From 34fc22a7c22777ca26b01b760e468c24e911492a Mon Sep 17 00:00:00 2001
From: Weaselbot <weaselbot@weaselab.dev>
Date: Mon, 29 Jun 2026 13:53:31 -0400
Subject: [PATCH] Handle null parser in WeaselJsonParser_reset and _destroy

WeaselJsonParser_create can return nullptr when allocation fails or the
requested stack size is too small. Previously, passing that nullptr to
WeaselJsonParser_reset or WeaselJsonParser_destroy dereferenced it before
doing any work, causing immediate undefined behavior.

Add an early null check to both functions so they behave like free(nullptr)
(i.e., are a safe no-op). Also add a doctest case covering both a null
returned from create and a literal nullptr.

Closes #41
---
 src/lib.cpp  |  6 ++++++
 src/test.cpp | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/lib.cpp b/src/lib.cpp
index cd1ea32..715f2c6 100644
--- a/src/lib.cpp
+++ b/src/lib.cpp
@@ -29,11 +29,17 @@ WeaselJsonParser_create(int stackSize, const WeaselJsonCallbacks *callbacks,
 
 __attribute__((visibility("default"))) void
 WeaselJsonParser_reset(WeaselJsonParser *parser) {
+  if (parser == nullptr) {
+    return;
+  }
   ((Parser3 *)parser)->reset();
 }
 
 __attribute__((visibility("default"))) void
 WeaselJsonParser_destroy(WeaselJsonParser *parser) {
+  if (parser == nullptr) {
+    return;
+  }
   ((Parser3 *)parser)->~Parser3();
   free(parser);
 }
diff --git a/src/test.cpp b/src/test.cpp
index eec6669..d13d353 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -246,6 +246,20 @@ TEST_CASE("create rejects too-small stack") {
   WeaselJsonParser_destroy(parser);
 }
 
+TEST_CASE("reset and destroy accept null parser") {
+  // Creation can legitimately fail and return null. The cleanup functions must
+  // tolerate a null pointer the same way free(nullptr) is a no-op.
+  auto c = noopCallbacks();
+  WeaselJsonParser *parser = WeaselJsonParser_create(-1, &c, nullptr, 0);
+  REQUIRE(parser == nullptr);
+  WeaselJsonParser_reset(parser);   // must not crash
+  WeaselJsonParser_destroy(parser); // must not crash
+
+  // Calling reset/destroy on literal nullptr directly must also be safe.
+  WeaselJsonParser_reset(nullptr);
+  WeaselJsonParser_destroy(nullptr);
+}
+
 TEST_CASE("parse rejects negative length") {
   auto c = noopCallbacks();
   auto *parser = WeaselJsonParser_create(1024, &c, nullptr, 0);