Merge pull request #16 from cybozu-go/sighup2

Fix SIGPIPE handling, take 2.

default.go

@@ -9,7 +9,7 @@ var (
 func init() {
 	defaultEnv = NewEnvironment(context.Background())
 	handleSignal(defaultEnv)
-	ignoreSigPipe()
+	handleSigPipe()
 }
 
 // Stop just declares no further Go will be called.

sigpipe.go

@@ -8,12 +8,43 @@ import (
 	"syscall"
 )
 
-func ignoreSigPipe() {
-	// signal.Ignore does NOT ignore signals; instead, it just stop
-	// relaying signals to the channel.
-	//signal.Ignore(syscall.SIGPIPE)
+const (
+	sigPipeExit = 2
+)
 
-	// unbuffered channel will effectively ignore the signal
-	c := make(chan os.Signal)
+// handleSigPipe catches SIGPIPE and exit abnormally with status code 2.
+//
+// Background:
+//
+// systemd interprets programs exited with SIGPIPE as
+// "successfully exited" because its default SuccessExitStatus=
+// includes SIGPIPE.
+// https://www.freedesktop.org/software/systemd/man/systemd.service.html
+//
+// Normal Go programs ignore SIGPIPE for file descriptors other than
+// stdout(1) and stderr(2).  If SIGPIPE is raised from stdout or stderr,
+// Go programs exit with a SIGPIPE signal.
+// https://golang.org/pkg/os/signal/#hdr-SIGPIPE
+//
+// journald is a service tightly integrated in systemd.  Go programs
+// running as a systemd service will normally connect its stdout and
+// stderr pipes to journald.  Unfortunately though, journald often
+// dies and restarts due to bugs, and once it restarts, programs
+// whose stdout and stderr was connected to journald will receive
+// SIGPIPE at their next writes to stdout or stderr.
+//
+// Combined these specifications and problems all together, Go programs
+// running as systemd services often die with SIGPIPE, but systemd will
+// not restarts them as they "successfully exited" except when the service
+// is configured with SuccessExitStatus= without SIGPIPE or Restart=always.
+//
+// Handling SIGPIPE manually and exiting with abnormal status code 2
+// can work around the problem.
+func handleSigPipe() {
+	c := make(chan os.Signal, 1)
 	signal.Notify(c, syscall.SIGPIPE)
+	go func() {
+		<-c
+		os.Exit(sigPipeExit)
+	}()
 }

sigpipe_windows.go

@@ -1,3 +1,3 @@
 package cmd
 
-func ignoreSigPipe() {}
+func handleSigPipe() {}