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feat(pass-style,marshal)!: ByteArray, a new binary Passable type
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,85 @@ | ||
| /// <reference types="ses"/> | ||
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| import { PASS_STYLE, assertChecker } from './passStyle-helpers.js'; | ||
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| /** @typedef {import('./types.js').ByteArray} ByteArray */ | ||
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| const { Fail } = assert; | ||
| const { setPrototypeOf } = Object; | ||
| const { apply } = Reflect; | ||
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| /** | ||
| * @type {WeakSet<ByteArray>} | ||
| */ | ||
| const genuineByteArray = new WeakSet(); | ||
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| const slice = ArrayBuffer.prototype.slice; | ||
| const sliceOf = (buffer, start, end) => apply(slice, buffer, [start, end]); | ||
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| /** | ||
| * A ByteArray is much like an ArrayBuffer, but immutable. | ||
| * It cannot be used as an ArrayBuffer argument when a genuine ArrayBuffer is | ||
| * needed. But a `byteArray.slice()` is a genuine ArrayBuffer, initially with | ||
| * a copy of the copyByte's data. | ||
| * | ||
| * On platforms that support freezing ArrayBuffer, like perhaps a future XS, | ||
| * (TODO) the intention is that `byteArray` could hold on to a single frozen | ||
| * one and return it for every call to `arrayBuffer.slice`, rather than making | ||
| * a fresh copy each time. | ||
| * | ||
| * @param {ArrayBuffer} arrayBuffer | ||
| * @returns {ByteArray} | ||
| */ | ||
| export const makeByteArray = arrayBuffer => { | ||
| try { | ||
| // Both validates and gets an exclusive copy. | ||
| // This `arrayBuffer` must not escape, to emulate immutability. | ||
| arrayBuffer = sliceOf(arrayBuffer); | ||
| } catch { | ||
| Fail`Expected genuine ArrayBuffer" ${arrayBuffer}`; | ||
| } | ||
| /** @type {ByteArray} */ | ||
| const byteArray = { | ||
| // Can't say it this way because it confuses TypeScript | ||
| // __proto__: ArrayBuffer.prototype, | ||
| byteLength: arrayBuffer.byteLength, | ||
| slice(start, end) { | ||
| return sliceOf(arrayBuffer, start, end); | ||
| }, | ||
| [PASS_STYLE]: 'byteArray', | ||
| [Symbol.toStringTag]: 'ByteArray', | ||
| }; | ||
| setPrototypeOf(byteArray, ArrayBuffer.prototype); | ||
| harden(byteArray); | ||
| genuineByteArray.add(byteArray); | ||
| return byteArray; | ||
| }; | ||
| harden(makeByteArray); | ||
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| /** | ||
| * TODO: This technique for recognizing genuine ByteArray is incompatible | ||
| * with our normal assumption of uncontrolled multiple instantiation of | ||
| * a single module. However, our only alternative to this technique is | ||
| * unprivileged re-validation of open data, which is incompat with our | ||
| * need to encapsulate `arrayBuffer`, the genuinely mutable ArrayBuffer. | ||
| * | ||
| * @param {unknown} candidate | ||
| * @param {import('./types.js').Checker} [check] | ||
| * @returns {boolean} | ||
| */ | ||
| const canBeValid = (candidate, check = undefined) => | ||
| // @ts-expect-error `has` argument can actually be anything. | ||
| genuineByteArray.has(candidate); | ||
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| /** | ||
| * @type {import('./internal-types.js').PassStyleHelper} | ||
| */ | ||
| export const ByteArrayHelper = harden({ | ||
| styleName: 'byteArray', | ||
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| canBeValid, | ||
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| assertValid: (candidate, _passStyleOfRecur) => { | ||
| canBeValid(candidate, assertChecker); | ||
| }, | ||
| }); |
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