1 files changed, 37 insertions, 0 deletions
diff --git a/internal/engine/proxy_port.go b/internal/engine/proxy_port.go
new file mode 100644
index 0000000..5e657c0
--- /dev/null
+++ b/internal/engine/proxy_port.go
@@ -0,0 +1,37 @@
+package engine
+
+import (
+	"fmt"
+	"net"
+
+	"vpnem/internal/config"
+)
+
+var localProxyPortCandidates = []int{config.LocalProxyPort, 10808, 10880, 18080, 20800}
+
+func ResolveLocalProxyPort() (int, error) {
+	for _, port := range localProxyPortCandidates {
+		if localProxyPortAvailable(port) {
+			return port, nil
+		}
+	}
+	listener, err := net.Listen("tcp", net.JoinHostPort(config.LocalProxyHost, "0"))
+	if err != nil {
+		return 0, err
+	}
+	defer listener.Close()
+	addr, ok := listener.Addr().(*net.TCPAddr)
+	if !ok {
+		return 0, fmt.Errorf("unexpected listener addr type %T", listener.Addr())
+	}
+	return addr.Port, nil
+}
+
+func localProxyPortAvailable(port int) bool {
+	listener, err := net.Listen("tcp", net.JoinHostPort(config.LocalProxyHost, fmt.Sprintf("%d", port)))
+	if err != nil {
+		return false
+	}
+	_ = listener.Close()
+	return true
+}