feat: Support $MODULE_PATH in StaticAssetHandler

src/server/middleware/StaticAssetHandler.ts

@@ -5,7 +5,7 @@ import { getLoggerFor } from '../../logging/LogUtil';
 import { APPLICATION_OCTET_STREAM } from '../../util/ContentTypes';
 import { NotFoundHttpError } from '../../util/errors/NotFoundHttpError';
 import { NotImplementedHttpError } from '../../util/errors/NotImplementedHttpError';
-import { joinFilePath } from '../../util/PathUtil';
+import { joinFilePath, resolveAssetPath } from '../../util/PathUtil';
 import { pipeSafely } from '../../util/StreamUtil';
 import type { HttpHandlerInput } from '../HttpHandler';
 import { HttpHandler } from '../HttpHandler';
@@ -13,6 +13,9 @@ import type { HttpRequest } from '../HttpRequest';
 
 /**
  * Handler that serves static resources on specific paths.
+ * Relative file paths are assumed to be relative to cwd.
+ * Relative file paths can be preceded by $PACKAGE_ROOT/, e.g. $PACKAGE_ROOT/foo/bar,
+ * in case they need to be relative to the module root.
  */
 export class StaticAssetHandler extends HttpHandler {
   private readonly mappings: Record<string, string>;
@@ -26,7 +29,10 @@ export class StaticAssetHandler extends HttpHandler {
    */
   public constructor(assets: Record<string, string>) {
     super();
-    this.mappings = { ...assets };
+    this.mappings = {};
+    for (const [ url, path ] of Object.entries(assets)) {
+      this.mappings[url] = resolveAssetPath(path);
+    }
     this.pathMatcher = this.createPathMatcher(assets);
   }
 

src/util/PathUtil.ts

@@ -165,3 +165,23 @@ export function createSubdomainRegexp(baseUrl: string): RegExp {
   const { scheme, rest } = extractScheme(baseUrl);
   return new RegExp(`^${scheme}(?:([^/]+)\\.)?${rest}`, 'u');
 }
+
+/**
+ * Returns the folder corresponding to the root of the Community Solid Server module
+ */
+export function getModuleRoot(): string {
+  return joinFilePath(__dirname, '../../');
+}
+
+/**
+ * Converts file path inputs into absolute paths.
+ * Works similar to `absoluteFilePath` but paths that start with '$PACKAGE_ROOT/'
+ * will be relative to the module directory instead of the cwd.
+ */
+export function resolveAssetPath(path: string): string {
+  const modulePath = '$PACKAGE_ROOT/';
+  if (path.startsWith(modulePath)) {
+    return joinFilePath(getModuleRoot(), path.slice(modulePath.length));
+  }
+  return absoluteFilePath(path);
+}