Add dns forwarding server library

dnsforward/helpers.go

@@ -0,0 +1,43 @@
+package dnsforward
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+)
+
+func isConnClosed(err error) bool {
+	if err == nil {
+		return false
+	}
+	nerr, ok := err.(*net.OpError)
+	if !ok {
+		return false
+	}
+
+	if strings.Contains(nerr.Err.Error(), "use of closed network connection") {
+		return true
+	}
+
+	return false
+}
+
+// ---------------------
+// debug logging helpers
+// ---------------------
+func trace(format string, args ...interface{}) {
+	pc := make([]uintptr, 10) // at least 1 entry needed
+	runtime.Callers(2, pc)
+	f := runtime.FuncForPC(pc[0])
+	var buf strings.Builder
+	buf.WriteString(fmt.Sprintf("%s(): ", path.Base(f.Name())))
+	text := fmt.Sprintf(format, args...)
+	buf.WriteString(text)
+	if len(text) == 0 || text[len(text)-1] != '\n' {
+		buf.WriteRune('\n')
+	}
+	fmt.Fprint(os.Stderr, buf.String())
+}