detection/from-stream-reader

Purpose

Internal module providing the toAsyncIterable helper and the drainViaReader legacy fallback for ReadableStream sources. This module is excluded from coverage measurement because the getReader() fallback path is only reachable on runtimes where ReadableStream does not implement Symbol.asyncIterator (pre-Node-18 and some embedded environments). In Bun and Node 18+, the fast path is always taken.

Features

toAsyncIterable(source) — coerces ReadableStream or AsyncIterable to AsyncIterable<Uint8Array>
drainViaReader(source) — async generator that pulls chunks via ReadableStream.getReader() with proper lock release in the finally block
Fast path: when Symbol.asyncIterator is present (Bun/Node 18+), the source is returned as-is with no overhead
Slow path: when Symbol.asyncIterator is absent, wraps getReader() in an async iterable adapter

Usage

This module is not part of the public API surface. It is imported by from-stream.ts:

// Internal usage only
import { toAsyncIterable } from "./from-stream-reader.js";
const iter = toAsyncIterable(source)[Symbol.asyncIterator]();

API Reference

`drainViaReader(source: ReadableStream<Uint8Array>): AsyncGenerator<Uint8Array>`

Pulls all chunks from a ReadableStream using the getReader() pull API. Releases the lock in the finally block to ensure cleanup even when the consumer aborts iteration.

`toAsyncIterable(source): AsyncIterable<Uint8Array>`

Coerces any ByteSource to AsyncIterable<Uint8Array>. Fast path if Symbol.asyncIterator is present; otherwise returns an adapter object backed by drainViaReader.

Implementation Notes

Bun and Node 18+ expose Symbol.asyncIterator on ReadableStream, making for await (const chunk of stream) work natively. The getReader() fallback exists for completeness (older Node, Deno, Cloudflare Workers pre-2023, some browser environments). This file is listed in the coverage exclude list in vitest.config.ts because the fallback cannot be exercised in the Bun test environment without significant test infrastructure for simulating legacy runtimes.

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