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 so this causes a CURLE_DEFER error but
                               otherwise the connection will be left intact
                               etc */
         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,
                           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  will  only   be   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 will replace the  old  host+key  into  the
              known_hosts file before continuing with the connection.  This will also add 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 will append it to the known_hosts file  before
              continuing  with  the  connection.  This  will  also  add 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 will continue with the connection. This will  also
              add  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 will deny the connection to continue and it  will
              be 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

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