ctrl-c closes stdin for plugins so that they are unblocked

packer.go

@@ -46,6 +46,9 @@ func main() {
 		packer.Version, packer.VersionPrerelease, packer.GitCommit)
 	log.Printf("Packer Target OS/Arch: %s %s", runtime.GOOS, runtime.GOARCH)
 
+	// Prepare stdin for plugin usage by switching it to a pipe
+	setupStdin()
+
 	config, err := loadConfig()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error loading configuration: \n\n%s\n", err)

signal.go

@@ -18,7 +18,7 @@ func setupSignalHandlers(env packer.Environment) {
 		// First interrupt. We mostly ignore this because it allows the
 		// plugins time to cleanup.
 		<-ch
-		log.Println("First interrupt. Ignoring, but closing stdin...")
+		log.Println("First interrupt. Ignoring to allow plugins to clean up.")
 
 		// Second interrupt. Go down hard.
 		<-ch

stdin.go

+package main
+
+import (
+	"io"
+	"log"
+	"os"
+	"os/signal"
+)
+
+// setupStdin switches out stdin for a pipe. We do this so that we can
+// close the writer end of the pipe when we receive an interrupt so plugins
+// blocked on reading from stdin are unblocked.
+func setupStdin() {
+	// Create the pipe and swap stdin for the reader end
+	r, w, _ := os.Pipe()
+	originalStdin := os.Stdin
+	os.Stdin = r
+
+	// Create a goroutine that copies data from the original stdin
+	// into the writer end of the pipe forever.
+	go func() {
+		defer w.Close()
+		io.Copy(w, originalStdin)
+	}()
+
+	// Register a signal handler for interrupt in order to close the
+	// writer end of our pipe so that readers get EOF downstream.
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, os.Interrupt)
+
+	go func() {
+		defer signal.Stop(ch)
+		defer w.Close()
+		<-ch
+		log.Println("Closing stdin because interrupt received.")
+	}()
+}