feat: support newline and comma-whitespace external host lists for auto-discovery (#468)

server/docker.go

@@ -199,7 +199,7 @@ func (w *dockerWatcherImpl) parseContainerData(container *dockertypes.Container)
 					Warnf("ignoring container with duplicate %s label", DockerRouterLabelHost)
 				return
 			}
-			data.hosts = strings.Split(value, ",")
+			data.hosts = SplitExternalHosts(value)
 		}
 
 		if key == DockerRouterLabelPort {

server/docker_swarm.go

@@ -247,7 +247,7 @@ func (w *dockerSwarmWatcherImpl) parseServiceData(service *swarm.Service, networ
 					Warnf("ignoring service with duplicate %s", DockerRouterLabelHost)
 				return
 			}
-			data.hosts = strings.Split(value, ",")
+			data.hosts = SplitExternalHosts(value)
 		}
 		if key == DockerRouterLabelPort {
 			if data.port != 0 {

server/k8s.go

@@ -3,6 +3,10 @@ package server
 import (
 	"context"
 	"fmt"
+	"net"
+	"strconv"
+	"sync"
+
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	apps "k8s.io/api/apps/v1"
@@ -14,10 +18,6 @@ import (
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/client-go/tools/clientcmd"
-	"net"
-	"strconv"
-	"strings"
-	"sync"
 )
 
 const (
@@ -238,7 +238,7 @@ func (w *K8sWatcher) extractRoutableServices(obj interface{}) []*routableService
 
 	routableServices := make([]*routableService, 0)
 	if externalServiceName, exists := service.Annotations[AnnotationExternalServerName]; exists {
-		serviceNames := strings.Split(externalServiceName, ",")
+		serviceNames := SplitExternalHosts(externalServiceName)
 		for _, serviceName := range serviceNames {
 			routableServices = append(routableServices, w.buildDetails(service, serviceName))
 		}

server/k8s_test.go

@@ -117,6 +117,59 @@ func TestK8sWatcherImpl_handleAddThenUpdate(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "comma with spaces",
+			initial: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "a.com, b.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: "1.1.1.1:25565"},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+				},
+			},
+			update: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "b.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: ""},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+				},
+			},
+		},
+		{
+			name: "newline separated",
+			initial: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "a.com\nb.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: "1.1.1.1:25565"},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+				},
+			},
+			update: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "b.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: ""},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+				},
+			},
+		},
+		{
+			name: "mixed comma and newline with spaces",
+			initial: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "a.com, \nb.com,  c.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: "1.1.1.1:25565"},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+					{server: "c.com", backend: "1.1.1.1:25565"},
+				},
+			},
+			update: svcAndScenarios{
+				svc: ` {"metadata": {"annotations": {"mc-router.itzg.me/externalServerName": "b.com"}}, "spec":{"clusterIP": "1.1.1.1"}}`,
+				scenarios: []scenario{
+					{server: "a.com", backend: ""},
+					{server: "b.com", backend: "1.1.1.1:25565"},
+					{server: "c.com", backend: ""},
+				},
+			},
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {

server/utils.go

@@ -0,0 +1,38 @@
+package server
+
+import (
+	"regexp"
+	"strings"
+)
+
+// splitPattern is the regex pattern used to split external host definitions.
+// kept as a const so the literal is easy to see and reuse in tests or docs.
+const splitPattern = ",|\n"
+
+// splitRe is the compiled regexp for splitPattern. Compiling once at package
+// initialization avoids repeated compilation on every call to
+// SplitExternalHosts and is slightly more efficient.
+var splitRe = regexp.MustCompile(splitPattern)
+
+// SplitExternalHosts splits a string containing external hostnames by comma and/or newline delimiters.
+// It trims whitespace around each hostname and filters out empty strings.
+// Examples:
+//   - "host1.com,host2.com" -> ["host1.com", "host2.com"]
+//   - "host1.com, host2.com" -> ["host1.com", "host2.com"]
+//   - "host1.com\nhost2.com" -> ["host1.com", "host2.com"]
+//   - "host1.com,\nhost2.com" -> ["host1.com", "host2.com"]
+func SplitExternalHosts(s string) []string {
+	// Use regexp to split on either comma or newline
+	parts := splitRe.Split(s, -1)
+
+	// Trim whitespace and filter out empty strings
+	result := make([]string, 0, len(parts))
+	for _, part := range parts {
+		trimmed := strings.TrimSpace(part)
+		if trimmed != "" {
+			result = append(result, trimmed)
+		}
+	}
+
+	return result
+}