1--- 2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3SPDX-License-Identifier: curl 4Title: CURLOPT_OPENSOCKETFUNCTION 5Section: 3 6Source: libcurl 7See-also: 8 - CURLOPT_CLOSESOCKETFUNCTION (3) 9 - CURLOPT_OPENSOCKETFUNCTION (3) 10 - CURLOPT_SOCKOPTFUNCTION (3) 11Protocol: 12 - All 13--- 14 15# NAME 16 17CURLOPT_OPENSOCKETFUNCTION - callback for opening socket 18 19# SYNOPSIS 20 21~~~c 22#include <curl/curl.h> 23 24typedef enum { 25 CURLSOCKTYPE_IPCXN, /* socket created for a specific IP connection */ 26} curlsocktype; 27 28struct curl_sockaddr { 29 int family; 30 int socktype; 31 int protocol; 32 unsigned int addrlen; 33 struct sockaddr addr; 34}; 35 36curl_socket_t opensocket_callback(void *clientp, 37 curlsocktype purpose, 38 struct curl_sockaddr *address); 39 40CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback); 41~~~ 42 43# DESCRIPTION 44 45Pass a pointer to your callback function, which should match the prototype 46shown above. 47 48This callback function gets called by libcurl instead of the *socket(2)* 49call. The callback's *purpose* argument identifies the exact purpose for 50this particular socket. *CURLSOCKTYPE_IPCXN* is for IP based connections 51and is the only purpose currently used in libcurl. Future versions of libcurl 52may support more purposes. 53 54The *clientp* pointer contains whatever user-defined value set using the 55CURLOPT_OPENSOCKETDATA(3) function. 56 57The callback gets the resolved peer address as the *address* argument and 58is allowed to modify the address or refuse to connect completely. The callback 59function should return the newly created socket or *CURL_SOCKET_BAD* in 60case no connection could be established or another error was detected. Any 61additional *setsockopt(2)* calls can of course be done on the socket at 62the user's discretion. A *CURL_SOCKET_BAD* return value from the callback 63function signals an unrecoverable error to libcurl and it returns 64*CURLE_COULDNT_CONNECT* from the function that triggered this callback. 65This return code can be used for IP address block listing. 66 67If you want to pass in a socket with an already established connection, pass 68the socket back with this callback and then use 69CURLOPT_SOCKOPTFUNCTION(3) to signal that it already is connected. 70 71# DEFAULT 72 73The default behavior is the equivalent of this: 74~~~c 75 return socket(addr->family, addr->socktype, addr->protocol); 76~~~ 77 78# EXAMPLE 79 80~~~c 81/* make libcurl use the already established socket 'sockfd' */ 82 83static curl_socket_t opensocket(void *clientp, 84 curlsocktype purpose, 85 struct curl_sockaddr *address) 86{ 87 curl_socket_t sockfd; 88 sockfd = *(curl_socket_t *)clientp; 89 /* the actual externally set socket is passed in via the OPENSOCKETDATA 90 option */ 91 return sockfd; 92} 93 94static int sockopt_callback(void *clientp, curl_socket_t curlfd, 95 curlsocktype purpose) 96{ 97 /* This return code was added in libcurl 7.21.5 */ 98 return CURL_SOCKOPT_ALREADY_CONNECTED; 99} 100 101int main(void) 102{ 103 CURL *curl = curl_easy_init(); 104 if(curl) { 105 CURLcode res; 106 extern int sockfd; /* the already connected one */ 107 /* libcurl thinks that you connect to the host 108 * and port that you specify in the URL option. */ 109 curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999"); 110 /* call this function to get a socket */ 111 curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket); 112 curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd); 113 114 /* call this function to set options for the socket */ 115 curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback); 116 117 res = curl_easy_perform(curl); 118 119 curl_easy_cleanup(curl); 120 } 121} 122~~~ 123 124# AVAILABILITY 125 126Added in 7.17.1. 127 128# RETURN VALUE 129 130Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. 131