NAME

       CURLOPT_SSH_KEYFUNCTION - callback for known host matching logic

SYNOPSIS

       #include <curl/curl.h>

       enum curl_khstat {
         CURLKHSTAT_FINE_ADD_TO_FILE,
         CURLKHSTAT_FINE,
         CURLKHSTAT_REJECT, /* reject the connection, return an error */
         CURLKHSTAT_DEFER,  /* do not accept it, but we cannot answer right
                               now. Causes a CURLE_PEER_FAILED_VERIFICATION error but
                               the connection is left intact */
         CURLKHSTAT_FINE_REPLACE
       };

       enum curl_khmatch {
         CURLKHMATCH_OK,       /* match */
         CURLKHMATCH_MISMATCH, /* host found, key mismatch! */
         CURLKHMATCH_MISSING,  /* no matching host/key found */
       };

       struct curl_khkey {
         const char *key; /* points to a null-terminated string encoded with
                             base64 if len is zero, otherwise to the "raw"
                             data */
         size_t len;
         enum curl_khtype keytype;
       };

       int ssh_keycallback(CURL *easy,
                           const struct curl_khkey *knownkey,
                           const struct curl_khkey *foundkey,
                           enum curl_khmatch match,
                           void *clientp);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_KEYFUNCTION,
                                 ssh_keycallback);

DESCRIPTION

       Pass a pointer to your callback function, which should match the prototype shown above.

       It gets called when the known_host matching has been done, to allow the application to act and decide for
       libcurl how to proceed. The callback is only called if CURLOPT_SSH_KNOWNHOSTS(3) is also set.

       This  callback  function gets passed the CURL handle, the key from the known_hosts file knownkey, the key
       from the remote site foundkey, info from libcurl on the matching status and a custom  pointer  (set  with
       CURLOPT_SSH_KEYDATA(3)). It MUST return one of the following return codes to tell libcurl how to act:

       CURLKHSTAT_FINE_REPLACE
              The  new  host+key  is  accepted  and  libcurl replaces the old host+key into the known_hosts file
              before continuing with the connection. This also adds the new host+key  combo  to  the  known_host
              pool kept in memory if it was not already present there. The adding of data to the file is done by
              completely  replacing  the  file  with a new copy, so the permissions of the file must allow this.
              (Added in 7.73.0)

       CURLKHSTAT_FINE_ADD_TO_FILE
              The host+key is accepted and libcurl appends it to the known_hosts file before continuing with the
              connection. This also adds the host+key combo to the known_host pool kept in memory if it was  not
              already  present  there.  The  adding of data to the file is done by completely replacing the file
              with a new copy, so the permissions of the file must allow this.

       CURLKHSTAT_FINE
              The host+key is accepted libcurl continues with the connection. This also adds the host+key  combo
              to the known_host pool kept in memory if it was not already present there.

       CURLKHSTAT_REJECT
              The host+key is rejected. libcurl denies the connection to continue and it is closed.

       CURLKHSTAT_DEFER
              The host+key is rejected, but the SSH connection is asked to be kept alive.  This feature could be
              used  when  the  app wants to somehow return back and act on the host+key situation and then retry
              without needing the overhead of setting it up from scratch again.

DEFAULT

       NULL

PROTOCOLS

       SFTP and SCP

EXAMPLE

       struct mine {
         void *custom;
       };

       static int keycb(CURL *easy,
                        const struct curl_khkey *knownkey,
                        const struct curl_khkey *foundkey,
                        enum curl_khmatch match,
                        void *clientp)
       {
         /* 'clientp' points to the callback_data struct */
         /* investigate the situation and return the correct value */
         return CURLKHSTAT_FINE_ADD_TO_FILE;
       }

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           struct mine callback_data;
           curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/thisfile.txt");
           curl_easy_setopt(curl, CURLOPT_SSH_KEYFUNCTION, keycb);
           curl_easy_setopt(curl, CURLOPT_SSH_KEYDATA, &callback_data);
           curl_easy_setopt(curl, CURLOPT_SSH_KNOWNHOSTS, "/home/user/known_hosts");

           curl_easy_perform(curl);
       }
       }

AVAILABILITY

       Added in 7.19.6

RETURN VALUE

       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

SEE ALSO

       CURLOPT_SSH_KEYDATA(3), CURLOPT_SSH_KNOWNHOSTS(3)

ibcurl 8.5.0                                    December 04, 2023                     CURLOPT_SSH_KEYFUNCTION(3)