Make git_message_prettify return bytes written

If you want to be absolutely safe with git_message_prettify, you
can now pass a NULL pointer for the buffer and get back the number
of bytes that would be copied into the buffer.

This means that an error is a non-negative return code and a
success will be greater than zero from this function.

3 files changed, 39 insertions, 30 deletions

diff --git a/include/git2/message.h b/include/git2/message.h
index 7f2558583..b42cb7677 100644
--- a/include/git2/message.h
+++ b/include/git2/message.h
@@ -23,8 +23,9 @@ GIT_BEGIN_DECL
  *
  * Optionally, can remove lines starting with a "#".
  *
- * @param message_out The user allocated buffer which will be filled with 
- * the cleaned up message.
+ * @param message_out The user allocated buffer which will be filled with
+ * the cleaned up message. Pass NULL if you just want to get the size of the
+ * prettified message as the output value.
  *
  * @param size The size of the allocated buffer message_out.
  *
@@ -32,7 +33,8 @@ GIT_BEGIN_DECL
  *
  * @param strip_comments 1 to remove lines starting with a "#", 0 otherwise.
  *
- * @return GIT_SUCCESS or an error code
+ * @return -1 on error, else number of characters in prettified message
+ * including the trailing NUL byte
  */
 GIT_EXTERN(int) git_message_prettify(char *message_out, size_t buffer_size, const char *message, int strip_comments);
 
diff --git a/src/message.c b/src/message.c
index a5cc26237..e6dedc9fb 100644
--- a/src/message.c
+++ b/src/message.c
@@ -62,23 +62,25 @@ int git_message__prettify(git_buf *message_out, const char *message, int strip_c
 int git_message_prettify(char *message_out, size_t buffer_size, const char *message, int strip_comments)
 {
 	git_buf buf = GIT_BUF_INIT;
+	ssize_t out_size = -1;
 
-	assert(message_out && buffer_size);
+	if (message_out && buffer_size)
+		*message_out = '\0';
 
-	*message_out = '\0';
+	if (git_message__prettify(&buf, message, strip_comments) < 0)
+		goto done;
 
-	if (git_message__prettify(&buf, message, strip_comments) < 0) {
-		git_buf_free(&buf);
-		return -1;
-	}
-
-	if (buf.size + 1 > buffer_size) { /* +1 for NUL byte */
+	if (message_out && buf.size + 1 > buffer_size) { /* +1 for NUL byte */
 		giterr_set(GITERR_INVALID, "Buffer too short to hold the cleaned message");
-		return -1;
+		goto done;
 	}
 
-	git_buf_copy_cstr(message_out, buffer_size, &buf);
-	git_buf_free(&buf);
+	if (message_out)
+		git_buf_copy_cstr(message_out, buffer_size, &buf);
 
-	return 0;
+	out_size = buf.size + 1;
+
+done:
+	git_buf_free(&buf);
+	return out_size;
 }
diff --git a/tests-clar/object/commit/commitstagedfile.c b/tests-clar/object/commit/commitstagedfile.c
index 1e4affb8c..882fb49ae 100644
--- a/tests-clar/object/commit/commitstagedfile.c
+++ b/tests-clar/object/commit/commitstagedfile.c
@@ -109,7 +109,7 @@ void test_object_commit_commitstagedfile__generate_predictable_object_ids(void)
 	cl_git_pass(git_signature_new(&signature, "nulltoken", "emeric.fermas@gmail.com", 1323847743, 60));
 	cl_git_pass(git_tree_lookup(&tree, repo, &tree_oid));
 
-	cl_git_pass(git_message_prettify(buffer, 128, "Initial commit", 0));
+	cl_assert_equal_i(16, git_message_prettify(buffer, 128, "Initial commit", 0));
 
 	cl_git_pass(git_commit_create_v(
 		&commit_oid,
@@ -133,34 +133,35 @@ void test_object_commit_commitstagedfile__message_prettify(void)
 {
 	char buffer[100];
 
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "", 0));
+	cl_assert(git_message_prettify(buffer, sizeof(buffer), "", 0) == 1);
 	cl_assert_equal_s(buffer, "");
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "", 1));
+	cl_assert(git_message_prettify(buffer, sizeof(buffer), "", 1) == 1);
 	cl_assert_equal_s(buffer, "");
 
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "Short", 0));
-	cl_assert_equal_s(buffer, "Short\n");
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "Short", 1));
-	cl_assert_equal_s(buffer, "Short\n");
+	cl_assert_equal_i(7, git_message_prettify(buffer, sizeof(buffer), "Short", 0));
+	cl_assert_equal_s("Short\n", buffer);
+	cl_assert_equal_i(7, git_message_prettify(buffer, sizeof(buffer), "Short", 1));
+	cl_assert_equal_s("Short\n", buffer);
 
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "This is longer\nAnd multiline\n# with some comments still in\n", 0));
+	cl_assert(git_message_prettify(buffer, sizeof(buffer), "This is longer\nAnd multiline\n# with some comments still in\n", 0) > 0);
 	cl_assert_equal_s(buffer, "This is longer\nAnd multiline\n# with some comments still in\n");
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer), "This is longer\nAnd multiline\n# with some comments still in\n", 1));
+
+	cl_assert(git_message_prettify(buffer, sizeof(buffer), "This is longer\nAnd multiline\n# with some comments still in\n", 1) > 0);
 	cl_assert_equal_s(buffer, "This is longer\nAnd multiline\n");
 
 	/* try out overflow */
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer),
+	cl_assert(git_message_prettify(buffer, sizeof(buffer),
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890"
 		"1234567890" "1234567890" "1234567890" "1234567890" "12345678",
-		0));
+		0) > 0);
 	cl_assert_equal_s(buffer,
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890"
 		"1234567890" "1234567890" "1234567890" "1234567890" "12345678\n");
 
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer),
+	cl_assert(git_message_prettify(buffer, sizeof(buffer),
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890"
 		"1234567890" "1234567890" "1234567890" "1234567890" "12345678\n",
-		0));
+		0) > 0);
 	cl_assert_equal_s(buffer,
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890"
 		"1234567890" "1234567890" "1234567890" "1234567890" "12345678\n");
@@ -182,9 +183,13 @@ void test_object_commit_commitstagedfile__message_prettify(void)
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890""x",
 		0));
 
-	cl_git_pass(git_message_prettify(buffer, sizeof(buffer),
+	cl_assert(git_message_prettify(buffer, sizeof(buffer),
 		"1234567890" "1234567890" "1234567890" "1234567890" "1234567890\n"
 		"# 1234567890" "1234567890" "1234567890" "1234567890" "1234567890\n"
 		"1234567890",
-		1));
+		1) > 0);
+
+	cl_assert(git_message_prettify(NULL, 0, "", 0) == 1);
+	cl_assert(git_message_prettify(NULL, 0, "Short test", 0) == 12);
+	cl_assert(git_message_prettify(NULL, 0, "Test\n# with\nComments", 1) == 15);
 }