assemblyscript/lib/loader/index.js

"use strict";

// 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 = 1 << 5;
const VAL_SIGNED = 1 << 10;
const VAL_FLOAT = 1 << 11;
const VAL_NULLABLE = 1 << 12;
const VAL_MANAGED = 1 << 13;
const KEY_ALIGN = 1 << 14;
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(U32, U16, ref) {
  var length = U32[(ref + SIZE_OFFSET) >>> 2] >>> 1;
  var offset = ref >>> 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, ref) {
    if (!memory) return "<yet unknown>";
    const buffer = memory.buffer;
    return getStringImpl(new Uint32Array(buffer), new Uint16Array(buffer), ref);
  }

  // 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

  // Provide views for all sorts of basic values
  var buffer, I8, U8, I16, U16, I32, U32, F32, F64, I64, U64;

  /** Updates memory views if memory has grown meanwhile. */
  function checkMem() {
    // see: https://github.com/WebAssembly/design/issues/1210
    if (buffer !== memory.buffer) {
      buffer = memory.buffer;
      I8  = new Int8Array(buffer);
      U8  = new Uint8Array(buffer);
      I16 = new Int16Array(buffer);
      U16 = new Uint16Array(buffer);
      I32 = new Int32Array(buffer);
      U32 = new Uint32Array(buffer);
      if (BIGINT) {
        I64 = new BigInt64Array(buffer);
        U64 = new BigUint64Array(buffer);
      }
      F32 = new Float32Array(buffer);
      F64 = new Float64Array(buffer);
    }
  }
  checkMem();

  /** Gets the runtime type info for the given id. */
  function getInfo(id) {
    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 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 or keys. */
  function getAlign(which, info) {
    return 31 - Math.clz32((info / which) & 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 ref = alloc(length << 1, STRING_ID);
    checkMem();
    for (let i = 0, j = ref >>> 1; i < length; ++i) U16[j + i] = str.charCodeAt(i);
    return ref;
  }

  baseModule.__allocString = __allocString;

  /** Reads a string from the module's memory by its pointer. */
  function __getString(ref) {
    checkMem();
    const id = U32[ref + ID_OFFSET >>> 2];
    if (id !== STRING_ID) throw Error("not a string: " + ref);
    return getStringImpl(U32, U16, ref);
  }

  baseModule.__getString = __getString;

  /** Gets the view matching the specified alignment, signedness and floatness. */
  function getView(align, signed, float) {
    if (float) {
      switch (align) {
        case 2: return F32;
        case 3: return F64;
      }
    } else {
      switch (align) {
        case 0: return signed ? I8 : U8;
        case 1: return signed ? I16 : U16;
        case 2: return signed ? I32 : U32;
        case 3: return signed ? I64 : U64;
      }
    }
    throw Error("unsupported align: " + align);
  }

  /** 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 = getAlign(VAL_ALIGN, info);
    const length = values.length;
    const buf = alloc(length << align, ARRAYBUFFER_ID);
    const arr = alloc(info & ARRAY ? ARRAY_SIZE : ARRAYBUFFERVIEW_SIZE, id);
    checkMem();
    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);
    for (let i = 0; i < length; ++i) view[(buf >> align) + i] = values[i];
    if (info & VAL_MANAGED) for (let i = 0; i < length; ++i) retain(values[i]);
    return arr;
  }

  baseModule.__allocArray = __allocArray;

  /** Gets a view on the values of an array in the module's memory. */
  function __getArrayView(arr) {
    checkMem();
    const id = U32[arr + ID_OFFSET >>> 2];
    const info = getInfo(id);
    if (!(info & ARRAYBUFFERVIEW)) throw Error("not an array: " + id);
    const align = getAlign(VAL_ALIGN, 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)
          .slice(buf >>>= align, buf + length);
  }

  baseModule.__getArrayView = __getArrayView;

  /** Reads (copies) the values of an array from the module's memory. */
  function __getArray(arr) {
    return Array.from(__getArrayView(arr));
  }

  baseModule.__getArray = __getArray;

  /** Tests whether an object is an instance of the class represented by the specified base id. */
  function __instanceof(ref, baseId) {
    var id = U32[(ref + 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, Object.defineProperties(baseModule, {
    I8: { get: function() { checkMem(); return I8; } },
    U8: { get: function() { checkMem(); return U8; } },
    I16: { get: function() { checkMem(); return I16; } },
    U16: { get: function() { checkMem(); return U16; } },
    I32: { get: function() { checkMem(); return I32; } },
    U32: { get: function() { checkMem(); return U32; } },
    I64: { get: function() { checkMem(); return I64; } },
    U64: { get: function() { checkMem(); return U64; } },
    F32: { get: function() { checkMem(); return F32; } },
    F64: { get: function() { checkMem(); return F64; } }
  }));
}

/** Wraps a WebAssembly function while also taking care of variable arguments. */
function wrapFunction(fn, setargc) {
  var wrap = (...args) => {
    setargc(args.length);
    return fn(...args);
  }
  wrap.original = fn;
  return wrap;
}

/** Instantiates an AssemblyScript module using the specified imports. */
function instantiate(module, imports) {
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    new WebAssembly.Instance(module, imports)
  );
}

exports.instantiate = instantiate;

/** Instantiates an AssemblyScript module from a buffer using the specified imports. */
function instantiateBuffer(buffer, imports) {
  return instantiate(new WebAssembly.Module(buffer), imports);
}

exports.instantiateBuffer = instantiateBuffer;

/** Instantiates an AssemblyScript module from a response using the specified imports. */
async function instantiateStreaming(response, imports) {
  return postInstantiate(
    preInstantiate(imports || (imports = {})),
    (await WebAssembly.instantiateStreaming(response, imports)).instance
  );
}

exports.instantiateStreaming = instantiateStreaming;

/** Demangles an AssemblyScript module's exports to a friendly object structure. */
function demangle(exports, baseModule) {
  var module = baseModule ? Object.create(baseModule) : {};
  var setargc = exports["__setargc"] || function() {};
  function hasOwnProperty(elem, prop) {
    return Object.prototype.hasOwnProperty.call(elem, prop);
  }
  for (let internalName in exports) {
    if (!hasOwnProperty(exports, internalName)) continue;
    let elem = exports[internalName];
    let parts = internalName.split(".");
    let curr = module;
    while (parts.length > 1) {
      let part = parts.shift();
      if (!hasOwnProperty(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 (!hasOwnProperty(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] = wrapFunction(elem, setargc);
        } else { // for methods
          Object.defineProperty(curr, name, {
            value: function (...args) {
              setargc(args.length);
              return elem(this[THIS], ...args);
            }
          });
        }
      }
    } else {
      if (/^(get|set):/.test(name)) {
        if (!hasOwnProperty(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") {
        curr[name] = wrapFunction(elem, setargc);
      } else {
        curr[name] = elem;
      }
    }
  }

  return module;
}

exports.demangle = demangle;