multi: add handle asserts in DEBUG builds

For GOOD_EASY_HANDLE and GOOD_MULTI_HANDLE checks

- allow NULL pointers to "just" return an error as before
- fail hard on nun-NULL pointers that no longer show the MAGICs

Closes #10812

2 files changed, 18 insertions, 0 deletions

diff --git a/lib/multi.c b/lib/multi.c
index 731b2598f..262321d9d 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -90,8 +90,17 @@
 
 #define CURL_MULTI_HANDLE 0x000bab1e
 
+#ifdef DEBUGBUILD
+/* On a debug build, we want to fail hard on multi handles that
+ * are not NULL, but no longer have the MAGIC touch. This gives
+ * us early warning on things only discovered by valgrind otherwise. */
+#define GOOD_MULTI_HANDLE(x) \
+  (((x) && (x)->magic == CURL_MULTI_HANDLE)? TRUE: \
+  (DEBUGASSERT(!(x)), FALSE))
+#else
 #define GOOD_MULTI_HANDLE(x) \
   ((x) && (x)->magic == CURL_MULTI_HANDLE)
+#endif
 
 static CURLMcode singlesocket(struct Curl_multi *multi,
                               struct Curl_easy *data);
diff --git a/lib/urldata.h b/lib/urldata.h
index 8b54518d2..86b3da718 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -208,8 +208,17 @@ typedef CURLcode (*Curl_datastream)(struct Curl_easy *data,
 #define UPLOADBUFFER_MIN CURL_MAX_WRITE_SIZE
 
 #define CURLEASY_MAGIC_NUMBER 0xc0dedbadU
+#ifdef DEBUGBUILD
+/* On a debug build, we want to fail hard on easy handles that
+ * are not NULL, but no longer have the MAGIC touch. This gives
+ * us early warning on things only discovered by valgrind otherwise. */
+#define GOOD_EASY_HANDLE(x) \
+  (((x) && ((x)->magic == CURLEASY_MAGIC_NUMBER))? TRUE: \
+  (DEBUGASSERT(!(x)), FALSE))
+#else
 #define GOOD_EASY_HANDLE(x) \
   ((x) && ((x)->magic == CURLEASY_MAGIC_NUMBER))
+#endif
 
 #ifdef HAVE_GSSAPI
 /* Types needed for krb5-ftp connections */