Cleanup Socket and Pidfile on exit

These were previously left intact, even when exiting gracefully. As the
daemon also fails if the socket already exists, it became the caller's
responsibilityto check for and cleanup old socket files when performing
graceful / deliberate restarts.

Signed-off-by: Emily Shepherd <emily@redcoat.dev>

plugins/ipam/dhcp/daemon.go

@@ -15,6 +15,7 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -23,9 +24,11 @@ import (
 	"net/http"
 	"net/rpc"
 	"os"
+	"os/signal"
 	"path/filepath"
 	"runtime"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/containernetworking/cni/pkg/skel"
@@ -195,11 +198,27 @@ func runDaemon(
 		return fmt.Errorf("Error getting listener: %v", err)
 	}
 
+	srv := http.Server{}
+	exit := make(chan os.Signal, 1)
+	done := make(chan bool, 1)
+	signal.Notify(exit, os.Interrupt, syscall.SIGTERM)
+
+	go func() {
+		<-exit
+		srv.Shutdown(context.TODO())
+		os.Remove(hostPrefix + socketPath)
+		os.Remove(pidfilePath)
+
+		done <- true
+	}()
+
 	dhcp := newDHCP(dhcpClientTimeout, resendMax)
 	dhcp.hostNetnsPrefix = hostPrefix
 	dhcp.broadcast = broadcast
 	rpc.Register(dhcp)
 	rpc.HandleHTTP()
-	http.Serve(l, nil)
+	srv.Serve(l)
+
+	<-done
 	return nil
 }