StepDownload uses packer version as user agent

common/step_download.go

@@ -70,6 +70,7 @@ func (s *StepDownload) Run(state multistep.StateBag) multistep.StepAction {
 			CopyFile:   false,
 			Hash:       HashForType(s.ChecksumType),
 			Checksum:   checksum,
+			UserAgent:  packer.VersionString(),
 		}
 
 		path, err, retry := s.download(config, state)

packer/version.go

@@ -31,6 +31,15 @@ func (versionCommand) Run(env Environment, args []string) int {
 	env.Ui().Machine("version-prelease", VersionPrerelease)
 	env.Ui().Machine("version-commit", GitCommit)
 
+	env.Ui().Say(VersionString())
+	return 0
+}
+
+func (versionCommand) Synopsis() string {
+	return "print Packer version"
+}
+
+func VersionString() string {
 	var versionString bytes.Buffer
 	fmt.Fprintf(&versionString, "Packer v%s", Version)
 	if VersionPrerelease != "" {
@@ -41,10 +50,5 @@ func (versionCommand) Run(env Environment, args []string) int {
 		}
 	}
 
-	env.Ui().Say(versionString.String())
-	return 0
-}
-
-func (versionCommand) Synopsis() string {
-	return "print Packer version"
+  return versionString.String()
 }