+/* Expand and convert an Exim list to a gnutls_datum list. False return for fail.
+NULL plist return for silent no-ALPN.
+*/
+
+static BOOL
+tls_alpn_plist(const uschar * tls_alpn, const gnutls_datum_t ** plist, unsigned * plen,
+ uschar ** errstr)
+{
+uschar * exp_alpn;
+
+if (!expand_check(tls_alpn, US"tls_alpn", &exp_alpn, errstr))
+ return FALSE;
+
+if (!exp_alpn)
+ {
+ DEBUG(D_tls) debug_printf("Setting TLS ALPN forced to fail, not sending\n");
+ *plist = NULL;
+ }
+else
+ {
+ const uschar * list = exp_alpn;
+ int sep = 0;
+ unsigned cnt = 0;
+ gnutls_datum_t * p;
+ uschar * s;
+
+ while (string_nextinlist(&list, &sep, NULL, 0)) cnt++;
+
+ p = store_get(sizeof(gnutls_datum_t) * cnt, is_tainted(exp_alpn));
+ list = exp_alpn;
+ for (int i = 0; s = string_nextinlist(&list, &sep, NULL, 0); i++)
+ { p[i].data = s; p[i].size = Ustrlen(s); }
+ *plist = (*plen = cnt) ? p : NULL;
+ }
+return TRUE;
+}
+