reftable: introduce `reftable_strdup()`

The reftable library provides the ability to swap out allocators. There
is a gap here though, because we continue to use `xstrdup()` even in the
case where all the other allocators have been swapped out.

Introduce `reftable_strdup()` that uses `reftable_malloc()` to do the
allocation.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reftable/basics.c

@@ -43,6 +43,16 @@ void *reftable_calloc(size_t nelem, size_t elsize)
 	return p;
 }
 
+char *reftable_strdup(const char *str)
+{
+	size_t len = strlen(str);
+	char *result = reftable_malloc(len + 1);
+	if (!result)
+		return NULL;
+	memcpy(result, str, len + 1);
+	return result;
+}
+
 void reftable_set_alloc(void *(*malloc)(size_t),
 			void *(*realloc)(void *, size_t), void (*free)(void *))
 {

reftable/basics.h

@@ -54,6 +54,7 @@ void *reftable_malloc(size_t sz);
 void *reftable_realloc(void *p, size_t sz);
 void reftable_free(void *p);
 void *reftable_calloc(size_t nelem, size_t elsize);
+char *reftable_strdup(const char *str);
 
 #define REFTABLE_ALLOC_ARRAY(x, alloc) (x) = reftable_malloc(st_mult(sizeof(*(x)), (alloc)))
 #define REFTABLE_CALLOC_ARRAY(x, alloc) (x) = reftable_calloc((alloc), sizeof(*(x)))