wgengine: use Tailscale-style peer identifiers in logs

Rewrite log lines on the fly, based on the set of known peers.

This enables us to use upstream wireguard-go logging,
but maintain the Tailscale-style peer public key identifiers
that the rest of our systems (and people) expect.

Fixes #1183

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

wgengine/wglog/wglog_test.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2020 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 wglog_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/tailscale/wireguard-go/wgcfg"
+	"tailscale.com/wgengine/wglog"
+)
+
+func TestLogger(t *testing.T) {
+	tests := []struct {
+		in   string
+		want string
+		omit bool
+	}{
+		{"hi", "hi", false},
+		{"Routine: starting", "", true},
+		{"peer(IMTB…r7lM) says it misses you", "[IMTBr] says it misses you", false},
+	}
+
+	c := make(chan string, 1)
+	logf := func(format string, args ...interface{}) {
+		s := fmt.Sprintf(format, args...)
+		select {
+		case c <- s:
+		default:
+			t.Errorf("wrote %q, but shouldn't have", s)
+		}
+	}
+
+	x := wglog.NewLogger(logf)
+	key, err := wgcfg.ParseHexKey("20c4c1ae54e1fd37cab6e9a532ca20646aff496796cc41d4519560e5e82bee53")
+	if err != nil {
+		t.Fatal(err)
+	}
+	x.SetPeers([]wgcfg.Peer{{PublicKey: key}})
+
+	for _, tt := range tests {
+		if tt.omit {
+			// Write a message ourselves into the channel.
+			// Then if logf also attempts to write into the channel, it'll fail.
+			c <- ""
+		}
+		x.DeviceLogger.Info.Println(tt.in)
+		got := <-c
+		if tt.omit {
+			continue
+		}
+		tt.want += "\n"
+		if got != tt.want {
+			t.Errorf("Println(%q) = %q want %q", tt.in, got, tt.want)
+		}
+	}
+}