ComicScanner

A local HTTPS server for scanning comic book barcodes via a mobile browser. Point your phone camera at a comic's barcode — the app decodes it into a standardized 17 or 18 digit string and returns it to your application.

This package does one thing: scan barcodes and produce the result. What you do with the result (API lookups, database writes, etc.) is up to you.

Screenshot

Example screenshot (Pixel 8 Pro on Chrome for Android).

Barcode format

Comics use two barcodes printed together:

Type	Format	Length
Single-issue	UPC-A (12) + EAN-5 supplement (5)	17 digits
Trade paperback	EAN-13/ISBN 978–979 (13) + EAN-5 supplement (5)	18 digits

The EAN-5 supplement encodes issue number (digits 1–3), cover variant (4), and printing number (5).

Requirements

• Go 1.26+
• mkcert for local TLS certificates
• just (optional, for the provided task runner)

HTTPS is required because browsers only grant camera access on secure origins.

Setup

just setup        # installs mkcert, creates local CA, generates certificate
just run          # starts the server

Or manually:

mkcert -install
mkcert -cert-file server.pem -key-file server-key.pem <YOUR_LOCAL_IP> localhost
go run ./cmd/

Open https://<YOUR_LOCAL_IP>:8080/scanner on your phone.

Once running, a QR code is printed to the terminal — scan it with your phone to open the scanner directly.

Trusting the certificate on your phone

The scanner uses a locally-signed certificate. Your phone needs to trust the root CA once.

Android:

1. Run just ca-path to find the rootCA.pem file
2. Copy it to your phone (download via USB, email, etc. — it must be saved locally before importing, not opened directly from cloud storage)
3. Settings → Security → Encryption & credentials → Install a certificate → CA certificate

iOS:

1. AirDrop or email the rootCA.pem to yourself
2. Settings → General → VPN & Device Management → install the profile
3. Settings → General → About → Certificate Trust Settings → enable the CA

Usage as a library

import "github.com/madhatter/comicscanner"

cfg := scanner.Config{
    Port:     ":8080",
    CertFile: "server.pem",
    KeyFile:  "server-key.pem",
}

// Stream: receive each scan as it comes in
results, err := scanner.StartStream(ctx, cfg)
for r := range results {
    fmt.Println(r.Barcode)      // full 17 or 18 digit string
    fmt.Println(r.SKU())        // main barcode without supplement
    fmt.Println(r.Supplement()) // 5-digit EAN-5 addon
}

// One-shot: block until a single barcode is scanned
result, err := scanner.Start(ctx, cfg)

API reference

Config

Field	Description
Port	Listen address, e.g. ":8080"
CertFile	Path to TLS certificate
KeyFile	Path to TLS private key

Result

Method/Field	Returns
result.Barcode	Full scanned code (17 or 18 digits)
result.Type()	BarcodeTypeComic, BarcodeTypeTradePaperback, or BarcodeTypeUnknown
result.SKU()	Main barcode without supplement (12 or 13 digits)
result.Supplement()	5-digit EAN-5 addon
result.ScannedAt	time.Time of when the server received the scan