問題描述
收聽推送消息？ (Listen to a push message?)
我必須無限期地收聽網絡服務的推送消息。只要內容有更新，我正在收聽的 Web 服務就會發送肥皂響應消息。收到消息後，我必須對其進行解析並將其存儲到結構中。以下是我的代碼。
CURL *curl;
CURLcode res;
const char *onlineWebServiceRequest = "<?xml version=\"1.0\" encoding=\"utf‑8\"?> <soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema‑instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\"> <soap:Body> <GetCitiesByCountry xmlns=\"http://www.webserviceX.NET\"> <CountryName>Netherlands</CountryName> </GetCitiesByCountry> </soap:Body> </soap:Envelope>";
if(curl){
curl_easy_setopt(curl, CURLOPT_URL, "http://www.webservicex.net/globalweather.asmx/GetCitiesByCountry" );
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, onlineWebServiceRequest);
res = curl_easy_perform(curl);
// call some other method to parse the res
curl_easy_cleanup(curl);
}
疑問：接收推送消息的方式是否正確？如果是的話，
上面的代碼沒有檢查與web服務的連接狀態。我該如何檢查？
如果沒有，我可能對開源還有哪些其他選擇？
提前致謝
參考解法
方法 1:
You'd better off checking for errors.
To do that you have to enable CURLOPT_ERRORBUFFER option.
curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errbuf);
And add a buffer (it must be at least CURL_ERROR_SIZE bytes big).
char errbuf[CURL_ERROR_SIZE];
Additionally, you could set CURLOPT_FAILONERROR to true, to force curl to convert all response codes >= 300 to errors.
curl_easy_setopt(curl, CURLOPT_FAILONERROR, 1L);
To get the actual output from the server you need to set a function to write the data (CURLOPT_WRITEFUNCTION) and a chunk of memory (CURLOPT_WRITEDATA).
A complete example adapted from [1] and [2]:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
struct MemoryStruct {
char *memory;
size_t size;
};
static size_t
WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
{
size_t realsize = size * nmemb;
struct MemoryStruct *mem = (struct MemoryStruct *)userp;
mem‑>memory = (char *)realloc(mem‑>memory, mem‑>size + realsize + 1);
if(mem‑>memory == NULL) {
/* out of memory! */
printf("not enough memory (realloc returned NULL)\n");
return 0;
}
memcpy(&(mem‑>memory[mem‑>size]), contents, realsize);
mem‑>size += realsize;
mem‑>memory[mem‑>size] = 0;
return realsize;
}
int main(void)
{
curl_global_init(CURL_GLOBAL_ALL);
/* init the curl session */
CURL curl = curl_easy_init();
if(curl) {
CURLcode res;
struct MemoryStruct chunk;
chunk.memory = (char *)malloc(1); /* will be grown as needed by the realloc above */
chunk.size = 0; /* no data at this point */
char errbuf[CURL_ERROR_SIZE];
/* specify URL to get */
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
/* send all data to this function */
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
/* we pass our 'chunk' struct to the callback function */
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);
/* force curl to fail error when http code >= 300 */
curl_easy_setopt(curl, CURLOPT_FAILONERROR, 1L);
/* provide a buffer to store errors in */
curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errbuf);
/* set the error buffer as empty before performing a request */
errbuf[0] = 0;
/* perform the request */
res = curl_easy_perform(curl);
/* if the request did not complete correctly, show the error
information. if no detailed error information was written to errbuf
show the more generic information from curl_easy_strerror instead.
*/
if(res != CURLE_OK) {
size_t len = strlen(errbuf);
fprintf(stderr, "\nlibcurl: (%d) ", res);
if(len)
fprintf(stderr, "%s%s", errbuf,
((errbuf[len ‑ 1] != '\n') ? "\n" : ""));
else
fprintf(stderr, "%s\n", curl_easy_strerror(res));
}
else {
/*
* Now, our chunk.memory points to a memory block that is chunk.size
* bytes big and contains the remote file.
*
* Do something nice with it!
*/
printf("%lu bytes retrieved\n", (long)chunk.size);
}
/* cleanup curl stuff */
curl_easy_cleanup(curl);
free(chunk.memory);
}
/* we're done with libcurl, so clean it up */
curl_global_cleanup();
return 0;
}