One-time download links are essential for scenarios requiring high privacy or compliance sensitivity: sharing confidential attachments, temporary credentials, private contracts, and sensitive documents. While tfLink provides the infrastructure for temporary file storage with API/CLI capabilities, implementing true "download-once-and-destroy" functionality requires strategic implementation approaches that we'll explore in this comprehensive guide.

Understanding One-Time File Sharing

One-time file sharing goes beyond simple temporary storage. It ensures that files can only be accessed once, providing an additional layer of security for sensitive information. This is particularly important for:

• Legal documents - Contracts, NDAs, and confidential agreements
• Temporary credentials - API keys, passwords, and access tokens
• Medical records - HIPAA-compliant document sharing
• Financial data - Reports, statements, and sensitive financial information
• Security audits - Vulnerability reports and penetration testing results

Three Implementation Approaches

Approach A: Platform Native Support (Simplest)

Approach B: Self-Built Proxy (Most Flexible, Recommended)

Node.js Proxy Implementation Example

const express = require('express');
const multer = require('multer');
const FormData = require('form-data');
const fetch = require('node-fetch');
const { v4: uuidv4 } = require('uuid');

const app = express();
const upload = multer({ storage: multer.memoryStorage() });

// In-memory token store (use Redis in production)
const tokenStore = new Map();

// Upload endpoint
app.post('/upload-once', upload.single('file'), async (req, res) => {
    try {
        // Upload to tfLink
        const formData = new FormData();
        formData.append('file', req.file.buffer, req.file.originalname);

        const tfLinkResponse = await fetch('https://tmpfile.link/api/upload', {
            method: 'POST',
            body: formData
        });

        const tfLinkData = await tfLinkResponse.json();

        // Generate one-time token
        const token = uuidv4();
        tokenStore.set(token, {
            downloadLink: tfLinkData.downloadLink,
            fileName: tfLinkData.fileName,
            createdAt: new Date(),
            expiresAt: new Date(Date.now() + 24 * 60 * 60 * 1000) // 24 hours
        });

        res.json({
            oneTimeLink: `https://yourapp.com/download/${token}`,
            expiresAt: tokenStore.get(token).expiresAt
        });
    } catch (error) {
        res.status(500).json({ error: 'Upload failed' });
    }
});

// One-time download endpoint
app.get('/download/:token', async (req, res) => {
    const { token } = req.params;
    const tokenData = tokenStore.get(token);

    if (!tokenData) {
        return res.status(410).json({ error: 'Link expired or already used' });
    }

    if (new Date() > tokenData.expiresAt) {
        tokenStore.delete(token);
        return res.status(410).json({ error: 'Link expired' });
    }

    // Immediately delete token to ensure one-time use
    tokenStore.delete(token);

    // Redirect to actual file
    res.redirect(tokenData.downloadLink);
});

app.listen(3000, () => {
    console.log('One-time link service running on port 3000');
});

Approach C: Client-Side Encryption + Short-Term Sharing (Most Secure)

Security Implementation Details

Essential Security Measures

• Short TTL: Combine one-time access with time limits (1-24 hours)
• Rate Limiting: Prevent brute force attacks on token endpoints
• IP Restrictions: Optionally bind links to specific IP addresses
• HTTPS Only: Ensure all transmissions are encrypted
• Secure Token Generation: Use cryptographically secure random tokens
• Audit Logging: Log all access attempts and download events

Advanced Security Features

// Enhanced token with additional security
const createSecureToken = (options = {}) => {
    const token = crypto.randomBytes(32).toString('hex');

    return {
        token,
        downloadLink: options.downloadLink,
        maxDownloads: options.maxDownloads || 1,
        downloadCount: 0,
        allowedIPs: options.allowedIPs || null,
        password: options.password || null,
        expiresAt: new Date(Date.now() + (options.ttlMinutes || 60) * 60 * 1000),
        createdAt: new Date(),
        createdBy: options.userId || 'anonymous'
    };
};

Production Deployment Considerations

Storage Backend

For production deployments, replace in-memory storage with persistent solutions:

• Redis: Fast access, automatic expiration, distributed caching
• Database: PostgreSQL or MongoDB for audit trails and complex queries
• Cloudflare KV: Serverless edge storage for global distribution

Monitoring and Alerts

// Example monitoring setup
const logAccess = (event, data) => {
    console.log(JSON.stringify({
        timestamp: new Date().toISOString(),
        event,
        tokenId: data.token,
        ip: data.ip,
        userAgent: data.userAgent,
        success: data.success
    }));

    // Send to monitoring service
    if (data.suspicious) {
        alertSecurityTeam(data);
    }
};

Compliance and Legal Considerations

GDPR Compliance

For EU users, ensure your one-time sharing system complies with GDPR:

• Document data processing purposes
• Implement data deletion requests
• Maintain minimal necessary logs
• Provide clear privacy notices

HIPAA Considerations

For healthcare data, additional measures are required:

• Business Associate Agreements (BAAs)
• Enhanced audit trails
• Encrypted storage and transmission
• Access controls and user authentication

Integration Examples

Workflow Management Integration

// Example: Integrate with workflow system
const createWorkflowLink = async (fileData, workflowId) => {
    const response = await fetch('/upload-once', {
        method: 'POST',
        body: fileData
    });

    const { oneTimeLink } = await response.json();

    // Update workflow with secure link
    await updateWorkflow(workflowId, {
        documentLink: oneTimeLink,
        linkCreated: new Date(),
        accessType: 'one-time'
    });

    return oneTimeLink;
};

Email Integration

// Secure email notification
const sendSecureDocument = async (recipientEmail, fileName, oneTimeLink) => {
    const emailTemplate = `
        A secure document has been shared with you: ${fileName}

        Download link (expires after one use or 24 hours): ${oneTimeLink}

        Security Notice: This link will only work once. Please download immediately.
        Do not share this link with others.
    `;

    await sendEmail({
        to: recipientEmail,
        subject: `Secure Document: ${fileName}`,
        body: emailTemplate
    });
};

Testing and Validation

Security Testing Checklist

• ✅ Verify tokens are truly single-use
• ✅ Test expiration timing accuracy
• ✅ Validate rate limiting effectiveness
• ✅ Check for token enumeration vulnerabilities
• ✅ Verify IP restrictions work correctly
• ✅ Test concurrent access scenarios
• ✅ Validate audit log completeness

Performance Optimization

Caching Strategy

// Efficient token validation with caching
const validateToken = async (token) => {
    // Check local cache first
    let tokenData = await cache.get(`token:${token}`);

    if (!tokenData) {
        // Fallback to database
        tokenData = await database.getToken(token);
        if (tokenData && !tokenData.used) {
            // Cache for short time
            await cache.set(`token:${token}`, tokenData, 300); // 5 minutes
        }
    }

    return tokenData;
};

Real-World Use Cases

Legal Firm Document Sharing

A law firm needs to share confidential client documents with external parties:

• Generate one-time links for each document
• Set 2-hour expiration windows
• Require password protection for highly sensitive files
• Maintain complete audit trails for compliance

Software Release Management

Distributing beta software to selected testers:

• One-time download links prevent unauthorized redistribution
• Track which testers have downloaded the software
• Automatic expiration after release deadline

Medical Records Transfer

Secure patient data sharing between healthcare providers:

• HIPAA-compliant one-time access
• Patient consent tracking
• Automatic deletion after viewing
• Encrypted storage and transmission