CURLOPT_SSH_KEYFUNCTION − callback for known host matching logic
#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);
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.
NULL
SFTP and SCP
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);
}
}
Added in 7.19.6
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
CURLOPT_SSH_KEYDATA(3), CURLOPT_SSH_KNOWNHOSTS(3)