refactor: simplify electron mirror management

pipeline/scripts/download-electron-mirror.js

@@ -8,22 +8,27 @@ const path = require('path');
 
 /*
 This script replaces existing electron & chromedriver modules
-with mirror dependencies specified by ELECTRON_MIRROR_VAR
-and ELECTRON_CUSTOM_DIR_VAR (see @electron/get). We use this 
-to avoid bundling non-freely-redistributable media codecs 
-in our release builds. The version of Electron published to npm 
-includes these as part of Chromium; our release builds use a 
+with mirror dependencies specified by `assetNumber` and pipeline
+build variables. We use this to avoid bundling non-freely-redistributable 
+media codecs in our release builds. The version of Electron published to 
+npm includes these as part of Chromium; our release builds use a 
 Microsoft-maintained build of Electron that removes those codecs.
 */
 
 if (
-    process.env.ELECTRON_MIRROR_VAR === undefined ||
-    process.env.ELECTRON_CUSTOM_DIR_VAR === undefined
+    process.env.ELECTRON_MIRROR_BASE_VAR === undefined ||
+    process.env.ELECTRON_MIRROR_CUSTOM_DIR_VAR === undefined
 ) {
-    console.error('ELECTRON_MIRROR_VAR and ELECTRON_CUSTOM_DIR_VAR must be defined');
+    console.error(
+        `Mirror variables are not set. Please ensure that
+        ELECTRON_MIRROR_BASE_VAR and ELECTRON_MIRROR_CUSTOM_DIR_VAR
+        are both set as variables in the pipeline`,
+    );
     process.exit(1);
 }
 
+const assetNumber = '4658637';
+
 const downloadMirrors = async () => {
     await downloadElectronArtifact('electron', 'node_modules/electron/dist');
     await downloadElectronArtifact('chromedriver', 'node_modules/electron-chromedriver/bin');
@@ -36,8 +41,9 @@ const downloadElectronArtifact = async (artifactName, destinationPath) => {
         version: `${pkg.dependencies.electron}`,
         artifactName,
         mirrorOptions: {
-            mirror: process.env.ELECTRON_MIRROR_VAR,
-            customDir: process.env.ELECTRON_CUSTOM_DIR_VAR,
+            mirror: process.env.ELECTRON_MIRROR_BASE_VAR,
+            customDir: process.env.ELECTRON_MIRROR_CUSTOM_DIR_VAR,
+            resolveAssetURL: resolveCustomAssetURL,
         },
         force: true,
     });
@@ -49,6 +55,17 @@ const downloadElectronArtifact = async (artifactName, destinationPath) => {
     await extract(zipFilePath, { dir: destinationPath });
 };
 
+const resolveCustomAssetURL = details => {
+    const opts = details.mirrorOptions;
+    const file = details.artifactName.startsWith('SHASUMS256')
+        ? details.artifactName
+        : `${[details.artifactName, details.version, details.platform, details.arch].join(
+              '-',
+          )}.zip`;
+    const strippedVer = details.version.replace(/^v/, '');
+    return `${opts.mirror}/${strippedVer}/${opts.customDir}/${assetNumber}/${file}`;
+};
+
 downloadMirrors().catch(err => {
     console.error(err);
     process.exit(1);

pipeline/unified/download-electron-mirror.yaml

@@ -3,6 +3,3 @@
 steps:
     - script: yarn download:electron-mirror
       displayName: download custom electron build
-      env:
-          ELECTRON_MIRROR_VAR: $(ELECTRON_822_MIRROR_VAR)
-          ELECTRON_CUSTOM_DIR_VAR: $(ELECTRON_822_CUSTOM_DIR_VAR)