thodg/libgit2

diff --git a/include/git2/commit.h b/include/git2/commit.h
index 44ea888..f63a906 100644
--- a/include/git2/commit.h
+++ b/include/git2/commit.h
@@ -440,6 +440,27 @@ GIT_EXTERN(int) git_commit_create_buffer(
 	size_t parent_count,
 	const git_commit *parents[]);
 
+/**
+ * Create a commit object from the given buffer and signature
+ *
+ * Given the unsigned commit object's contents, its signature and the
+ * header field in which to store the signature, attach the signature
+ * to the commit and write it into the given repository.
+ *
+ * @param out the resulting commit id
+ * @param commit_content the content of the unsigned commit object
+ * @param signature the signature to add to the commit
+ * @param signature_field which header field should contain this
+ * signature. Leave `NULL` for the default of "gpgsig"
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_commit_create_with_signature(
+	git_oid *out,
+	git_repository *repo,
+	const char *commit_content,
+	const char *signature,
+	const char *signature_field);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/commit.c b/src/commit.c
index 905407a..aaefacd 100644
--- a/src/commit.c
+++ b/src/commit.c
@@ -820,3 +820,67 @@ int git_commit_create_buffer(git_buf *out,
 	git_array_clear(parents_arr);
 	return error;
 }
+
+/**
+ * Append to 'out' properly marking continuations when there's a newline in 'content'
+ */
+static void format_header_field(git_buf *out, const char *field, const char *content)
+{
+	const char *lf;
+
+	assert(out && field && content);
+
+	git_buf_puts(out, field);
+	git_buf_putc(out, ' ');
+
+	while ((lf = strchr(content, '\n')) != NULL) {
+		git_buf_put(out, content, lf - content);
+		git_buf_puts(out, "\n ");
+		content = lf + 1;
+	}
+
+	git_buf_puts(out, content);
+	git_buf_putc(out, '\n');
+}
+
+int git_commit_create_with_signature(
+	git_oid *out,
+	git_repository *repo,
+	const char *commit_content,
+	const char *signature,
+	const char *signature_field)
+{
+	git_odb *odb;
+	int error = 0;
+	const char *field;
+	const char *header_end;
+	git_buf commit = GIT_BUF_INIT;
+
+	/* We start by identifying the end of the commit header */
+	header_end = strstr(commit_content, "\n\n");
+	if (!header_end) {
+		giterr_set(GITERR_INVALID, "malformed commit contents");
+		return -1;
+	}
+
+	field = signature_field ? signature_field : "gpgsig";
+
+	/* The header ends after the first LF */
+	header_end++;
+	git_buf_put(&commit, commit_content, header_end - commit_content);
+	format_header_field(&commit, field, signature);
+	git_buf_puts(&commit, header_end);
+
+	if (git_buf_oom(&commit))
+		return -1;
+
+	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0)
+		goto cleanup;
+
+	if ((error = git_odb_write(out, odb, commit.ptr, commit.size, GIT_OBJ_COMMIT)) < 0)
+		goto cleanup;
+
+cleanup:
+	git_buf_free(&commit);
+	return error;
+}
diff --git a/tests/commit/write.c b/tests/commit/write.c
index 9d1ae78..030d415 100644
--- a/tests/commit/write.c
+++ b/tests/commit/write.c
@@ -298,3 +298,103 @@ void test_commit_write__can_validate_objects(void)
 	git_oid_fromstr(&parent_id, tree_id_str);
 	cl_git_fail(create_commit_from_ids(&commit_id, &tree_id, &parent_id));
 }
+
+void test_commit_write__attach_singleline_signature(void)
+{
+	const char *sig = "magic word: pretty please";
+
+	const char *data =  "tree 6b79e22d69bf46e289df0345a14ca059dfc9bdf6\n\
+parent 34734e478d6cf50c27c9d69026d93974d052c454\n\
+author Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+committer Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+\n\
+a simple commit which works\n";
+
+	const char *complete =  "tree 6b79e22d69bf46e289df0345a14ca059dfc9bdf6\n\
+parent 34734e478d6cf50c27c9d69026d93974d052c454\n\
+author Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+committer Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+magicsig magic word: pretty please\n\
+\n\
+a simple commit which works\n";
+
+	git_oid id;
+	git_odb *odb;
+	git_odb_object *obj;
+
+	cl_git_pass(git_commit_create_with_signature(&id, g_repo, data, sig, "magicsig"));
+
+	cl_git_pass(git_repository_odb(&odb, g_repo));
+	cl_git_pass(git_odb_read(&obj, odb, &id));
+	cl_assert_equal_s(complete, git_odb_object_data(obj));
+
+	git_odb_object_free(obj);
+	git_odb_free(odb);
+}
+
+void test_commit_write__attach_multiline_signature(void)
+{
+		const char *gpgsig = "-----BEGIN PGP SIGNATURE-----\n\
+Version: GnuPG v1.4.12 (Darwin)\n\
+\n\
+iQIcBAABAgAGBQJQ+FMIAAoJEH+LfPdZDSs1e3EQAJMjhqjWF+WkGLHju7pTw2al\n\
+o6IoMAhv0Z/LHlWhzBd9e7JeCnanRt12bAU7yvYp9+Z+z+dbwqLwDoFp8LVuigl8\n\
+JGLcnwiUW3rSvhjdCp9irdb4+bhKUnKUzSdsR2CK4/hC0N2i/HOvMYX+BRsvqweq\n\
+AsAkA6dAWh+gAfedrBUkCTGhlNYoetjdakWqlGL1TiKAefEZrtA1TpPkGn92vbLq\n\
+SphFRUY9hVn1ZBWrT3hEpvAIcZag3rTOiRVT1X1flj8B2vGCEr3RrcwOIZikpdaW\n\
+who/X3xh/DGbI2RbuxmmJpxxP/8dsVchRJJzBwG+yhwU/iN3MlV2c5D69tls/Dok\n\
+6VbyU4lm/ae0y3yR83D9dUlkycOnmmlBAHKIZ9qUts9X7mWJf0+yy2QxJVpjaTGG\n\
+cmnQKKPeNIhGJk2ENnnnzjEve7L7YJQF6itbx5VCOcsGh3Ocb3YR7DMdWjt7f8pu\n\
+c6j+q1rP7EpE2afUN/geSlp5i3x8aXZPDj67jImbVCE/Q1X9voCtyzGJH7MXR0N9\n\
+ZpRF8yzveRfMH8bwAJjSOGAFF5XkcR/RNY95o+J+QcgBLdX48h+ZdNmUf6jqlu3J\n\
+7KmTXXQcOVpN6dD3CmRFsbjq+x6RHwa8u1iGn+oIkX908r97ckfB/kHKH7ZdXIJc\n\
+cpxtDQQMGYFpXK/71stq\n\
+=ozeK\n\
+-----END PGP SIGNATURE-----";
+
+	const char *data =  "tree 6b79e22d69bf46e289df0345a14ca059dfc9bdf6\n\
+parent 34734e478d6cf50c27c9d69026d93974d052c454\n\
+author Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+committer Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+\n\
+a simple commit which works\n";
+
+const char *complete = "tree 6b79e22d69bf46e289df0345a14ca059dfc9bdf6\n\
+parent 34734e478d6cf50c27c9d69026d93974d052c454\n\
+author Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+committer Ben Burkert <ben@benburkert.com> 1358451456 -0800\n\
+gpgsig -----BEGIN PGP SIGNATURE-----\n\
+ Version: GnuPG v1.4.12 (Darwin)\n\
+ \n\
+ iQIcBAABAgAGBQJQ+FMIAAoJEH+LfPdZDSs1e3EQAJMjhqjWF+WkGLHju7pTw2al\n\
+ o6IoMAhv0Z/LHlWhzBd9e7JeCnanRt12bAU7yvYp9+Z+z+dbwqLwDoFp8LVuigl8\n\
+ JGLcnwiUW3rSvhjdCp9irdb4+bhKUnKUzSdsR2CK4/hC0N2i/HOvMYX+BRsvqweq\n\
+ AsAkA6dAWh+gAfedrBUkCTGhlNYoetjdakWqlGL1TiKAefEZrtA1TpPkGn92vbLq\n\
+ SphFRUY9hVn1ZBWrT3hEpvAIcZag3rTOiRVT1X1flj8B2vGCEr3RrcwOIZikpdaW\n\
+ who/X3xh/DGbI2RbuxmmJpxxP/8dsVchRJJzBwG+yhwU/iN3MlV2c5D69tls/Dok\n\
+ 6VbyU4lm/ae0y3yR83D9dUlkycOnmmlBAHKIZ9qUts9X7mWJf0+yy2QxJVpjaTGG\n\
+ cmnQKKPeNIhGJk2ENnnnzjEve7L7YJQF6itbx5VCOcsGh3Ocb3YR7DMdWjt7f8pu\n\
+ c6j+q1rP7EpE2afUN/geSlp5i3x8aXZPDj67jImbVCE/Q1X9voCtyzGJH7MXR0N9\n\
+ ZpRF8yzveRfMH8bwAJjSOGAFF5XkcR/RNY95o+J+QcgBLdX48h+ZdNmUf6jqlu3J\n\
+ 7KmTXXQcOVpN6dD3CmRFsbjq+x6RHwa8u1iGn+oIkX908r97ckfB/kHKH7ZdXIJc\n\
+ cpxtDQQMGYFpXK/71stq\n\
+ =ozeK\n\
+ -----END PGP SIGNATURE-----\n\
+\n\
+a simple commit which works\n";
+
+	git_oid one, two;
+	git_odb *odb;
+	git_odb_object *obj;
+
+	cl_git_pass(git_commit_create_with_signature(&one, g_repo, data, gpgsig, "gpgsig"));
+	cl_git_pass(git_commit_create_with_signature(&two, g_repo, data, gpgsig, NULL));
+
+	cl_assert(!git_oid_cmp(&one, &two));
+	cl_git_pass(git_repository_odb(&odb, g_repo));
+	cl_git_pass(git_odb_read(&obj, odb, &one));
+	cl_assert_equal_s(complete, git_odb_object_data(obj));
+
+	git_odb_object_free(obj);
+	git_odb_free(odb);
+}