packer/plugin: Killed bool to avoid panics when killing clients

packer/plugin/builder.go

@@ -40,7 +40,7 @@ func (b *cmdBuilder) Cancel() {
 func (c *cmdBuilder) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() && cb != nil {
 		cb()
-	} else if p != nil {
+	} else if p != nil && !Killed {
 		log.Panic(p)
 	}
 }

packer/plugin/client.go

@@ -20,6 +20,10 @@ import (
 	"unicode"
 )
 
+// If this is true, then the "unexpected EOF" panic will not be
+// raised throughout the clients.
+var Killed = false
+
 // This is a slice of the "managed" clients which are cleaned up when
 // calling Cleanup
 var managedClients = make([]*Client, 0, 5)

packer/plugin/command.go

@@ -45,7 +45,7 @@ func (c *cmdCommand) Synopsis() (result string) {
 func (c *cmdCommand) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() {
 		cb()
-	} else if p != nil {
+	} else if p != nil && !Killed {
 		log.Panic(p)
 	}
 }

packer/plugin/hook.go

@@ -22,7 +22,7 @@ func (c *cmdHook) Run(name string, ui packer.Ui, comm packer.Communicator, data
 func (c *cmdHook) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() {
 		cb()
-	} else if p != nil {
+	} else if p != nil && !Killed {
 		log.Panic(p)
 	}
 }

packer/plugin/post_processor.go

@@ -31,7 +31,7 @@ func (c *cmdPostProcessor) PostProcess(ui packer.Ui, a packer.Artifact) (packer.
 func (c *cmdPostProcessor) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() {
 		cb()
-	} else if p != nil {
+	} else if p != nil && !Killed {
 		log.Panic(p)
 	}
 }

packer/plugin/provisioner.go

@@ -31,7 +31,7 @@ func (c *cmdProvisioner) Provision(ui packer.Ui, comm packer.Communicator) error
 func (c *cmdProvisioner) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() {
 		cb()
-	} else if p != nil {
+	} else if p != nil && !Killed {
 		log.Panic(p)
 	}
 }

signal.go

@@ -26,7 +26,9 @@ func setupSignalHandlers(env packer.Environment) {
 
 		env.Ui().Error("Interrupt signal received twice. Forcefully exiting now.")
 
-		// Force kill all the plugins
+		// Force kill all the plugins, but mark that we're killing them
+		// first so that we don't get panics everywhere.
+		plugin.Killed = true
 		plugin.CleanupClients()
 		os.Exit(1)
 	}()