Expose logger (#34)

This closes #13 and gives ability to set your own logger with your custom prefixes and other logic.

Done:
- New function `SetLogger` added to be able to set logger
- Flag `gracehttp.log` removed just not to confuse people with logs from nowhere

gracehttp/http.go

@@ -5,7 +5,6 @@ package gracehttp
 import (
 	"bytes"
 	"crypto/tls"
-	"flag"
 	"fmt"
 	"log"
 	"net"
@@ -20,7 +19,7 @@ import (
 )
 
 var (
-	verbose    = flag.Bool("gracehttp.log", true, "Enable logging.")
+	logger     *log.Logger
 	didInherit = os.Getenv("LISTEN_FDS") != ""
 	ppid       = os.Getppid()
 )
@@ -129,17 +128,17 @@ func Serve(servers ...*http.Server) error {
 	}
 
 	// Some useful logging.
-	if *verbose {
+	if logger != nil {
 		if didInherit {
 			if ppid == 1 {
-				log.Printf("Listening on init activated %s", pprintAddr(a.listeners))
+				logger.Printf("Listening on init activated %s", pprintAddr(a.listeners))
 			} else {
 				const msg = "Graceful handoff of %s with new pid %d and old pid %d"
-				log.Printf(msg, pprintAddr(a.listeners), os.Getpid(), ppid)
+				logger.Printf(msg, pprintAddr(a.listeners), os.Getpid(), ppid)
 			}
 		} else {
 			const msg = "Serving %s with pid %d"
-			log.Printf(msg, pprintAddr(a.listeners), os.Getpid())
+			logger.Printf(msg, pprintAddr(a.listeners), os.Getpid())
 		}
 	}
 
@@ -166,8 +165,8 @@ func Serve(servers ...*http.Server) error {
 		}
 		return err
 	case <-waitdone:
-		if *verbose {
+		if logger != nil {
-			log.Printf("Exiting pid %d.", os.Getpid())
+			logger.Printf("Exiting pid %d.", os.Getpid())
 		}
 		return nil
 	}
@@ -184,3 +183,8 @@ func pprintAddr(listeners []net.Listener) []byte {
 	}
 	return out.Bytes()
 }
+
+// SetLogger sets logger to be able to grab some useful logs
+func SetLogger(l *log.Logger) {
+	logger = l
+}

gracehttp/testbin_test.go

@@ -113,11 +113,6 @@ func testbinMain() {
 		},
 	}
 
-	err := flag.Set("gracehttp.log", "false")
-	if err != nil {
-		log.Fatalf("Error setting gracehttp.log: %s", err)
-	}
-
 	// print json to stderr once we can successfully connect to all three
 	// addresses. the ensures we only print the line once we're ready to serve.
 	go func() {
@@ -133,7 +128,7 @@ func testbinMain() {
 		}
 	}()
 
-	err = gracehttp.Serve(
+	err := gracehttp.Serve(
 		&http.Server{Addr: httpAddr, Handler: newHandler()},
 		httpsServer(httpsAddr),
 	)