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Next.js Route Handlers

Overview

Route Handlers allow you to create API endpoints using the Web Request and Response APIs. They're defined in route.ts files within the app directory.

Basic Structure

File Convention

Route handlers use route.ts (or route.js):

app/
├── api/
│   ├── users/
│   │   └── route.ts      # /api/users
│   └── posts/
│       ├── route.ts      # /api/posts
│       └── [id]/
│           └── route.ts  # /api/posts/:id

HTTP Methods

Export functions named after HTTP methods:

// app/api/users/route.ts
import { NextResponse } from 'next/server'

export async function GET() {
  const users = await db.user.findMany()
  return NextResponse.json(users)
}

export async function POST(request: Request) {
  const body = await request.json()
  const user = await db.user.create({ data: body })
  return NextResponse.json(user, { status: 201 })
}

Supported methods: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS

Request Handling

Reading Request Body

export async function POST(request: Request) {
  // JSON body
  const json = await request.json()

  // Form data
  const formData = await request.formData()
  const name = formData.get('name')

  // Text body
  const text = await request.text()

  return NextResponse.json({ received: true })
}

URL Parameters

Dynamic route parameters:

// app/api/posts/[id]/route.ts
interface RouteContext {
  params: Promise<{ id: string }>
}

export async function GET(
  request: Request,
  context: RouteContext
) {
  const { id } = await context.params
  const post = await db.post.findUnique({ where: { id } })

  if (!post) {
    return NextResponse.json(
      { error: 'Not found' },
      { status: 404 }
    )
  }

  return NextResponse.json(post)
}

Query Parameters

export async function GET(request: Request) {
  const { searchParams } = new URL(request.url)
  const page = searchParams.get('page') ?? '1'
  const limit = searchParams.get('limit') ?? '10'

  const posts = await db.post.findMany({
    skip: (parseInt(page) - 1) * parseInt(limit),
    take: parseInt(limit),
  })

  return NextResponse.json(posts)
}

Request Headers

export async function GET(request: Request) {
  const authHeader = request.headers.get('authorization')

  if (!authHeader?.startsWith('Bearer ')) {
    return NextResponse.json(
      { error: 'Unauthorized' },
      { status: 401 }
    )
  }

  const token = authHeader.split(' ')[1]
  // Validate token...

  return NextResponse.json({ authenticated: true })
}

Response Handling

JSON Response

import { NextResponse } from 'next/server'

export async function GET() {
  return NextResponse.json(
    { message: 'Hello' },
    { status: 200 }
  )
}

Setting Headers

export async function GET() {
  return NextResponse.json(
    { data: 'value' },
    {
      headers: {
        'Cache-Control': 'max-age=3600',
        'X-Custom-Header': 'custom-value',
      },
    }
  )
}

Setting Cookies

import { cookies } from 'next/headers'

export async function POST(request: Request) {
  const cookieStore = await cookies()

  // Set cookie
  cookieStore.set('session', 'abc123', {
    httpOnly: true,
    secure: process.env.NODE_ENV === 'production',
    sameSite: 'lax',
    maxAge: 60 * 60 * 24 * 7, // 1 week
  })

  return NextResponse.json({ success: true })
}

Redirects

import { redirect } from 'next/navigation'
import { NextResponse } from 'next/server'

export async function GET() {
  // Option 1: redirect function (throws)
  redirect('/login')

  // Option 2: NextResponse.redirect
  return NextResponse.redirect(new URL('/login', request.url))
}

Streaming Responses

Text Streaming

export async function GET() {
  const encoder = new TextEncoder()
  const stream = new ReadableStream({
    async start(controller) {
      for (let i = 0; i < 10; i++) {
        controller.enqueue(encoder.encode(`data: ${i}\n\n`))
        await new Promise(resolve => setTimeout(resolve, 100))
      }
      controller.close()
    },
  })

  return new Response(stream, {
    headers: {
      'Content-Type': 'text/event-stream',
      'Cache-Control': 'no-cache',
      'Connection': 'keep-alive',
    },
  })
}

AI/LLM Streaming

export async function POST(request: Request) {
  const { prompt } = await request.json()

  const response = await openai.chat.completions.create({
    model: 'gpt-4',
    messages: [{ role: 'user', content: prompt }],
    stream: true,
  })

  const stream = new ReadableStream({
    async start(controller) {
      for await (const chunk of response) {
        const text = chunk.choices[0]?.delta?.content || ''
        controller.enqueue(new TextEncoder().encode(text))
      }
      controller.close()
    },
  })

  return new Response(stream, {
    headers: { 'Content-Type': 'text/plain' },
  })
}

CORS Configuration

export async function OPTIONS() {
  return new Response(null, {
    status: 204,
    headers: {
      'Access-Control-Allow-Origin': '*',
      'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE',
      'Access-Control-Allow-Headers': 'Content-Type, Authorization',
    },
  })
}

export async function GET() {
  return NextResponse.json(
    { data: 'value' },
    {
      headers: {
        'Access-Control-Allow-Origin': '*',
      },
    }
  )
}

Caching

Static (Default for GET)

// Cached by default
export async function GET() {
  const data = await fetch('https://api.example.com/data')
  return NextResponse.json(await data.json())
}

Opt-out of Caching

export const dynamic = 'force-dynamic'

export async function GET() {
  // Always fresh
}

// Or use cookies/headers (auto opts out)
import { cookies } from 'next/headers'

export async function GET() {
  const cookieStore = await cookies()
  // Now dynamic
}

Error Handling

export async function GET(request: Request) {
  try {
    const data = await riskyOperation()
    return NextResponse.json(data)
  } catch (error) {
    console.error('API Error:', error)

    if (error instanceof ValidationError) {
      return NextResponse.json(
        { error: error.message },
        { status: 400 }
      )
    }

    return NextResponse.json(
      { error: 'Internal Server Error' },
      { status: 500 }
    )
  }
}

Resources

For detailed patterns, see:

• references/http-methods.md - Complete HTTP method guide
• references/streaming-responses.md - Advanced streaming patterns
• examples/crud-api.md - Full CRUD API example

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