[PATCHv3] gpg-interface: check gpg signature creation status

[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 signature creation status to catch these cases
better. Really, --status-fd parsing is the only way to check gpg status
reliably. We do the same for verify already.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
---
That must be the real real thing now...

 gpg-interface.c | 22 +++++++++++++++-------
 t/t7004-tag.sh  | 10 +++++++++-
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index c4b1e8c..850dc81 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -150,17 +150,19 @@ const char *get_signing_key(void)
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
-	const char *args[4];
-	ssize_t len;
+	const char *args[5];
 	size_t i, j, bottom;
+	struct strbuf err = STRBUF_INIT;
 
 	gpg.argv = args;
 	gpg.in = -1;
 	gpg.out = -1;
+	gpg.err = -1;
 	args[0] = gpg_program;
-	args[1] = "-bsau";
-	args[2] = signing_key;
-	args[3] = NULL;
+	args[1] = "--status-fd=2";
+	args[2] = "-bsau";
+	args[3] = signing_key;
+	args[4] = NULL;
 
 	if (start_command(&gpg))
 		return error(_("could not run gpg."));
@@ -174,19 +176,25 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 	if (write_in_full(gpg.in, buffer->buf, buffer->len) != buffer->len) {
 		close(gpg.in);
 		close(gpg.out);
+		close(gpg.err);
 		finish_command(&gpg);
 		return error(_("gpg did not accept the data"));
 	}
 	close(gpg.in);
 
 	bottom = signature->len;
-	len = strbuf_read(signature, gpg.out, 1024);
+	strbuf_read(signature, gpg.out, 1024);
+	strbuf_read(&err, gpg.err, 0);
 	close(gpg.out);
+	close(gpg.err);
 
 	sigchain_pop(SIGPIPE);
 
-	if (finish_command(&gpg) || !len || len < 0)
+	if (finish_command(&gpg) || !strstr(err.buf, "\n[GNUPG:] SIG_CREATED ")) {
+		strbuf_release(&err);
 		return error(_("gpg failed to sign the data"));
+	}
+	strbuf_release(&err);
 
 	/* Strip CR from the line endings, in case we are on Windows. */
 	for (i = j = bottom; i < signature->len; i++)
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index f9b7d79..467e968 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -1202,10 +1202,18 @@ test_expect_success GPG,RFC1991 \
 # try to sign with bad user.signingkey
 git config user.signingkey BobTheMouse
 test_expect_success GPG \
-	'git tag -s fails if gpg is misconfigured' \
+	'git tag -s fails if gpg is misconfigured (bad key)' \
 	'test_must_fail git tag -s -m tail tag-gpg-failure'
 git config --unset user.signingkey
 
+# try to produce invalid signature
+git config gpg.program echo
+test_expect_success GPG \
+	'git tag -s fails if gpg is misconfigured (bad signature format)' \
+	'test_must_fail git tag -s -m tail tag-gpg-failure'
+git config --unset gpg.program
+
+
 # try to verify without gpg:
 
 rm -rf gpghome
-- 
2.9.0.382.g87fd384