streamEvents

SUPPORT · function · Runtime value

Bridge a push-style producer to a pull-style async iterable with a one-slot rendezvous.

The producer must await every emit call before emitting again; concurrent emissions are rejected rather than buffered. The slot is released only after the consumer receives the event, so backpressure is exact.

Import

TypeScript

import { streamEvents } from '@jangts/agent-core/support';

JavaScript

import { streamEvents } from '@jangts/agent-core/support';

Other public entry points:@jangts/agent-core/support.

Definition

Type parameters

Type parameter	Constraint	Default type
Event	—	—

Call

streamEvents<Event>(operation: (emit: (event: Event) => Promise<void>) => Promise<void>, { signal }: import("../structs/common.js").ExecutionContext): AsyncIterable<Event>

Bridge a push-style producer to a pull-style async iterable with a one-slot rendezvous.

The producer must await every emit call before emitting again; concurrent emissions are rejected rather than buffered. The slot is released only after the consumer receives the event, so backpressure is exact.

Type parameter	Constraint	Default type
Event	—	—

Parameter	Type	Passing	Description
operation	(emit: (event: Event) => Promise<void>) => Promise<void>	Required	—
__1	ExecutionContext	Required	—

Fields of __1

Field	Type	Required	Description
logger	SubFlowLog | undefined	Optional	Read-only. Explicit optional recorder for this operation; never inferred from diagnostics.
signal	AbortSignal	Required	Read-only. Non-optional cancellation signal; never undefined once execution has started.
diagnostics	DiagnosticContext | undefined	Optional	Read-only. Diagnostic scope of the enclosing call, when recording is enabled.

Returns: AsyncIterable<Event>.

Examples

• SSE, JSON frames, and bounded event streams: Reuse transport mechanics while preserving cancellation and backpressure; protocol parsing and business validation remain separate.

Parse one SSE frame locally

Beginner · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const frame = Support.encodeSseEvent({ event: 'status', data: JSON.stringify({ phase: 'thinking' }) });
const body = new Response(frame).body!;
for await (const event of Support.readSse(body)) console.log(event.event, event.data);

JavaScript

import { Support } from '@jangts/agent-core';
const frame = Support.encodeSseEvent({ event: 'status', data: JSON.stringify({ phase: 'thinking' }) });
const body = new Response(frame).body;
for await (const event of Support.readSse(body))
    console.log(event.event, event.data);

Producer waits for each event delivery

Configuration · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const signal = new AbortController().signal;
const stream = Support.streamEvents<{ phase: string }>(async emit => {
  await emit({ phase: 'preparing' });
  await emit({ phase: 'complete' });
}, { signal });
for await (const event of stream) console.log(event.phase);

JavaScript

import { Support } from '@jangts/agent-core';
const signal = new AbortController().signal;
const stream = Support.streamEvents(async (emit) => {
    await emit({ phase: 'preparing' });
    await emit({ phase: 'complete' });
}, { signal });
for await (const event of stream)
    console.log(event.phase);

Explicitly limit JSON frame count and surrounding content

Extension · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const text = '{"kind":"reply","answer":"服务正常"}';
console.log(Support.scanJsonObjectFrames(text));
console.log(Support.parseJsonFrames(text, { maxFrames: 1, maxExtraClosings: 0 }));
const sent: string[] = [];
await Support.writeSseFrame({
  writer: { write(frame) { sent.push(frame); return true; }, async waitForDrain() {} },
  frame: Support.encodeSseEvent({ event: 'answer', data: text }),
}, { signal: new AbortController().signal });
console.log(sent);

JavaScript

import { Support } from '@jangts/agent-core';
const text = '{"kind":"reply","answer":"服务正常"}';
console.log(Support.scanJsonObjectFrames(text));
console.log(Support.parseJsonFrames(text, { maxFrames: 1, maxExtraClosings: 0 }));
const sent = [];
await Support.writeSseFrame({
    writer: { write(frame) { sent.push(frame); return true; }, async waitForDrain() { } },
    frame: Support.encodeSseEvent({ event: 'answer', data: text }),
}, { signal: new AbortController().signal });
console.log(sent);

Related policy source

• Single-slot handoff and backpressure in event streams

Related definitions

• ExecutionContext