plumbing: object, don't add extra newline on PGP signature

Tag encoding/decoding seems to be a lot more sensitive to requiring the
exact expected format in the object, which generally includes messages
canonicalized so that they have a newline on the end (even if they
didn't before).

As such, the message should be written with the newline (no need for an
extra), and the PGP signature right after that, which will be newline
split already, so there's no need to split it again.

All of this means it's very important for the caller to send the message
in the correct format - which I'm correcting in the next commit.

Signed-off-by: Chris Marchesi <[email protected]>

plumbing/object/tag.go

@@ -195,8 +195,13 @@ func (t *Tag) encode(o plumbing.EncodedObject, includeSig bool) (err error) {
 		return err
 	}
 
+	// Note that this is highly sensitive to what it sent along in the message.
+	// Message *always* needs to end with a newline, or else the message and the
+	// signature will be concatenated into a corrupt object. Since this is a
+	// lower-level method, we assume you know what you are doing and have already
+	// done the needful on the message in the caller.
 	if includeSig {
-		if _, err = fmt.Fprint(w, "\n"+t.PGPSignature); err != nil {
+		if _, err = fmt.Fprint(w, t.PGPSignature); err != nil {
 			return err
 		}
 	}