1 files changed, 19 insertions, 9 deletions

diff --git a/upb/def.c b/upb/def.c
index a1dc192..abb5b05 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -722,33 +722,43 @@ const char *upb_fielddef_name(const upb_fielddef *f) {
   return upb_def_fullname(upb_fielddef_upcast(f));
 }
 
-bool upb_fielddef_getjsonname(const upb_fielddef *f, char *buf) {
+size_t upb_fielddef_getjsonname(const upb_fielddef *f, char *buf, size_t len) {
   const char *name = upb_fielddef_name(f);
-  size_t i, j;
+  size_t src, dst = 0;
   bool ucase_next = false;
 
-  if (!name) return false;
+#define WRITE(byte) \
+  ++dst; \
+  if (dst < len) buf[dst - 1] = byte; \
+  else if (dst == len) buf[dst - 1] = '\0'
+
+  if (!name) {
+    WRITE('\0');
+    return 0;
+  }
 
   /* Implement the transformation as described in the spec:
    *   1. upper case all letters after an underscore.
    *   2. remove all underscores.
    */
-  for (i = 0, j = 0; name[i]; i++) {
-    if (name[i] == '_') {
+  for (src = 0; name[src]; src++) {
+    if (name[src] == '_') {
       ucase_next = true;
       continue;
     }
 
     if (ucase_next) {
-      buf[j++] = toupper(name[i]);
+      WRITE(toupper(name[src]));
       ucase_next = false;
     } else {
-      buf[j++] = name[i];
+      WRITE(name[src]);
     }
   }
 
-  buf[j] = '\0';
-  return true;
+  WRITE('\0');
+  return dst;
+
+#undef WRITE
 }
 
 const upb_msgdef *upb_fielddef_containingtype(const upb_fielddef *f) {