Tribblix: manual page: CURLOPT_SSH

CURLOPT_SSH_KEYFUNCTION(3) Introduction to Library Functions

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 return and act on the host+key situation and then retry
without needing the overhead of setting it up from scratch
again.

DEFAULT

NULL

PROTOCOLS

This functionality affects scp and sftp

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 curl 7.19.6

RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).