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import { createParser } from 'eventsource-parser'
export async function* streamAsyncIterable<T>(stream: ReadableStream<T>) {
const reader = stream.getReader()
try {
while (true) {
const { done, value } = await reader.read()
if (done) {
return
}
yield value
}
} finally {
reader.releaseLock()
}
}
export class llmError extends Error {
statusCode?: number;
statusText?: string;
isFinal?: boolean;
accountId?: string;
cause?: any;
constructor(message: string, cause?: any) {
super(message);
if (cause) {
this.cause = cause;
}
// Set the prototype explicitly.
Object.setPrototypeOf(this, llmError.prototype);
}
}
export async function fetchSSE(
url: string,
options: Parameters<typeof fetch>[1] & {
onMessage: (data: string) => void
onError?: (error: any) => void
},
) {
const { onMessage, onError, ...fetchOptions } = options
const res = await fetch(url, fetchOptions)
if (!res.ok) {
let reason: string
try {
reason = await res.text()
} catch (err) {
reason = res.statusText
}
const msg = `llm error ${res.status}: ${reason}`
const error = new llmError(msg, { cause: res })
error.statusCode = res.status
error.statusText = res.statusText
throw error
}
const parser = createParser((event) => {
onMessage(event.data)
})
// handle special response errors
const feed = (chunk: string) => {
let response = null
try {
response = JSON.parse(chunk)
} catch {
// ignore
}
if (response?.detail?.type === 'invalid_request_error') {
const msg = `llm error ${response.detail.message}: ${response.detail.code} (${response.detail.type})`
const error = new llmError(msg, { cause: response })
error.statusCode = response.detail.code
error.statusText = response.detail.message
if (onError) {
onError(error)
} else {
console.error(error)
}
// don't feed to the event parser
return
}
parser.feed(chunk)
}
if (!res?.body?.getReader) {
// Vercel polyfills `fetch` with `node-fetch`, which doesn't conform to
// web standards, so this is a workaround...
const body: NodeJS.ReadableStream = res.body as any
if (!body.on || !body.read) {
throw new llmError('unsupported "fetch" implementation')
}
body.on('readable', () => {
let chunk: string | Buffer
while (null !== (chunk = body.read())) {
feed(chunk.toString())
}
})
} else {
for await (const chunk of streamAsyncIterable(res.body)) {
const str = new TextDecoder().decode(chunk)
feed(str)
}
}
} |