CURLOPT_SSH_KEYFUNCTION(3) curl_easy_setopt options 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 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 proto-
type 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 CUR-
LOPT_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 re-
placing 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 connec-
tion. 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),
libcurl 7.81.0 October 31, 2021 CURLOPT_SSH_KEYFUNCTION(3)
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