misc/wasm: expect environment to provide polyfills

The list of environments to support with wasm_exec.js was becoming too
large to maintain. With this change, wasm_exec.js expects that the
environment provides all necessary polyfills.

The standardized "globalThis" is used for accessing the environment.
wasm_exec.js now only provides stub fallbacks for globalThis.fs and
globalThis.process.

All code specific to Node.js is now in a separate file.

Change-Id: I076febbd94d4d7845260faad972f450f74a7b983
Reviewed-on: https://go-review.googlesource.com/c/go/+/347353
Trust: Richard Musiol <neelance@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

3 files changed, 66 insertions, 100 deletions

diff --git a/misc/wasm/go_js_wasm_exec b/misc/wasm/go_js_wasm_exec
index b700722dfe..fcbd0e4fc8 100755
--- a/misc/wasm/go_js_wasm_exec
+++ b/misc/wasm/go_js_wasm_exec
@@ -11,4 +11,4 @@ while [ -h "$SOURCE" ]; do
 done
 DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
 
-exec node "$DIR/wasm_exec.js" "$@"
+exec node "$DIR/wasm_exec_node.js" "$@"
diff --git a/misc/wasm/wasm_exec.js b/misc/wasm/wasm_exec.js
index e2f3cda995..30044a6f85 100644
--- a/misc/wasm/wasm_exec.js
+++ b/misc/wasm/wasm_exec.js
@@ -1,49 +1,19 @@
 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
+
 "use strict";
 
 (() => {
-	// Map multiple JavaScript environments to a single common API,
-	// preferring web standards over Node.js API.
-	//
-	// Environments considered:
-	// - Browsers
-	// - Node.js
-	// - Electron
-	// - Parcel
-	// - Webpack
-
-	if (typeof global !== "undefined") {
-		// global already exists
-	} else if (typeof window !== "undefined") {
-		window.global = window;
-	} else if (typeof self !== "undefined") {
-		self.global = self;
-	} else {
-		throw new Error("cannot export Go (neither global, window nor self is defined)");
-	}
-
-	if (!global.require && typeof require !== "undefined") {
-		global.require = require;
-	}
-
-	if (!global.fs && global.require) {
-		const fs = require("fs");
-		if (typeof fs === "object" && fs !== null && Object.keys(fs).length !== 0) {
-			global.fs = fs;
-		}
-	}
-
 	const enosys = () => {
 		const err = new Error("not implemented");
 		err.code = "ENOSYS";
 		return err;
 	};
 
-	if (!global.fs) {
+	if (!globalThis.fs) {
 		let outputBuf = "";
-		global.fs = {
+		globalThis.fs = {
 			constants: { O_WRONLY: -1, O_RDWR: -1, O_CREAT: -1, O_TRUNC: -1, O_APPEND: -1, O_EXCL: -1 }, // unused
 			writeSync(fd, buf) {
 				outputBuf += decoder.decode(buf);
@@ -88,8 +58,8 @@
 		};
 	}
 
-	if (!global.process) {
-		global.process = {
+	if (!globalThis.process) {
+		globalThis.process = {
 			getuid() { return -1; },
 			getgid() { return -1; },
 			geteuid() { return -1; },
@@ -103,47 +73,26 @@
 		}
 	}
 
-	if (!global.crypto && global.require) {
-		const nodeCrypto = require("crypto");
-		global.crypto = {
-			getRandomValues(b) {
-				nodeCrypto.randomFillSync(b);
-			},
-		};
-	}
-	if (!global.crypto) {
-		throw new Error("global.crypto is not available, polyfill required (getRandomValues only)");
+	if (!globalThis.crypto) {
+		throw new Error("globalThis.crypto is not available, polyfill required (crypto.getRandomValues only)");
 	}
 
-	if (!global.performance) {
-		global.performance = {
-			now() {
-				const [sec, nsec] = process.hrtime();
-				return sec * 1000 + nsec / 1000000;
-			},
-		};
+	if (!globalThis.performance) {
+		throw new Error("globalThis.performance is not available, polyfill required (performance.now only)");
 	}
 
-	if (!global.TextEncoder && global.require) {
-		global.TextEncoder = require("util").TextEncoder;
-	}
-	if (!global.TextEncoder) {
-		throw new Error("global.TextEncoder is not available, polyfill required");
+	if (!globalThis.TextEncoder) {
+		throw new Error("globalThis.TextEncoder is not available, polyfill required");
 	}
 
-	if (!global.TextDecoder && global.require) {
-		global.TextDecoder = require("util").TextDecoder;
+	if (!globalThis.TextDecoder) {
+		throw new Error("globalThis.TextDecoder is not available, polyfill required");
 	}
-	if (!global.TextDecoder) {
-		throw new Error("global.TextDecoder is not available, polyfill required");
-	}
-
-	// End of polyfills for common API.
 
 	const encoder = new TextEncoder("utf-8");
 	const decoder = new TextDecoder("utf-8");
 
-	global.Go = class {
+	globalThis.Go = class {
 		constructor() {
 			this.argv = ["js"];
 			this.env = {};
@@ -518,7 +467,7 @@
 				null,
 				true,
 				false,
-				global,
+				globalThis,
 				this,
 			];
 			this._goRefCounts = new Array(this._values.length).fill(Infinity); // number of references that Go has to a JS value, indexed by reference id
@@ -527,7 +476,7 @@
 				[null, 2],
 				[true, 3],
 				[false, 4],
-				[global, 5],
+				[globalThis, 5],
 				[this, 6],
 			]);
 			this._idPool = [];   // unused ids that have been garbage collected
@@ -602,36 +551,4 @@
 			};
 		}
 	}
-
-	if (
-		typeof module !== "undefined" &&
-		global.require &&
-		global.require.main === module &&
-		global.process &&
-		global.process.versions &&
-		!global.process.versions.electron
-	) {
-		if (process.argv.length < 3) {
-			console.error("usage: go_js_wasm_exec [wasm binary] [arguments]");
-			process.exit(1);
-		}
-
-		const go = new Go();
-		go.argv = process.argv.slice(2);
-		go.env = Object.assign({ TMPDIR: require("os").tmpdir() }, process.env);
-		go.exit = process.exit;
-		WebAssembly.instantiate(fs.readFileSync(process.argv[2]), go.importObject).then((result) => {
-			process.on("exit", (code) => { // Node.js exits if no event handler is pending
-				if (code === 0 && !go.exited) {
-					// deadlock, make Go print error and stack traces
-					go._pendingEvent = { id: 0 };
-					go._resume();
-				}
-			});
-			return go.run(result.instance);
-		}).catch((err) => {
-			console.error(err);
-			process.exit(1);
-		});
-	}
 })();
diff --git a/misc/wasm/wasm_exec_node.js b/misc/wasm/wasm_exec_node.js
new file mode 100644
index 0000000000..f9200ca950
--- /dev/null
+++ b/misc/wasm/wasm_exec_node.js
@@ -0,0 +1,49 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+"use strict";
+
+if (process.argv.length < 3) {
+	console.error("usage: go_js_wasm_exec [wasm binary] [arguments]");
+	process.exit(1);
+}
+
+globalThis.require = require;
+globalThis.fs = require("fs");
+globalThis.TextEncoder = require("util").TextEncoder;
+globalThis.TextDecoder = require("util").TextDecoder;
+
+globalThis.performance = {
+	now() {
+		const [sec, nsec] = process.hrtime();
+		return sec * 1000 + nsec / 1000000;
+	},
+};
+
+const crypto = require("crypto");
+globalThis.crypto = {
+	getRandomValues(b) {
+		crypto.randomFillSync(b);
+	},
+};
+
+require("./wasm_exec");
+
+const go = new Go();
+go.argv = process.argv.slice(2);
+go.env = Object.assign({ TMPDIR: require("os").tmpdir() }, process.env);
+go.exit = process.exit;
+WebAssembly.instantiate(fs.readFileSync(process.argv[2]), go.importObject).then((result) => {
+	process.on("exit", (code) => { // Node.js exits if no event handler is pending
+		if (code === 0 && !go.exited) {
+			// deadlock, make Go print error and stack traces
+			go._pendingEvent = { id: 0 };
+			go._resume();
+		}
+	});
+	return go.run(result.instance);
+}).catch((err) => {
+	console.error(err);
+	process.exit(1);
+});