logpolicy: fix, test LogHost to work as documented

Change-Id: I225c9602a7587c69c237e336d0714fc8315ea6bd
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

logpolicy/logpolicy.go

@@ -74,7 +74,9 @@ func getLogTarget() string {
 // logtail server, or the default.
 func LogHost() string {
 	if v := getLogTarget(); v != "" {
-		return v
+		if u, err := url.Parse(v); err == nil {
+			return u.Hostname()
+		}
 	}
 	return logtail.DefaultHost
 }

logpolicy/logpolicy_test.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2022 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 logpolicy
+
+import (
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestLogHost(t *testing.T) {
+	v := reflect.ValueOf(&getLogTargetOnce).Elem()
+	reset := func() {
+		v.Set(reflect.Zero(v.Type()))
+	}
+	defer reset()
+
+	tests := []struct {
+		env  string
+		want string
+	}{
+		{"", "log.tailscale.io"},
+		{"http://foo.com", "foo.com"},
+		{"https://foo.com", "foo.com"},
+		{"https://foo.com/", "foo.com"},
+		{"https://foo.com:123/", "foo.com"},
+	}
+	for _, tt := range tests {
+		reset()
+		os.Setenv("TS_LOG_TARGET", tt.env)
+		if got := LogHost(); got != tt.want {
+			t.Errorf("for env %q, got %q, want %q", tt.env, got, tt.want)
+		}
+	}
+}