Stream in Node.js

Node.js 18 and later ship fetch with streaming response bodies, so no library is needed. The second tab uses the openai package pointed at Syntic.

// stream.mjs  (node stream.mjs)
const res = await fetch('https://app.syntic.ai/v1/chat/completions', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.SYNTIC_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    model: 'Amara S1.2',
    messages: [{ role: 'user', content: 'Describe a lighthouse at night in four sentences.' }],
  }),
})
if (!res.ok) {
  console.error(res.status, await res.text())
  process.exit(1)
}
console.error('request id:', res.headers.get('x-syntic-request-id'))
 
const decoder = new TextDecoder()
let buffer = ''
let usage = null
let done = false
 
for await (const bytes of res.body) {
  buffer += decoder.decode(bytes, { stream: true })
  const lines = buffer.split('\n')
  buffer = lines.pop() // keep a partial line for the next chunk
  for (const line of lines) {
    if (!line.startsWith('data: ')) continue
    const payload = line.slice(6)
    if (payload === '[DONE]') { done = true; continue }
    const event = JSON.parse(payload)
    if (event.error) throw new Error(`stream failed: ${event.detail}`)
    const piece = event.choices?.[0]?.delta?.content
    if (piece) process.stdout.write(piece)
    if (event.usage) usage = event.usage
  }
}
process.stdout.write('\n')
if (!done) console.error('[stream ended early; reply is incomplete]')
console.error('usage:', usage)

Forward the stream to a browser

In a server route, pass text through as it arrives instead of collecting it first. With Express:

app.post('/api/ask', async (req, res) => {
  const upstream = await fetch('https://app.syntic.ai/v1/chat/completions', {
    method: 'POST',
    headers: { Authorization: `Bearer ${process.env.SYNTIC_API_KEY}`, 'Content-Type': 'application/json' },
    body: JSON.stringify({ model: 'Amara Quick', messages: [{ role: 'user', content: String(req.body.q) }] }),
  })
  if (!upstream.ok) return res.status(502).json({ error: 'upstream', status: upstream.status })
  res.setHeader('Content-Type', 'text/event-stream')
  res.setHeader('Cache-Control', 'no-cache')
  for await (const bytes of upstream.body) res.write(bytes)   // events pass through unchanged
  res.end()
})

The browser can then read /api/ask with the same parsing loop as the fetch tab. The API key stays on the server.

Notes

The buffer logic matters: a network chunk can end in the middle of a line, and parsing half an event throws.
Check res.ok before reading. Errors before the stream starts are ordinary JSON.
usage arrives near the end of the stream; keep the last value.

Stream in Python Stream in Go

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Stream in Node.js

Forward the stream to a browser

Notes

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