fix incorrect empty message commit serialization

* Fixes incorrect signature verification for commits with an empty message,
  as encoded by CGit (#1429)

dulwich/objects.py

@@ -728,8 +728,8 @@ def _format_message(headers, body):
         yield git_line(field, lines[0])
         for line in lines[1:]:
             yield b" " + line + b"\n"
+    yield b"\n"  # There must be a new line after the headers
     if body:
-        yield b"\n"  # There must be a new line after the headers
         yield body
 
 

tests/compat/test_porcelain.py

@@ -91,3 +91,74 @@ def test_verify(self):
         tag = self.repo[b"refs/tags/verifyme"]
         self.assertNotEqual(tag.signature, None)
         tag.verify()
+
+
+@skipIf(
+    platform.python_implementation() == "PyPy" or sys.platform == "win32",
+    "gpgme not easily available or supported on Windows and PyPy",
+)
+class CommitCreateSignTestCase(PorcelainGpgTestCase, CompatTestCase):
+    def test_sign(self):
+        # Test that dulwich signatures can be verified by CGit
+        cfg = self.repo.get_config()
+        cfg.set(("user",), "signingKey", PorcelainGpgTestCase.DEFAULT_KEY_ID)
+        self.import_default_key()
+
+        porcelain.commit(
+            self.repo.path,
+            b"messy message messiah",
+            b"foo <[email protected]>",
+            signoff=True,
+        )
+
+        run_git_or_fail(
+            [f"--git-dir={self.repo.controldir()}", "verify-commit", "-v", "HEAD"],
+            env={"GNUPGHOME": os.environ["GNUPGHOME"]},
+        )
+
+    def test_verify(self):
+        # Test that CGit signatures can be verified by dulwich
+        self.import_default_key()
+
+        run_git_or_fail(
+            [
+                f"--git-dir={self.repo.controldir()}",
+                "commit",
+                "--allow-empty",
+                "-S" + PorcelainGpgTestCase.DEFAULT_KEY_ID,
+                "-m",
+                "foo",
+            ],
+            env={
+                "GNUPGHOME": os.environ["GNUPGHOME"],
+                "GIT_COMMITTER_NAME": "Joe Example",
+                "GIT_COMMITTER_EMAIL": "[email protected]",
+            },
+        )
+        commit = self.repo[b"HEAD"]
+        self.assertNotEqual(commit.gpgsig, None)
+        commit.verify()
+
+    def test_verify_with_empty_message(self):
+        # Test that CGit signatures can be verified by dulwich
+        self.import_default_key()
+
+        run_git_or_fail(
+            [
+                f"--git-dir={self.repo.controldir()}",
+                "commit",
+                "--allow-empty",
+                "-S" + PorcelainGpgTestCase.DEFAULT_KEY_ID,
+                "--allow-empty-message",
+                "-m",
+                "",
+            ],
+            env={
+                "GNUPGHOME": os.environ["GNUPGHOME"],
+                "GIT_COMMITTER_NAME": "Joe Example",
+                "GIT_COMMITTER_EMAIL": "[email protected]",
+            },
+        )
+        commit = self.repo[b"HEAD"]
+        self.assertNotEqual(commit.gpgsig, None)
+        commit.verify()

tests/test_objects.py

@@ -1066,7 +1066,7 @@ def test_serialize_none_message(self):
                 b"type blob\n"
                 b"tag 0.1\n"
                 b"tagger Jelmer Vernooij <[email protected]> "
-                b"423423423 +0000\n"
+                b"423423423 +0000\n\n"
             ),
             x.as_raw_string(),
         )