Ensure that source files only contain ASCII

This change should have no user impact. This is a defense-in-depth
against someone opening a malicious patch that has non-ASCII
characters.

package.json

@@ -5,6 +5,7 @@
     "@rollup/plugin-typescript": "^11.1.6",
     "@types/connect": "^3.4.38",
     "@types/jest": "^29.5.12",
+    "@types/node": "^20.12.7",
     "@types/node-zopfli": "^2.0.5",
     "@types/supertest": "^6.0.2",
     "@typescript-eslint/eslint-plugin": "^7.7.1",

test/content-security-policy.test.ts

@@ -297,12 +297,12 @@ describe("Content-Security-Policy middleware", () => {
     const invalidNames = [
       "",
       ";",
-      "á",
+      "\u00e1",
       "default src",
       "default;src",
       "default,src",
       "default!src",
-      "defáult-src",
+      "def\u00e1ult-src",
       "default_src",
       "__proto__",
     ];

test/source-files.test.ts

@@ -0,0 +1,64 @@
+import { promisify } from "node:util";
+import * as fs from "node:fs/promises";
+import * as path from "node:path";
+import * as childProcess from "node:child_process";
+import { ReadableStream } from "node:stream/web";
+
+const EXTNAMES_THAT_DONT_HAVE_TO_BE_ASCII: ReadonlySet<string> = new Set([
+  ".md",
+]);
+const NEWLINE = "\n".charCodeAt(0);
+const SPACE = " ".charCodeAt(0);
+const TILDE = "~".charCodeAt(0);
+
+const exec = promisify(childProcess.exec);
+const root = path.resolve(__dirname, "..");
+
+describe("source files", () => {
+  it('only has "normal" ASCII characters in the source files', async () => {
+    for await (const { sourceFile, chunk, index } of getSourceFileChunks()) {
+      const abnormalByte = chunk.find((byte) => !isNormalAsciiByte(byte));
+      if (typeof abnormalByte === "number") {
+        throw new Error(
+          `${sourceFile} must only contain "normal" ASCII characters but contained 0x${abnormalByte.toString(16)} at index ${index + chunk.indexOf(abnormalByte)}`,
+        );
+      }
+    }
+  });
+});
+
+const getSourceFileChunks = (): AsyncIterable<{
+  sourceFile: string;
+  chunk: Uint8Array;
+  index: number;
+}> =>
+  new ReadableStream({
+    async start(controller) {
+      await Promise.all(
+        (await getSourceFiles()).map(async (sourceFile) => {
+          const handle = await fs.open(sourceFile);
+          let index = 0;
+          for await (const chunk of handle.readableWebStream({
+            type: "bytes",
+          })) {
+            controller.enqueue({ sourceFile, chunk, index });
+            index += chunk.byteLength;
+          }
+          await handle.close();
+        }),
+      );
+      controller.close();
+    },
+  });
+
+const getSourceFiles = async (): Promise<Array<string>> =>
+  (await exec("git ls-files", { cwd: root, env: {} })).stdout
+    .split(/\r?\n/g)
+    .filter(
+      (file) => !EXTNAMES_THAT_DONT_HAVE_TO_BE_ASCII.has(path.extname(file)),
+    )
+    .filter(Boolean)
+    .map((line) => path.resolve(root, line));
+
+const isNormalAsciiByte = (byte: number): boolean =>
+  byte === NEWLINE || (byte >= SPACE && byte <= TILDE);