Prevent infinite redirect for doc-router /doc[^/]

Previously, it would just put the slice in the Location with no regards
for what was in there. If there was no slash after the `/doc`, it would
issue a relative redirect, which was still under `/doc`, causing an
infinite redirect.

- /docs/std -> s/std
- /docs/s/std -> s/s/std
- /docs/s/s/s/std -> ...

We prevent this behavior here by only applying the `/doc` redirect if
there is a slash directly after it, causing the default /stable rewrite
fallback to be applied to everything else, which will in practice lead
to nice 404 page.

This should not break anything as all such queries currently run into
these loops, including plain `/doc`.

Author: Noratrieb

terragrunt/modules/release-distribution/lambdas/doc-router/index.js

@@ -110,7 +110,7 @@ exports.handler = (event, context, callback) => {
     }
 
     // Docs used to be under /doc, so redirect those for now
-    if (request.uri.startsWith('/doc')) {
+    if (request.uri.startsWith('/doc/')) {
         return redirect(request.uri.slice(4), callback);
     }
 

terragrunt/modules/release-distribution/lambdas/doc-router/test.mjs

@@ -1,13 +1,18 @@
+// A test that asserts that the redirects work correctly.
+// It can be run with
+// node --test test.mjs
+
 import { test } from "node:test";
 import assert from "node:assert";
 import lambda from "./index.js";
 
 function invokeHandler(uri) {
-  return new Promise((res) => {
-    const cb = (_, response) => {
-      res(response);
+  return new Promise((resolve) => {
+    const callback = (_, response) => {
+      resolve(response);
     };
 
+    // Invoke the lambda handler with an event containing the request URI
     lambda.handler(
       {
         Records: [
@@ -21,16 +26,16 @@ function invokeHandler(uri) {
         ],
       },
       undefined,
-      cb
+      callback
     );
   });
 }
 
 test("example expected redirects", async (t) => {
   const redirects = [
     // root
-    { from: "/", to: "https://www.rust-lang.org/learn" },
-    { from: "/index.html", to: "https://www.rust-lang.org/learn" },
+    { from: "/", to: "/stable/" },
+    { from: "/index.html", to: "/stable/" },
     // crate redirects
     { from: "/regex", to: "https://docs.rs/regex" },
     { from: "/log", to: "https://docs.rs/log" },
@@ -68,3 +73,8 @@ test("ensure the default rewrite to /stable", async (t) => {
   const request = await invokeHandler("/std");
   assert.strictEqual(request.uri, "/stable/std");
 });
+
+test("ensure no infinite redirect for /doc[^/]", async (t) => {
+  const request = await invokeHandler("/docs/std");
+  assert.strictEqual(request.uri, "/stable/docs/std");
+});