refactor(sandbox, arns): switch params to config

As both middlewares need the root host's subdomain count,
moving it to the config eliminates duplicates.

This also allows to remove the rootHost constructor param and take it
directly from the config.

src/app.ts

@@ -83,14 +83,12 @@ if (config.ARNS_ROOT_HOST !== undefined) {
   app.use(
     createArnsMiddleware({
       dataHandler,
-      rootHost: config.ARNS_ROOT_HOST,
       nameResolver: system.nameResolver,
     }),
   );
 
   app.use(
     createSandboxMiddleware({
-      rootHost: config.ARNS_ROOT_HOST,
       sandboxProtocol: config.SANDBOX_PROTOCOL,
     }),
   );

src/config.ts

@@ -70,6 +70,8 @@ export const ANS104_INDEX_FILTER = createFilter(
   JSON.parse(ANS104_INDEX_FILTER_STRING),
 );
 export const ARNS_ROOT_HOST = env.varOrUndefined('ARNS_ROOT_HOST');
+export const ROOT_HOST_SUBDOMAIN_LENGTH =
+  ARNS_ROOT_HOST !== undefined ? ARNS_ROOT_HOST.split('.').length - 2 : 0;
 export const SANDBOX_PROTOCOL = env.varOrUndefined('SANDBOX_PROTOCOL');
 export const START_WRITERS =
   env.varOrDefault('START_WRITERS', 'true') === 'true';

src/middleware/arns.ts

@@ -18,31 +18,29 @@
 import { Handler } from 'express';
 import { asyncMiddleware } from 'middleware-async';
 
+import * as config from '../config.js';
 import { sendNotFound } from '../routes/data.js';
 import { NameResolver } from '../types.js';
 
 const EXCLUDED_SUBDOMAINS = new Set('www');
 
 export const createArnsMiddleware = ({
   dataHandler,
-  rootHost,
   nameResolver,
 }: {
   dataHandler: Handler;
-  rootHost: string;
   nameResolver: NameResolver;
 }): Handler =>
   asyncMiddleware(async (req, res, next) => {
-    const rootHostSubdomainLength = rootHost.split('.').length - 2;
     if (
       // Ignore subdomains that are part of the ArNS root hostname.
       !Array.isArray(req.subdomains) ||
-      req.subdomains.length === rootHostSubdomainLength
+      req.subdomains.length === config.ROOT_HOST_SUBDOMAIN_LENGTH
     ) {
       next();
       return;
     }
-    const arnsSubdomain = req.subdomains[req.subdomains.length - 1];
+    const arnsSubdomain = req.subdomains[config.ROOT_HOST_SUBDOMAIN_LENGTH - 1];
     if (
       EXCLUDED_SUBDOMAINS.has(arnsSubdomain) ||
       // Avoid collisions with sandbox URLs by ensuring the subdomain length

src/middleware/sandbox.ts

@@ -19,11 +19,12 @@ import { Handler, Request } from 'express';
 import url from 'node:url';
 import { base32 } from 'rfc4648';
 
+import * as config from '../config.js';
 import { fromB64Url } from '../lib/encoding.js';
 
 function getRequestSandbox(req: Request): string | undefined {
-  if (req.subdomains.length === 1) {
-    return req.subdomains[0];
+  if (req.subdomains.length > config.ROOT_HOST_SUBDOMAIN_LENGTH) {
+    return req.subdomains[req.subdomains.length - 1];
   }
   return undefined;
 }
@@ -37,14 +38,12 @@ function sandboxFromId(id: string): string {
 }
 
 export function createSandboxMiddleware({
-  rootHost,
   sandboxProtocol,
 }: {
-  rootHost?: string;
   sandboxProtocol?: string;
 }): Handler {
   return (req, res, next) => {
-    if (rootHost === undefined) {
+    if (config.ARNS_ROOT_HOST === undefined) {
       next();
       return;
     }
@@ -63,7 +62,7 @@ export function createSandboxMiddleware({
       const protocol = sandboxProtocol ?? (req.secure ? 'https' : 'http');
       return res.redirect(
         302,
-        `${protocol}://${idSandbox}.${rootHost}${path}?${queryString}`,
+        `${protocol}://${idSandbox}.${config.ARNS_ROOT_HOST}${path}?${queryString}`,
       );
     }