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 13Added-in: 7.17.1 14--- 15 16# NAME 17 18CURLOPT_OPENSOCKETFUNCTION - callback for opening socket 19 20# SYNOPSIS 21 22~~~c 23#include <curl/curl.h> 24 25typedef enum { 26 CURLSOCKTYPE_IPCXN, /* socket created for a specific IP connection */ 27} curlsocktype; 28 29struct curl_sockaddr { 30 int family; 31 int socktype; 32 int protocol; 33 unsigned int addrlen; 34 struct sockaddr addr; 35}; 36 37curl_socket_t opensocket_callback(void *clientp, 38 curlsocktype purpose, 39 struct curl_sockaddr *address); 40 41CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback); 42~~~ 43 44# DESCRIPTION 45 46Pass a pointer to your callback function, which should match the prototype 47shown above. 48 49This callback function gets called by libcurl instead of the *socket(2)* 50call. The callback's *purpose* argument identifies the exact purpose for 51this particular socket. *CURLSOCKTYPE_IPCXN* is for IP based connections 52and is the only purpose currently used in libcurl. Future versions of libcurl 53may support more purposes. 54 55The *clientp* pointer contains whatever user-defined value set using the 56CURLOPT_OPENSOCKETDATA(3) function. 57 58The callback gets the resolved peer address as the *address* argument and 59is allowed to modify the address or refuse to connect completely. The callback 60function should return the newly created socket or *CURL_SOCKET_BAD* in 61case no connection could be established or another error was detected. Any 62additional *setsockopt(2)* calls can of course be done on the socket at 63the user's discretion. 64 65If *CURL_SOCKET_BAD* is returned by the callback then libcurl treats it as a 66failed connection and tries to open a socket to connect to a different IP 67address associated with the transfer. If there are no more addresses to try 68then libcurl fails the transfer with error code *CURLE_COULDNT_CONNECT*. 69 70You can get the IP address that curl is opening the socket for by casting 71*address-\>addr* to `sockaddr_in` if *address-\>family* is `AF_INET`, or to 72`sockaddr_in6` if *address-\>family* is `AF_INET6`. For an example of how that 73data can be compared against refer to *docs/examples/block_ip.c*. 74 75If you want to pass in a socket with an already established connection, pass 76the socket back with this callback and then use CURLOPT_SOCKOPTFUNCTION(3) to 77signal that it already is connected. 78 79# DEFAULT 80 81The equivalent of this: 82~~~c 83 return socket(addr->family, addr->socktype, addr->protocol); 84~~~ 85 86# %PROTOCOLS% 87 88# EXAMPLE 89 90~~~c 91/* make libcurl use the already established socket 'sockfd' */ 92 93static curl_socket_t opensocket(void *clientp, 94 curlsocktype purpose, 95 struct curl_sockaddr *address) 96{ 97 curl_socket_t sockfd; 98 sockfd = *(curl_socket_t *)clientp; 99 /* the actual externally set socket is passed in via the OPENSOCKETDATA 100 option */ 101 return sockfd; 102} 103 104static int sockopt_callback(void *clientp, curl_socket_t curlfd, 105 curlsocktype purpose) 106{ 107 /* This return code was added in libcurl 7.21.5 */ 108 return CURL_SOCKOPT_ALREADY_CONNECTED; 109} 110 111int main(void) 112{ 113 CURL *curl = curl_easy_init(); 114 if(curl) { 115 CURLcode res; 116 extern int sockfd; /* the already connected one */ 117 /* libcurl thinks that you connect to the host 118 * and port that you specify in the URL option. */ 119 curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999"); 120 /* call this function to get a socket */ 121 curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket); 122 curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd); 123 124 /* call this function to set options for the socket */ 125 curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback); 126 127 res = curl_easy_perform(curl); 128 129 curl_easy_cleanup(curl); 130 } 131} 132~~~ 133 134# %AVAILABILITY% 135 136# RETURN VALUE 137 138curl_easy_setopt(3) returns a CURLcode indicating success or error. 139 140CURLE_OK (0) means everything was OK, non-zero means an error occurred, see 141libcurl-errors(3). 142