File-based response support & static server

- Clean up UniversalPath implementation
    - Use Readable/Writable types correctly for stream methods
    - Add .list() methods for getting child files

- Make Response body specify explicit types and support
  writing Readable streams to the body

- Create a static file server that supports directory listing

src/util/support/path/LocalFilesystem.ts

@@ -4,6 +4,7 @@ import * as path from 'path'
 import {UniversalPath} from '../path'
 import * as rimraf from 'rimraf'
 import * as mkdirp from 'mkdirp'
+import { Collection } from '../../collection/Collection'
 
 export interface LocalFilesystemConfig {
     baseDir: string
@@ -87,6 +88,8 @@ export class LocalFilesystem extends Filesystem {
                 accessed: stat.atime,
                 modified: stat.mtime,
                 created: stat.ctime,
+                isDirectory: stat.isDirectory(),
+                isFile: stat.isFile(),
             }
         } catch (e) {
             if ( e?.code === 'ENOENT' ) {
@@ -95,6 +98,8 @@ export class LocalFilesystem extends Filesystem {
                     exists: false,
                     sizeInBytes: 0,
                     tags: [],
+                    isFile: false,
+                    isDirectory: false,
                 }
             }
 
@@ -166,4 +171,13 @@ export class LocalFilesystem extends Filesystem {
     protected metadataPath(storePath: string): string {
         return path.resolve(this.baseConfig.baseDir, 'meta', storePath + '.json')
     }
+
+    /**
+     * List all immediate children of the given path.
+     * @param storePath
+     */
+    public async list(storePath: string): Promise<Collection<string>> {
+        const paths = await fs.promises.readdir(this.storePath(storePath))
+        return Collection.collect<string>(paths)
+    }
 }