Building a DNS Email Validation Service with Cloudflare Workers & ApyHub API

• Receive and parse the CSV file of email addresses
• Validate the email address and assign it to a category. ( validEmails and invalidEmails)
• After all, emails are processed, the function generates and returns a new output CSV file that contains valid and invalid email addresses.

1. Standard IDE ( VSCode/Sublime)
2. Node.js installed on your computer.
3. An account with Cloudflare Workers.
4. An API key from ApyHub after signing up for their DNS Email Validation API

Want to test the API beforehand?

PART 1: Setting Up Your Project

Step 1: Create a new directory for your project and navigate into it:

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cloudflare-email-validator
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cd cloudflare-email-validator

Step 2: Install the Wrangler package

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npm install wrangler --save-dev

Step 3: Create a new Worker project

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npm create cloudflare@latest

• In which directory do you want to create your application? Write email-validation-worker and press Enter.
• What type of application do you want to create? Select Hello World worker and press Enter.
• Do you want to use TypeScript? Select Yes and press Enter.
• Do you want to deploy your application? Select Yes, you will be asked to authenticate using your Cloudflare account (if not logged in already)

PART 2: Writing a Serverless Function

Step 1: Handling the Incoming Request

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export default {
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	async fetch(request: Request, env: any, ctx: any): Promise<Response> {
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		if (request.method !== 'POST') {
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            return new Response('Expected POST',{ status: 405 });
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   }

Step 2: Parsing the Uploaded CSV File

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const formData = await request.formData();
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const file = formData.get('file');
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if (!file || !(file instanceof File)) {
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    return new Response('No file uploaded', { status: 400 });
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}
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// The content of the file is read as text, and each line is split into individual email addresses. 
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// Empty lines are filtered out.
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const text = await file.text();
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const emails = text.split('\n').map(email => email.trim()).filter(email => email !== '');

Step 3: Validating Emails in Batches

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for (let i = 0; i < emails.length; i++) {
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            const email = emails[i];
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            const result : any = await this.validateEmail(email);
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            if (result.data) {
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                validEmails.push(email);
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            } else {
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                invalidEmails.push(email);
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            }
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            // Wait for 1 second before processing the next email
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            await new Promise(resolve => setTimeout(resolve, 1000))
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}

Step 5: Generating a New CSV File

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let csvContent = 'Emails,Invalid Emails\n';
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emails.forEach((email, index) => {
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    csvContent += `${email},${invalidEmails[index]}\n`;
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});
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//`csvContent` is then returned as a response with the appropriate headers to indicate the content type as CSV and to prompt the user to download the file named `email_validation_result.csv.`
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return new Response(csvContent.replaceAll('undefined', ''), {
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    headers: {
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        'Content-Type': 'text/csv',
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        'Content-Disposition': 'attachment; filename="email_validation_result.csv"'
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    }
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});

Step 6: Validating an Email with ApyHub's API

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const apiResponse = await fetch('https://api.apyhub.com/validate/email/dns', {
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    method: 'POST',
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    headers: {
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        'Content-Type': 'application/json',
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        'apy-token': 'YOUR_SECRET_API_KEY' //provide your secret-token-here
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    },
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    body: JSON.stringify({email})
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});

Step 7: Testing Your Function

Step 8: Deploy your function to Cloudflare Workers.

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npx wrangler deploy

That's it! 👏

References: