From 943bded9108997b47d7b3f4beecae88103cb1189 Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Sun, 9 Aug 2020 20:19:50 +0200
Subject: [PATCH] cmd/tailscale: don't duplicate log output

logtail.Log by default writes log output to stderr, but stderr is taken over by
filch's ReplaceStderr, resulting in duplicate logs sent to Tailscale.
ReplaceStderr is useful for capturing stack dumps from panics.

Configure logtail to route logs to the Android logger, which stops the
duplicate logging and replaces an existing MultiWriter setup for the same
purpose.

Reduce the scope of the logtail logger while here.

Fixes tailscale/tailscale#646

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 cmd/tailscale/backend.go | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/cmd/tailscale/backend.go b/cmd/tailscale/backend.go
index e434713..8624bde 100644
--- a/cmd/tailscale/backend.go
+++ b/cmd/tailscale/backend.go
@@ -7,7 +7,6 @@ package main
 import (
 	"errors"
 	"fmt"
-	"io"
 	"log"
 	"path/filepath"
 	"reflect"
@@ -31,7 +30,6 @@ import (
 type backend struct {
 	engine   wgengine.Engine
 	backend  *ipn.LocalBackend
-	logger   logtail.Logger
 	devices  *multiTUN
 	settings func(*router.Config) error
 	lastCfg  *router.Config
@@ -283,6 +281,7 @@ func (b *backend) SetupLogs(logDir string, logID logtail.PrivateID) {
 	logcfg := logtail.Config{
 		Collection: "tailnode.log.tailscale.io",
 		PrivateID:  logID,
+		Stderr:     log.Writer(),
 	}
 	logcfg.LowMemory = true
 	drainCh := make(chan struct{})
@@ -310,13 +309,10 @@ func (b *backend) SetupLogs(logDir string, logID logtail.PrivateID) {
 	}
 
 	logf := wgengine.RusagePrefixLog(log.Printf)
-	b.logger = logtail.Log(logcfg, logf)
+	tlog := logtail.Log(logcfg, logf)
 
 	log.SetFlags(0)
-	log.SetOutput(io.MultiWriter(
-		log.Writer(),
-		b.logger,
-	))
+	log.SetOutput(tlog)
 
 	log.Printf("goSetupLogs: success")