Subresource integrity ftw!

src/static/app.mjs

@@ -1,5 +1,3 @@
-import __INDEX__ from "./index.html";
-
 import make_router from './js/routes_client.mjs';
 
 window.addEventListener("load", (_event) => {

src/static/esbuild.mjs

@@ -1,21 +1,45 @@
 #!/usr/bin/env node
 "use strict";
 
+import fs from 'fs';
 import path from 'path';
+import crypto from 'crypto';
 
 import esbuild from 'esbuild';
 
 const __dirname = import.meta.url.slice(7, import.meta.url.lastIndexOf("/"));
 
+/**
+ * Hashes the contents of a file.
+ * @ref		https://stackoverflow.com/a/44643479/1460422
+ * @param	{string}	hashName	The name of the hash algorithm to use.
+ * @param	{string}	path		The path to the file to hash.
+ * @return	{string}	The resulting hash as a hexadecimal string.
+ */
+function hash_file(hashName, path) {
+	return new Promise((resolve, reject) => {
+		const hash = crypto.createHash(hashName);
+		const stream = fs.createReadStream(path);
+		stream.once("error", reject);
+		stream.on("data", chunk => hash.update(chunk));
+		stream.once("end", () => {
+			stream.off("error", reject);
+			resolve(hash.digest('base64'));
+		});
+	});
+}
+
 (async () => {
 	"use strict";
 	
+	const outdir = path.resolve(__dirname, "../static-dist");
+	
 	const result = await esbuild.build({
 		entryPoints: [
 			"./app.mjs",
 			"./app.css"
 		].map(filepath => path.resolve(__dirname, filepath)),
-		outdir: path.resolve(__dirname, "../static-dist"),
+		outdir,
 		bundle: true,
 		minify: true,
 		sourcemap: true,
@@ -28,9 +52,23 @@ const __dirname = import.meta.url.slice(7, import.meta.url.lastIndexOf("/"));
 			".ttf": "file"
 		}
 	});
+	if(result.errors.length > 0 || result.warnings.length > 0)
 		console.log(result);
 	
+	// We *would* use SHA3 here, but we need to use SHA2 for subresource integrity
+	let algorithm = "sha256";
+	let css_hash = await hash_file(algorithm, path.join(outdir, "app.css"));
+	let js_hash = await hash_file(algorithm, path.join(outdir, "app.js"));
+	
+	let html = (await fs.promises.readFile(path.join(__dirname, "index.html"), "utf-8"))
+		.replace(/\{JS_HASH\}/g, js_hash)
+		.replace(/\{CSS_HASH\}/g, css_hash)
+		.replace(/\{JS_HASH_SHORT\}/g, js_hash.substring(0, 7).replace(/[+/=]/, ""))
+		.replace(/\{CSS_HASH_SHORT\}/g, css_hash.substring(0, 7).replace(/[+/=]/, ""))
+		.replace(/\{ALGO\}/g, algorithm);
 	// TODO: Use fs.promises.copyFile() for index.html here, and also maybe find & replace for css/js filenames that we can then randomise?
 	
+	await fs.promises.writeFile(path.join(outdir, "index.html"), html);
+	
 	// console.log(await esbuild.analyzeMetafile(result.metafile));
 })();

src/static/index.html

@@ -18,7 +18,7 @@
 		</nav>
 		
 		<!---------------->
-		<link rel="stylesheet" href="/static/app.css" />
+		<link rel="stylesheet" href="/static/app.css?hash={CSS_HASH_SHORT}" integrity="{ALGO}-{CSS_HASH}" />
-		<script src="/static/app.js" charset="utf-8"></script>
+		<script src="/static/app.js?hash={JS_HASH_SHORT}" integrity="{ALGO}-{JS_HASH}" charset="utf-8"></script>
 	</body>
 </html>