portlist: report a better process name for .Net on linux.

Fixes #1440.

Signed-off-by: David Anderson <danderson@tailscale.com>

portlist/clean.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package portlist
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// argvSubject takes a command and its flags, and returns the
+// short/pretty name for the process. This is usually the basename of
+// the binary being executed, but can sometimes vary (e.g. so that we
+// don't report all Java programs as "java").
+func argvSubject(argv ...string) string {
+	if len(argv) == 0 {
+		return ""
+	}
+	ret := filepath.Base(argv[0])
+
+	// Handle special cases.
+	switch {
+	case ret == "mono" && len(argv) >= 2:
+		// .Net programs execute as `mono actualProgram.exe`.
+		ret = filepath.Base(argv[1])
+	}
+
+	// Remove common noise.
+	ret = strings.TrimSpace(ret)
+	ret = strings.TrimSuffix(ret, ".exe")
+
+	return ret
+}