From cf2bf606c7a08b566aaf8322f4601757af464a92 Mon Sep 17 00:00:00 2001
From: Eli Grey <elijah@transcend.io>
Date: Mon, 2 Nov 2020 19:43:53 -0800
Subject: [PATCH] Only request worker script on browsers that support
 WritableStream & TransformStream (#170)

---
 package.json      |  2 +-
 src/API.ts        | 10 ++++------
 src/ua-support.ts | 10 ++++++----
 src/workers.ts    |  5 +++++
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/package.json b/package.json
index 2465ce96..d399c980 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@transcend-io/penumbra",
-  "version": "4.18.5",
+  "version": "4.18.6",
   "description": "Crypto streams for the browser.",
   "main": "build/penumbra.js",
   "types": "ts-build/src/index.d.ts",
diff --git a/src/API.ts b/src/API.ts
index 13ab192e..f6e60211 100644
--- a/src/API.ts
+++ b/src/API.ts
@@ -29,7 +29,7 @@ import {
 import { PenumbraZipWriter } from './zip';
 import { blobCache, isNumber, isViewableText } from './utils';
 import { getWorker, setWorkerLocation } from './workers';
-import { supported } from './ua-support';
+import { advancedStreamsSupported, supported } from './ua-support';
 import { preconnect, preload } from './resource-hints';
 
 const resolver = document.createElementNS(
@@ -37,8 +37,6 @@ const resolver = document.createElementNS(
   'a',
 ) as HTMLAnchorElement;
 
-const writableStreamsSupported = 'WritableStream' in self;
-
 const { createWriteStream } = streamSaver;
 if (!WritableStreamIsNative) {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -52,7 +50,7 @@ async function getJob(...resources: RemoteResource[]): Promise<PenumbraFile[]> {
   if (resources.length === 0) {
     throw new Error('penumbra.get() called without arguments');
   }
-  if (writableStreamsSupported) {
+  if (advancedStreamsSupported) {
     // WritableStream constructor supported
     const worker = await getWorker();
     const DecryptionChannel = worker.comlink;
@@ -308,7 +306,7 @@ async function encryptJob(
   });
 
   // We stream the encryption if supported by the browser
-  if (writableStreamsSupported) {
+  if (advancedStreamsSupported) {
     // WritableStream constructor supported
     const worker = await getWorker();
     const EncryptionChannel = worker.comlink;
@@ -427,7 +425,7 @@ async function decryptJob(
   if (files.length === 0) {
     throw new Error('penumbra.decrypt() called without arguments');
   }
-  if (writableStreamsSupported) {
+  if (advancedStreamsSupported) {
     // WritableStream constructor supported
     const worker = await getWorker();
     const DecryptionChannel = worker.comlink;
diff --git a/src/ua-support.ts b/src/ua-support.ts
index 664625c7..7f8c05fd 100644
--- a/src/ua-support.ts
+++ b/src/ua-support.ts
@@ -1,5 +1,8 @@
 import { PenumbraSupportLevel } from './enums';
 
+/** Whether WritableStream and TransformStream are natively supported */
+export const advancedStreamsSupported =
+  'WritableStream' in self && 'TransformStream' in self;
 let supportLevel: PenumbraSupportLevel = PenumbraSupportLevel.none;
 
 // Event/CustomEvent is non-instantiable, among many various other incompatibilities in IE11
@@ -11,10 +14,9 @@ if (
   typeof self.Response === 'function' &&
   typeof self.fetch === 'function'
 ) {
-  supportLevel =
-    'WritableStream' in self && 'TransformStream' in self
-      ? PenumbraSupportLevel.full
-      : PenumbraSupportLevel.size_limited;
+  supportLevel = advancedStreamsSupported
+    ? PenumbraSupportLevel.full
+    : PenumbraSupportLevel.size_limited;
 }
 
 /** Get Penumbra user agent support level */
diff --git a/src/workers.ts b/src/workers.ts
index adcdd1c7..e8639de2 100644
--- a/src/workers.ts
+++ b/src/workers.ts
@@ -11,6 +11,7 @@ import {
   WorkerLocationOptions,
   ProgressEmit,
 } from './types';
+import { advancedStreamsSupported } from './ua-support';
 
 // ////// //
 // Config //
@@ -254,6 +255,10 @@ view.addEventListener('beforeunload', cleanup);
 export async function setWorkerLocation(
   options: WorkerLocationOptions | string,
 ): Promise<void> {
+  // Workers require WritableStream & TransformStream
+  if (!advancedStreamsSupported) {
+    return undefined;
+  }
   if (initialized) {
     console.warn('Penumbra Workers are already active. Reinitializing...');
     await cleanup();