Update the UserData Module to support base64 encoded userdata

The UserData Module previously didn't support base64 encoding. With the
new changes to the UserData Module, decoding of base64 userdata is now
supported. This change maintains consistency with Amazon Linux 2's
cloud-init.

Signed-off-by: Matthew Carter <[email protected]>
Signed-off-by: Jon Oikawa <[email protected]>

lib/ec2macosinit/userdata.go

@@ -33,6 +33,15 @@ func (c *UserDataModule) Do(ctx *ModuleContext) (message string, err error) {
 		return "", fmt.Errorf("ec2macosinit: received an unexpected response code from IMDS: %d - %s\n", respCode, err)
 	}
 
+	// Attempt to base64 decode userdata.
+	// This maintains consistency alongside Amazon Linux 2's cloud-init, which states:
+	//     "Some tools and users will base64 encode their data before handing it to
+	//      an API like boto, which will base64 encode it again, so we try to decode."
+	decoded, err := decodeBase64(ud)
+	if err == nil {
+		ud = decoded
+	}
+
 	// Write user data to file
 	userDataFile := path.Join(baseDir, ctx.IMDS.InstanceID, fileName)
 	f, err := os.OpenFile(userDataFile, os.O_CREATE|os.O_WRONLY, 0755)

lib/ec2macosinit/util.go

@@ -2,6 +2,7 @@ package ec2macosinit
 
 import (
 	"bytes"
+	"encoding/base64"
 	"fmt"
 	"io"
 	"os"
@@ -194,3 +195,13 @@ func getOSProductVersion() (version string, err error) {
 
 	return version, nil
 }
+
+// decodeBase64 attempts to decode base64 data and returns the decoded string if successful
+func decodeBase64(base64Data string) (decodedString string, err error) {
+	decodedBytes, err := base64.StdEncoding.DecodeString(base64Data)
+	if err != nil {
+		return "", fmt.Errorf("ec2macosinit: failed to decode base64 string: %s\n", err)
+	}
+
+	return string(decodedBytes), nil
+}