_QUERY, strlen(server_query), server_query);
printf ("         Query: len %d %s\n", strlen(server_query), server_query);
sprintf (server_query, "device=%s", aszDevName);
coap_add_option(request, COAP_OPTION_URI_QUERY, strlen(server_query), server_query);
printf ("         Query: len %d %s\n", strlen(server_query), server_query);
sprintf (server_query, "tempo=%s", aszTempoName);
coap_add_option(request, COAP_OPTION_URI_QUERY, strlen(server_query), server_query);
printf ("         Query: len %d %s\n", strlen(server_query), server_query);

这些语句使用一组参数或查询选项创建对特定URI的CoAP请求，以便URI的服务器处理程序可以向请求提供特定的响应。在本例中，使用的变量使用如下所示的值进行硬编码：

char *aszDevName = "DEV-01-203";
char *aszTempoName = "TEMPO-12345";
int  iItem = 5;

const char*       server_uri = "coap://127.0.0.1/hello";

这两个示例程序可以在两个单独的终端窗口中运行，首先启动服务器。尝试客户机三次，第一次使用URI "hello"，第二次使用URI“告别”，第三次使用URI "hello“，我们将看到以下输出。

从服务器：

pi@raspberrypi:~/Documents/raspberrypi/coap $ ./server
 request hello
    option  len 6
         item=5 
    option  len 17
         device=DEV-01-203 
    option  len 17
         tempo=TEMPO-12345 
 request hello
    option  len 6
         item=5 
    option  len 17
         device=DEV-01-203 
    option  len 17
         tempo=TEMPO-12345 

在客户端的终端窗口中：

pi@raspberrypi:~/Documents/raspberrypi/coap $ ./client
 Request URI: path 5 hello
         Query: len 6 item=5
         Query: len 17 device=DEV-01-203
         Query: len 17 tempo=TEMPO-12345
Received: {"device": "DEV-01-123", "item" : 0 } -> item = 0
pi@raspberrypi:~/Documents/raspberrypi/coap $ ./client goodbye
 Request URI: path 7 goodbye
         Query: len 6 item=5
         Query: len 17 device=DEV-01-203
         Query: len 17 tempo=TEMPO-12345

COAP_RESPONSE_CLASS() unknown.
pi@raspberrypi:~/Documents/raspberrypi/coap $ ./client
 Request URI: path 5 hello
         Query: len 6 item=5
         Query: len 17 device=DEV-01-203
         Query: len 17 tempo=TEMPO-12345
Received: {"device": "DEV-01-123", "item" : 1 } -> item = 1
pi@raspberrypi:~/Documents/raspberrypi/coap $