libssh2_session_banner_set man page
libssh2_session_banner_set — set the SSH protocol banner for the local client
int libssh2_session_banner_set(LIBSSH2_SESSION *session, const char *banner);
session - Session instance as returned by libssh2_session_init_ex(3)
banner - A pointer to a zero-terminated string holding the user defined banner
Set the banner that will be sent to the remote host when the SSH session is started with libssh2_session_handshake(3) This is optional; a banner corresponding to the protocol and libssh2 version will be sent by default.
Returns 0 on success or negative on failure. It returns LIBSSH2_ERROR_EAGAIN when it would otherwise block. While LIBSSH2_ERROR_EAGAIN is a negative number, it isn't really a failure per se.
LIBSSH2_ERROR_ALLOC - An internal memory allocation call failed.
Added in 1.4.0.
Before 1.4.0 this function was known as libssh2_banner_set(3)