--- c: Copyright (C) Daniel Stenberg, , et al. SPDX-License-Identifier: curl Title: CURLOPT_OPENSOCKETFUNCTION Section: 3 Source: libcurl See-also: - CURLOPT_CLOSESOCKETFUNCTION (3) - CURLOPT_OPENSOCKETFUNCTION (3) - CURLOPT_SOCKOPTFUNCTION (3) Protocol: - All Added-in: 7.17.1 --- # NAME CURLOPT_OPENSOCKETFUNCTION - callback for opening socket # SYNOPSIS ~~~c #include typedef enum { CURLSOCKTYPE_IPCXN, /* socket created for a specific IP connection */ } curlsocktype; struct curl_sockaddr { int family; int socktype; int protocol; unsigned int addrlen; struct sockaddr addr; }; curl_socket_t opensocket_callback(void *clientp, curlsocktype purpose, struct curl_sockaddr *address); CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback); ~~~ # DESCRIPTION Pass a pointer to your callback function, which should match the prototype shown above. This callback function gets called by libcurl instead of the *socket(2)* call. The callback's *purpose* argument identifies the exact purpose for this particular socket. *CURLSOCKTYPE_IPCXN* is for IP based connections and is the only purpose currently used in libcurl. Future versions of libcurl may support more purposes. The *clientp* pointer contains whatever user-defined value set using the CURLOPT_OPENSOCKETDATA(3) function. The callback gets the resolved peer address as the *address* argument and is allowed to modify the address or refuse to connect completely. The callback function should return the newly created socket or *CURL_SOCKET_BAD* in case no connection could be established or another error was detected. Any additional *setsockopt(2)* calls can of course be done on the socket at the user's discretion. A *CURL_SOCKET_BAD* return value from the callback function signals an unrecoverable error to libcurl and it returns *CURLE_COULDNT_CONNECT* from the function that triggered this callback. This return code can be used for IP address block listing. If you want to pass in a socket with an already established connection, pass the socket back with this callback and then use CURLOPT_SOCKOPTFUNCTION(3) to signal that it already is connected. # DEFAULT The equivalent of this: ~~~c return socket(addr->family, addr->socktype, addr->protocol); ~~~ # %PROTOCOLS% # EXAMPLE ~~~c /* make libcurl use the already established socket 'sockfd' */ static curl_socket_t opensocket(void *clientp, curlsocktype purpose, struct curl_sockaddr *address) { curl_socket_t sockfd; sockfd = *(curl_socket_t *)clientp; /* the actual externally set socket is passed in via the OPENSOCKETDATA option */ return sockfd; } static int sockopt_callback(void *clientp, curl_socket_t curlfd, curlsocktype purpose) { /* This return code was added in libcurl 7.21.5 */ return CURL_SOCKOPT_ALREADY_CONNECTED; } int main(void) { CURL *curl = curl_easy_init(); if(curl) { CURLcode res; extern int sockfd; /* the already connected one */ /* libcurl thinks that you connect to the host * and port that you specify in the URL option. */ curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999"); /* call this function to get a socket */ curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket); curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd); /* call this function to set options for the socket */ curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback); res = curl_easy_perform(curl); curl_easy_cleanup(curl); } } ~~~ # %AVAILABILITY% # RETURN VALUE Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.