CURLOPT_SSH_KEYFUNCTION(3)

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
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;
}
{
  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),