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CURLOPT_S...EYFUNCTION(3)  Library Functions Manual  CURLOPT_S...EYFUNCTION(3)

NAME
       CURLOPT_SSH_HOSTKEYFUNCTION - callback to check host key

SYNOPSIS
       #include	<curl/curl.h>

       int keycallback(void *clientp,
		       int keytype,
		       const char *key,
		       size_t keylen);

       CURLcode	curl_easy_setopt(CURL *handle, CURLOPT_SSH_HOSTKEYFUNCTION,
				 keycallback);

DESCRIPTION
       Pass a pointer to your callback function, which should match the	proto-
       type shown above. It overrides CURLOPT_SSH_KNOWNHOSTS(3).

       This  callback gets called when the verification	of the SSH host	key is
       needed.

       key is keylen bytes long	and is the key to  check.  keytype  says  what
       type it is, from	the CURLKHTYPE_* series	in the curl_khtype enum.

       clientp is a custom pointer set with CURLOPT_SSH_HOSTKEYDATA(3).

       The  callback  MUST  return  one	 of the	following return codes to tell
       libcurl how to act:

       CURLKHMATCH_OK
	      The host key is accepted,	the connection should continue.

       CURLKHMATCH_MISMATCH
	      the host key is rejected,	the connection is canceled.

DEFAULT
       NULL

PROTOCOLS
       This functionality affects scp and sftp

EXAMPLE
       struct mine {
	 void *custom;
       };

       int hostkeycb(void *clientp,    /* passed with CURLOPT_SSH_HOSTKEYDATA */
		     int keytype,      /* CURLKHTYPE */
		     const char	*key,  /* host key to check */
		     size_t keylen)    /* length of the	key */
       {
	 /* 'clientp' points to	the callback_data struct */
	 /* investigate	the situation and return the correct value */
	 return	CURLKHMATCH_OK;
       }
       int main(void)
       {
	 struct	mine callback_data;
	 CURL *curl = curl_easy_init();
	 if(curl) {
	   curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/thisfile.txt");
	   curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYFUNCTION, hostkeycb);
	   curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYDATA, &callback_data);

	   curl_easy_perform(curl);
	 }
       }

NOTES
       Work only with the libssh2 backend.

AVAILABILITY
       Added in	curl 7.84.0

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).

SEE ALSO
       CURLOPT_SSH_HOSTKEYDATA(3), CURLOPT_SSH_KNOWNHOSTS(3)

libcurl				  2025-06-03	     CURLOPT_S...EYFUNCTION(3)

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