assemblyscript_loader.js

/**
 * This file is adapted from the AssemblyScript project. See original source at:
 * https://github.com/AssemblyScript/assemblyscript/blob/b942d611aafa63f0be12f75dbdd5470361fac13a/lib/loader/index.js
 *
 * The code is under the Apache License 2.0. See the license at:
 * https://github.com/AssemblyScript/assemblyscript/blob/b942d611aafa63f0be12f75dbdd5470361fac13a/LICENSE
 */

// Runtime header offsets
const ID_OFFSET = -8;
const SIZE_OFFSET = -4;

// Runtime ids
const ARRAYBUFFER_ID = 0;
const STRING_ID = 1;
const ARRAYBUFFERVIEW_ID = 2;

// Runtime type information
const ARRAYBUFFERVIEW = 1 << 0;
const ARRAY = 1 << 1;
const SET = 1 << 2;
const MAP = 1 << 3;
const VAL_ALIGN_OFFSET = 5;
const VAL_ALIGN = 1 << VAL_ALIGN_OFFSET;
const VAL_SIGNED = 1 << 10;
const VAL_FLOAT = 1 << 11;
const VAL_NULLABLE = 1 << 12;
const VAL_MANAGED = 1 << 13;
const KEY_ALIGN_OFFSET = 14;
const KEY_ALIGN = 1 << KEY_ALIGN_OFFSET;
const KEY_SIGNED = 1 << 19;
const KEY_FLOAT = 1 << 20;
const KEY_NULLABLE = 1 << 21;
const KEY_MANAGED = 1 << 22;

// Array(BufferView) layout
const ARRAYBUFFERVIEW_BUFFER_OFFSET = 0;
const ARRAYBUFFERVIEW_DATASTART_OFFSET = 4;
const ARRAYBUFFERVIEW_DATALENGTH_OFFSET = 8;
const ARRAYBUFFERVIEW_SIZE = 12;
const ARRAY_LENGTH_OFFSET = 12;
const ARRAY_SIZE = 16;

const BIGINT = typeof BigUint64Array !== "undefined";
const THIS = Symbol();
const CHUNKSIZE = 1024;

/** Gets a string from an U32 and an U16 view on a memory. */
function getStringImpl(buffer, ptr) {
  const U32 = new Uint32Array(buffer);
  const U16 = new Uint16Array(buffer);
  var length = U32[(ptr + SIZE_OFFSET) >>> 2] >>> 1;
  var offset = ptr >>> 1;
  if (length <= CHUNKSIZE) return String.fromCharCode.apply(String, U16.subarray(offset, offset + length));
  const parts = [];
  do {
    const last = U16[offset + CHUNKSIZE - 1];
    const size = last >= 0xD800 && last < 0xDC00 ? CHUNKSIZE - 1 : CHUNKSIZE;
    parts.push(String.fromCharCode.apply(String, U16.subarray(offset, offset += size)));
    length -= size;
  } while (length > CHUNKSIZE);
  return parts.join("") + String.fromCharCode.apply(String, U16.subarray(offset, offset + length));
}

/** Prepares the base module prior to instantiation. */
function preInstantiate(imports) {
  const baseModule = {};

  function getString(memory, ptr) {
    if (!memory) return "<yet unknown>";
    return getStringImpl(memory.buffer, ptr);
  }

  // add common imports used by stdlib for convenience
  const env = (imports.env = imports.env || {});
  env.abort = env.abort || function abort(mesg, file, line, colm) {
    const memory = baseModule.memory || env.memory; // prefer exported, otherwise try imported
    throw Error("abort: " + getString(memory, mesg) + " at " + getString(memory, file) + ":" + line + ":" + colm);
  }
  env.trace = env.trace || function trace(mesg, n) {
    const memory = baseModule.memory || env.memory;
    console.log("trace: " + getString(memory, mesg) + (n ? " " : "") + Array.prototype.slice.call(arguments, 2, 2 + n).join(", "));
  }
  imports.Math = imports.Math || Math;
  imports.Date = imports.Date || Date;

  return baseModule;
}

/** Prepares the final module once instantiation is complete. */
function postInstantiate(baseModule, instance) {
  const rawExports = instance.exports;
  const memory = rawExports.memory;
  const table = rawExports.table;
  const alloc = rawExports["__alloc"];
  const retain = rawExports["__retain"];
  const rttiBase = rawExports["__rtti_base"] || ~0; // oob if not present

  /** Gets the runtime type info for the given id. */
  function getInfo(id) {
    const U32 = new Uint32Array(memory.buffer);
    const count = U32[rttiBase >>> 2];
    if ((id >>>= 0) >= count) throw Error("invalid id: " + id);
    return U32[(rttiBase + 4 >>> 2) + id * 2];
  }

  /** Gets the runtime base id for the given id. */
  function getBase(id) {
    const U32 = new Uint32Array(memory.buffer);
    const count = U32[rttiBase >>> 2];
    if ((id >>>= 0) >= count) throw Error("invalid id: " + id);
    return U32[(rttiBase + 4 >>> 2) + id * 2 + 1];
  }

  /** Gets the runtime alignment of a collection's values. */
  function getValueAlign(info) {
    return 31 - Math.clz32((info >>> VAL_ALIGN_OFFSET) & 31); // -1 if none
  }

  /** Gets the runtime alignment of a collection's keys. */
  function getKeyAlign(info) {
    return 31 - Math.clz32((info >>> KEY_ALIGN_OFFSET) & 31); // -1 if none
  }

  /** Allocates a new string in the module's memory and returns its retained pointer. */
  function __allocString(str) {
    const length = str.length;
    const ptr = alloc(length << 1, STRING_ID);
    const U16 = new Uint16Array(memory.buffer);
    for (var i = 0, p = ptr >>> 1; i < length; ++i) U16[p + i] = str.charCodeAt(i);
    return ptr;
  }

  baseModule.__allocString = __allocString;

  /** Reads a string from the module's memory by its pointer. */
  function __getString(ptr) {
    const buffer = memory.buffer;
    const id = new Uint32Array(buffer)[ptr + ID_OFFSET >>> 2];
    if (id !== STRING_ID) throw Error("not a string: " + ptr);
    return getStringImpl(buffer, ptr);
  }

  baseModule.__getString = __getString;

  /** Gets the view matching the specified alignment, signedness and floatness. */
  function getView(alignLog2, signed, float) {
    const buffer = memory.buffer;
    if (float) {
      switch (alignLog2) {
        case 2: return new Float32Array(buffer);
        case 3: return new Float64Array(buffer);
      }
    } else {
      switch (alignLog2) {
        case 0: return new (signed ? Int8Array : Uint8Array)(buffer);
        case 1: return new (signed ? Int16Array : Uint16Array)(buffer);
        case 2: return new (signed ? Int32Array : Uint32Array)(buffer);
        case 3: return new (signed ? BigInt64Array : BigUint64Array)(buffer);
      }
    }
    throw Error("unsupported align: " + alignLog2);
  }

  /** Allocates a new array in the module's memory and returns its retained pointer. */
  function __allocArray(id, values) {
    const info = getInfo(id);
    if (!(info & (ARRAYBUFFERVIEW | ARRAY))) throw Error("not an array: " + id + " @ " + info);
    const align = getValueAlign(info);
    const length = values.length;
    const buf = alloc(length << align, ARRAYBUFFER_ID);
    const arr = alloc(info & ARRAY ? ARRAY_SIZE : ARRAYBUFFERVIEW_SIZE, id);
    const U32 = new Uint32Array(memory.buffer);
    U32[arr + ARRAYBUFFERVIEW_BUFFER_OFFSET >>> 2] = retain(buf);
    U32[arr + ARRAYBUFFERVIEW_DATASTART_OFFSET >>> 2] = buf;
    U32[arr + ARRAYBUFFERVIEW_DATALENGTH_OFFSET >>> 2] = length << align;
    if (info & ARRAY) U32[arr + ARRAY_LENGTH_OFFSET >>> 2] = length;
    const view = getView(align, info & VAL_SIGNED, info & VAL_FLOAT);
    if (info & VAL_MANAGED) {
      for (let i = 0; i < length; ++i) view[(buf >>> align) + i] = retain(values[i]);
    } else {
      view.set(values, buf >>> align);
    }
    return arr;
  }

  baseModule.__allocArray = __allocArray;

  /** Gets a live view on an array's values in the module's memory. Infers the array type from RTTI. */
  function __getArrayView(arr) {
    const U32 = new Uint32Array(memory.buffer);
    const id = U32[arr + ID_OFFSET >>> 2];
    const info = getInfo(id);
    if (!(info & ARRAYBUFFERVIEW)) throw Error("not an array: " + id);
    const align = getValueAlign(info);
    var buf = U32[arr + ARRAYBUFFERVIEW_DATASTART_OFFSET >>> 2];
    const length = info & ARRAY
      ? U32[arr + ARRAY_LENGTH_OFFSET >>> 2]
      : U32[buf + SIZE_OFFSET >>> 2] >>> align;
    return getView(align, info & VAL_SIGNED, info & VAL_FLOAT)
          .subarray(buf >>>= align, buf + length);
  }

  baseModule.__getArrayView = __getArrayView;

  /** Copies an array's values from the module's memory. Infers the array type from RTTI. */
  function __getArray(arr) {
    const input = __getArrayView(arr);
    const len = input.length;
    const out = new Array(len);
    for (let i = 0; i < len; i++) out[i] = input[i];
    return out;
  }

  baseModule.__getArray = __getArray;

  /** Copies an ArrayBuffer's value from the module's memory. */
  function __getArrayBuffer(ptr) {
    const buffer = memory.buffer;
    const length = new Uint32Array(buffer)[ptr + SIZE_OFFSET >>> 2];
    return buffer.slice(ptr, ptr + length);
  }

  baseModule.__getArrayBuffer = __getArrayBuffer;

  /** Copies a typed array's values from the module's memory. */
  function getTypedArray(Type, alignLog2, ptr) {
    return new Type(getTypedArrayView(Type, alignLog2, ptr));
  }

  /** Gets a live view on a typed array's values in the module's memory. */
  function getTypedArrayView(Type, alignLog2, ptr) {
    const buffer = memory.buffer;
    const U32 = new Uint32Array(buffer);
    const bufPtr = U32[ptr + ARRAYBUFFERVIEW_DATASTART_OFFSET >>> 2];
    return new Type(buffer, bufPtr, U32[bufPtr + SIZE_OFFSET >>> 2] >>> alignLog2);
  }

  baseModule.__getInt8Array = getTypedArray.bind(null, Int8Array, 0);
  baseModule.__getInt8ArrayView = getTypedArrayView.bind(null, Int8Array, 0);
  baseModule.__getUint8Array = getTypedArray.bind(null, Uint8Array, 0);
  baseModule.__getUint8ArrayView = getTypedArrayView.bind(null, Uint8Array, 0);
  baseModule.__getUint8ClampedArray = getTypedArray.bind(null, Uint8ClampedArray, 0);
  baseModule.__getUint8ClampedArrayView = getTypedArrayView.bind(null, Uint8ClampedArray, 0);
  baseModule.__getInt16Array = getTypedArray.bind(null, Int16Array, 1);
  baseModule.__getInt16ArrayView = getTypedArrayView.bind(null, Int16Array, 1);
  baseModule.__getUint16Array = getTypedArray.bind(null, Uint16Array, 1);
  baseModule.__getUint16ArrayView = getTypedArrayView.bind(null, Uint16Array, 1);
  baseModule.__getInt32Array = getTypedArray.bind(null, Int32Array, 2);
  baseModule.__getInt32ArrayView = getTypedArrayView.bind(null, Int32Array, 2);
  baseModule.__getUint32Array = getTypedArray.bind(null, Uint32Array, 2);
  baseModule.__getUint32ArrayView = getTypedArrayView.bind(null, Uint32Array, 2);
  if (BIGINT) {
    baseModule.__getInt64Array = getTypedArray.bind(null, BigInt64Array, 3);
    baseModule.__getInt64ArrayView = getTypedArrayView.bind(null, BigInt64Array, 3);
    baseModule.__getUint64Array = getTypedArray.bind(null, BigUint64Array, 3);
    baseModule.__getUint64ArrayView = getTypedArrayView.bind(null, BigUint64Array, 3);
  }
  baseModule.__getFloat32Array = getTypedArray.bind(null, Float32Array, 2);
  baseModule.__getFloat32ArrayView = getTypedArrayView.bind(null, Float32Array, 2);
  baseModule.__getFloat64Array = getTypedArray.bind(null, Float64Array, 3);
  baseModule.__getFloat64ArrayView = getTypedArrayView.bind(null, Float64Array, 3);

  /** Tests whether an object is an instance of the class represented by the specified base id. */
  function __instanceof(ptr, baseId) {
    const U32 = new Uint32Array(memory.buffer);
    var id = U32[(ptr + ID_OFFSET) >>> 2];
    if (id <= U32[rttiBase >>> 2]) {
      do if (id == baseId) return true;
      while (id = getBase(id));
    }
    return false;
  }

  baseModule.__instanceof = __instanceof;

  // Pull basic exports to baseModule so code in preInstantiate can use them
  baseModule.memory = baseModule.memory || memory;
  baseModule.table  = baseModule.table  || table;

  // Demangle exports and provide the usual utility on the prototype
  return demangle(rawExports, baseModule);
}

function isResponse(o) {
  return typeof Response !== "undefined" && o instanceof Response;
}

/** Asynchronously instantiates an AssemblyScript module from anything that can be instantiated. */
export async function instantiate(source, imports) {
  if (isResponse(source = await source)) return instantiateStreaming(source, imports);
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    await WebAssembly.instantiate(
      source instanceof WebAssembly.Module
        ? source
        : await WebAssembly.compile(source),
      imports
    )
  );
}

/** Synchronously instantiates an AssemblyScript module from a WebAssembly.Module or binary buffer. */
export function instantiateSync(source, imports) {
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    new WebAssembly.Instance(
      source instanceof WebAssembly.Module
        ? source
        : new WebAssembly.Module(source),
      imports
    )
  )
}

/** Asynchronously instantiates an AssemblyScript module from a response, i.e. as obtained by `fetch`. */
export async function instantiateStreaming(source, imports) {
  if (!WebAssembly.instantiateStreaming) {
    return instantiate(
      isResponse(source = await source)
        ? source.arrayBuffer()
        : source,
      imports
    );
  }
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    (await WebAssembly.instantiateStreaming(source, imports)).instance
  );
}

/** Demangles an AssemblyScript module's exports to a friendly object structure. */
export function demangle(exports, baseModule) {
  var module = baseModule ? Object.create(baseModule) : {};
  var setArgumentsLength = exports["__argumentsLength"]
    ? function(length) { exports["__argumentsLength"].value = length; }
    : exports["__setArgumentsLength"] || exports["__setargc"] || function() {};
  for (let internalName in exports) {
    if (!Object.prototype.hasOwnProperty.call(exports, internalName)) continue;
    const elem = exports[internalName];
    let parts = internalName.split(".");
    let curr = module;
    while (parts.length > 1) {
      let part = parts.shift();
      if (!Object.prototype.hasOwnProperty.call(curr, part)) curr[part] = {};
      curr = curr[part];
    }
    let name = parts[0];
    let hash = name.indexOf("#");
    if (hash >= 0) {
      let className = name.substring(0, hash);
      let classElem = curr[className];
      if (typeof classElem === "undefined" || !classElem.prototype) {
        let ctor = function(...args) {
          return ctor.wrap(ctor.prototype.constructor(0, ...args));
        };
        ctor.prototype = {
          valueOf: function valueOf() {
            return this[THIS];
          }
        };
        ctor.wrap = function(thisValue) {
          return Object.create(ctor.prototype, { [THIS]: { value: thisValue, writable: false } });
        };
        if (classElem) Object.getOwnPropertyNames(classElem).forEach(name =>
          Object.defineProperty(ctor, name, Object.getOwnPropertyDescriptor(classElem, name))
        );
        curr[className] = ctor;
      }
      name = name.substring(hash + 1);
      curr = curr[className].prototype;
      if (/^(get|set):/.test(name)) {
        if (!Object.prototype.hasOwnProperty.call(curr, name = name.substring(4))) {
          let getter = exports[internalName.replace("set:", "get:")];
          let setter = exports[internalName.replace("get:", "set:")];
          Object.defineProperty(curr, name, {
            get: function() { return getter(this[THIS]); },
            set: function(value) { setter(this[THIS], value); },
            enumerable: true
          });
        }
      } else {
        if (name === 'constructor') {
          (curr[name] = (...args) => {
            setArgumentsLength(args.length);
            return elem(...args);
          }).original = elem;
        } else { // instance method
          (curr[name] = function(...args) { // !
            setArgumentsLength(args.length);
            return elem(this[THIS], ...args);
          }).original = elem;
        }
      }
    } else {
      if (/^(get|set):/.test(name)) {
        if (!Object.prototype.hasOwnProperty.call(curr, name = name.substring(4))) {
          Object.defineProperty(curr, name, {
            get: exports[internalName.replace("set:", "get:")],
            set: exports[internalName.replace("get:", "set:")],
            enumerable: true
          });
        }
      } else if (typeof elem === "function" && elem !== setArgumentsLength) {
        (curr[name] = (...args) => {
          setArgumentsLength(args.length);
          return elem(...args);
        }).original = elem;
      } else {
        curr[name] = elem;
      }
    }
  }
  return module;
}