feat(publicip): support custom API url echoip#https://... (#2529)

internal/publicip/api/api.go

@@ -3,7 +3,11 @@ package api
 import (
 	"errors"
 	"fmt"
+	"maps"
 	"net/http"
+	"net/url"
+	"regexp"
+	"slices"
 	"strings"
 )
 
@@ -16,6 +20,8 @@ const (
 	IP2Location Provider = "ip2location"
 )
 
+const echoipPrefix = "echoip#"
+
 type NameToken struct {
 	Name  string
 	Token string
@@ -30,15 +36,19 @@ func New(nameTokenPairs []NameToken, client *http.Client) (
 		if err != nil {
 			return nil, fmt.Errorf("parsing API name: %w", err)
 		}
-		switch provider {
-		case Cloudflare:
+		switch {
+		case provider == Cloudflare:
 			fetchers[i] = newCloudflare(client)
-		case IfConfigCo:
-			fetchers[i] = newIfConfigCo(client)
-		case IPInfo:
+		case provider == IfConfigCo:
+			const ifConfigCoURL = "https://ifconfig.co"
+			fetchers[i] = newEchoip(client, ifConfigCoURL)
+		case provider == IPInfo:
 			fetchers[i] = newIPInfo(client, nameTokenPair.Token)
-		case IP2Location:
+		case provider == IP2Location:
 			fetchers[i] = newIP2Location(client, nameTokenPair.Token)
+		case strings.HasPrefix(string(provider), echoipPrefix):
+			url := strings.TrimPrefix(string(provider), echoipPrefix)
+			fetchers[i] = newEchoip(client, url)
 		default:
 			panic("provider not valid: " + provider)
 		}
@@ -46,20 +56,88 @@ func New(nameTokenPairs []NameToken, client *http.Client) (
 	return fetchers, nil
 }
 
+var regexEchoipURL = regexp.MustCompile(`^http(s|):\/\/.+$`)
+
 var ErrProviderNotValid = errors.New("API name is not valid")
 
 func ParseProvider(s string) (provider Provider, err error) {
-	switch strings.ToLower(s) {
-	case "cloudflare":
-		return Cloudflare, nil
-	case string(IfConfigCo):
-		return IfConfigCo, nil
-	case "ipinfo":
-		return IPInfo, nil
-	case "ip2location":
-		return IP2Location, nil
-	default:
-		return "", fmt.Errorf(`%w: %q can only be "cloudflare", "ifconfigco", "ip2location" or "ipinfo"`,
-			ErrProviderNotValid, s)
+	possibleProviders := []Provider{
+		Cloudflare,
+		IfConfigCo,
+		IP2Location,
+		IPInfo,
 	}
+	stringToProvider := make(map[string]Provider, len(possibleProviders))
+	for _, provider := range possibleProviders {
+		stringToProvider[string(provider)] = provider
+	}
+	provider, ok := stringToProvider[strings.ToLower(s)]
+	if ok {
+		return provider, nil
+	}
+
+	customPrefixToURLRegex := map[string]*regexp.Regexp{
+		echoipPrefix: regexEchoipURL,
+	}
+	for prefix, urlRegex := range customPrefixToURLRegex {
+		match, err := checkCustomURL(s, prefix, urlRegex)
+		if !match {
+			continue
+		} else if err != nil {
+			return "", err
+		}
+		return Provider(s), nil
+	}
+
+	providerStrings := make([]string, 0, len(stringToProvider)+len(customPrefixToURLRegex))
+	for _, providerString := range slices.Sorted(maps.Keys(stringToProvider)) {
+		providerStrings = append(providerStrings, `"`+providerString+`"`)
+	}
+	for _, prefix := range slices.Sorted(maps.Keys(customPrefixToURLRegex)) {
+		providerStrings = append(providerStrings, "a custom "+prefix+" url")
+	}
+
+	return "", fmt.Errorf(`%w: %q can only be %s`,
+		ErrProviderNotValid, s, orStrings(providerStrings))
+}
+
+var ErrCustomURLNotValid = errors.New("custom URL is not valid")
+
+func checkCustomURL(s, prefix string, regex *regexp.Regexp) (match bool, err error) {
+	if !strings.HasPrefix(s, prefix) {
+		return false, nil
+	}
+	s = strings.TrimPrefix(s, prefix)
+	_, err = url.Parse(s)
+	if err != nil {
+		return true, fmt.Errorf("%s %w: %w", prefix, ErrCustomURLNotValid, err)
+	}
+
+	if regex.MatchString(s) {
+		return true, nil
+	}
+
+	return true, fmt.Errorf("%s %w: %q does not match regular expression: %s",
+		prefix, ErrCustomURLNotValid, s, regex)
+}
+
+func orStrings(strings []string) (result string) {
+	return joinStrings(strings, "or")
+}
+
+func joinStrings(strings []string, lastJoin string) (result string) {
+	if len(strings) == 0 {
+		return ""
+	}
+
+	result = strings[0]
+	for i := 1; i < len(strings); i++ {
+		if i < len(strings)-1 {
+			result += ", " + strings[i]
+		} else {
+			result += " " + lastJoin + " " + strings[i]
+		}
+	}
+
+	return result
 }