generate _headers file to override static chunks cache control (#141)

Author: lindsaylevine

index.js

@@ -4,6 +4,7 @@ const copyNextAssets = require("./lib/steps/copyNextAssets");
 const setupPages = require("./lib/steps/setupPages");
 const setupImageFunction = require("./lib/steps/setupImageFunction");
 const setupRedirects = require("./lib/steps/setupRedirects");
+const setupHeaders = require("./lib/steps/setupHeaders");
 const {
   NETLIFY_PUBLISH_PATH,
   NETLIFY_FUNCTIONS_PATH,
@@ -30,6 +31,8 @@ const nextOnNetlify = (options = {}) => {
   setupImageFunction(functionsPath);
 
   setupRedirects(publishPath);
+
+  setupHeaders(publishPath);
 };
 
 module.exports = nextOnNetlify;

lib/config.js

@@ -28,6 +28,9 @@ const FUNCTION_TEMPLATE_PATH = join(TEMPLATES_DIR, "netlifyFunction.js");
 // This is the file where custom redirects can be configured
 const CUSTOM_REDIRECTS_PATH = join(".", "_redirects");
 
+// This is the file where custom headers can be configured
+const CUSTOM_HEADERS_PATH = join(".", "_headers");
+
 // This is the name used for copying our imageFunction template and for
 // creating the next/image redirect
 const NEXT_IMAGE_FUNCTION_NAME = "next_image";
@@ -41,5 +44,6 @@ module.exports = {
   TEMPLATES_DIR,
   FUNCTION_TEMPLATE_PATH,
   CUSTOM_REDIRECTS_PATH,
+  CUSTOM_HEADERS_PATH,
   NEXT_IMAGE_FUNCTION_NAME,
 };

lib/steps/setupHeaders.js

@@ -0,0 +1,33 @@
+const { join } = require("path");
+const { existsSync, readFileSync, writeFileSync } = require("fs-extra");
+const { logTitle, logItem } = require("../helpers/logger");
+const { CUSTOM_HEADERS_PATH } = require("../config");
+
+// Setup _headers file to override specific header rules for next assets
+const setupHeaders = (publishPath) => {
+  logTitle("🔀 Setting up headers");
+
+  // Collect custom redirects defined by the user
+  const headers = [];
+  if (existsSync(CUSTOM_HEADERS_PATH)) {
+    logItem("# Prepending custom headers");
+    headers.push(readFileSync(CUSTOM_HEADERS_PATH, "utf8"));
+  }
+
+  // Add NoN section heading
+  headers.push("# Next-on-Netlify Headers");
+
+  // Add rule to override cache control for static chunks
+  const staticChunkRule = [
+    `/_next/static/chunks/*:`,
+    `\n`,
+    `  `,
+    `cache-control: public,max-age=31536000,immutable`,
+  ].join("");
+  headers.push(staticChunkRule);
+
+  // Write redirects to _redirects file
+  writeFileSync(join(publishPath, "_headers"), headers.join("\n"));
+};
+
+module.exports = setupHeaders;

tests/__snapshots__/defaults.test.js.snap

@@ -1,5 +1,11 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`Headers creates Netlify headers 1`] = `
+"# Next-on-Netlify Headers
+/_next/static/chunks/*:
+  cache-control: public,max-age=31536000,immutable"
+`;
+
 exports[`Routing creates Netlify redirects 1`] = `
 "# Next-on-Netlify Redirects
 /  /.netlify/functions/next_index  200

tests/defaults.test.js

@@ -317,3 +317,16 @@ describe("Routing", () => {
     expect(redirects).toMatchSnapshot();
   });
 });
+
+describe("Headers", () => {
+  test("creates Netlify headers", async () => {
+    // Read _headers file
+    const contents = readFileSync(
+      join(PROJECT_PATH, "out_publish", "_headers")
+    );
+    let headers = contents.toString();
+
+    // Check that headers match
+    expect(headers).toMatchSnapshot();
+  });
+});