rpc/communicator fix race condition that causes stdout from ssh provisioner to be truncated

packer/rpc/communicator.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"net/rpc"
 	"os"
+	"sync"
 
 	"github.com/hashicorp/packer/packer"
 )
@@ -67,19 +68,33 @@ func (c *communicator) Start(cmd *packer.RemoteCmd) (err error) {
 	var args CommunicatorStartArgs
 	args.Command = cmd.Command
 
+	var wg sync.WaitGroup
+
 	if cmd.Stdin != nil {
+		wg.Add(1)
 		args.StdinStreamId = c.mux.NextId()
-		go serveSingleCopy("stdin", c.mux, args.StdinStreamId, nil, cmd.Stdin)
+		go func() {
+			defer wg.Done()
+			serveSingleCopy("stdin", c.mux, args.StdinStreamId, nil, cmd.Stdin)
+		}()
 	}
 
 	if cmd.Stdout != nil {
+		wg.Add(1)
 		args.StdoutStreamId = c.mux.NextId()
-		go serveSingleCopy("stdout", c.mux, args.StdoutStreamId, cmd.Stdout, nil)
+		go func() {
+			defer wg.Done()
+			serveSingleCopy("stdout", c.mux, args.StdoutStreamId, cmd.Stdout, nil)
+		}()
 	}
 
 	if cmd.Stderr != nil {
+		wg.Add(1)
 		args.StderrStreamId = c.mux.NextId()
-		go serveSingleCopy("stderr", c.mux, args.StderrStreamId, cmd.Stderr, nil)
+		go func() {
+			defer wg.Done()
+			serveSingleCopy("stderr", c.mux, args.StderrStreamId, cmd.Stderr, nil)
+		}()
 	}
 
 	responseStreamId := c.mux.NextId()
@@ -97,7 +112,9 @@ func (c *communicator) Start(cmd *packer.RemoteCmd) (err error) {
 
 		var finished CommandFinished
 		decoder := gob.NewDecoder(conn)
-		if err := decoder.Decode(&finished); err != nil {
+		err = decoder.Decode(&finished)
+		wg.Wait()
+		if err != nil {
 			log.Printf("[ERR] Error decoding response stream %d: %s",
 				responseStreamId, err)
 			cmd.SetExited(123)