fix: normalize trailing slashes in middleware redirect

Paths like /about/ produced /about/.md instead of /about.md. Strip
trailing slashes before inspecting or constructing the redirect URL.
Also reorders checks to parse the URL only after confirming the Accept
header matches.

Author: jamestelfer

functions/_middleware.test.ts

@@ -107,6 +107,27 @@ describe("markdown content negotiation middleware", () => {
     expect(response.headers.get("Location")).toBe("/contributing.md?ref=footer")
   })
 
+  it("strips trailing slash before redirecting", async () => {
+    const context = createContext("https://example.com/contributing/", {
+      headers: { Accept: "text/markdown" },
+    })
+
+    const response = await onRequest(context)
+
+    expect(response.status).toBe(302)
+    expect(response.headers.get("Location")).toBe("/contributing.md")
+  })
+
+  it("passes through when URL with trailing slash has a file extension", async () => {
+    const context = createContext("https://example.com/styles/main.css/", {
+      headers: { Accept: "text/markdown" },
+    })
+
+    await onRequest(context)
+
+    expect(context.next).toHaveBeenCalled()
+  })
+
   it("passes through when no Accept header is present", async () => {
     const context = createContext("https://example.com/contributing")
 

functions/_middleware.ts

@@ -10,20 +10,36 @@ export async function onRequest(context: Context): Promise<Response> {
     return context.next()
   }
 
-  const url = new URL(request.url)
-  const lastSegment = url.pathname.split("/").pop() ?? ""
-  if (lastSegment.includes(".")) {
+  const accept = request.headers.get("Accept") ?? ""
+  if (!accept.includes("text/markdown")) {
     return context.next()
   }
 
-  const accept = request.headers.get("Accept") ?? ""
-  if (!accept.includes("text/markdown")) {
+  const url = new URL(request.url)
+  const pathname = cutSuffix(url.pathname, "/")
+  const lastSegment = cutEnd(pathname, "/")
+  if (lastSegment.includes(".")) {
     return context.next()
   }
 
-  const path = url.pathname === "/" ? "/index" : url.pathname
+  const path = pathname === "" ? "/index" : pathname
   return new Response(null, {
     status: 302,
     headers: { Location: `${path}.md${url.search}` },
   })
 }
+
+function cutSuffix(path: string, suffix: string): string {
+  if (path.endsWith(suffix)) {
+    return path.slice(0, -suffix.length)
+  }
+  return path
+}
+
+function cutEnd(str: string, sep: string): string {
+  const index = str.lastIndexOf(sep)
+  if (index === -1) {
+    return str
+  }
+  return str.slice(index)
+}