191 lines
7.9 KiB
TypeScript
191 lines
7.9 KiB
TypeScript
/** Lossless-JSON validation and detached snapshots for durable session data. @module @deepseek-ai/dsh-session/json */
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/**
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* A value that round-trips losslessly through JSON: `null`, a boolean, a finite
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* number other than negative zero, a string, an array of such values, or a
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* plain object whose values are such values. Arrays may carry only their dense
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* indexed elements; extra own properties would be discarded by JSON. TypeScript
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* cannot distinguish `-0` from `number`, so {@link isJsonValue} and
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* {@link snapshotJsonValue} enforce these details at runtime. Use this type for
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* a payload that must survive session-log persistence and replay byte-identically
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* — e.g. a tool's private presentation `meta`.
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*/
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export type JsonValue = null | boolean | number | string | JsonValue[] | { [key: string]: JsonValue }
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/** Whether a realm-owned intrinsic prototype is backed by its native constructor. */
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function hasIntrinsicConstructor(prototype: object, name: 'Array' | 'Object'): boolean {
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const descriptor = Object.getOwnPropertyDescriptor(prototype, 'constructor')
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const constructor: unknown = descriptor?.value
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if (typeof constructor !== 'function') return false
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try {
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return constructor.name === name
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&& constructor.prototype === prototype
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&& Function.prototype.toString.call(constructor) === `function ${name}() { [native code] }`
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} catch {
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return false
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}
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}
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/** Whether a candidate is one realm's intrinsic `Object.prototype`. */
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function isIntrinsicObjectPrototype(value: object): boolean {
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return Object.getPrototypeOf(value) === null && hasIntrinsicConstructor(value, 'Object')
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}
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/** Whether an array uses one realm's intrinsic `Array.prototype`, not a subclass or forged prototype. */
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function hasPlainArrayPrototype(value: unknown[]): boolean {
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const prototype: unknown = Object.getPrototypeOf(value)
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if (!Array.isArray(prototype) || !hasIntrinsicConstructor(prototype, 'Array')) return false
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const objectPrototype: unknown = Object.getPrototypeOf(prototype)
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return typeof objectPrototype === 'object'
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&& objectPrototype !== null
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&& isIntrinsicObjectPrototype(objectPrototype)
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}
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/** Whether an object is a plain or null-prototype record from any JavaScript realm. */
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function hasPlainObjectPrototype(value: object): boolean {
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const prototype: unknown = Object.getPrototypeOf(value)
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return prototype === null
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|| typeof prototype === 'object' && isIntrinsicObjectPrototype(prototype)
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}
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/** Return every JSON-visible object key, or reject own data JSON would discard. */
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function enumerableStringKeys(value: object): string[] | undefined {
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const keys = Reflect.ownKeys(value)
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if (keys.some(key => typeof key !== 'string' || !Object.prototype.propertyIsEnumerable.call(value, key))) return undefined
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return keys as string[]
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}
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type SnapshotDestination =
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| { kind: 'root' }
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| { kind: 'array'; target: JsonValue[]; index: number }
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| { kind: 'object'; target: { [key: string]: JsonValue }; key: string }
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type JsonWalkTask =
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| { kind: 'visit'; value: unknown; destination?: SnapshotDestination }
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| { kind: 'array-item'; source: unknown[]; index: number; target?: JsonValue[] }
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| { kind: 'object-property'; source: Record<string, unknown>; key: string; target?: { [key: string]: JsonValue } }
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| { kind: 'leave'; source: object }
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/** Validate lossless JSON iteratively, optionally materializing a detached snapshot. */
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function walkJsonValue(value: unknown, detach: boolean): JsonValue | true | undefined {
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const ancestors = new Set<object>()
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let root: JsonValue | undefined
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const assign = (destination: SnapshotDestination | undefined, item: JsonValue): void => {
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if (destination === undefined) return
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if (destination.kind === 'root') {
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root = item
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} else if (destination.kind === 'array') {
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destination.target[destination.index] = item
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} else {
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Object.defineProperty(destination.target, destination.key, {
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value: item,
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enumerable: true,
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configurable: true,
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writable: true,
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})
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}
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}
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const tasks: JsonWalkTask[] = [{
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kind: 'visit',
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value,
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...(detach ? { destination: { kind: 'root' } as const } : {}),
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}]
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for (let task = tasks.pop(); task !== undefined; task = tasks.pop()) {
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if (task.kind === 'leave') {
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ancestors.delete(task.source)
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continue
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}
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if (task.kind === 'array-item') {
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if (!Object.prototype.hasOwnProperty.call(task.source, task.index)) return undefined
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tasks.push({
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kind: 'visit',
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value: task.source[task.index],
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...(task.target === undefined ? {} : { destination: { kind: 'array', target: task.target, index: task.index } as const }),
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})
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continue
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}
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if (task.kind === 'object-property') {
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tasks.push({
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kind: 'visit',
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value: task.source[task.key],
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...(task.target === undefined ? {} : { destination: { kind: 'object', target: task.target, key: task.key } as const }),
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})
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continue
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}
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const current = task.value
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if (current === null) {
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assign(task.destination, null)
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continue
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}
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if (typeof current === 'boolean' || typeof current === 'string') {
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assign(task.destination, current)
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continue
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}
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if (typeof current === 'number') {
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if (!Number.isFinite(current) || Object.is(current, -0)) return undefined
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assign(task.destination, current)
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continue
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}
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if (typeof current !== 'object') return undefined
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if (ancestors.has(current)) return undefined
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if (Array.isArray(current)) {
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if (!hasPlainArrayPrototype(current)) return undefined
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const length = current.length
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if (Reflect.ownKeys(current).length !== length + 1) return undefined
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const target = detach ? [] as JsonValue[] : undefined
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if (target !== undefined) assign(task.destination, target)
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ancestors.add(current)
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tasks.push({ kind: 'leave', source: current })
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for (let index = length - 1; index >= 0; index--) {
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tasks.push({ kind: 'array-item', source: current, index, ...(target === undefined ? {} : { target }) })
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}
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continue
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}
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if (!hasPlainObjectPrototype(current)) return undefined
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const keys = enumerableStringKeys(current)
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if (keys === undefined) return undefined
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const target = detach ? {} as { [key: string]: JsonValue } : undefined
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if (target !== undefined) assign(task.destination, target)
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ancestors.add(current)
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tasks.push({ kind: 'leave', source: current })
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for (let index = keys.length - 1; index >= 0; index--) {
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const key = keys[index]
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/* v8 ignore next -- the loop is bounded by the captured key count. */
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if (key === undefined) return undefined
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tasks.push({ kind: 'object-property', source: current as Record<string, unknown>, key, ...(target === undefined ? {} : { target }) })
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}
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}
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return detach ? root : true
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}
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/**
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* Validate and detach lossless JSON in one read per property, so a stateful
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* getter cannot change between validation and copying. Traversal is iterative,
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* so valid nesting is bounded by available memory rather than the JavaScript
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* call stack. Accepts ordinary arrays, plain or null-prototype objects, and JSON
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* scalars; rejects sparse, cyclic, exotic, negative-zero, and non-finite values.
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* Getter throws propagate.
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*
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* @param value - the candidate value to validate and detach.
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* @returns the detached snapshot, or `undefined` when the value is not
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* losslessly JSON-serializable.
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*/
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export function snapshotJsonValue<T>(value: T): T | undefined {
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return walkJsonValue(value, true) as T | undefined
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}
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/**
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* Test the same lossless JSON boundary as {@link snapshotJsonValue} without
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* detaching it. Only own enumerable string properties participate; `toJSON`
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* is ignored and getters run, so persistence boundaries use the snapshotter.
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* @param value - the candidate event data to test.
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* @returns whether `value` survives JSON round-trip losslessly.
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*/
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export function isJsonValue(value: unknown): boolean {
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return walkJsonValue(value, false) === true
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}
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