From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 26 Sep 2022 17:36:38 +0000 (-0400)
Subject: Fix: Handle empty string in lttng_event_field_value_string_create_with_size
X-Git-Url: https://git.efficios.com/?a=commitdiff_plain;h=8ce733e56bbab1ca5507b868e8093f4cb5cc87b7;p=deliverable%2Flttng-tools.git

Fix: Handle empty string in lttng_event_field_value_string_create_with_size

When using the event notification capture API, empty strings are
represented by a NULL pointer with a size=0 in the msgpack object.
The NULL pointer is unexpected, which triggers an assertion in
lttng_event_field_value_string_create_with_size.

Fix this by duplicating an empty string ("") when a size=0 is
encountered. This ensures that users of the API don't end up with an
unexpected NULL pointer. Indeed, the sample program notif-app.c in the
LTTng website documentation does not expect a NULL pointer.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I7c3a839dbbeeb95a1b3bf6ddc3205a2f6b4538e3
---

diff --git a/src/common/event-field-value.c b/src/common/event-field-value.c
index b57c7c53e..15ff36f4b 100644
--- a/src/common/event-field-value.c
+++ b/src/common/event-field-value.c
@@ -190,8 +190,16 @@ struct lttng_event_field_value *lttng_event_field_value_string_create_with_size(
 		goto error;
 	}
 
-	assert(val);
-	field_val->val = strndup(val, size);
+	if (size) {
+		assert(val);
+		field_val->val = strndup(val, size);
+	} else {
+		/*
+		 * User code do not expect a NULL string pointer.
+		 * Populate with an empty string when length is 0.
+		 */
+		field_val->val = strdup("");
+	}
 	if (!field_val->val) {
 		goto error;
 	}