add: str_append(_h, CONTACT, CONTACT_L);
context: static int add_contact_hf(str* _h, int _l, str *_c){	if (_l < CONTACT_L + _c->len + CRLF_L) {		paerrno = PA_SMALL_BUFFER;		LOG(L_ERR, "add_contact_hf(): Buffer too small\n");		return -1;	}	/* prevent double insertion of Content-Type with SIP URI */#if 0	str_append(_h, CONTENT_TYPE, CONTENT_TYPE_L);	str_append(_h, _c->s, _c->len);	str_append(_h, CRLF, CRLF_L);#endif	return 0;}