luci-base: implement http header plugins

This implements the injection of custom http headers via
the new plugin architecture.

Signed-off-by: Paul Donald <newtwen+github@gmail.com>

modules/luci-base/ucode/http.uc

@@ -13,6 +13,12 @@ import {
 	stdin, stdout, mkstemp
 } from 'fs';
 
+import {
+	openlog, syslog, closelog, LOG_NOTICE, LOG_LOCAL0
+} from 'log';
+
+import { run_plugins } from 'luciplugins';
+
 // luci.http module scope
 export let HTTP_MAX_CONTENT = 1024*100;		// 100 kB maximum content size
 
@@ -504,6 +510,37 @@ const Class = {
 		if (!this.headers?.['x-content-type-options'])
 			this.header('X-Content-Type-Options', 'nosniff');
 
+		/* http header plugins */
+		let log_class = 'http.uc';
+		openlog(log_class);
+		for (let plugin_id, p_output in run_plugins('/luci/plugins/http/headers', 'http_headers_enabled')) {
+
+			/* header plugins shall return e.g.: ['X-Header', 'foo'] */
+			if (type(p_output) !== 'array' || length(p_output) !== 2)
+				continue;
+
+			if (type(p_output[0]) !== 'string' || type(p_output[1]) !== 'string')
+				continue;
+
+			if (!match(p_output[0], /^[A-Za-z0-9-]+$/)) {
+				syslog(LOG_NOTICE|LOG_LOCAL0,
+					sprintf("Invalid header name from plugin %s output: %s", plugin_id, p_output[0]));
+				continue;
+			}
+
+			/* header plugin values shall not contain line-feeds */
+			if (match(p_output[1], /[\r\n]/)) {
+				syslog(LOG_NOTICE|LOG_LOCAL0,
+					sprintf("\\r and/or \\n in plugin %s output", plugin_id));
+				continue;
+			}
+
+			if(!this.headers?.[p_output[0]])
+				this.header(p_output[0], p_output[1]);
+
+		}
+		closelog();
+
 		this.output('Status: ');
 		this.output(this.status_code);
 		this.output(' ');

modules/luci-base/ucode/luciplugins.uc

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import {
+	lsdir
+} from 'fs';
+
+import {
+	syslog, LOG_NOTICE, LOG_LOCAL0
+} from 'log';
+
+import { cursor } from 'uci';
+
+
+/* generic plugin handler */
+export function run_plugins(plugin_class_path, plugin_class_enable) {
+	let uci = cursor();
+	const require_path = replace(plugin_class_path, '/', '.');
+
+	if (uci.get('luci_plugins', 'global', 'enabled') == 1 &&
+		uci.get('luci_plugins', 'global', plugin_class_enable) == 1) {
+		const PLUGINS_PATH = '/usr/share/ucode' + plugin_class_path;
+		const results = {};
+
+		for (let fn in lsdir(PLUGINS_PATH)) {
+			const plugin_id = replace(fn, /.uc$/, '');
+			/* plugins shall have a <32_char_UUID_no_hyphens>.uc filename */
+			if (!match(plugin_id, /^[a-f0-9]+$/) || length(plugin_id) !== 32) {
+				syslog(LOG_NOTICE|LOG_LOCAL0,
+					sprintf("Invalid plugin name: %s", plugin_id));
+				continue;
+			}
+
+			if (uci.get('luci_plugins', plugin_id, 'enabled')) {
+				const mod = require(require_path + `.${plugin_id}`);
+				if (type(mod) === 'function') {
+					try {
+						results[plugin_id] = mod(plugin_id);
+					} catch (e) {
+						syslog(LOG_NOTICE|LOG_LOCAL0,
+							sprintf("Could not execute plugin %s: %s",
+							join('/', [PLUGINS_PATH, plugin_id]), e));
+					};
+				}
+			}
+		}
+
+		return results;
+	}
+};