handle signals correctly

Change-Id: Ida075f41113c30b4ec1a12f90ab2e6a4d57eba97

Author: Francesc Campoy

logpipe.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/signal"
 
 	flags "github.com/jessevdk/go-flags"
 
@@ -41,10 +42,10 @@ func main() {
 	// Check if Standard In is coming from a pipe
 	fi, err := os.Stdin.Stat()
 	if err != nil {
-		errorf("Could not stat standard input: %v\n", err)
+		errorf("Could not stat standard input: %v", err)
 	}
 	if fi.Mode()&os.ModeNamedPipe == 0 {
-		errorf("Nothing is piped in so there is nothing to log!\n")
+		errorf("Nothing is piped in so there is nothing to log!")
 	}
 
 	// Creates a client.
@@ -53,27 +54,47 @@ func main() {
 	if err != nil {
 		errorf("Failed to create client: %v", err)
 	}
-
 	// Selects the log to write to.
 	logger := client.Logger(opts.LogName)
 
-	// Read from Stdin and log it to Stdout and Stackdriver
-	s := bufio.NewScanner(io.TeeReader(os.Stdin, os.Stdout))
-	for s.Scan() {
-		logger.Log(logging.Entry{Payload: s.Text()})
+	lines := make(chan string)
+	go func() {
+		defer close(lines)
+		// Read from Stdin and log it to Stdout and Stackdriver
+		s := bufio.NewScanner(io.TeeReader(os.Stdin, os.Stdout))
+		for s.Scan() {
+			lines <- s.Text()
+		}
+		if err := s.Err(); err != nil {
+			fmt.Fprintf(os.Stderr, "Failed to scan input: %v\n", err)
+		}
+	}()
+
+	signals := make(chan os.Signal)
+	signal.Notify(signals, os.Interrupt)
+
+loop:
+	for {
+		select {
+		case line, ok := <-lines:
+			if !ok {
+				break loop
+			}
+			logger.Log(logging.Entry{Payload: line})
+		case s := <-signals:
+			fmt.Fprintf(os.Stderr, "Terminating program after received signal: %v\n", s)
+			break loop
+		}
 	}
 
 	// Closes the client and flushes the buffer to the Stackdriver Logging
 	// service.
 	if err := client.Close(); err != nil {
 		errorf("Failed to close client: %v", err)
 	}
-	if err := s.Err(); err != nil {
-		errorf("Failed to scan input: %v", err)
-	}
 }
 
 func errorf(format string, args ...interface{}) {
-	fmt.Fprintf(os.Stderr, format, args...)
+	fmt.Fprintf(os.Stderr, format+"\n", args...)
 	os.Exit(2)
 }