Tribblix: manual page: curl_easy

curl_easy_recv(3) Introduction to Library Functions curl_easy_recv(3)

NAME

curl_easy_recv - receives raw data on an "easy" connection

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_recv(CURL *curl, void *buffer, size_t buflen, size_t *n);

DESCRIPTION

This function receives raw data from the established connection. You
may use it together with curl_easy_send(3) to implement custom
protocols using libcurl. This functionality can be particularly
useful if you use proxies and/or SSL encryption: libcurl takes care
of proxy negotiation and connection setup.

buffer is a pointer to your buffer memory that gets populated by the
received data. buflen is the maximum amount of data you can get in
that buffer. The variable n points to receives the number of received
bytes.

To establish the connection, set CURLOPT_CONNECT_ONLY(3) option
before calling curl_easy_perform(3) or curl_multi_perform(3). Note
that curl_easy_recv(3) does not work on connections that were created
without this option.

The call returns CURLE_AGAIN if there is no data to read - the socket
is used in non-blocking mode internally. When CURLE_AGAIN is
returned, use your operating system facilities like select(2) to wait
for data. The socket may be obtained using curl_easy_getinfo(3) with
CURLINFO_ACTIVESOCKET(3).

Wait on the socket only if curl_easy_recv(3) returns CURLE_AGAIN.
The reason for this is libcurl or the SSL library may internally
cache some data, therefore you should call curl_easy_recv(3) until
all data is read which would include any cached data.

Furthermore if you wait on the socket and it tells you there is data
to read, curl_easy_recv(3) may return CURLE_AGAIN if the only data
that was read was for internal SSL processing, and no other data is
available.

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
/* Do not do the transfer - only connect to host */
curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
res = curl_easy_perform(curl);

if(res == CURLE_OK) {
char buf[256];
size_t nread;
long sockfd;

/* Extract the socket from the curl handle - we need it for waiting. */
res = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);

/* read data */
res = curl_easy_recv(curl, buf, sizeof(buf), &nread);
}
}
}

AVAILABILITY

Added in curl 7.18.2

RETURN VALUE

On success, returns CURLE_OK, stores the received data into buffer,
and the number of bytes it actually read into *n.

On failure, returns the appropriate error code.

The function may return CURLE_AGAIN. In this case, use your operating
system facilities to wait until data can be read, and retry.

Reading exactly 0 bytes indicates a closed connection.

If there is no socket available to use from the previous transfer,
this function returns CURLE_UNSUPPORTED_PROTOCOL.