VoCat/internal/device/carrier_db.go

package device

import (
	_ "embed"
	"encoding/json"
	"strings"
)

// The offline table is generated by scripts/update-carriers.py from Android's
// versioned carrier ID database, with the previous global table retained as a
// fallback for PLMNs that Android does not yet catalogue.
//
//go:embed mccmnc.json
var carrierDatabaseJSON []byte

type carrierDatabase struct {
	Carriers map[string][]string `json:"c"`
}

var globalCarrierDatabase = func() carrierDatabase {
	var database carrierDatabase
	if err := json.Unmarshal(carrierDatabaseJSON, &database); err != nil {
		panic("device: invalid embedded MCC/MNC database: " + err.Error())
	}
	return database
}()

// CarrierForPLMN returns the offline carrier display name and ISO alpha-2
// country/territory code for a numeric five- or six-digit PLMN.
func CarrierForPLMN(plmn string) (name, countryCode string, ok bool) {
	plmn = strings.TrimSpace(plmn)
	if !decimalDigits(plmn, 5, 6) {
		return "", "", false
	}
	entry, ok := globalCarrierDatabase.Carriers[plmn]
	if !ok || len(entry) == 0 || strings.TrimSpace(entry[0]) == "" {
		return "", "", false
	}
	name = strings.TrimSpace(entry[0])
	if len(entry) > 1 {
		countryCode = strings.ToUpper(strings.TrimSpace(entry[1]))
	}
	return name, countryCode, true
}