node: address review — add BUFSIZE_MAX, drop realloc NULL check, document allocator contract

Per @nwellnhof feedback:
- Remove realloc NULL check (allocators are assumed non-NULL by design).
- Add BUFSIZE_MAX macro to buffer.h; use it in both node.c and buffer.c
  instead of hardcoded INT32_MAX.

Per @jgm + @nwellnhof:
- Document the allocator contract in cmark.h: allocation functions must
  not return NULL.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Alearner12

src/buffer.c

@@ -40,10 +40,10 @@ void cmark_strbuf_grow(cmark_strbuf *buf, bufsize_t target_size) {
   if (target_size < buf->asize)
     return;
 
-  if (target_size > (bufsize_t)(INT32_MAX / 2)) {
+  if (target_size > (bufsize_t)(BUFSIZE_MAX / 2)) {
     fprintf(stderr,
       "[cmark] cmark_strbuf_grow requests buffer with size > %d, aborting\n",
-         (INT32_MAX / 2));
+         (BUFSIZE_MAX / 2));
     abort();
   }
 

src/buffer.h

@@ -14,6 +14,7 @@ extern "C" {
 #endif
 
 typedef int32_t bufsize_t;
+#define BUFSIZE_MAX INT32_MAX
 
 typedef struct {
   cmark_mem *mem;

src/cmark.h

@@ -93,7 +93,9 @@ typedef struct cmark_iter cmark_iter;
  */
 
 /** Defines the memory allocation functions to be used by CMark
- * when parsing and allocating a document tree
+ * when parsing and allocating a document tree.  Allocation functions
+ * must not return NULL; if they are unable to satisfy a request,
+ * they must abort the program (e.g. by calling abort()).
  */
 typedef struct cmark_mem {
   void *(*calloc)(size_t, size_t);

src/node.c

@@ -1,5 +1,4 @@
 #include <stdbool.h>
-#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -272,26 +271,19 @@ static bufsize_t cmark_set_cstr(cmark_mem *mem, unsigned char **dst,
   bufsize_t len;
 
   if (src && src[0]) {
-      size_t srclen = strlen(src);
-      if (srclen > (size_t)(INT32_MAX - 1)) {
-        fprintf(stderr,
-                "[cmark] cmark_set_cstr: input exceeds %d bytes, aborting\n",
-                INT32_MAX - 1);
-        abort();
-      }
-      len = (bufsize_t)srclen;
-      unsigned char *buf =
-          (unsigned char *)mem->realloc(NULL, (size_t)len + 1);
-      if (buf == NULL) {
-        fprintf(stderr,
-                "[cmark] cmark_set_cstr: allocator returned NULL, aborting\n");
-        abort();
-      }
-      memcpy(buf, src, (size_t)len + 1);
-      *dst = buf;
+    size_t srclen = strlen(src);
+    if (srclen > (size_t)BUFSIZE_MAX - 1) {
+      fprintf(stderr,
+              "[cmark] cmark_set_cstr: input exceeds %d bytes, aborting\n",
+              BUFSIZE_MAX - 1);
+      abort();
+    }
+    len = (bufsize_t)srclen;
+    *dst = (unsigned char *)mem->realloc(NULL, (size_t)len + 1);
+    memcpy(*dst, src, (size_t)len + 1);
   } else {
-      len = 0;
-      *dst = NULL;
+    len = 0;
+    *dst = NULL;
   }
   if (old) {
     mem->free(old);