[PATCH 6/8] gpg-interface: find the last gpg signature line

[Ben Toews]

From: Jeff King <p...@peff.net>

A signed tag has a detached signature like this:

  object ...
  [...more header...]

  This is the tag body.

  -----BEGIN PGP SIGNATURE-----
  [opaque gpg data]
  -----END PGP SIGNATURE-----

Our parser finds the _first_ line that appears to start a
PGP signature block, meaning we may be confused by a
signature (or a signature-like line) in the actual body.
Let's keep parsing and always find the final block, which
should be the detached signature over all of the preceding
content.
---
 gpg-interface.c | 12 +++++++++---
 t/t7004-tag.sh  | 11 +++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/gpg-interface.c b/gpg-interface.c
index 79333c1ee8..0647bd6348 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -110,11 +110,17 @@ static int is_gpg_start(const char *line)
 size_t parse_signature(const char *buf, size_t size)
 {
        size_t len = 0;
-       while (len < size && !is_gpg_start(buf + len)) {
-               const char *eol = memchr(buf + len, '\n', size - len);
+       size_t match = size;
+       while (len < size) {
+               const char *eol;
+
+               if (is_gpg_start(buf + len))
+                       match = len;
+
+               eol = memchr(buf + len, '\n', size - len);
                len += eol ? eol - (buf + len) + 1 : size - len;
        }
-       return len;
+       return match;
 }
 
 void set_signing_key(const char *key)
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index ee093b393d..e3f1e014aa 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -1059,6 +1059,17 @@ test_expect_success GPG \
        git tag -v blanknonlfile-signed-tag
 '
 
+test_expect_success GPG 'signed tag with embedded PGP message' '
+       cat >msg <<-\EOF &&
+       -----BEGIN PGP MESSAGE-----
+
+       this is not a real PGP message
+       -----END PGP MESSAGE-----
+       EOF
+       git tag -s -F msg confusing-pgp-message &&
+       git tag -v confusing-pgp-message
+'
+
 # messages with commented lines for signed tags:
 
 cat >sigcommentsfile <<EOF
-- 
2.15.1 (Apple Git-101)