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

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
+}