wasm_exec.js

// 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.

(() => {
	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)");
	}

	const encoder = new TextEncoder('utf-8');
	const decoder = new TextDecoder('utf-8');

    const filesystem = {};

    let workingDirectory = '/';

    let absPath = (path) => {
        if (path[0] == '/') {
            return path;
        }
        return workingDirectory + path.replace(/^\.\/?/, '');
    };

    global.readFromGoFilesystem = (path) => filesystem[absPath(path)];
    global.writeToGoFilesystem = (path, content) => {
        if (typeof content === 'string') {
            filesystem[absPath(path)] = encoder.encode(content);
        } else {
            filesystem[absPath(path)] = content;
        }
    };
    global.goStdout = (buf) => {};
    global.goStderr = (buf) => {};

    const openFiles = new Map();
    let nextFd = 1000;

    let stat = (path, callback) => {
        let mode = 0;
        if (path === '/') {
            mode |= 0x80000000;
        } else if (filesystem[path] === undefined) {
            const err = new Error('no such file');
            err.code = 'ENOENT';
            callback(err);
            return;
        }
        callback(null, {
            mode,
            dev: 0,
            ino: 0,
            nlink: 0,
            uid: 0,
            gid: 0,
            rdev: 0,
            size: 0,
            blksize: 0,
            blocks: 0,
            atimeMs: 0,
            mtimeMs: 0,
            ctimeMs: 0,
            isDirectory: () => !!(mode & 0x80000000),
        });
    };

    const constants = {
        O_WRONLY: 1 << 0,
        O_RDWR: 1 << 1,
        O_CREAT: 1 << 2,
        O_TRUNC: 1 << 3,
        O_APPEND: 1 << 4,
        O_EXCL: 1 << 5,
    };

    let outputBuf = "";
    global.fs = {
        constants,
        writeSync(fd, buf) {
            if (fd === 1) {
                global.goStdout(buf);
            } else if (fd === 2) {
                global.goStderr(buf);
            } else {
                const file = openFiles[fd];
                const source = filesystem[file.path];
                let destLength = source.length + buf.length;
                if (file.offset < source.length) {
                    destLength = file.offset + buf.length;
                    if (destLength < source.length) {
                        destLength = source.length;
                    }
                }
                const dest = new Uint8Array(destLength);
                for (let i = 0; i < source.length; ++i) {
                    dest[i] = source[i];
                }
                for (let i = 0; i < buf.length; ++i) {
                    dest[file.offset + i] = buf[i];
                }
                openFiles[fd].offset += buf.length;
                filesystem[file.path] = dest;
            }
        },
        write(fd, buf, offset, length, position, callback) {
            if (offset !== 0 || length !== buf.length) {
                throw new Error('write not fully implemented: ' + offset + ', ' + length + '/' + buf.length);
            }
            if (position !== null) {
                openFiles[fd].offset = position;
            }
            this.writeSync(fd, buf);
            callback(null, length);
        },
        open(path, flags, mode, callback) {
            console.log('open(' + path + ', ' + mode + ')');
            path = absPath(path);
            if (!filesystem[path]) {
                if (flags & constants.O_CREAT) {
                    filesystem[path] = new Uint8Array(0);
                } else {
                    const err = new Error('no such file');
                    err.code = 'ENOENT';
                    callback(err);
                    return;
                }
            }
            if (flags & constants.O_TRUNC) {
                filesystem[path] = new Uint8Array(0);
            }
            const fd = nextFd++;
            openFiles[fd] = {
                offset: 0,
                path,
            };
            callback(null, fd);
        },
        read(fd, buffer, offset, length, position, callback) {
            if (offset !== 0) {
                throw new Error('read not fully implemented: ' + offset);
            }
            if (position !== null) {
                openFiles[fd].offset = position;
            }
            const file = openFiles[fd];
            const source = filesystem[file.path];
            let n = length;
            if (file.offset + length > source.length) {
                n = source.length - file.offset;
            }
            for (let i = 0; i < n; ++i) {
                buffer[i] = source[file.offset + i];
            }
            openFiles[fd].offset += n;
            callback(null, n);
        },
        close(fd, callback) {
            console.log('close(' + fd + ')');
            openFiles.delete(fd);
            callback(null);
        },
        fsync(fd, callback) {
            callback(null);
        },
        unlink(path, callback) {
            console.log('unlink(' + path + ')');
            callback(null);
        },
        fstat(fd, callback) {
            console.log('fstat(' + fd + ')');
            stat(openFiles[fd].path, callback);
        },
        stat(path, callback) {
            console.log('stat(' + path + ')');
            stat(absPath(path), callback);
        },
        lstat(path, callback) {
            console.log('lstat(' + path + ')');
            stat(absPath(path), callback);
        },
        fchmod(fd, mode, callback) {
            console.log('fchmod(' + fd + ', ' + mode + ')');
            callback(null);
        },
    };

    global.process = {
        cwd() {
            console.log('cwd()');
            return workingDirectory;
        },
    };

	global.Go = class {
		constructor() {
			this.argv = ["js"];
			this.env = {};
			this.exit = (code) => {
				if (code !== 0) {
					console.warn("exit code:", code);
				}
			};
			this._exitPromise = new Promise((resolve) => {
				this._resolveExitPromise = resolve;
			});
			this._pendingEvent = null;
			this._scheduledTimeouts = new Map();
			this._nextCallbackTimeoutID = 1;

			const mem = () => {
				// The buffer may change when requesting more memory.
				return new DataView(this._inst.exports.mem.buffer);
			}

			const setInt64 = (addr, v) => {
				mem().setUint32(addr + 0, v, true);
				mem().setUint32(addr + 4, Math.floor(v / 4294967296), true);
			}

			const getInt64 = (addr) => {
				const low = mem().getUint32(addr + 0, true);
				const high = mem().getInt32(addr + 4, true);
				return low + high * 4294967296;
			}

			const loadValue = (addr) => {
				const f = mem().getFloat64(addr, true);
				if (f === 0) {
					return undefined;
				}
				if (!isNaN(f)) {
					return f;
				}

				const id = mem().getUint32(addr, true);
				return this._values[id];
			}

			const storeValue = (addr, v) => {
				const nanHead = 0x7FF80000;

				if (typeof v === "number") {
					if (isNaN(v)) {
						mem().setUint32(addr + 4, nanHead, true);
						mem().setUint32(addr, 0, true);
						return;
					}
					if (v === 0) {
						mem().setUint32(addr + 4, nanHead, true);
						mem().setUint32(addr, 1, true);
						return;
					}
					mem().setFloat64(addr, v, true);
					return;
				}

				switch (v) {
					case undefined:
						mem().setFloat64(addr, 0, true);
						return;
					case null:
						mem().setUint32(addr + 4, nanHead, true);
						mem().setUint32(addr, 2, true);
						return;
					case true:
						mem().setUint32(addr + 4, nanHead, true);
						mem().setUint32(addr, 3, true);
						return;
					case false:
						mem().setUint32(addr + 4, nanHead, true);
						mem().setUint32(addr, 4, true);
						return;
				}

				let ref = this._refs.get(v);
				if (ref === undefined) {
					ref = this._values.length;
					this._values.push(v);
					this._refs.set(v, ref);
				}
				let typeFlag = 0;
				switch (typeof v) {
					case "string":
						typeFlag = 1;
						break;
					case "symbol":
						typeFlag = 2;
						break;
					case "function":
						typeFlag = 3;
						break;
				}
				mem().setUint32(addr + 4, nanHead | typeFlag, true);
				mem().setUint32(addr, ref, true);
			}

			const loadSlice = (addr) => {
				const array = getInt64(addr + 0);
				const len = getInt64(addr + 8);
				return new Uint8Array(this._inst.exports.mem.buffer, array, len);
			}

			const loadSliceOfValues = (addr) => {
				const array = getInt64(addr + 0);
				const len = getInt64(addr + 8);
				const a = new Array(len);
				for (let i = 0; i < len; i++) {
					a[i] = loadValue(array + i * 8);
				}
				return a;
			}

			const loadString = (addr) => {
				const saddr = getInt64(addr + 0);
				const len = getInt64(addr + 8);
				return decoder.decode(new DataView(this._inst.exports.mem.buffer, saddr, len));
			}

			const timeOrigin = Date.now() - performance.now();
			this.importObject = {
				go: {
					// Go's SP does not change as long as no Go code is running. Some operations (e.g. calls, getters and setters)
					// may synchronously trigger a Go event handler. This makes Go code get executed in the middle of the imported
					// function. A goroutine can switch to a new stack if the current stack is too small (see morestack function).
					// This changes the SP, thus we have to update the SP used by the imported function.

					// func wasmExit(code int32)
					"runtime.wasmExit": (sp) => {
						const code = mem().getInt32(sp + 8, true);
						this.exited = true;
						delete this._inst;
						delete this._values;
						delete this._refs;
						this.exit(code);
					},

					// func wasmWrite(fd uintptr, p unsafe.Pointer, n int32)
					"runtime.wasmWrite": (sp) => {
						const fd = getInt64(sp + 8);
						const p = getInt64(sp + 16);
						const n = mem().getInt32(sp + 24, true);
						fs.writeSync(fd, new Uint8Array(this._inst.exports.mem.buffer, p, n));
					},

					// func nanotime() int64
					"runtime.nanotime": (sp) => {
						setInt64(sp + 8, (timeOrigin + performance.now()) * 1000000);
					},

					// func walltime() (sec int64, nsec int32)
					"runtime.walltime": (sp) => {
						const msec = (new Date).getTime();
						setInt64(sp + 8, msec / 1000);
						mem().setInt32(sp + 16, (msec % 1000) * 1000000, true);
					},

					// func scheduleTimeoutEvent(delay int64) int32
					"runtime.scheduleTimeoutEvent": (sp) => {
						const id = this._nextCallbackTimeoutID;
						this._nextCallbackTimeoutID++;
						this._scheduledTimeouts.set(id, setTimeout(
							() => { this._resume(); },
							getInt64(sp + 8) + 1, // setTimeout has been seen to fire up to 1 millisecond early
						));
						mem().setInt32(sp + 16, id, true);
					},

					// func clearTimeoutEvent(id int32)
					"runtime.clearTimeoutEvent": (sp) => {
						const id = mem().getInt32(sp + 8, true);
						clearTimeout(this._scheduledTimeouts.get(id));
						this._scheduledTimeouts.delete(id);
					},

					// func getRandomData(r []byte)
					"runtime.getRandomData": (sp) => {
						crypto.getRandomValues(loadSlice(sp + 8));
					},

					// func stringVal(value string) ref
					"syscall/js.stringVal": (sp) => {
						storeValue(sp + 24, loadString(sp + 8));
					},

					// func valueGet(v ref, p string) ref
					"syscall/js.valueGet": (sp) => {
						const result = Reflect.get(loadValue(sp + 8), loadString(sp + 16));
						sp = this._inst.exports.getsp(); // see comment above
						storeValue(sp + 32, result);
					},

					// func valueSet(v ref, p string, x ref)
					"syscall/js.valueSet": (sp) => {
						Reflect.set(loadValue(sp + 8), loadString(sp + 16), loadValue(sp + 32));
					},

					// func valueIndex(v ref, i int) ref
					"syscall/js.valueIndex": (sp) => {
						storeValue(sp + 24, Reflect.get(loadValue(sp + 8), getInt64(sp + 16)));
					},

					// valueSetIndex(v ref, i int, x ref)
					"syscall/js.valueSetIndex": (sp) => {
						Reflect.set(loadValue(sp + 8), getInt64(sp + 16), loadValue(sp + 24));
					},

					// func valueCall(v ref, m string, args []ref) (ref, bool)
					"syscall/js.valueCall": (sp) => {
						try {
							const v = loadValue(sp + 8);
							const m = Reflect.get(v, loadString(sp + 16));
							const args = loadSliceOfValues(sp + 32);
							const result = Reflect.apply(m, v, args);
							sp = this._inst.exports.getsp(); // see comment above
							storeValue(sp + 56, result);
							mem().setUint8(sp + 64, 1);
						} catch (err) {
							storeValue(sp + 56, err);
							mem().setUint8(sp + 64, 0);
						}
					},

					// func valueInvoke(v ref, args []ref) (ref, bool)
					"syscall/js.valueInvoke": (sp) => {
						try {
							const v = loadValue(sp + 8);
							const args = loadSliceOfValues(sp + 16);
							const result = Reflect.apply(v, undefined, args);
							sp = this._inst.exports.getsp(); // see comment above
							storeValue(sp + 40, result);
							mem().setUint8(sp + 48, 1);
						} catch (err) {
							storeValue(sp + 40, err);
							mem().setUint8(sp + 48, 0);
						}
					},

					// func valueNew(v ref, args []ref) (ref, bool)
					"syscall/js.valueNew": (sp) => {
						try {
							const v = loadValue(sp + 8);
							const args = loadSliceOfValues(sp + 16);
							const result = Reflect.construct(v, args);
							sp = this._inst.exports.getsp(); // see comment above
							storeValue(sp + 40, result);
							mem().setUint8(sp + 48, 1);
						} catch (err) {
							storeValue(sp + 40, err);
							mem().setUint8(sp + 48, 0);
						}
					},

					// func valueLength(v ref) int
					"syscall/js.valueLength": (sp) => {
						setInt64(sp + 16, parseInt(loadValue(sp + 8).length));
					},

					// valuePrepareString(v ref) (ref, int)
					"syscall/js.valuePrepareString": (sp) => {
						const str = encoder.encode(String(loadValue(sp + 8)));
						storeValue(sp + 16, str);
						setInt64(sp + 24, str.length);
					},

					// valueLoadString(v ref, b []byte)
					"syscall/js.valueLoadString": (sp) => {
						const str = loadValue(sp + 8);
						loadSlice(sp + 16).set(str);
					},

					// func valueInstanceOf(v ref, t ref) bool
					"syscall/js.valueInstanceOf": (sp) => {
						mem().setUint8(sp + 24, loadValue(sp + 8) instanceof loadValue(sp + 16));
					},

					"debug": (value) => {
						console.log(value);
					},
				}
			};
		}

		async run(instance) {
			this._inst = instance;
			this._values = [ // TODO: garbage collection
				NaN,
				0,
				null,
				true,
				false,
				global,
				this._inst.exports.mem,
				this,
			];
			this._refs = new Map();
			this.exited = false;

			const mem = new DataView(this._inst.exports.mem.buffer)

			// Pass command line arguments and environment variables to WebAssembly by writing them to the linear memory.
			let offset = 4096;

			const strPtr = (str) => {
				let ptr = offset;
				new Uint8Array(mem.buffer, offset, str.length + 1).set(encoder.encode(str + "\0"));
				offset += str.length + (8 - (str.length % 8));
				return ptr;
			};

			const argc = this.argv.length;

			const argvPtrs = [];
			this.argv.forEach((arg) => {
				argvPtrs.push(strPtr(arg));
			});

			const keys = Object.keys(this.env).sort();
			argvPtrs.push(keys.length);
			keys.forEach((key) => {
				argvPtrs.push(strPtr(`${key}=${this.env[key]}`));
			});

			const argv = offset;
			argvPtrs.forEach((ptr) => {
				mem.setUint32(offset, ptr, true);
				mem.setUint32(offset + 4, 0, true);
				offset += 8;
			});

			this._inst.exports.run(argc, argv);
			if (this.exited) {
				this._resolveExitPromise();
			}
			await this._exitPromise;
		}

		_resume() {
			if (this.exited) {
				throw new Error("Go program has already exited");
			}
			this._inst.exports.resume();
			if (this.exited) {
				this._resolveExitPromise();
			}
		}

		_makeFuncWrapper(id) {
			const go = this;
			return function () {
				const event = { id: id, this: this, args: arguments };
				go._pendingEvent = event;
				go._resume();
				return event.result;
			};
		}
	}
})();