feat: add support for fallback file

Author: johanbook

README.md

@@ -1,8 +1,8 @@
 # file-domain-server
 
-**file-domain-server** is a simplistic Nodejs HTTP file server that serve
+**file-domain-server** is a simplistic Nodejs HTTP file server that serves
 different folders depending on the HTTP `Host` header. It is mainly intended to
-run an internal network with its own DNS server.
+run on an internal network with its own DNS server.
 
 ## Get started
 
@@ -52,6 +52,10 @@ The following can be configured as environment variables:
 
 - **DEFAULT_INDEX_FILE** name of file served on paths ending with a trailing
   slash (default `index.html`).
+- **FALLBACK_FILE** name of file served as a fallback if requested file is not
+  found. Set to `index.html` to enable client-side routing or to e.g.
+  `error.html` to display an error page (note that response still returns a 200
+  status code). It is undefined by default and no fallback file will be served.
 - **PORT** the port the server should listen on (default 8080).
 - **ROOT_FILE_PATH** root directory of served file tree (default `build`).
 

src/index.js

@@ -4,6 +4,7 @@ const mime = require("mime");
 const path = require("path");
 
 const DEFAULT_INDEX_FILE = process.env.DEFAULT_INDEX_FILE || "index.html";
+const FALLBACK_FILE = process.env.FALLBACK_FILE || null;
 const PORT = process.env.PORT || 8080;
 const ROOT_FILE_PATH = process.env.ROOT_FILE_PATH || "build";
 
@@ -45,7 +46,14 @@ function handleRequest(req, res) {
   console.debug("Requesting", domain, filePath);
 
   const actualFilePath = createFilePath(domain, filePath);
-  const file = getFile(actualFilePath);
+  let file = getFile(actualFilePath);
+
+  if (!file && FALLBACK_FILE) {
+    const fallbackFilePath = createFilePath(domain, FALLBACK_FILE);
+    console.debug("Serving fallback file:", fallbackFilePath);
+    file = getFile(fallbackFilePath);
+  }
+
   if (!file) {
     res.writeHead(404);
     res.end();
@@ -62,4 +70,4 @@ function handleRequest(req, res) {
 const server = http.createServer(handleRequest);
 server.listen(PORT);
 
-console.info(`Listening on port ${PORT}`)
+console.info(`Listening on port ${PORT}`);