fix(settings): validation for DoH and DoT providers

internal/config/settings/doh.go

@@ -1,7 +1,6 @@
 package settings
 
 import (
-	"errors"
 	"fmt"
 	"time"
 
@@ -30,21 +29,10 @@ func (d *DoH) setDefaults() {
 	d.Self.setDefaults()
 }
 
-var (
-	ErrDoHProviderNotValid = errors.New("DoH provider is not valid")
-)
-
 func (d *DoH) validate() (err error) {
-	allProviders := provider.All()
-	allProvidersSet := make(map[string]struct{}, len(allProviders))
-	for _, provider := range allProviders {
-		allProvidersSet[provider.Name] = struct{}{}
-	}
-
-	for _, provider := range d.DoHProviders {
-		if _, ok := allProvidersSet[provider]; !ok {
-			return fmt.Errorf("%w: %s", ErrDoHProviderNotValid, provider)
-		}
+	err = checkProviderNames(d.DoHProviders)
+	if err != nil {
+		return fmt.Errorf("DoH provider: %w", err)
 	}
 
 	const minTimeout = time.Millisecond

internal/config/settings/dot.go

@@ -43,24 +43,18 @@ func (d *DoT) setDefaults() {
 }
 
 var (
-	ErrTimeoutTooSmall     = errors.New("timeout is too small")
-	ErrDoTProviderNotValid = errors.New("DoT provider is not valid")
-	ErrDNSProviderNotValid = errors.New("plaintext DNS provider is not valid")
+	ErrTimeoutTooSmall = errors.New("timeout is too small")
 )
 
 func (d *DoT) validate() (err error) {
-	allProvidersSet := allProvidersStringSet()
-
-	for _, provider := range d.DoTProviders {
-		if _, ok := allProvidersSet[provider]; !ok {
-			return fmt.Errorf("%w: %s", ErrDoTProviderNotValid, provider)
-		}
+	err = checkProviderNames(d.DoTProviders)
+	if err != nil {
+		return fmt.Errorf("DoT provider: %w", err)
 	}
 
-	for _, provider := range d.DNSProviders {
-		if _, ok := allProvidersSet[provider]; !ok {
-			return fmt.Errorf("%w: %s", ErrDNSProviderNotValid, provider)
-		}
+	err = checkProviderNames(d.DNSProviders)
+	if err != nil {
+		return fmt.Errorf("fallback DNS plaintext provider: %w", err)
 	}
 
 	const minTimeout = time.Millisecond

internal/config/settings/helpers.go

@@ -1,6 +1,14 @@
 package settings
 
 func andStrings(strings []string) (result string) {
+	return joinStrings(strings, "and")
+}
+
+func orStrings(strings []string) (result string) {
+	return joinStrings(strings, "or")
+}
+
+func joinStrings(strings []string, lastJoin string) (result string) {
 	if len(strings) == 0 {
 		return ""
 	}
@@ -10,7 +18,7 @@ func andStrings(strings []string) (result string) {
 		if i < len(strings)-1 {
 			result += strings[i] + ", "
 		} else {
-			result += " and " + strings[i]
+			result += " " + lastJoin + " " + strings[i]
 		}
 	}
 

internal/config/settings/validation.go

@@ -40,11 +40,26 @@ func checkListeningAddress(address string) (err error) {
 	return err
 }
 
-func allProvidersStringSet() (set map[string]struct{}) {
-	providers := provider.All()
-	set = make(map[string]struct{}, len(providers))
-	for _, provider := range providers {
-		set[provider.Name] = struct{}{}
+func checkProviderNames(providerNames []string) (err error) {
+	allProviders := provider.All()
+	allProviderNames := make([]string, len(allProviders))
+	for i, provider := range allProviders {
+		allProviderNames[i] = provider.Name
 	}
-	return set
+
+	for _, providerName := range providerNames {
+		valid := false
+		for _, acceptedProviderName := range allProviderNames {
+			if strings.EqualFold(providerName, acceptedProviderName) {
+				valid = true
+				break
+			}
+		}
+		if !valid {
+			return fmt.Errorf("%w: %q must be one of: %s",
+				ErrValueNotOneOf, providerName, orStrings(allProviderNames))
+		}
+	}
+
+	return nil
 }