Mobile: Fixes #4268: Fix "Not implemented" error when downloading resources with S3 sync target (#4279)

Since the RNFetchBlob API doesn't support writing binary data directly
it creates a custom Writable which is doing the base64 encoding per 
chunk.

This also fixes a problem with the S3 synchronization code using the
shim.fsDriver().writeBinaryFile().

Tested with AVD Android 10.0 target.

Signed-off-by: Jan Blunck <jblunck@users.noreply.github.com>

packages/app-mobile/index.js

@@ -44,3 +44,6 @@ LogBox.ignoreLogs([
 ]);
 
 AppRegistry.registerComponent('Joplin', () => Root);
+
+// Using streams on react-native requires to polyfill process.nextTick()
+global.process.nextTick = setImmediate;

packages/app-mobile/package-lock.json

@@ -8379,6 +8379,27 @@
         "emitter-component": "^1.1.1"
       }
     },
+    "stream-browserify": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/stream-browserify/-/stream-browserify-3.0.0.tgz",
+      "integrity": "sha512-H73RAHsVBapbim0tU2JwwOiXUj+fikfiaoYAKHF3VJfA0pe2BCzkhAHBlLG6REzE+2WNZcxOXjK7lkso+9euLA==",
+      "requires": {
+        "inherits": "~2.0.4",
+        "readable-stream": "^3.5.0"
+      },
+      "dependencies": {
+        "readable-stream": {
+          "version": "3.6.0",
+          "resolved": "https://registry.npmjs.org/readable-stream/-/readable-stream-3.6.0.tgz",
+          "integrity": "sha512-BViHy7LKeTz4oNnkcLJ+lVSL6vpiFeX6/d3oSH8zCW7UxP2onchk+vTGB143xuFjHS3deTgkKoXXymXqymiIdA==",
+          "requires": {
+            "inherits": "^2.0.3",
+            "string_decoder": "^1.1.1",
+            "util-deprecate": "^1.0.1"
+          }
+        }
+      }
+    },
     "stream-buffers": {
       "version": "2.2.0",
       "resolved": "https://registry.npmjs.org/stream-buffers/-/stream-buffers-2.2.0.tgz",

packages/app-mobile/package.json

@@ -53,14 +53,15 @@
     "redux": "4.0.0",
     "rn-fetch-blob": "^0.12.0",
     "stream": "0.0.2",
+    "stream-browserify": "^3.0.0",
     "string-natural-compare": "^2.0.2",
     "timers": "^0.1.1",
     "valid-url": "^1.0.9"
   },
   "devDependencies": {
-    "@joplin/tools": "^1.0.9",
     "@babel/core": "^7.11.6",
     "@babel/runtime": "^7.11.2",
+    "@joplin/tools": "^1.0.9",
     "@types/node": "^14.14.6",
     "@types/react": "^16.9.55",
     "execa": "^4.0.0",

packages/app-mobile/utils/fs-driver-rn.js

@@ -1,6 +1,8 @@
 const RNFS = require('react-native-fs');
 const FsDriverBase = require('@joplin/lib/fs-driver-base').default;
 const RNFetchBlob = require('rn-fetch-blob').default;
+const { Writable } = require('stream-browserify');
+const { Buffer } = require('buffer');
 
 class FsDriverRN extends FsDriverBase {
 	appendFileSync() {
@@ -24,8 +26,25 @@ class FsDriverRN extends FsDriverBase {
 		return await this.unlink(path);
 	}
 
-	writeBinaryFile() {
+	writeBinaryFile(path, content) {
-		throw new Error('Not implemented');
+		const buffer = Buffer.from(content);
+		return RNFetchBlob.fs.writeStream(path, 'base64').then(stream => {
+			const fileStream = new Writable({
+				write(chunk, encoding, callback) {
+					this.stream.write(chunk.toString('base64'));
+					callback();
+				},
+				final(callback) {
+					this.stream.close();
+					callback();
+				},
+			});
+			// using options.construct is not implemented in readable-stream so lets
+			// pass the stream from RNFetchBlob to the Writable instance here
+			fileStream.stream = stream;
+			fileStream.write(buffer);
+			fileStream.end();
+		});
 	}
 
 	// Returns a format compatible with Node.js format