@walkeros/server-transformer-file

File serving transformer for walkerOS server flows. Serves static files through any Store backend, making it I/O-agnostic. Works with FsStore for disk, MemoryStore for pre-loaded assets, or any custom Store implementation.

How it works

1. Extracts ingest.path from the request
2. Strips optional URL prefix (e.g., /static)
3. Calls store.get(filePath) to fetch content
4. Responds with content, correct Content-Type, and Content-Length
5. Returns false to stop the transformer chain

If the file is not found or no store is provided, the event passes through unchanged.

Installation

npm install @walkeros/server-transformer-file

Configuration

Settings

| Option | Type | Default | Description | | ----------- | ------------------------ | ------- | ----------------------------------- | | prefix | string | — | URL prefix to strip before lookup | | headers | Record<string, string> | — | Default headers for all responses | | mimeTypes | Record<string, string> | — | Extension overrides (.ext → type) |

Env

| Option | Type | Description | | ------- | ----------- | --------------------------------------------------- | | store | FileStore | Store providing file content (required for serving) |

Example with FsStore

import { startFlow } from '@walkeros/collector';
import { transformerFile } from '@walkeros/server-transformer-file';
import { storeFsInit } from '@walkeros/server-store-fs';

const fileStore = storeFsInit({
  collector,
  logger,
  config: { settings: { basePath: './public' } },
  env: {},
  id: 'fs',
});

await startFlow({
  transformers: {
    file: {
      code: transformerFile,
      config: {
        settings: {
          prefix: '/static',
          headers: { 'Cache-Control': 'public, max-age=3600' },
        },
      },
      env: { store: fileStore },
    },
  },
});

Built-in MIME types

.js, .mjs, .css, .html, .json, .wasm, .map, .txt, .xml, .svg, .png, .jpg, .gif, .ico, .webp, .woff, .woff2

Unknown extensions default to application/octet-stream. Override with the mimeTypes setting.

Behavior notes

• I/O-agnostic — delegates all storage to the injected Store
• No store = passthrough — warns and lets the event continue
• No path = passthrough — skips when ingest.path is missing
• Prefix mismatch = passthrough — only serves paths matching the prefix
• Stops chain on serve — returns false after responding