feat: merge exisiting headers with ones loader/action sets

.changeset/eight-planes-suffer.md

@@ -0,0 +1,5 @@
+---
+"@mcansh/remix-fastify": minor
+---
+
+merge exisiting fastify reply headers with ones loader/action sets

packages/remix-fastify/__tests__/index.test.ts

@@ -10,6 +10,7 @@ import "@remix-run/node/install";
 import type { MockedFunction } from "vitest";
 import { afterAll, afterEach, describe, expect, it, vi } from "vitest";
 
+import type { GetLoadContextFunction, HttpServer } from "../src/server";
 import {
   createRemixHeaders,
   createRemixRequest,
@@ -31,18 +32,20 @@ let mockedCreateRequestHandler = createRemixRequestHandler as MockedFunction<
   typeof createRemixRequestHandler
 >;
 
-function createApp() {
+function createApp(getLoadContext?: GetLoadContextFunction<HttpServer>) {
   let app = fastify();
 
-  app.all(
-    "*",
-    createRequestHandler({
+  app.all("*", (request, reply) => {
+    let handler = createRequestHandler({
       // We don't have a real app to test, but it doesn't matter. We
       // won't ever call through to the real createRequestHandler
       // @ts-expect-error
       build: undefined,
-    }),
-  );
+      getLoadContext,
+    });
+
+    return handler(request, reply);
+  });
 
   return app;
 }
@@ -134,6 +137,26 @@ describe("fastify createRequestHandler", () => {
       expect(response.statusCode).toBe(204);
     });
 
+    it("merges headers set by the server and by remix", async () => {
+      mockedCreateRequestHandler.mockImplementation(() => async () => {
+        return new Response(null, {
+          headers: { Link: "</style.css>; rel=preload; as=style" },
+        });
+      });
+
+      let app = createApp((_request, reply) => {
+        reply.header("Link", "</script.js>; rel=preload; as=script");
+        return {};
+      });
+
+      let response = await app.inject("/");
+
+      expect(response.headers["link"]).toEqual([
+        "</style.css>; rel=preload; as=style",
+        "</script.js>; rel=preload; as=script",
+      ]);
+    });
+
     it("sets headers", async () => {
       mockedCreateRequestHandler.mockImplementation(() => async () => {
         let headers = new Headers({ "X-Time-Of-Year": "most wonderful" });

packages/remix-fastify/src/plugin.ts

@@ -155,7 +155,7 @@ export let remixFastify = fp<RemixFastifyOptions>(
         done(null, payload);
       });
 
-      let basepath = basename.replace(/\/+$/, "") + "/*";
+      let basepath = basename.replace(/\/+$/, "/*");
 
       childServer.all(basepath, remixHandler);
     });

packages/remix-fastify/src/server.ts

@@ -124,8 +124,36 @@ export async function sendRemixResponse<Server extends HttpServer>(
 ): Promise<void> {
   reply.status(nodeResponse.status);
 
-  for (let [key, values] of nodeResponse.headers.entries()) {
-    reply.headers({ [key]: values });
+  let appliedHeaders = new Map<string, Set<string>>();
+
+  for (let [key, value] of nodeResponse.headers.entries()) {
+    let currentFastifyHeader = reply.getHeader(key);
+    let currentValues = appliedHeaders.get(key) || new Set();
+
+    if (currentFastifyHeader) {
+      if (Array.isArray(currentFastifyHeader)) {
+        for (let header of currentFastifyHeader) {
+          currentValues.add(value);
+          currentValues.add(header);
+        }
+      } else {
+        currentValues.add(value);
+        currentValues.add(currentFastifyHeader as string);
+      }
+    } else {
+      currentValues.add(value);
+    }
+
+    appliedHeaders.set(key, currentValues);
+  }
+
+  for (let [key, values] of appliedHeaders.entries()) {
+    if (values.size === 1) {
+      reply.header(key, values.values().next().value);
+      continue;
+    }
+
+    reply.header(key, [...values]);
   }
 
   if (nodeResponse.body) {