fix: ensure config does not have duplicate hosts

.golangci.yml

@@ -6,7 +6,10 @@ linters:
   disable-all: true
   enable:
     - bodyclose
+    - errname
+    - errorlint
     - errcheck
+    - exhaustive
     - gofumpt
     - gosec
     - gosimple

config/config.go

@@ -17,6 +17,7 @@ var (
 	errInvalidConfig      = fmt.Errorf("invalid config")
 	errMustHaveOneService = fmt.Errorf("must have exactly one service")
 	errNoServiceWithName  = fmt.Errorf("no service with name")
+	errDuplicateHost      = fmt.Errorf("duplicate host")
 )
 
 type serviceMap map[string]struct {
@@ -32,11 +33,19 @@ type Config struct {
 	ReadTimeout time.Duration  `yaml:"readTimeout"`
 }
 
+// validate returns true if every service has exactly one service and
+// there are no duplicate hosts.
 func (s *serviceMap) validate() error {
+	hosts := make(map[string]bool)
 	for name, service := range *s {
 		if !service.Services.Validate() {
 			return fmt.Errorf("%s: %w", name, errMustHaveOneService)
 		}
+
+		if _, ok := hosts[service.Host]; ok {
+			return fmt.Errorf("%w %s", errDuplicateHost, service.Host)
+		}
+		hosts[service.Host] = true
 	}
 	return nil
 }

config/config_test.go

@@ -81,6 +81,19 @@ func TestServiceMapValidate(t *testing.T) {
 			},
 			errMustHaveOneService,
 		},
+		"services with duplicate host": {
+			serviceMap{
+				"a": {
+					Config:   services.Config{Host: "b"},
+					Services: services.Services{Redirect: "c"},
+				},
+				"d": {
+					Config:   services.Config{Host: "b"},
+					Services: services.Services{Redirect: "c"},
+				},
+			},
+			errDuplicateHost,
+		},
 	}
 	for name, test := range tests {
 		t.Run(name, func(t *testing.T) {
@@ -410,7 +423,7 @@ func TestConfigServiceListWithContainers(t *testing.T) {
 	}
 }
 
-func TestServiceListLoadBalancerError(t *testing.T) {
+func TestConfigServiceListLoadBalancerError(t *testing.T) {
 	tests := map[string]struct {
 		lbInfo services.LoadBalancerInfo
 	}{
@@ -453,27 +466,6 @@ func TestServiceListLoadBalancerError(t *testing.T) {
 	}
 }
 
-func TestServiceList(t *testing.T) {
-	conf := Config{
-		Services: serviceMap{
-			"foo": {
-				Config: services.Config{Host: "a"},
-				Services: services.Services{
-					LoadBalancer: &services.LoadBalancerInfo{
-						Strategy: "not a valid strategy",
-					},
-				},
-			},
-		},
-	}
-
-	_, err := conf.ServiceList(dockerapi.NewMock(nil))
-
-	if !errors.Is(err, errInvalidConfig) {
-		t.Errorf("expected error %v got error %v", errInvalidConfig, err)
-	}
-}
-
 func TestConfigTLSHosts(t *testing.T) {
 	tests := map[string]struct {
 		conf     Config