From 234508376ae6efe7b4180598ea43aa72906a3871 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Thu, 25 Jul 2013 23:27:13 -0700
Subject: [PATCH] ctrl-c closes stdin for plugins so that they are unblocked

---
 packer.go |  3 +++
 signal.go |  2 +-
 stdin.go  | 37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 stdin.go

diff --git a/packer.go b/packer.go
index c2a3422cf..590e7ea3c 100644
--- a/packer.go
+++ b/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)
diff --git a/signal.go b/signal.go
index c7b4deab1..2808bdf54 100644
--- a/signal.go
+++ b/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
diff --git a/stdin.go b/stdin.go
new file mode 100644
index 000000000..2df4153f5
--- /dev/null
+++ b/stdin.go
@@ -0,0 +1,37 @@
+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.")
+	}()
+}