body of ModelClient.asBrowserStream wrongly typed as ReadableStream

[coding101-hk]

• Package Name: @azure-rest/ai-inference
• Package Version: 1.0.0-beta.5
• Operating system:
• nodejs
  • version: v.18.17.1
• browser
  • name/version:
• typescript
  • version: ^5.5.3
• Is the bug related to documentation in
  • README.md
  • source code documentation
  • SDK API docs on https://learn.microsoft.com

Describe the bug

I wished to pipe the body to TextDecoderStream to EventSourceParserStream, but it turned out that res.body isn't ReadableStream so body.pipeThrough(new TextDecoderStream()) fails at runtime.

However in TypeScript it's wrongly declared as ReadableStream so body.pipeThrough(new TextDecoderStream()) didn't raise any error.

Upon inspecting the inheritance chain, the body is in fact IncomingMessage -> Readable -> Stream -> EventEmitter -> Object.

To Reproduce
Steps to reproduce the behavior:

1. Try to run the following code:

import ModelClient from '@azure-rest/ai-inference';
import { AzureKeyCredential } from '@azure/core-auth';

// override the variables here:

const BASE_URL = '...';
const API_KEY = '...';

const modelClient = ModelClient(
	`https://${BASE_URL}/models`,
	new AzureKeyCredential(API_KEY)
);

(async () => {
	const response = await modelClient
		.path('/chat/completions')
		.post({
			body: {
				model: 'DeepSeek-R1',
				max_tokens: 10000,
				messages: [{ role: 'user', content: "9/3(1+2) = ?. Don't overthink" }],
				stream: true,
			},
		})
		.asBrowserStream();
	if (!response.body) {
		throw 'connectionError';
	}
	const textStream = response.body.pipeThrough(new TextDecoderStream())
})();

Expected behavior

1. TypeScript shows no error.
2. No error at runtime.

Screenshots

Additional context

The inheritance is inspected with:

export function logInheritanceInfo(obj: any) {
	let proto = obj;
	const chain = [];

	while (proto) {
		if (proto.constructor && proto.constructor.name) {
			chain.push(proto.constructor.name);
		} else {
			chain.push('[Unknown]');
		}
		proto = Object.getPrototypeOf(proto);
	}

	console.log('Inheritance Chain:', chain.join(' -> '));
}

[xirzec]

@coding101-hk If I understand correctly, you are using node, but wanted to use the browser stream primitives? That's an interesting scenario if so, as I don't believe we intended asBrowserStream to be anything other than a type helper for what behavior was happening in the browser at runtime.

/cc @joheredi @deyaaeldeen @timovv

[dargilco]

FYI @glharper

[timovv]

As @xirzec says, asBrowserStream was intended for use in the browser environment only. In Node, asNodeStream can be used to obtain a NodeJS.ReadableStream instead. If you want a web stream version of the body in Node, you can call Readable.toWeb on the stream returned from asNodeStream and that should get you what you need.

That said, it's definitely confusing and seems incorrect that asBrowserStream returns a Node stream (which, as you note, is the wrong type) in a non-browser environment. I think we can update these as<X>Stream methods to throw when called in the wrong environment instead. Some docs to help clarify wouldn't go amiss either. I'll take a look.