Allow users to replace allocator and handle OOM everywhere. (#800)

* Adds an indirection to every allocation/deallocation to allow users to 
  plug in ones of their choosing (use custom functions, jemalloc, etc).

* Gracefully handle OOM everywhere in hiredis.  This should make it possible
  for users of the library to have more flexibility in how they handle such situations.

* Changes `redisReaderTask->elements` from an `int` to a `long long` to prevent
  a possible overflow when transferring the task elements into a `redisReply`.

* Adds a configurable `max elements` member to `redisReader` that defaults to
  2^32 - 1.  This can be set to "unlimited" by setting the value to zero.

1 files changed, 44 insertions, 6 deletions

diff --git a/alloc.h b/alloc.h
index 2c9b04e..b581e56 100644
--- a/alloc.h
+++ b/alloc.h
@@ -31,23 +31,61 @@
 #ifndef HIREDIS_ALLOC_H
 #define HIREDIS_ALLOC_H
 
-#include <stdlib.h> /* for size_t */
-
-#ifndef HIREDIS_OOM_HANDLER
-#define HIREDIS_OOM_HANDLER abort()
-#endif
+#include <stddef.h> /* for size_t */
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/* Structure pointing to our actually configured allocators */
+typedef struct hiredisAllocFuncs {
+    void *(*malloc)(size_t);
+    void *(*calloc)(size_t,size_t);
+    void *(*realloc)(void*,size_t);
+    char *(*strdup)(const char*);
+    void (*free)(void*);
+} hiredisAllocFuncs;
+
+hiredisAllocFuncs hiredisSetAllocators(hiredisAllocFuncs *ha);
+void hiredisResetAllocators(void);
+
+#ifndef _WIN32
+
+/* Hiredis' configured allocator function pointer struct */
+extern hiredisAllocFuncs hiredisAllocFns;
+
+static inline void *hi_malloc(size_t size) {
+    return hiredisAllocFns.malloc(size);
+}
+
+static inline void *hi_calloc(size_t nmemb, size_t size) {
+    return hiredisAllocFns.calloc(nmemb, size);
+}
+
+static inline void *hi_realloc(void *ptr, size_t size) {
+    return hiredisAllocFns.realloc(ptr, size);
+}
+
+static inline char *hi_strdup(const char *str) {
+    return hiredisAllocFns.strdup(str);
+}
+
+static inline void hi_free(void *ptr) {
+    hiredisAllocFns.free(ptr);
+}
+
+#else
+
 void *hi_malloc(size_t size);
 void *hi_calloc(size_t nmemb, size_t size);
 void *hi_realloc(void *ptr, size_t size);
 char *hi_strdup(const char *str);
+void hi_free(void *ptr);
+
+#endif
 
 #ifdef __cplusplus
 }
 #endif
 
-#endif  /* HIREDIS_ALLOC_H */
+#endif /* HIREDIS_ALLOC_H */