[PATCH] gpg-interface: check gpg signature for correct header

[Michael J Gruber <git@drmicha.warpmail.net>]

When we create a signature, it may happen that gpg returns with
"success" but not with an actual detached signature on stdout.

Check for the correct header to catch these cases better.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
---
This catches at least my echo example.

We could do a full blown gpg signature check, of course.

 gpg-interface.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index c4b1e8c..664796f 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -185,7 +185,7 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 
 	sigchain_pop(SIGPIPE);
 
-	if (finish_command(&gpg) || !len || len < 0)
+	if (finish_command(&gpg) || !len || len < 0 || strncmp(signature->buf, PGP_SIGNATURE, strlen(PGP_SIGNATURE)))
 		return error(_("gpg failed to sign the data"));
 
 	/* Strip CR from the line endings, in case we are on Windows. */
-- 
2.9.0.382.g87fd384