firebase-storage

@jezweb/firebase-storage

jezweb

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Updated 4/6/2026

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Build with Firebase Cloud Storage - file uploads, downloads, and secure access. Use when: uploading images/files, generating download URLs, implementing file pickers, setting up storage security rules, or troubleshooting storage/unauthorized, cors errors, quota exceeded, or upload failed errors. Prevents 9 documented errors.

Installation

$npx agent-skills-cli install @jezweb/firebase-storage

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Repositoryjezweb/claude-skills

Pathskills/firebase-storage/SKILL.md

Branchmain

Scoped Name@jezweb/firebase-storage

Usage

After installing, this skill will be available to your AI coding assistant.

Verify installation:

npx agent-skills-cli list

Skill Instructions

name: firebase-storage description: | Build with Firebase Cloud Storage - file uploads, downloads, and secure access. Use when: uploading images/files, generating download URLs, implementing file pickers, setting up storage security rules, or troubleshooting storage/unauthorized, cors errors, quota exceeded, or upload failed errors. Prevents 9 documented errors. user-invocable: true

Firebase Cloud Storage

Status: Production Ready Last Updated: 2026-01-25 Dependencies: None (standalone skill) Latest Versions: firebase@12.8.0, firebase-admin@13.6.0

Quick Start (5 Minutes)

1. Initialize Firebase Storage (Client)

// src/lib/firebase.ts
import { initializeApp } from 'firebase/app';
import { getStorage } from 'firebase/storage';

const firebaseConfig = {
  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY,
  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN,
  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
  // ... other config
};

const app = initializeApp(firebaseConfig);
export const storage = getStorage(app);

2. Initialize Firebase Admin Storage (Server)

// src/lib/firebase-admin.ts
import { initializeApp, cert, getApps } from 'firebase-admin/app';
import { getStorage } from 'firebase-admin/storage';

if (!getApps().length) {
  initializeApp({
    credential: cert({
      projectId: process.env.FIREBASE_PROJECT_ID,
      clientEmail: process.env.FIREBASE_CLIENT_EMAIL,
      privateKey: process.env.FIREBASE_PRIVATE_KEY?.replace(/\\n/g, '\n'),
    }),
    storageBucket: process.env.FIREBASE_STORAGE_BUCKET,
  });
}

export const adminStorage = getStorage().bucket();

File Upload (Client SDK)

Basic Upload

import { ref, uploadBytes, getDownloadURL } from 'firebase/storage';
import { storage } from './firebase';

async function uploadFile(file: File, path: string): Promise<string> {
  const storageRef = ref(storage, path);

  // Upload file
  const snapshot = await uploadBytes(storageRef, file);

  // Get download URL
  const downloadURL = await getDownloadURL(snapshot.ref);

  return downloadURL;
}

// Usage
const url = await uploadFile(file, `uploads/${userId}/${file.name}`);

Upload with Progress

import { ref, uploadBytesResumable, getDownloadURL, UploadTask } from 'firebase/storage';
import { storage } from './firebase';

function uploadFileWithProgress(
  file: File,
  path: string,
  onProgress: (progress: number) => void
): Promise<string> {
  return new Promise((resolve, reject) => {
    const storageRef = ref(storage, path);
    const uploadTask = uploadBytesResumable(storageRef, file);

    uploadTask.on(
      'state_changed',
      (snapshot) => {
        const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
        onProgress(progress);
      },
      (error) => {
        reject(error);
      },
      async () => {
        const downloadURL = await getDownloadURL(uploadTask.snapshot.ref);
        resolve(downloadURL);
      }
    );
  });
}

// Usage with React state
const [progress, setProgress] = useState(0);
const url = await uploadFileWithProgress(file, path, setProgress);

Upload with Metadata

import { ref, uploadBytes, getDownloadURL, UploadMetadata } from 'firebase/storage';
import { storage } from './firebase';

async function uploadWithMetadata(file: File, path: string) {
  const storageRef = ref(storage, path);

  const metadata: UploadMetadata = {
    contentType: file.type,
    customMetadata: {
      uploadedBy: userId,
      originalName: file.name,
      uploadTime: new Date().toISOString(),
    },
  };

  const snapshot = await uploadBytes(storageRef, file, metadata);
  const downloadURL = await getDownloadURL(snapshot.ref);

  return { downloadURL, metadata: snapshot.metadata };
}

Upload from Data URL / Base64

import { ref, uploadString, getDownloadURL } from 'firebase/storage';
import { storage } from './firebase';

// Upload base64 string
async function uploadBase64(base64String: string, path: string) {
  const storageRef = ref(storage, path);

  // For data URL (includes prefix like "data:image/png;base64,")
  const snapshot = await uploadString(storageRef, base64String, 'data_url');

  // For raw base64 (no prefix)
  // const snapshot = await uploadString(storageRef, base64String, 'base64');

  const downloadURL = await getDownloadURL(snapshot.ref);
  return downloadURL;
}

File Download

Get Download URL

import { ref, getDownloadURL } from 'firebase/storage';
import { storage } from './firebase';

async function getFileURL(path: string): Promise<string> {
  const storageRef = ref(storage, path);
  const downloadURL = await getDownloadURL(storageRef);
  return downloadURL;
}

Download File as Blob

import { ref, getBlob } from 'firebase/storage';
import { storage } from './firebase';

async function downloadFile(path: string): Promise<Blob> {
  const storageRef = ref(storage, path);
  const blob = await getBlob(storageRef);
  return blob;
}

// Trigger browser download
async function downloadAndSave(path: string, filename: string) {
  const blob = await downloadFile(path);
  const url = URL.createObjectURL(blob);

  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  a.click();

  URL.revokeObjectURL(url);
}

Get File Metadata

import { ref, getMetadata } from 'firebase/storage';
import { storage } from './firebase';

async function getFileMetadata(path: string) {
  const storageRef = ref(storage, path);
  const metadata = await getMetadata(storageRef);

  return {
    name: metadata.name,
    size: metadata.size,
    contentType: metadata.contentType,
    created: metadata.timeCreated,
    updated: metadata.updated,
    customMetadata: metadata.customMetadata,
  };
}

File Management

Delete File

import { ref, deleteObject } from 'firebase/storage';
import { storage } from './firebase';

async function deleteFile(path: string): Promise<void> {
  const storageRef = ref(storage, path);
  await deleteObject(storageRef);
}

List Files in Directory

import { ref, listAll, list, getDownloadURL } from 'firebase/storage';
import { storage } from './firebase';

// List all files in a directory
async function listAllFiles(directoryPath: string) {
  const storageRef = ref(storage, directoryPath);
  const result = await listAll(storageRef);

  const files = await Promise.all(
    result.items.map(async (itemRef) => ({
      name: itemRef.name,
      fullPath: itemRef.fullPath,
      downloadURL: await getDownloadURL(itemRef),
    }))
  );

  const folders = result.prefixes.map((folderRef) => ({
    name: folderRef.name,
    fullPath: folderRef.fullPath,
  }));

  return { files, folders };
}

// Paginated list (for large directories)
async function listFilesPaginated(directoryPath: string, pageSize = 100) {
  const storageRef = ref(storage, directoryPath);
  const result = await list(storageRef, { maxResults: pageSize });

  // Get next page
  if (result.nextPageToken) {
    const nextPage = await list(storageRef, {
      maxResults: pageSize,
      pageToken: result.nextPageToken,
    });
  }

  return result;
}

Update Metadata

import { ref, updateMetadata } from 'firebase/storage';
import { storage } from './firebase';

async function updateFileMetadata(path: string, newMetadata: object) {
  const storageRef = ref(storage, path);
  const updatedMetadata = await updateMetadata(storageRef, {
    customMetadata: newMetadata,
  });
  return updatedMetadata;
}

Server-Side Operations (Admin SDK)

Upload from Server

import { adminStorage } from './firebase-admin';

async function uploadFromServer(
  buffer: Buffer,
  destination: string,
  contentType: string
) {
  const file = adminStorage.file(destination);

  await file.save(buffer, {
    contentType,
    metadata: {
      metadata: {
        uploadedBy: 'server',
        uploadTime: new Date().toISOString(),
      },
    },
  });

  // Make file publicly accessible (if needed)
  await file.makePublic();

  // Get public URL
  const publicUrl = `https://storage.googleapis.com/${adminStorage.name}/${destination}`;

  return publicUrl;
}

Generate Signed URL

import { adminStorage } from './firebase-admin';

async function generateSignedUrl(
  path: string,
  expiresInMinutes = 60
): Promise<string> {
  const file = adminStorage.file(path);

  const [signedUrl] = await file.getSignedUrl({
    action: 'read',
    expires: Date.now() + expiresInMinutes * 60 * 1000,
  });

  return signedUrl;
}

// For uploads (write access)
async function generateUploadUrl(path: string): Promise<string> {
  const file = adminStorage.file(path);

  const [signedUrl] = await file.getSignedUrl({
    action: 'write',
    expires: Date.now() + 15 * 60 * 1000, // 15 minutes
    contentType: 'application/octet-stream',
  });

  return signedUrl;
}

Delete from Server

import { adminStorage } from './firebase-admin';

async function deleteFromServer(path: string): Promise<void> {
  const file = adminStorage.file(path);
  await file.delete();
}

// Delete entire directory
async function deleteDirectory(directoryPath: string): Promise<void> {
  await adminStorage.deleteFiles({
    prefix: directoryPath,
  });
}

Security Rules

Basic Rules Structure

// storage.rules
rules_version = '2';

service firebase.storage {
  match /b/{bucket}/o {

    // Helper functions
    function isAuthenticated() {
      return request.auth != null;
    }

    function isOwner(userId) {
      return request.auth.uid == userId;
    }

    function isValidImage() {
      return request.resource.contentType.matches('image/.*')
        && request.resource.size < 5 * 1024 * 1024; // 5MB
    }

    function isValidDocument() {
      return request.resource.contentType.matches('application/pdf')
        && request.resource.size < 10 * 1024 * 1024; // 10MB
    }

    // User uploads (private to user)
    match /users/{userId}/{allPaths=**} {
      allow read: if isOwner(userId);
      allow write: if isOwner(userId)
        && (isValidImage() || isValidDocument());
    }

    // Public uploads (anyone can read)
    match /public/{allPaths=**} {
      allow read: if true;
      allow write: if isAuthenticated() && isValidImage();
    }

    // Profile pictures
    match /profiles/{userId}/avatar.{ext} {
      allow read: if true;
      allow write: if isOwner(userId)
        && request.resource.contentType.matches('image/.*')
        && request.resource.size < 2 * 1024 * 1024; // 2MB
    }

    // Deny all other access
    match /{allPaths=**} {
      allow read, write: if false;
    }
  }
}

Deploy Rules

firebase deploy --only storage

CORS Configuration

Configure CORS (Required for Web)

Create cors.json:

[
  {
    "origin": ["https://your-domain.com", "http://localhost:3000"],
    "method": ["GET", "PUT", "POST", "DELETE"],
    "maxAgeSeconds": 3600
  }
]

Apply CORS configuration:

gsutil cors set cors.json gs://your-bucket-name.appspot.com

CRITICAL: Without CORS configuration, uploads from browsers will fail with CORS errors.

React Components

File Upload Component

// components/FileUpload.tsx
'use client';

import { useState, useRef } from 'react';
import { ref, uploadBytesResumable, getDownloadURL } from 'firebase/storage';
import { storage } from '@/lib/firebase';

interface FileUploadProps {
  path: string;
  onUploadComplete: (url: string) => void;
  accept?: string;
  maxSize?: number; // in bytes
}

export function FileUpload({
  path,
  onUploadComplete,
  accept = 'image/*',
  maxSize = 5 * 1024 * 1024, // 5MB
}: FileUploadProps) {
  const [uploading, setUploading] = useState(false);
  const [progress, setProgress] = useState(0);
  const [error, setError] = useState<string | null>(null);
  const inputRef = useRef<HTMLInputElement>(null);

  const handleFileChange = async (e: React.ChangeEvent<HTMLInputElement>) => {
    const file = e.target.files?.[0];
    if (!file) return;

    // Validate file size
    if (file.size > maxSize) {
      setError(`File size must be less than ${maxSize / 1024 / 1024}MB`);
      return;
    }

    setError(null);
    setUploading(true);
    setProgress(0);

    try {
      const storageRef = ref(storage, `${path}/${Date.now()}-${file.name}`);
      const uploadTask = uploadBytesResumable(storageRef, file);

      uploadTask.on(
        'state_changed',
        (snapshot) => {
          const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
          setProgress(progress);
        },
        (error) => {
          setError(error.message);
          setUploading(false);
        },
        async () => {
          const downloadURL = await getDownloadURL(uploadTask.snapshot.ref);
          onUploadComplete(downloadURL);
          setUploading(false);
          setProgress(100);
        }
      );
    } catch (err: any) {
      setError(err.message);
      setUploading(false);
    }
  };

  return (
    <div>
      <input
        ref={inputRef}
        type="file"
        accept={accept}
        onChange={handleFileChange}
        disabled={uploading}
        className="hidden"
      />
      <button
        onClick={() => inputRef.current?.click()}
        disabled={uploading}
        className="px-4 py-2 bg-blue-500 text-white rounded disabled:opacity-50"
      >
        {uploading ? `Uploading... ${Math.round(progress)}%` : 'Upload File'}
      </button>
      {error && <p className="text-red-500 mt-2">{error}</p>}
    </div>
  );
}

Image Preview with Upload

// components/ImageUpload.tsx
'use client';

import { useState } from 'react';
import { ref, uploadBytesResumable, getDownloadURL } from 'firebase/storage';
import { storage } from '@/lib/firebase';
import Image from 'next/image';

interface ImageUploadProps {
  currentImage?: string;
  path: string;
  onUploadComplete: (url: string) => void;
}

export function ImageUpload({
  currentImage,
  path,
  onUploadComplete,
}: ImageUploadProps) {
  const [preview, setPreview] = useState<string | null>(currentImage || null);
  const [uploading, setUploading] = useState(false);
  const [progress, setProgress] = useState(0);

  const handleFileChange = async (e: React.ChangeEvent<HTMLInputElement>) => {
    const file = e.target.files?.[0];
    if (!file) return;

    // Show preview immediately
    const reader = new FileReader();
    reader.onloadend = () => {
      setPreview(reader.result as string);
    };
    reader.readAsDataURL(file);

    // Upload
    setUploading(true);
    const storageRef = ref(storage, `${path}/${Date.now()}-${file.name}`);
    const uploadTask = uploadBytesResumable(storageRef, file);

    uploadTask.on(
      'state_changed',
      (snapshot) => {
        setProgress((snapshot.bytesTransferred / snapshot.totalBytes) * 100);
      },
      (error) => {
        console.error('Upload error:', error);
        setUploading(false);
      },
      async () => {
        const downloadURL = await getDownloadURL(uploadTask.snapshot.ref);
        onUploadComplete(downloadURL);
        setUploading(false);
      }
    );
  };

  return (
    <div className="relative w-32 h-32">
      {preview ? (
        <Image
          src={preview}
          alt="Preview"
          fill
          className="object-cover rounded-full"
        />
      ) : (
        <div className="w-full h-full bg-gray-200 rounded-full flex items-center justify-center">
          <span className="text-gray-500">No image</span>
        </div>
      )}

      <label className="absolute bottom-0 right-0 bg-blue-500 text-white p-2 rounded-full cursor-pointer">
        <input
          type="file"
          accept="image/*"
          onChange={handleFileChange}
          disabled={uploading}
          className="hidden"
        />
        {uploading ? `${Math.round(progress)}%` : '+'}
      </label>
    </div>
  );
}

Error Handling

Common Storage Errors

Error Code	Description	Solution
`storage/unauthorized`	User not allowed to access	Check security rules, ensure user authenticated
`storage/canceled`	Upload/download canceled	Handle gracefully, allow retry
`storage/unknown`	Unknown error	Check network, retry with backoff
`storage/object-not-found`	File doesn't exist	Verify path, handle missing files
`storage/bucket-not-found`	Bucket doesn't exist	Check storageBucket config
`storage/quota-exceeded`	Storage quota exceeded	Upgrade plan or delete files
`storage/unauthenticated`	User not authenticated	Sign in user first
`storage/invalid-checksum`	File corrupted during upload	Retry upload
`storage/retry-limit-exceeded`	Too many retries	Check network, try later

Error Handler Utility

export function getStorageErrorMessage(error: any): string {
  const messages: Record<string, string> = {
    'storage/unauthorized': 'You do not have permission to access this file',
    'storage/canceled': 'Upload was canceled',
    'storage/object-not-found': 'File not found',
    'storage/quota-exceeded': 'Storage quota exceeded',
    'storage/unauthenticated': 'Please sign in to upload files',
    'storage/invalid-checksum': 'Upload failed. Please try again',
    'storage/retry-limit-exceeded': 'Upload failed after multiple retries',
  };

  return messages[error.code] || 'An unexpected error occurred';
}

Known Issues Prevention

This skill prevents 9 documented Firebase Storage errors:

Issue #	Error/Issue	Description	How to Avoid	Source
#1	`storage/unauthorized`	Security rules blocking access	Test rules, ensure user authenticated	Common
#2	CORS errors	Browser blocked cross-origin request	Configure CORS with `gsutil cors set`	Docs
#3	Large file timeout	Upload times out	Use `uploadBytesResumable` for large files	Common
#4	Memory issues	Loading large file into memory	Stream large files, use signed URLs	Common
#5	Missing content type	File served with wrong MIME type	Always set `contentType` in metadata	Common
#6	URL expiration	Download URL stops working	Regenerate URLs, use signed URLs for temp access	Common
#7	`storage/quota-exceeded`	Free tier limit reached	Monitor usage, upgrade plan	Common
#8	Private key newline issue	Admin SDK fails to initialize	Use `.replace(/\\n/g, '\n')`	Common
#9	Duplicate uploads	Same file uploaded multiple times	Add timestamp/UUID to filename	Best practice

Best Practices

Always Do

Validate file type and size before upload
Use uploadBytesResumable for large files (supports pause/resume)
Set content type in metadata
Use unique filenames (add timestamp or UUID)
Handle upload errors gracefully with retry
Unsubscribe from upload tasks on component unmount
Configure CORS for web applications
Use security rules to protect files
Generate signed URLs for temporary access

Never Do

Never upload without authentication (unless truly public)
Never trust client-provided file extension (check content type)
Never store sensitive data without encryption
Never expose Admin SDK in client code
Never allow unlimited file sizes (DoS risk)

Firebase CLI Commands

# Initialize Storage
firebase init storage

# Deploy security rules
firebase deploy --only storage

# Start emulator
firebase emulators:start --only storage

Package Versions (Verified 2026-01-25)

{
  "dependencies": {
    "firebase": "^12.8.0"
  },
  "devDependencies": {
    "firebase-admin": "^13.6.0"
  }
}

Official Documentation

Storage Overview: https://firebase.google.com/docs/storage
Web Get Started: https://firebase.google.com/docs/storage/web/start
Upload Files: https://firebase.google.com/docs/storage/web/upload-files
Download Files: https://firebase.google.com/docs/storage/web/download-files
Security Rules: https://firebase.google.com/docs/storage/security
Admin SDK: https://firebase.google.com/docs/storage/admin/start

Last verified: 2026-01-25 | Skill version: 1.0.0

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