communicator/ssh: buffer file on disk to read length [GH-561]

CHANGELOG.md

@@ -13,6 +13,8 @@ BUG FIXES:
 * builder/openstack: Properly scrub password from logs [GH-554]
 * common/uuid: Use cryptographically secure PRNG when generating
   UUIDs. [GH-552]
+* communicator/ssh: File uploads that exceed the size of memory no longer
+  cause crashes. [GH-561]
 
 ## 0.3.10 (October 20, 2013)
 

communicator/ssh/communicator.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"github.com/mitchellh/packer/packer"
 	"io"
+	"io/ioutil"
 	"log"
 	"net"
 	"os"
@@ -362,30 +363,49 @@ func checkSCPStatus(r *bufio.Reader) error {
 }
 
 func scpUploadFile(dst string, src io.Reader, w io.Writer, r *bufio.Reader) error {
-	// Determine the length of the upload content by copying it
-	// into an in-memory buffer. Note that this means what we upload
-	// must fit into memory.
-	log.Println("Copying input data into in-memory buffer so we can get the length")
-	inputBuf := new(bytes.Buffer)
-	if _, err := io.Copy(inputBuf, src); err != nil {
+	// Create a temporary file where we can copy the contents of the src
+	// so that we can determine the length, since SCP is length-prefixed.
+	tf, err := ioutil.TempFile("", "packer-upload")
+	if err != nil {
+		return fmt.Errorf("Error creating temporary file for upload: %s", err)
+	}
+	defer os.Remove(tf.Name())
+	defer tf.Close()
+
+	log.Println("Copying input data into temporary file so we can read the length")
+	if _, err := io.Copy(tf, src); err != nil {
 		return err
 	}
 
+	// Sync the file so that the contents are definitely on disk, then
+	// read the length of it.
+	if err := tf.Sync(); err != nil {
+		return fmt.Errorf("Error creating temporary file for upload: %s", err)
+	}
+
+	// Seek the file to the beginning so we can re-read all of it
+	if _, err := tf.Seek(0, 0); err != nil {
+		return fmt.Errorf("Error creating temporary file for upload: %s", err)
+	}
+
+	fi, err := tf.Stat()
+	if err != nil {
+		return fmt.Errorf("Error creating temporary file for upload: %s", err)
+	}
+
 	// Start the protocol
 	log.Println("Beginning file upload...")
-	fmt.Fprintln(w, "C0644", inputBuf.Len(), dst)
-	err := checkSCPStatus(r)
-	if err != nil {
+	fmt.Fprintln(w, "C0644", fi.Size(), dst)
+	if err := checkSCPStatus(r); err != nil {
 		return err
 	}
 
-	if _, err := io.Copy(w, inputBuf); err != nil {
+	if _, err := io.Copy(w, tf); err != nil {
 		return err
 	}
 
 	fmt.Fprint(w, "\x00")
-	err = checkSCPStatus(r)
-	if err != nil {
+	if err := checkSCPStatus(r); err != nil {
 		return err
 	}