In C++, I want to use libcurl to check that a URL is text/html, and if yes, to then download the body, else it stops.
I want this todo in one step , not first sending HEAD, if HEAD is ok, requesting the page again to download.
If this is not possible with libcurl, does it give other libaries for C++, which would support this?
To send a HTTP HEAD request, you need to set this option up:
curl_easy_setopt(ctx,CURLOPT_NOBODY ,1 );
and you can also have a look at this question: help needed on libcurl programming in sending HTTP HEAD Request
to separate headers from body (don't know if it is really needed), you can have a look at :
http://curl.haxx.se/libcurl/c/sepheaders.html
to download lot of different URLs libcurl-multi, you should have a look at :
http://curl.haxx.se/libcurl/c/libcurl-multi.html
slight modification of http://curl.haxx.se/libcurl/c/sendrecv.html :
#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
/* Auxiliary function that waits on the socket. */
static int wait_on_socket(curl_socket_t sockfd, int for_recv, long timeout_ms)
{
struct timeval tv;
fd_set infd, outfd, errfd;
int res;
tv.tv_sec = timeout_ms / 1000;
tv.tv_usec= (timeout_ms % 1000) * 1000;
FD_ZERO(&infd);
FD_ZERO(&outfd);
FD_ZERO(&errfd);
FD_SET(sockfd, &errfd); /* always check for error */
if(for_recv)
{
FD_SET(sockfd, &infd);
}
else
{
FD_SET(sockfd, &outfd);
}
/* select() returns the number of signalled sockets or -1 */
res = select(sockfd + 1, &infd, &outfd, &errfd, &tv);
return res;
}
int main(void)
{
CURL *curl;
CURLcode res;
/* Minimalistic http request */
const char *request = "GET / HTTP/1.0\r\nHost: m0g.net\r\n\r\n";
curl_socket_t sockfd; /* socket */
long sockextr;
size_t iolen;
curl_off_t nread;
curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "http://m0g.net");
/* Do not do the transfer - only connect to host */
curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
res = curl_easy_perform(curl);
if(CURLE_OK != res)
{
printf("Error: %s\n", strerror(res));
return 1;
}
/* Extract the socket from the curl handle - we'll need it for waiting.
* Note that this API takes a pointer to a 'long' while we use
* curl_socket_t for sockets otherwise.
*/
res = curl_easy_getinfo(curl, CURLINFO_LASTSOCKET, &sockextr);
if(CURLE_OK != res)
{
printf("Error: %s\n", curl_easy_strerror(res));
return 1;
}
sockfd = sockextr;
/* wait for the socket to become ready for sending */
if(!wait_on_socket(sockfd, 0, 60000L))
{
printf("Error: timeout.\n");
return 1;
}
puts("Sending request.");
/* Send the request. Real applications should check the iolen
* to see if all the request has been sent */
res = curl_easy_send(curl, request, strlen(request), &iolen);
if(CURLE_OK != res)
{
printf("Error: %s\n", curl_easy_strerror(res));
return 1;
}
puts("Reading response.");
char data[2048];
int idxread=0;
/* read the response */
for(;;)
{
char buf[1024];
wait_on_socket(sockfd, 1, 60000L);
res = curl_easy_recv(curl, buf, 32, &iolen);
if(CURLE_OK != res)
break;
if (nread+idxread > 2048)
break;
strncpy(data+idxread,buf,nread);
idxread+=nread;
if (strstr(data,"\r\n\r\n") != NULL) {
if (strstr(data,"Content-Type: text/html") == NULL) {
printf("not an html document.");
return 2;
}
}
nread = (curl_off_t)iolen;
printf("Received %" CURL_FORMAT_CURL_OFF_T " bytes.\n", nread);
}
printf("'''%s'''\n", data);
/* always cleanup */
curl_easy_cleanup(curl);
}
return 0;
}
This is a few years late, but here's an alternative way of doing this proposed by Linus Nielsen Feltzing, the original author of cURL.
#include <curl/curl.h>
int main(int argc, char *argv[])
{
CURLcode ret;
CURL *hnd = curl_easy_init();
curl_easy_setopt(hnd, CURLOPT_URL, "http://www.haxx.se");
curl_easy_setopt(hnd, CURLOPT_HEADER, 1);
curl_easy_setopt(hnd, CURLOPT_NOBODY, 1);
ret = curl_easy_perform(hnd);
curl_easy_cleanup(hnd);
}
Linus proposed this in a 2007 thread on the curl-library
mailing list.
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