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curl_easy_recv(3) libcurl Manual curl_easy_recv(3)


curl_easy_recv - receives raw data on an "easy" connection


#include <curl/easy.h>

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


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 will take care of proxy negotiation and connection set-up.

buffer is a pointer to your buffer that will get the received data. buflen is the maximum amount of data you can get in that buffer. The variable n points to will receive 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 will return 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.


Added in 7.18.2.


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's no socket available to use from the previous transfer, this function returns CURLE_UNSUPPORTED_PROTOCOL.


See sendrecv.c in docs/examples directory for usage example.


curl_easy_setopt(3), curl_easy_perform(3), curl_easy_getinfo(3), curl_easy_send(3)

November 5, 2020 libcurl 7.74.0