CURLOPT_SSH_HOSTKEYFUNCTION(3) Library Functions Manual CURLOPT_SSH_HOSTKEYFUNCTION(3)

CURLOPT_SSH_HOSTKEYFUNCTION - callback to check host key

#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);

Pass a pointer to your callback function, which should match the prototype 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:

The host key is accepted, the connection should continue.
the host key is rejected, the connection is canceled.

NULL

SCP and SFTP

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);
  }
}

Added in 7.84.0 , work only with libssh2 backend.

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLOPT_SSH_HOSTKEYDATA(3), CURLOPT_SSH_KNOWNHOSTS(3)

2024-05-22 libcurl