How to Prevent File Overwrite in Firebase Storage

1import { getStorage, ref, uploadBytes, getDownloadURL } from 'firebase/storage'
2
3const storage = getStorage()
4
5// This OVERWRITES if 'uploads/avatar.png' already exists
6async function uploadAvatar(file: File) {
7  const storageRef = ref(storage, 'uploads/avatar.png')
8  await uploadBytes(storageRef, file)
9  const url = await getDownloadURL(storageRef)
10  // The old file at this path is gone — old download URLs are invalid
11  return url
12}

1import { ref, uploadBytes, getDownloadURL } from 'firebase/storage'
2import { v4 as uuidv4 } from 'uuid'
3
4async function uploadFile(userId: string, file: File) {
5  // Generate unique filename: userId/uuid-originalname
6  const uniqueName = `${uuidv4()}-${file.name}`
7  const storagePath = `uploads/${userId}/${uniqueName}`
8  const storageRef = ref(storage, storagePath)
9
10  const snapshot = await uploadBytes(storageRef, file, {
11    contentType: file.type,
12    customMetadata: {
13      originalName: file.name,
14      uploadedBy: userId,
15    },
16  })
17
18  const downloadURL = await getDownloadURL(snapshot.ref)
19  return { downloadURL, path: storagePath }
20}
21
22// Alternative: use timestamp
23function uniqueFilename(originalName: string): string {
24  const timestamp = Date.now()
25  const ext = originalName.split('.').pop()
26  const baseName = originalName.replace(/\.[^.]+$/, '')
27  return `${baseName}_${timestamp}.${ext}`
28  // avatar_1711612800000.png
29}

1// storage.rules
2rules_version = '2';
3service firebase.storage {
4  match /b/{bucket}/o {
5
6    // User uploads: only allow if file does not already exist
7    match /uploads/{userId}/{fileName} {
8      // Allow read if authenticated
9      allow read: if request.auth != null;
10
11      // Allow create ONLY — file must not exist
12      allow create: if request.auth != null
13        && request.auth.uid == userId
14        && resource == null              // No existing file
15        && request.resource.size < 10 * 1024 * 1024;  // Max 10MB
16
17      // Block updates and deletes
18      allow update: if false;
19      allow delete: if request.auth != null
20        && request.auth.uid == userId;
21    }
22  }
23}

1import { ref, getDownloadURL, uploadBytes } from 'firebase/storage'
2
3async function uploadIfNotExists(path: string, file: File) {
4  const storageRef = ref(storage, path)
5
6  try {
7    // Check if file already exists
8    await getDownloadURL(storageRef)
9    // If we reach here, the file exists
10    throw new Error(`File already exists at ${path}`)
11  } catch (error: any) {
12    if (error.code === 'storage/object-not-found') {
13      // File does not exist — safe to upload
14      const snapshot = await uploadBytes(storageRef, file)
15      return getDownloadURL(snapshot.ref)
16    }
17    throw error // Re-throw other errors
18  }
19}
20
21// Usage
22try {
23  const url = await uploadIfNotExists('uploads/report.pdf', file)
24  console.log('Uploaded:', url)
25} catch (error: any) {
26  if (error.message.includes('already exists')) {
27    console.log('File exists — ask user to rename or confirm overwrite')
28  }
29}

1import { doc, updateDoc, arrayUnion, serverTimestamp } from 'firebase/firestore'
2import { ref, uploadBytes, getDownloadURL } from 'firebase/storage'
3
4async function uploadNewVersion(
5  userId: string,
6  fileGroupId: string,
7  file: File
8) {
9  const version = Date.now()
10  const storagePath = `files/${userId}/${fileGroupId}/v${version}-${file.name}`
11  const storageRef = ref(storage, storagePath)
12
13  // Upload the file
14  const snapshot = await uploadBytes(storageRef, file)
15  const downloadURL = await getDownloadURL(snapshot.ref)
16
17  // Log the version in Firestore
18  await updateDoc(doc(db, 'file_groups', fileGroupId), {
19    currentVersion: {
20      url: downloadURL,
21      path: storagePath,
22      uploadedAt: serverTimestamp(),
23      size: file.size,
24    },
25    versions: arrayUnion({
26      url: downloadURL,
27      path: storagePath,
28      version,
29      size: file.size,
30      name: file.name,
31    }),
32  })
33
34  return downloadURL
35}