chore: Refactor IP address retrieval logic in main.go

main.go

@@ -154,25 +154,30 @@ func updateDatabase(urlTemplate, dstFilename string, updateFunc func(*maxminddb.
 var invalidIPBytes = []byte("Please provide a valid IP address.")
 
 type dataStruct struct {
-	IP            string `json:"ip"`
+	IP            *string `json:"ip"`
-	Hostname      string `json:"hostname"`
+	Hostname      *string `json:"hostname"`
-	ASN           string `json:"asn"`
+	ASN           *string `json:"asn"`
-	Organization  string `json:"organization"`
+	Organization  *string `json:"organization"`
-	City          string `json:"city"`
+	City          *string `json:"city"`
-	Region        string `json:"region"`
+	Region        *string `json:"region"`
-	Country       string `json:"country"`
+	Country       *string `json:"country"`
-	CountryFull   string `json:"country_full"`
+	CountryFull   *string `json:"country_full"`
-	Continent     string `json:"continent"`
+	Continent     *string `json:"continent"`
-	ContinentFull string `json:"continent_full"`
+	ContinentFull *string `json:"continent_full"`
-	Loc           string `json:"loc"`
+	Loc           *string `json:"loc"`
 }
 
 func handler(w http.ResponseWriter, r *http.Request) {
 	requestedThings := strings.Split(r.URL.Path, "/")
 
-	var IPAddress string
+	var IPAddress, field string
-	if len(requestedThings) > 1 {
+	if len(requestedThings) > 1 && net.ParseIP(requestedThings[1]) != nil {
 		IPAddress = requestedThings[1]
+		if len(requestedThings) > 2 {
+			field = requestedThings[2]
+		}
+	} else if len(requestedThings) > 1 {
+		field = requestedThings[1]
 	}
 
 	if IPAddress == "" || IPAddress == "self" {
@@ -192,6 +197,19 @@ func handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if field != "" {
+		value := getField(data, field)
+		if value != nil {
+			w.Header().Set("Content-Type", "application/json; charset=utf-8")
+			json.NewEncoder(w).Encode(map[string]*string{field: value})
+			return
+		} else {
+			w.Header().Set("Content-Type", "application/json; charset=utf-8")
+			json.NewEncoder(w).Encode(map[string]*string{field: nil})
+			return
+		}
+	}
+
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
 	callback := r.URL.Query().Get("callback")
 	enableJSONP := callback != "" && len(callback) < 2000 && callbackJSONP.MatchString(callback)
@@ -209,6 +227,35 @@ func handler(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func getField(data *dataStruct, field string) *string {
+	switch field {
+	case "ip":
+		return data.IP
+	case "hostname":
+		return data.Hostname
+	case "asn":
+		return data.ASN
+	case "organization":
+		return data.Organization
+	case "city":
+		return data.City
+	case "region":
+		return data.Region
+	case "country":
+		return data.Country
+	case "country_full":
+		return data.CountryFull
+	case "continent":
+		return data.Continent
+	case "continent_full":
+		return data.ContinentFull
+	case "loc":
+		return data.Loc
+	default:
+		return nil
+	}
+}
+
 func getRealIP(r *http.Request) string {
 	if realIP := r.Header.Get("CF-Connecting-IP"); realIP != "" {
 		return realIP
@@ -264,26 +311,34 @@ func lookupIPData(ip net.IP) *dataStruct {
 		hostname = []string{""}
 	}
 
-	var sd string
+	var sd *string
 	if len(cityRecord.Subdivisions) > 0 {
-		sd = cityRecord.Subdivisions[0].Names["en"]
+		name := cityRecord.Subdivisions[0].Names["en"]
+		sd = &name
 	}
 
 	return &dataStruct{
-		IP:            ip.String(),
+		IP:            toPtr(ip.String()),
-		Hostname:      strings.TrimSuffix(hostname[0], "."),
+		Hostname:      toPtr(strings.TrimSuffix(hostname[0], ".")),
-		ASN:           fmt.Sprintf("%d", asnRecord.AutonomousSystemNumber),
+		ASN:           toPtr(fmt.Sprintf("%d", asnRecord.AutonomousSystemNumber)),
-		Organization:  asnRecord.AutonomousSystemOrganization,
+		Organization:  toPtr(asnRecord.AutonomousSystemOrganization),
-		Country:       cityRecord.Country.IsoCode,
+		Country:       toPtr(cityRecord.Country.IsoCode),
-		CountryFull:   cityRecord.Country.Names["en"],
+		CountryFull:   toPtr(cityRecord.Country.Names["en"]),
-		City:          cityRecord.City.Names["en"],
+		City:          toPtr(cityRecord.City.Names["en"]),
 		Region:        sd,
-		Continent:     cityRecord.Continent.Code,
+		Continent:     toPtr(cityRecord.Continent.Code),
-		ContinentFull: cityRecord.Continent.Names["en"],
+		ContinentFull: toPtr(cityRecord.Continent.Names["en"]),
-		Loc:           fmt.Sprintf("%.4f,%.4f", cityRecord.Location.Latitude, cityRecord.Location.Longitude),
+		Loc:           toPtr(fmt.Sprintf("%.4f,%.4f", cityRecord.Location.Latitude, cityRecord.Location.Longitude)),
 	}
 }
 
+func toPtr(s string) *string {
+	if s == "" {
+		return nil
+	}
+	return &s
+}
+
 var callbackJSONP = regexp.MustCompile(`^[a-zA-Z_\$][a-zA-Z0-9_\$]*$`)
 
 // Extract the IP address from a string, removing unwanted characters.