CURLOPT_SS...KEYFUNCTION(3) Library Functions Manual CURLOPT_SS...KEYFUNCTION(3) NAME CURLOPT_SSH_HOSTKEYFUNCTION - callback to check host key SYNOPSIS #include <curl/curl.h> int keycallback(void *clientp, int keytype, const char *key, size_t keylen); CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_HOSTKEYFUNCTION, keycallback); DESCRIPTION Pass a pointer to your callback function, which should match the prototype shown above. It overrides CURLOPT_SSH_KNOWNHOSTS(3). This callback gets called when the verification of the SSH host key is needed. key is keylen bytes long and is the key to check. keytype says what type it is, from the CURLKHTYPE_* series in the curl_khtype enum. clientp is a custom pointer set with CURLOPT_SSH_HOSTKEYDATA(3). This option is used to verify new SSH connections only. Once the connection has been vetted by this callback it is deemed vetted and may be reused again without invoking this callback again. The callback must return one of the following return codes to tell libcurl how to act: CURLKHMATCH_OK The host key is accepted, the connection should continue. CURLKHMATCH_MISMATCH the host key is rejected, the connection is canceled. DEFAULT NULL PROTOCOLS This functionality affects scp and sftp EXAMPLE struct mine { void *custom; }; int hostkeycb(void *clientp, /* passed with CURLOPT_SSH_HOSTKEYDATA */ int keytype, /* CURLKHTYPE */ const char *key, /* host key to check */ size_t keylen) /* length of the key */ { /* 'clientp' points to the callback_data struct */ /* investigate the situation and return the correct value */ return CURLKHMATCH_OK; } int main(void) { struct mine callback_data; CURL *curl = curl_easy_init(); if(curl) { CURLcode result; curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/thisfile.txt"); curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYFUNCTION, hostkeycb); curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYDATA, &callback_data); result = curl_easy_perform(curl); curl_easy_cleanup(curl); } } NOTES Work only with the libssh2 backend. AVAILABILITY Added in curl 7.84.0 RETURN VALUE curl_easy_setopt(3) returns a CURLcode indicating success or error. CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3). SEE ALSO CURLOPT_SSH_HOSTKEYDATA(3), CURLOPT_SSH_KNOWNHOSTS(3) libcurl 2026-08-27 CURLOPT_SS...KEYFUNCTION(3)
NAME | SYNOPSIS | DESCRIPTION | DEFAULT | PROTOCOLS | EXAMPLE | NOTES | AVAILABILITY | RETURN VALUE | SEE ALSO
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