jsonrpc: SDK serving surface as plugins (dsh-jsonrpc + dsh-jsonrpc-agent)
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imccyu
215
packages/ui/jsonrpc/src/transport.ts
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215
packages/ui/jsonrpc/src/transport.ts
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/**
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* Newline-delimited JSON-RPC 2.0 transport over a byte stream pair (the SDK
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* server's stdio channel). One JSON frame per line; a frame with `id`+`method`
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* is an incoming request, `id` alone matches a pending outgoing request, and
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* `method` alone is a notification. Malformed lines are ignored (a resilient
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* wire reader, not a validator); handler failures become JSON-RPC error
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* responses, never a crashed transport.
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*
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* @module @deepseek-ai/dsh-jsonrpc/transport
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*/
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import { randomUUID } from 'node:crypto'
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import type { Readable, Writable } from 'node:stream'
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type JsonRpcId = string | number
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type RequestHandler = (method: string, params: Record<string, unknown>) => Promise<unknown>
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type NotificationHandler = (method: string, params: Record<string, unknown>) => void
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/**
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* The outbound half of a JSON-RPC peer — what {@link HarnessSdkServer} needs
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* to talk BACK to the host: awaited `request`s and fire-and-forget `notify`s.
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* Narrow on purpose so tests substitute a recording fake without a stream pair.
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*/
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export interface JsonRpcTransportPeer {
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/**
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* Send a request to the remote peer and await its response.
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* @param method - the JSON-RPC method name.
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* @param params - the request parameters object.
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* @returns the remote peer's `result`; rejects on a JSON-RPC `error`
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* response, a write failure, or transport/input closure.
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*/
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request(method: string, params: Record<string, unknown>): Promise<unknown>
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/**
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* Send a notification (no response expected). An omitted `params` sends no
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* `params` member at all.
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* @param method - the JSON-RPC method name.
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* @param params - the optional notification parameters object.
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*/
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notify(method: string, params?: Record<string, unknown>): void
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}
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interface PendingRequest {
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resolve: (value: unknown) => void
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reject: (error: Error) => void
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}
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/**
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* Line-delimited JSON-RPC 2.0 endpoint over a `Readable`/`Writable` pair.
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* Inert until {@link start} attaches the input listeners; {@link close}
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* detaches them and rejects every pending outgoing request (dispose-safe: the
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* streams themselves are not destroyed — the caller owns them). Incoming
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* requests are dispatched to the single {@link onRequest} handler (a missing
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* handler answers `-32601 method not found`; a throwing handler answers
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* `-32603` with the message); incoming notifications go to {@link
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* onNotification} and are dropped without one.
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*/
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export class JsonRpcLineTransport implements JsonRpcTransportPeer {
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private buffer = ''
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private started = false
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private requestHandler: RequestHandler | undefined
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private notificationHandler: NotificationHandler | undefined
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private readonly pending = new Map<JsonRpcId, PendingRequest>()
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constructor(
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private readonly input: Readable,
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private readonly output: Writable,
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) {}
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/** Attach the input listeners and begin reading frames. Idempotent. */
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start(): void {
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if (this.started) return
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this.started = true
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this.input.on('data', this.onData)
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this.input.on('error', this.onInputError)
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this.input.on('end', this.onInputEnd)
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}
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/**
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* Detach the input listeners and reject every pending outgoing request with
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* "JSON-RPC transport closed". Safe to call without a prior {@link start}.
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*/
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close(): void {
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this.input.off('data', this.onData)
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this.input.off('error', this.onInputError)
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this.input.off('end', this.onInputEnd)
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this.failPending(new Error('JSON-RPC transport closed'))
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}
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/**
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* Install THE handler for incoming requests (a later call replaces it).
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* @param handler - resolves to the response `result`; a rejection becomes a
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* `-32603` error response carrying the message.
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*/
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onRequest(handler: RequestHandler): void {
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this.requestHandler = handler
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}
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/**
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* Install THE handler for incoming notifications (a later call replaces it).
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* @param handler - invoked per notification with the method and normalized
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* params object.
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*/
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onNotification(handler: NotificationHandler): void {
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this.notificationHandler = handler
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}
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request(method: string, params: Record<string, unknown>): Promise<unknown> {
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const id = `req_${randomUUID().replaceAll('-', '')}`
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const message = { jsonrpc: '2.0', id, method, params }
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return new Promise((resolve, reject) => {
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this.pending.set(id, { resolve, reject })
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try {
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this.write(message)
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} catch (error) {
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this.pending.delete(id)
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reject(error instanceof Error ? error : new Error(String(error)))
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}
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})
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}
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notify(method: string, params?: Record<string, unknown>): void {
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this.write(params === undefined ? { jsonrpc: '2.0', method } : { jsonrpc: '2.0', method, params })
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}
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private readonly onData = (chunk: Buffer | string): void => {
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this.buffer += typeof chunk === 'string' ? chunk : chunk.toString('utf8')
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for (;;) {
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const newline = this.buffer.indexOf('\n')
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if (newline < 0) break
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const line = this.buffer.slice(0, newline).trim()
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this.buffer = this.buffer.slice(newline + 1)
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if (!line) continue
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void this.handleLine(line)
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}
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}
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private readonly onInputError = (error: Error): void => {
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this.failPending(error)
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}
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private readonly onInputEnd = (): void => {
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this.failPending(new Error('JSON-RPC input closed'))
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}
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private async handleLine(line: string): Promise<void> {
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let message: unknown
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try {
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message = JSON.parse(line)
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} catch {
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// Swallows ONLY JSON.parse syntax errors: a malformed wire line is a
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// peer bug this resilient reader skips; nothing else runs in the try.
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return
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}
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if (!message || typeof message !== 'object') return
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const frame = message as Record<string, unknown>
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const id = frame.id
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const method = frame.method
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if ((typeof id === 'string' || typeof id === 'number') && typeof method === 'string') {
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await this.handleIncomingRequest(id, method, objectParams(frame.params))
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return
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}
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if (typeof id === 'string' || typeof id === 'number') {
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this.handleIncomingResponse(id, frame)
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return
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}
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if (typeof method === 'string') {
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this.notificationHandler?.(method, objectParams(frame.params))
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}
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}
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private async handleIncomingRequest(id: JsonRpcId, method: string, params: Record<string, unknown>): Promise<void> {
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const handler = this.requestHandler
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if (!handler) {
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this.writeError(id, -32601, `method not found: ${method}`)
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return
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}
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try {
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const result = await handler(method, params)
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this.write({ jsonrpc: '2.0', id, result })
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} catch (error) {
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this.writeError(id, -32603, error instanceof Error ? error.message : String(error))
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}
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}
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private handleIncomingResponse(id: JsonRpcId, frame: Record<string, unknown>): void {
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const pending = this.pending.get(id)
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if (!pending) return
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this.pending.delete(id)
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if (frame.error && typeof frame.error === 'object') {
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const error = frame.error as Record<string, unknown>
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pending.reject(new Error(typeof error.message === 'string' ? error.message : 'JSON-RPC error'))
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return
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}
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pending.resolve(frame.result)
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}
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private writeError(id: JsonRpcId, code: number, message: string): void {
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this.write({ jsonrpc: '2.0', id, error: { code, message } })
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}
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private write(message: Record<string, unknown>): void {
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this.output.write(`${JSON.stringify(message)}\n`)
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}
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private failPending(error: Error): void {
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const pending = [...this.pending.values()]
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this.pending.clear()
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for (const waiter of pending) waiter.reject(error)
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}
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}
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/** Normalize JSON-RPC `params` to a plain object (arrays and scalars collapse to `{}`). */
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function objectParams(params: unknown): Record<string, unknown> {
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return params && typeof params === 'object' && !Array.isArray(params) ? params as Record<string, unknown> : {}
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}
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