Why Standard REST Calls Fail for Mobile AI UX

When integrating Large Language Models (LLMs) and Retrieval-Augmented Generation (RAG) into mobile apps, waiting 5 to 10 seconds for a complete JSON payload blocks the user interface and makes the application feel unresponsive. By consuming Server-Sent Events (SSE) over a Dart Stream, we can render tokens in real time as soon as the vector retrieval step finishes.

Creating the Dart SSE Stream Client Using the standard http package, we can send a http.Request and listen directly to the chunked byte stream instead of awaiting http.post:

import 'dart:convert';

import 'package:http/http.dart' as http;

class RagStreamService {

final http.Client _client = http.Client();

Stream streamQuery({

required String prompt,

required List retrievedContextIds,

}) async* {

final request = http.Request(

'POST',

Uri.parse(' https://api.example.com/v1/rag/stream' ),

);

request.headers['Content-Type'] = 'application/json';

request.headers['Accept'] =…