Convert the TTX driver code to promises

This commit removes the final callbacks in this code by switching to a
promises-based interface, overall simplifying the code. Moreover, we
document why we write to files on disk and modernize the code using e.g.
template strings.

test/font/ttxdriver.mjs

@@ -21,42 +21,51 @@ import { spawn } from "child_process";
 
 let ttxTaskId = Date.now();
 
-function runTtx(fontPath, callback) {
+function runTtx(fontPath) {
-  const ttx = spawn("ttx", [fontPath], { stdio: "ignore" });
+  return new Promise((resolve, reject) => {
-  let ttxRunError;
+    const ttx = spawn("ttx", [fontPath], { stdio: "ignore" });
-  ttx.on("error", function (errorTtx) {
+    ttx.on("error", () => {
-    ttxRunError = errorTtx;
+      reject(
-    callback(
+        new Error(
-      "Unable to execute `ttx`; make sure the `fonttools` dependency is installed"
+          "Unable to execute `ttx`; make sure the `fonttools` dependency is installed"
-    );
+        )
-  });
+      );
-  ttx.on("close", function (code) {
+    });
-    if (ttxRunError) {
+    ttx.on("close", () => {
-      return;
+      resolve();
-    }
+    });
-    callback();
   });
 }
 
-function translateFont(content, callback) {
+async function translateFont(content) {
   const buffer = Buffer.from(content, "base64");
   const taskId = (ttxTaskId++).toString();
   const fontPath = path.join(os.tmpdir(), `pdfjs-font-test-${taskId}.otf`);
   const resultPath = path.join(os.tmpdir(), `pdfjs-font-test-${taskId}.ttx`);
 
+  // Write the font data to a temporary file on disk (because TTX only accepts
+  // files as input).
   fs.writeFileSync(fontPath, buffer);
-  runTtx(fontPath, function (err) {
+
-    fs.unlinkSync(fontPath);
+  // Run TTX on the temporary font file.
-    if (err) {
+  let ttxError;
-      console.error(err);
+  try {
-      callback(err);
+    await runTtx(fontPath);
-    } else if (!fs.existsSync(resultPath)) {
+  } catch (error) {
-      callback("Output was not generated");
+    ttxError = error;
-    } else {
+  }
-      callback(null, fs.readFileSync(resultPath));
+
-      fs.unlinkSync(resultPath);
+  // Remove the temporary font/result files and report on the outcome.
-    }
+  fs.unlinkSync(fontPath);
-  });
+  if (ttxError) {
+    throw ttxError;
+  }
+  if (!fs.existsSync(resultPath)) {
+    throw new Error("TTX did not generate output");
+  }
+  const xml = fs.readFileSync(resultPath);
+  fs.unlinkSync(resultPath);
+  return xml;
 }
 
 export { translateFont };

test/test.mjs

@@ -840,12 +840,14 @@ function unitTestPostHandler(req, res) {
   req.on("data", function (data) {
     body += data;
   });
-  req.on("end", function () {
+  req.on("end", async function () {
     if (pathname === "/ttx") {
-      translateFont(body, function (err, xml) {
+      res.writeHead(200, { "Content-Type": "text/xml" });
-        res.writeHead(200, { "Content-Type": "text/xml" });
+      try {
-        res.end(err ? "<error>" + err + "</error>" : xml);
+        res.end(await translateFont(body));
-      });
+      } catch (error) {
+        res.end(`<error>${error}</error>`);
+      }
       return;
     }