feat(interceptor): add applyForwardedHeaders request interceptor

CHANGELOG.md

@@ -10,6 +10,11 @@ and this project adheres to
 
 This changelog will need to be split between individual packages
 
+### Added
+
+- [@http/interceptor] new RequestInterceptor `applyForwardedHeaders` to apply
+  `x-forwarded-*` to the Request URL
+
 ## [0.23.1]
 
 ### Fixed

packages/interceptor/apply_forwarded_headers.test.ts

@@ -0,0 +1,22 @@
+import { assertEquals } from "@std/assert/equals";
+import { applyForwardedHeaders } from "./apply_forwarded_headers.ts";
+
+Deno.test("x-forwarded", () => {
+  const incomingBody = new ReadableStream();
+
+  const incomingReq = new Request("http://localhost:8000/yeah?this=that", {
+    method: "PUT",
+    headers: {
+      "X-Forwarded-Proto": "https",
+      "X-Forwarded-Host": "something.cool",
+      "X-Forwarded-Port": "443",
+    },
+    body: incomingBody,
+  });
+
+  const adjustedReq = applyForwardedHeaders(incomingReq);
+
+  assertEquals(adjustedReq.url, "https://something.cool/yeah?this=that");
+  assertEquals(adjustedReq.method, "PUT");
+  assertEquals(adjustedReq.body, incomingBody);
+});

packages/interceptor/apply_forwarded_headers.ts

@@ -0,0 +1,35 @@
+/**
+ * A RequestInterceptor that applies any `X-Forwarded-*` headers
+ * to the URL of the Request object.
+ *
+ * Useful where your server may be behind a proxy that forwards the
+ * request and set these headers.
+ *
+ * Deno Deploy conveniently supplies you with a Request object with
+ * the original URL, so this interceptor isn't required in Deploy.
+ *
+ * @example
+ * ```ts
+ * Deno.serve(intercept(handler, { request: applyForwardedHeaders }));
+ * ```
+ *
+ * TODO: check and parse the `Forwarded` header too.
+ *
+ * @param req The request
+ * @returns either the original Request or a new Request with the adjusted URL
+ */
+export function applyForwardedHeaders(req: Request): Request {
+  const proto = req.headers.get("x-forwarded-proto");
+  const host = req.headers.get("x-forwarded-host");
+  const port = req.headers.get("x-forwarded-port");
+
+  if (proto || host || port) {
+    const url = new URL(req.url);
+    url.protocol = proto ?? url.protocol;
+    url.host = host ?? url.host;
+    url.port = port ?? url.port;
+    return new Request(url, req);
+  }
+
+  return req;
+}

packages/interceptor/deno.json

@@ -2,6 +2,7 @@
   "name": "@http/interceptor",
   "version": "0.23.0",
   "exports": {
+    "./apply-forwarded-headers": "./apply_forwarded_headers.ts",
     "./catch-response": "./catch_response.ts",
     "./cors": "./cors.ts",
     "./intercept": "./intercept.ts",