Expose replaceTemplates to plugins

This is mainly so they can get relative paths in their HTML, in
particular code-server's static base so they can use the favicon and
service worker.

src/node/plugin.ts

@@ -5,6 +5,7 @@ import * as path from "path"
 import * as semver from "semver"
 import * as pluginapi from "../../typings/pluginapi"
 import { version } from "./constants"
+import { replaceTemplates } from "./http"
 import { proxy } from "./proxy"
 import * as util from "./util"
 import { Router as WsRouter, WebsocketRouter, wss } from "./wsRouter"
@@ -23,6 +24,7 @@ require("module")._load = function (request: string, parent: object, isMain: boo
       field,
       Level,
       proxy,
+      replaceTemplates,
       WsRouter,
       wss,
     }

typings/pluginapi.d.ts

@@ -123,8 +123,20 @@ export { express }
  */
 export { field, Level, Logger }
 
+/**
+ * code-server's proxy server.
+ */
 export const proxy: ProxyServer
 
+/**
+ * Replace variables in HTML: TO, BASE, CS_STATIC_BASE, and OPTIONS.
+ */
+export function replaceTemplates<T extends object>(
+  req: express.Request,
+  content: string,
+  extraOpts?: Omit<T, "base" | "csStaticBase" | "logLevel">,
+): string
+
 /**
  * Your plugin module must have a top level export "plugin" that implements this interface.
  *