Work around parse errors of a bogus git.git commit

The C Git source code repository itself contains a commit with bogus
`gpgsig` lines: 5f549aa2f783 (pretty: %G[?GS] placeholders, 2011-10-21).
Basically, this commit's headers contain a GPG signature that _should_
have been a multi-line header, but instead every line of that signature
was added individually as a `gpgsig` header. Crucially, this includes a
header line that starts with `gpgsig` followed by a space and that's
already the end of the line.

Gitoxide's commit header parser was not prepared for that. Even worse:
the error message in that instance was simply empty.

Let's make the parser more robust by accepting such commit headers, and
add a test to verify that the commit in question _can_ be parsed by
Gitoxide.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

gix-object/src/commit/decode.rs

@@ -51,7 +51,7 @@ pub fn commit<'a, E: ParserError<&'a [u8]> + AddContext<&'a [u8], StrContext>>(
             alt((
                 parse::any_header_field_multi_line.map(|(k, o)| (k.as_bstr(), Cow::Owned(o))),
                 |i: &mut _| {
-                    parse::any_header_field(i, take_till(1.., NL))
+                    parse::any_header_field(i, take_till(0.., NL))
                         .map(|(k, o)| (k.as_bstr(), Cow::Borrowed(o.as_bstr())))
                 },
             )),

gix-object/tests/fixtures/commit/bogus-gpgsig-lines-in-git.git.txt

@@ -0,0 +1,31 @@
+tree db079155794727ac821adfba2eb68b330cc0c120
+parent 33a11a20eb7610771268e34211509cbbdee76b1e
+author Junio C Hamano <gitster@pobox.com> 1319256362 -0700
+committer Junio C Hamano <gitster@pobox.com> 1319259176 -0700
+gpgsig -----BEGIN PGP SIGNATURE-----
+gpgsig Version: GnuPG v1.4.10 (GNU/Linux)
+gpgsig 
+gpgsig iQIcBAABAgAGBQJOokwoAAoJELC16IaWr+bL0WoP/2QKYkWpEyXF608m2L/cB9Qx
+gpgsig /N0oBjyL1guIjPX9B3Wxq80dnLLEPnpnO39aiQIXFoJS0L6KEurqK6uDPHy3/ULa
+gpgsig QsAug2HeCLsDnIFbzFSpSIMv/bP/72FDb/idMBT99xTcQj5UJEUgj7AAtx0vnKvQ
+gpgsig pQIXtPu5GBUdhl3SiGgiJFRyp4r5EgV5I40GBwx/ty9cPEIN7ukJ3CR9+KC8eIGx
+gpgsig Az7qngi3dhTn7g+3Z8XX5OYFDMSt9xn1gxqWXOMNlG0mxCvpFe59kwciugp26KVp
+gpgsig n+yJ0UOdoxyZX8pdqXQjvklmoo7e55aaxtbHe7KSD56ebL7h7vHhkGWORU1dOp+h
+gpgsig Iv5dQItkKSR8afB7FmRjo8+B/2g0wZDKRTGhzm7d1gooO5gpXvuvm4GRl5Io+IEj
+gpgsig c7Li3EYmXADWUZWJtbDKDgKGKIOmWv72Qrz52iaESrhZ909HiXfn/jhHBuDRmLtQ
+gpgsig /4v3T4O25uhdZ4p/PjHQn/ZroCmDyMwmnrtw/tt5fSNrl4qGcYg8Jj/1ynfF1AtS
+gpgsig dM2LR65sOwXzSsqAbQjyRFYMLSWhHd/h8BcpZHDXmNBkZJVPm4zvD3ZVaAo6rtZD
+gpgsig WJ9YXWXtPhuf09OgYBzcBlamTrk9ByH+NCIdrFkqfhNF1YI5dArSZytIXJhpPI1e
+gpgsig TrmQAZf0BiI5J6PYN0AI
+gpgsig =Qg/+
+gpgsig -----END PGP SIGNATURE-----
+
+pretty: %G[?GS] placeholders
+
+Add new placeholders related to the GPG signature on signed commits.
+
+ - %GG to show the raw verification message from GPG;
+ - %G? to show either "G" for Good, "B" for Bad;
+ - %GS to show the name of the signer.
+
+Signed-off-by: Junio C Hamano <gitster@pobox.com>

gix-object/tests/object/commit/from_bytes.rs

@@ -342,3 +342,20 @@ fn newline_right_after_signature_multiline_header() -> crate::Result {
     assert!(commit.message.starts_with(b"Rollup"));
     Ok(())
 }
+
+#[test]
+fn bogus_multi_gpgsig_header() -> crate::Result {
+    let fixture = fixture_name("commit", "bogus-gpgsig-lines-in-git.git.txt");
+    let commit = CommitRef::from_bytes(&fixture)?;
+    let pgp_sig = crate::commit::BEGIN_PGP_SIGNATURE.as_bstr();
+    assert_eq!(commit.extra_headers[0].1.as_ref(), pgp_sig);
+    assert_eq!(commit.extra_headers().pgp_signature(), Some(pgp_sig));
+    assert_eq!(
+        commit.extra_headers().find(gix_object::commit::SIGNATURE_FIELD_NAME),
+        Some(pgp_sig)
+    );
+    assert_eq!(commit.extra_headers().find_pos("gpgsig"), Some(0));
+    assert_eq!(commit.extra_headers().find_pos("something else"), None);
+    assert!(commit.message.starts_with(b"pretty: %G[?GS] placeholders"));
+    Ok(())
+}

gix-object/tests/object/commit/mod.rs

@@ -149,6 +149,8 @@ iyBBl69jASy41Ug/BlFJbw4+ItkShpXwkJKuBBV/JExChmvbxYWaS7QnyYC9UO0=
 
 ";
 
+const BEGIN_PGP_SIGNATURE: &[u8] = b"-----BEGIN PGP SIGNATURE-----";
+
 mod method {
     use gix_object::CommitRef;
     use pretty_assertions::assert_eq;