valid the bootstraps before passing to NewBootstrapSingleCmd

Author: wchengru

cmd/aws-lambda-rie/main.go

@@ -62,12 +62,23 @@ func getBootstrap(args []string, opts options) (*rapidcore.Bootstrap, string) {
 	currentWorkingDir := "/var/task" // default value
 
 	if len(args) <= 1 {
-		bootstrapLookupCmd = []string{
+
+	    var bootstrapCmdCandidates = []string{
 			fmt.Sprintf("%s/bootstrap", currentWorkingDir),
 			optBootstrap,
 			runtimeBootstrap,
 		}
 
+		// set default value to /var/task/bootstrap, but switch to the other options if it doesn't exist
+		bootstrapLookupCmd = []string{bootstrapCmdCandidates[0]}
+
+        for i, bootstrapCandidate := range bootstrapCmdCandidates {
+            if file, err := os.Stat(bootstrapCandidate); !os.IsNotExist(err) && !file.IsDir() {
+                bootstrapLookupCmd = []string{bootstrapCmdCandidates[i]}
+                break
+            }
+        }
+
 		// handler is used later to set an env var for Lambda Image support
 		handler = ""
 	} else if len(args) > 1 {