add server

Author: charleslien

backend/package.json

@@ -36,6 +36,7 @@
     "cors": "^2.8.5",
     "diff": "5.2.0",
     "dotenv": "16.4.5",
+    "eventsource": "^4.0.0",
     "express": "4.19.2",
     "gpt-tokenizer": "2.8.1",
     "ignore": "5.3.2",

backend/src/api/chat/completions.ts

@@ -0,0 +1,46 @@
+import type { Request, Response } from 'express'
+
+const RECONNECT_TIME_MS = 5000
+
+export function completionsStreamHandler(req: Request, res: Response) {
+  // Mandatory SSE headers
+  res.setHeader('Content-Type', 'text/event-stream')
+  res.setHeader('Cache-Control', 'no-cache')
+  res.setHeader('Connection', 'keep-alive')
+  // (optional) allow local browser demos
+  res.setHeader('Access-Control-Allow-Origin', '*')
+
+  // Flush the headers immediately
+  res.flushHeaders?.()
+
+  // Recommended: send a comment or retry hint right away so the client knows we're live
+  res.write(`: connected ${new Date().toISOString()}\n`)
+  const heartbeat = setInterval(() => {
+    res.write(`: heartbeat ${new Date().toISOString()}\n`)
+  }, 30000)
+  res.write(`retry: ${RECONNECT_TIME_MS}\n\n`)
+
+  // Send a few messages, then end
+  const messages = ['hello', 'from', 'the', 'server']
+  let i = 0
+
+  const timer = setInterval(() => {
+    if (i >= messages.length) {
+      // End the SSE stream gracefully
+      res.write('event: asdf\ndata: bye\n\n')
+      clearInterval(timer)
+      clearInterval(heartbeat)
+      res.end()
+      return
+    }
+    // Each SSE message must end with a blank line
+    res.write(`data: ${messages[i++]}\n\n`)
+  }, 600)
+
+  // Clean up if the client disconnects
+  req.on('close', () => {
+    clearInterval(timer)
+    clearInterval(heartbeat)
+    res.end()
+  })
+}

backend/src/index.ts

@@ -11,6 +11,7 @@ import {
   relabelForUserHandler,
 } from './admin/relabelRuns'
 import { validateAgentNameHandler } from './api/agents'
+import { completionsStreamHandler } from './api/chat/completions'
 import { isRepoCoveredHandler } from './api/org'
 import usageHandler from './api/usage'
 import { checkAdmin } from './util/check-auth'
@@ -37,6 +38,7 @@ app.get('/healthz', (req, res) => {
   res.send('ok')
 })
 
+app.post('/api/chat/completions', completionsStreamHandler)
 app.post('/api/usage', usageHandler)
 app.post('/api/orgs/is-repo-covered', isRepoCoveredHandler)
 app.get('/api/agents/validate-name', validateAgentNameHandler)

bun.lock

@@ -39,6 +39,7 @@
   },
   "dependencies": {
     "@t3-oss/env-nextjs": "^0.7.3",
+    "eventsource": "^4.0.0",
     "zod": "3.25.67"
   },
   "overrides": {