[Backend] Complete Vaccination Certificate PDF Generation and Download Endpoint

[llinsss]

⚠️ This is a backend issue — work is done inside the backend/ folder

Description

backend/src/modules/certificates/certificates.service.ts imports PDFDocument from pdfkit and defines a VaccinationCertificate interface, but the PDF generation method is incomplete — it builds the document structure but never writes the pet owner section, vet clinic stamp, or QR code verification link. The resulting PDF is missing critical information.

Current State

• CertificatesService — partial PDF generation, missing owner/clinic/QR sections
• VaccinationCertificate interface — fully defined with all required fields
• No GET /certificates/:id/download endpoint exists
• No certificate storage — PDFs are generated on-the-fly but not cached

What Needs to Be Built

1. Complete PDF Layout

The generated PDF must include:

• Header: PetChain logo, certificate title, issue date
• Pet Section: name, species, breed, DOB, microchip number
• Vaccination Section: vaccine name, administered date, expiry date, batch number, manufacturer
• Veterinarian Section: vet name, clinic name, address, phone
• Owner Section: owner name, email (currently missing)
• QR Code: scannable link to /verify/{certificateCode} for tamper-proof verification
• Footer: certificate code, blockchain anchor hash (if available)

2. QR Code Embedding

• Use qrcode package (already used in MedicalRecordsService) to generate QR as PNG buffer
• Embed QR image into PDF using pdfkit's image() method

3. Download Endpoint

GET /certificates/:vaccinationId/download

• Generate or retrieve cached PDF
• Stream response with headers:
  Content-Type: application/pdf
Content-Disposition: attachment; filename=certificate-{code}.pdf

4. Caching

• Cache generated PDFs in S3/CDN via StorageModule
• Invalidate cache if vaccination record is updated

Acceptance Criteria

• PDF contains all sections: pet, vaccination, vet, owner, QR code, footer
• QR code links to a valid verification URL
• GET /certificates/:vaccinationId/download streams the PDF correctly
• Generated PDFs are cached and reused on subsequent requests
• Cache is invalidated when the vaccination record changes
• Integration test verifies PDF is non-empty and contains expected text

Files to Modify

• backend/src/modules/certificates/certificates.service.ts
• backend/src/modules/certificates/certificates.controller.ts (add download endpoint)
• backend/src/modules/certificates/certificates.module.ts (import StorageModule)

Priority

Medium — certificates are a key trust feature for vet visits and travel

Estimated Effort

2 days

[sevencat2004]

@sevencat2004 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I would love to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sevencat2004 to this issue.

[ndii-dev]

@ndii-dev has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ndii-dev to this issue.

[drips-wave]

Congratulations, @ndii-dev! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @ndii-dev: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

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