Use name-value tuples for headers (vercel/turborepo#3848)

This is a small cleanup extracted out of the WIP `basePath` PR.

crates/next-core/js/src/entry/app-renderer.tsx

@@ -33,7 +33,7 @@ import "@vercel/turbopack-next/polyfill/async-local-storage";
 import { RenderOpts, renderToHTMLOrFlight } from "next/dist/server/app-render";
 import { PassThrough } from "stream";
 import { ServerResponseShim } from "@vercel/turbopack-next/internal/http";
-import { headersFromEntries } from "@vercel/turbopack-next/internal/utils";
+import { headersFromEntries } from "@vercel/turbopack-next/internal/headers";
 import { parse, ParsedUrlQuery } from "node:querystring";
 
 globalThis.__next_require__ = (data) => {

crates/next-core/js/src/entry/router.ts

@@ -3,6 +3,7 @@ import type { IncomingMessage, ServerResponse } from "node:http";
 import { Buffer } from "node:buffer";
 import { join } from "node:path";
 import { createServer, makeRequest } from "@vercel/turbopack-next/ipc/server";
+import { toPairs } from "@vercel/turbopack-next/internal/headers";
 import { makeResolver } from "next/dist/server/router.js";
 import loadConfig from "next/dist/server/config";
 import { PHASE_DEVELOPMENT_SERVER } from "next/dist/shared/lib/constants";
@@ -14,8 +15,7 @@ import middlewareChunkGroup from "MIDDLEWARE_CHUNK_GROUP";
 type RouterRequest = {
   method: string;
   pathname: string;
-  // TODO: not passed to request
-  rawHeaders: Array<[string, string]>;
+  rawHeaders: [string, string][];
   rawQuery: string;
 };
 
@@ -49,12 +49,12 @@ type MessageData =
 
 type RewriteResponse = {
   url: string;
-  headers: string[];
+  headers: [string, string][];
 };
 
 type MiddlewareHeadersResponse = {
   statusCode: number;
-  headers: string[];
+  headers: [string, string][];
 };
 
 let resolveRouteMemo: Promise<
@@ -166,15 +166,15 @@ async function handleClientResponse(
           type: "rewrite",
           data: {
             url: data.url,
-            headers: Object.entries(data.headers).flat(),
+            headers: Object.entries(data.headers),
           },
         };
     }
   }
 
   const responseHeaders: MiddlewareHeadersResponse = {
     statusCode: clientResponse.statusCode!,
-    headers: clientResponse.rawHeaders,
+    headers: toPairs(clientResponse.rawHeaders),
   };
 
   // TODO: support streaming middleware

crates/next-core/js/src/internal/api-server-handler.ts

@@ -7,6 +7,7 @@ import type { Ipc } from "@vercel/turbopack-next/ipc/index";
 import type { ClientRequest, IncomingMessage, Server } from "node:http";
 import type { ServerResponse } from "node:http";
 import { createServer, makeRequest } from "@vercel/turbopack-next/ipc/server";
+import { toPairs } from "@vercel/turbopack-next/internal/headers";
 import { Buffer } from "node:buffer";
 
 const ipc = IPC as Ipc<IpcIncomingMessage, IpcOutgoingMessage>;
@@ -34,7 +35,7 @@ type IpcOutgoingMessage =
 
 type ResponseHeaders = {
   status: number;
-  headers: string[];
+  headers: [string, string][];
 };
 
 type Handler = (data: {
@@ -139,7 +140,7 @@ export default function startHandler(handler: Handler): void {
     const responseData: Buffer[] = [];
     const responseHeaders: ResponseHeaders = {
       status: clientResponse.statusCode!,
-      headers: clientResponse.rawHeaders,
+      headers: toPairs(clientResponse.rawHeaders),
     };
 
     ipc.send({

crates/next-core/js/src/internal/utils.ts → crates/next-core/js/src/internal/headers.ts

@@ -19,3 +19,25 @@ export function headersFromEntries(
   }
   return headers;
 }
+
+/**
+ * Transforms an array of elements into an array of pairs of elements.
+ *
+ * ## Example
+ *
+ * ```ts
+ * toPairs(["a", "b", "c", "d"]) // => [["a", "b"], ["c", "d"]]
+ * ```
+ */
+export function toPairs<T>(arr: T[]): Array<[T, T]> {
+  if (arr.length % 2 !== 0) {
+    throw new Error("toPairs: expected an even number of elements");
+  }
+
+  const pairs: Array<[T, T]> = [];
+  for (let i = 0; i < arr.length; i += 2) {
+    pairs.push([arr[i], arr[i + 1]]);
+  }
+
+  return pairs;
+}

crates/next-core/js/src/internal/page-server-handler.tsx

@@ -15,7 +15,7 @@ import type { BuildManifest } from "next/dist/server/get-page-files";
 import type { ReactLoadableManifest } from "next/dist/server/load-components";
 
 import { ServerResponseShim } from "@vercel/turbopack-next/internal/http";
-import { headersFromEntries } from "@vercel/turbopack-next/internal/utils";
+import { headersFromEntries } from "@vercel/turbopack-next/internal/headers";
 import type { Ipc } from "@vercel/turbopack-next/ipc/index";
 import type { RenderData } from "types/turbopack";
 import type { ChunkGroup } from "types/next";

crates/next-core/js/src/ipc/server.ts

@@ -1,7 +1,7 @@
 import type { ClientRequest, IncomingMessage, Server } from "node:http";
 import type { AddressInfo } from "node:net";
 import http, { ServerResponse } from "node:http";
-import { headersFromEntries } from "@vercel/turbopack-next/internal/utils";
+import { headersFromEntries } from "@vercel/turbopack-next/internal/headers";
 
 /**
  * Creates a server that listens a random port.
@@ -24,7 +24,7 @@ export function makeRequest(
   method: string,
   path: string,
   rawQuery?: string,
-  rawHeaders?: Array<[string, string]>
+  rawHeaders?: [string, string][]
 ): Promise<{
   clientRequest: ClientRequest;
   clientResponsePromise: Promise<IncomingMessage>;

crates/next-core/src/next_image/mod.rs

@@ -77,7 +77,7 @@ impl ContentSource for NextImageContentSource {
             ContentSourceContent::HttpProxy(
                 ProxyResult {
                     status: 302,
-                    headers: vec!["Location".to_string(), url.clone()],
+                    headers: vec![("Location".to_string(), url.clone())],
                     body: "".into(),
                 }
                 .cell(),

crates/next-core/src/router.rs

@@ -77,15 +77,15 @@ pub struct RouterRequest {
 #[serde(rename_all = "camelCase")]
 pub struct RewriteResponse {
     pub url: String,
-    pub headers: Vec<String>,
+    pub headers: Vec<(String, String)>,
 }
 
 #[turbo_tasks::value(shared)]
 #[derive(Debug, Clone, Default)]
 #[serde(rename_all = "camelCase")]
 pub struct MiddlewareHeadersResponse {
     pub status_code: u16,
-    pub headers: Vec<String>,
+    pub headers: Vec<(String, String)>,
 }
 
 #[turbo_tasks::value(shared)]

crates/turbopack-dev-server/src/http.rs

@@ -120,7 +120,7 @@ pub async fn process_request_with_content_source(
             let mut response = Response::builder().status(proxy_result.status);
             let headers = response.headers_mut().expect("headers must be defined");
 
-            for [name, value] in proxy_result.headers.array_chunks() {
+            for (name, value) in &proxy_result.headers {
                 headers.append(
                     HeaderName::from_bytes(name.as_bytes())?,
                     hyper::header::HeaderValue::from_str(value)?,

crates/turbopack-dev-server/src/source/mod.rs

@@ -27,7 +27,7 @@ pub struct ProxyResult {
     /// The HTTP status code to return.
     pub status: u16,
     /// Headers arranged as contiguous (name, value) pairs.
-    pub headers: Vec<String>,
+    pub headers: Vec<(String, String)>,
     /// The body to return.
     pub body: Rope,
 }

crates/turbopack-node/src/lib.rs

@@ -236,7 +236,7 @@ pub async fn get_intermediate_asset(
 #[turbo_tasks::value(shared)]
 pub struct ResponseHeaders {
     pub status: u16,
-    pub headers: Vec<String>,
+    pub headers: Vec<(String, String)>,
 }
 
 #[derive(Serialize)]

crates/turbopack-node/src/render/render_proxy.rs

@@ -146,10 +146,10 @@ async fn proxy_error(
 
     Ok(ProxyResult {
         status: 500,
-        headers: vec![
+        headers: vec![(
             "content-type".to_string(),
             "text/html; charset=utf-8".to_string(),
-        ],
+        )],
         body: body.into(),
     }
     .cell())