Please use "error and out" logic (Re: [PATCH] Avoid privileged segfault in GetNCChanges and add many more tests)

[Ralph Böhme]

On Wed, Aug 09, 2017 at 09:10:22AM -0400, Simo via samba-technical wrote:
> Thanks metze,
> readability and modifiability of code are very important, and become
> even more important as a project grows and ages.
> 
> It would be nice to add a style section to the docs that more
> forcefully and clearly explain these subtle coding style issues.

patch attached.

Cheerio!
-slow
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From 7e2fa6d9c53a0d80b2f1b6c0b867ccbcb5e0716b Mon Sep 17 00:00:00 2001
From: Ralph Boehme <slow at samba.org>
Date: Wed, 9 Aug 2017 15:24:41 +0200
Subject: [PATCH] README.Coding: add "Error and out logic"

Signed-off-by: Ralph Boehme <slow at samba.org>
---
 README.Coding | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 STEPS.org     |  1 -
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/README.Coding b/README.Coding
index 19a363f..e89925c 100644
--- a/README.Coding
+++ b/README.Coding
@@ -445,6 +445,55 @@ The only exception is the test code that depends repeated use of calls
 like CHECK_STATUS, CHECK_VAL and others.
 
 
+Error and out logic
+-------------------
+
+Don't do this:
+
+	frame = talloc_stackframe();
+
+	if (ret == LDB_SUCCESS) {
+		if (result->count == 0) {
+			ret = LDB_ERR_NO_SUCH_OBJECT;
+		} else {
+			struct ldb_message *match =
+				get_best_match(dn, result);
+			if (match == NULL) {
+				TALLOC_FREE(frame);
+				return LDB_ERR_OPERATIONS_ERROR;
+			}
+			*msg = talloc_move(mem_ctx, &match);
+		}
+	}
+
+	TALLOC_FREE(frame);
+	return ret;
+
+It should be:
+
+	frame = talloc_stackframe();
+
+	if (ret != LDB_SUCCESS) {
+		TALLOC_FREE(frame);
+		return ret;
+	}
+
+	if (result->count == 0) {
+		TALLOC_FREE(frame);
+		return LDB_ERR_NO_SUCH_OBJECT;
+	}
+
+	match = get_best_match(dn, result);
+	if (match == NULL) {
+		TALLOC_FREE(frame);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	*msg = talloc_move(mem_ctx, &match);
+	TALLOC_FREE(frame);
+	return LDB_SUCCESS;
+
+
 DEBUG statements
 ----------------
 
diff --git a/STEPS.org b/STEPS.org
index 1986640..cb532fe 100644
--- a/STEPS.org
+++ b/STEPS.org
@@ -89,7 +89,6 @@ In *struct share_mode_data* and *struct share_mode_entry*:
 - bool *shared_persistent* in share_mode_entry
 See [[Design][Design]] for an explenation.
 
-
 * Implementation
 ** SMB layer
 *** Flag checks in SMB2_CREATE_DURABLE_HANDLE_RECONNECT_V2 (MS-SMB2 3.3.5.9.12)
-- 
2.9.4