[core] do not emit req/response hdrs w/ blank val

src/http-header-glue.c

@@ -991,7 +991,7 @@ int http_cgi_headers (server *srv, connection *con, http_cgi_opts *opts, http_cg
 
     for (n = 0; n < con->request.headers->used; n++) {
         data_string *ds = (data_string *)con->request.headers->data[n];
-        if (!buffer_is_empty(ds->value) && !buffer_is_empty(ds->key)) {
+        if (!buffer_string_is_empty(ds->value) && !buffer_is_empty(ds->key)) {
             /* Security: Do not emit HTTP_PROXY in environment.
              * Some executables use HTTP_PROXY to configure
              * outgoing proxy.  See also https://httpoxy.org/ */

src/mod_proxy.c

@@ -697,7 +697,7 @@ static int proxy_create_env(server *srv, handler_ctx *hctx) {
 
 		ds = (data_string *)con->request.headers->data[i];
 
-		if (!buffer_is_empty(ds->value) && !buffer_is_empty(ds->key)) {
+		if (!buffer_string_is_empty(ds->value) && !buffer_is_empty(ds->key)) {
 			if (replace_http_host &&
 			    buffer_is_equal_caseless_string(ds->key, CONST_STR_LEN("Host"))) continue;
 			if (buffer_is_equal_caseless_string(ds->key, CONST_STR_LEN("Connection"))) continue;

src/response.c

@@ -70,7 +70,7 @@ int http_response_write_header(server *srv, connection *con) {
 
 		ds = (data_string *)con->response.headers->data[i];
 
-		if (!buffer_is_empty(ds->value) && !buffer_is_empty(ds->key) &&
+		if (!buffer_string_is_empty(ds->value) && !buffer_is_empty(ds->key) &&
 		    0 != strncasecmp(ds->key->ptr, CONST_STR_LEN("X-LIGHTTPD-")) &&
 			0 != strncasecmp(ds->key->ptr, CONST_STR_LEN("X-Sendfile"))) {
 			if (0 == strcasecmp(ds->key->ptr, "Date")) have_date = 1;