@async-util/fetch

A super lightweight lib for parsing ReadableStream which is the type of Response.body of fetch api, implement by async generator fuction, so we can write code in AsyncIterableIterator style.

Parser & fetchParser

The parser ctor accepts a ReadableStream.
``js
import { Parser } from '@async-util/fetch';

async function foo() {
const resp = await fetch('https://your/stream/url', opts);
const parser = new Parser(resp.body);
}
`

If you are parsing data from fetch response, use fetchParser, the arg is exactly the same as fetch.
`js
imoport fetchParser from '@async-util/fetch';
// or
imoport { fetchParser } from '@async-util/fetch';

async function foo() {
const parser = await fetchParser('https://your/stream/url', opts);
}
`

Read data from stream


Here's a exmaple of read the data of OPENAI chat completions api with stream = true.
`js
import fetchParser from '@async-util/fetch';

const openAiKey = process.env.OPENAI_KEY;

(async function () {
const parser = await fetchParser('https://api.openai.com/v1/chat/completions', {
method: 'POST',
headers: {
'Content-Type': 'application/json',
'Authorization': Bearer ${openAiKey}
},
body: JSON.stringify({
stream: true,
model: 'gpt-3.5-turbo',
messages: [
{ role: 'system', content: 'You are a helpful assistant.' },
{ role: 'user', content: 'Hello, how are you?' }
]
})
});

for await (const { data } of parser.sse(true / event.data is json, except the last one '[DONE]' /)) {
console.log(data.choices?.[0] || data);
}
})().catch(console.error);
`
Results looks like:
`
{
index: 0,
delta: { role: 'assistant', content: '' },
finish_reason: null
}
{ index: 0, delta: { content: 'Hello' }, finish_reason: null }
{ index: 0, delta: { content: '!' }, finish_reason: null }
{ index: 0, delta: { content: ' I' }, finish_reason: null }
{ index: 0, delta: { content: "'m" }, finish_reason: null }
{ index: 0, delta: { content: ' an' }, finish_reason: null }
{ index: 0, delta: { content: ' AI' }, finish_reason: null }
{ index: 0, delta: { content: ' assistant' }, finish_reason: null }
{ index: 0, delta: { content: ',' }, finish_reason: null }
{ index: 0, delta: { content: ' so' }, finish_reason: null }
{ index: 0, delta: { content: ' I' }, finish_reason: null }
{ index: 0, delta: { content: ' don' }, finish_reason: null }
{ index: 0, delta: { content: "'t" }, finish_reason: null }
{ index: 0, delta: { content: ' have' }, finish_reason: null }
{ index: 0, delta: { content: ' feelings' }, finish_reason: null }
{ index: 0, delta: { content: ',' }, finish_reason: null }
{ index: 0, delta: { content: ' but' }, finish_reason: null }
{ index: 0, delta: { content: ' I' }, finish_reason: null }
{ index: 0, delta: { content: "'m" }, finish_reason: null }
{ index: 0, delta: { content: ' here' }, finish_reason: null }
{ index: 0, delta: { content: ' to' }, finish_reason: null }
{ index: 0, delta: { content: ' help' }, finish_reason: null }
{ index: 0, delta: { content: ' you' }, finish_reason: null }
{ index: 0, delta: { content: '.' }, finish_reason: null }
{ index: 0, delta: { content: ' How' }, finish_reason: null }
{ index: 0, delta: { content: ' can' }, finish_reason: null }
{ index: 0, delta: { content: ' I' }, finish_reason: null }
{ index: 0, delta: { content: ' assist' }, finish_reason: null }
{ index: 0, delta: { content: ' you' }, finish_reason: null }
{ index: 0, delta: { content: ' today' }, finish_reason: null }
{ index: 0, delta: { content: '?' }, finish_reason: null }
{ index: 0, delta: {}, finish_reason: 'stop' }
[DONE]
`

Or write data to stdout, you will feel it is typing the response.
`js
for await (const { data } of parser.sse(true)) {
const delta = data.choices?.[0].delta?.content;
if (delta) process.stdout.write(delta);
}
`

$3


If the data source is Server Sent Events
`js
async function foo() {
const parser = await fetchParser('https://your/stream/url', opts);
for await (const evt of paser.sse(true / if the data of event is json format. /)) {
console.log(evt.event, evt.id, evt.data);
}
}
`

#### lines
`js
async function foo() {
const parser = await fetchParser('https://your/stream/url', opts);
for await (const line of paser.lines()) {
console.log(line);
}
}
`

#### json data
If every non-empty line is valid json:
`js
async function foo() {
const parser = await fetchParser('https://your/stream/url', opts);
for await (const j of paser.json()) {
console.log(j);
}
}
`

#### chunks
`js
async function foo() {
const parser = await fetchParser('https://your/stream/url', opts);
for await (const chunk of paser.chunks()) {
console.log(chunk);
}
}
``