undefined

**Server Upload**:
```typescript
'use server';
import { put } from '@vercel/blob';

export async function uploadFile(formData: FormData) {
  const file = formData.get('file') as File;
  const blob = await put(file.name, file, { access: 'public' });
  return blob.url;
}

'use server';
import { handleUpload } from '@vercel/blob/client';

export async function getUploadToken(filename: string) {
  return await handleUpload({
    body: {
      type: 'blob.generate-client-token',
      payload: { pathname: `uploads/${filename}`, access: 'public' }
    },
    request: new Request('https://dummy'),
    onBeforeGenerateToken: async (pathname) => ({
      allowedContentTypes: ['image/jpeg', 'image/png'],
      maximumSizeInBytes: 5 * 1024 * 1024
    })
  });
}

'use client';
import { upload } from '@vercel/blob/client';

const tokenResponse = await getUploadToken(file.name);
const blob = await upload(file.name, file, {
  access: 'public',
  handleUploadUrl: tokenResponse.url
});

import { list, del } from '@vercel/blob';

// List with pagination
const { blobs, cursor } = await list({ prefix: 'uploads/', cursor });

// Delete
await del(blobUrl);

import { createMultipartUpload, uploadPart, completeMultipartUpload } from '@vercel/blob';

const upload = await createMultipartUpload('large-video.mp4', { access: 'public' });
// Upload chunks in loop...
await completeMultipartUpload({ uploadId: upload.uploadId, parts });

// ❌ Server-side upload fails at 4.5MB
export async function POST(request: Request) {
  const formData = await request.formData();
  const file = formData.get('file') as File; // Fails if >4.5MB
  await put(file.name, file, { access: 'public' });
}

// ✅ Client upload bypasses 4.5MB limit (supports up to 500MB)
const blob = await upload(file.name, file, {
  access: 'public',
  handleUploadUrl: '/api/upload/token',
  multipart: true, // For files >500MB, use multipart
});

// For large files (>100MB), extend token expiration
const jsonResponse = await handleUpload({
  body,
  request,
  onBeforeGenerateToken: async (pathname) => {
    return {
      maximumSizeInBytes: 200 * 1024 * 1024,
      validUntil: Date.now() + 300000, // 5 minutes
    };
  },
});

// v2.0.0+ for non-Vercel hosting
await handleUpload({
  body,
  request,
  onBeforeGenerateToken: async (pathname) => {
    return {
      callbackUrl: 'https://example.com', // Required for non-Vercel hosting
    };
  },
  onUploadCompleted: async ({ blob, tokenPayload }) => {
    // Now fires correctly
  },
});

// For local development with ngrok:
// VERCEL_BLOB_CALLBACK_URL=https://abc123.ngrok-free.app

// ❌ Works in Chrome/Edge, hangs in Firefox
const stream = new ReadableStream({ /* ... */ });
await put('file.bin', stream, { access: 'public' }); // Never completes in Firefox

// ✅ Convert stream to Blob for cross-browser support
const chunks: Uint8Array[] = [];
const reader = stream.getReader();
while (true) {
  const { done, value } = await reader.read();
  if (done) break;
  chunks.push(value);
}
const blob = new Blob(chunks);
await put('file.bin', blob, { access: 'public' });

// Client: Construct pathname before upload
await upload(`uploads/${Date.now()}-${file.name}`, file, {
  access: 'public',
  handleUploadUrl: '/api/upload',
  clientPayload: JSON.stringify({ userId: '123' }),
});

// Server: Validate pathname matches expected pattern
await handleUpload({
  body,
  request,
  onBeforeGenerateToken: async (pathname, clientPayload) => {
    const { userId } = JSON.parse(clientPayload || '{}');

    // Validate pathname starts with expected prefix
    if (!pathname.startsWith(`uploads/`)) {
      throw new Error('Invalid upload path');
    }

    return {
      allowedContentTypes: ['image/jpeg', 'image/png'],
      tokenPayload: JSON.stringify({ userId }), // Pass to onUploadCompleted
    };
  },
});

// ❌ Manual multipart upload fails (can't upload 5MB chunks via serverless function)
const upload = await createMultipartUpload('large.mp4', { access: 'public' });
// uploadPart() requires 5MB minimum - hits serverless limit

// ✅ Use automatic multipart via client upload
await upload('large.mp4', file, {
  access: 'public',
  handleUploadUrl: '/api/upload',
  multipart: true, // Automatically handles 5MB+ chunks
});

// ❌ Fails with confusing error
await upload('user-12345', file, {
  access: 'public',
  handleUploadUrl: '/api/upload',
}); // Error: Access denied

// ✅ Extract extension and include in pathname
const extension = file.name.split('.').pop();
await upload(`user-${userId}.${extension}`, file, {
  access: 'public',
  handleUploadUrl: '/api/upload',
});

'use server';
import { put, del } from '@vercel/blob';

export async function updateAvatar(userId: string, formData: FormData) {
  const file = formData.get('avatar') as File;
  if (!file.type.startsWith('image/')) throw new Error('Only images allowed');

  const user = await db.query.users.findFirst({ where: eq(users.id, userId) });
  if (user?.avatarUrl) await del(user.avatarUrl); // Delete old

  const blob = await put(`avatars/${userId}.jpg`, file, { access: 'public' });
  await db.update(users).set({ avatarUrl: blob.url }).where(eq(users.id, userId));
  return blob.url;
}

const blob = await put(`documents/${userId}/${file.name}`, file, { access: 'private' });