Addressed code review comments.

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) {

upb/def.h

@@ -307,11 +307,26 @@ class upb::FieldDef {
   uint32_t number() const;   /* Returns 0 if uninitialized. */
   bool is_extension() const;
 
-  /* Get the JSON name for this field.  This will copy the JSON name into the
-   * given buffer, which must have size of at least "strlen(name()) + 1".
-   * The string will be NULL-terminated.  Returns false if uninitialized.
+  /* Copies the JSON name for this field into the given buffer.  Returns the
+   * actual size of the JSON name, including the NULL terminator.  If the
+   * return value is 0, the JSON name is unset.  If the return value is
+   * greater than len, the JSON name was truncated.  The buffer is always
+   * NULL-terminated if len > 0.
+   *
+   * The JSON name always defaults to a camelCased version of the regular
+   * name.  However if the regular name is unset, the JSON name will be unset
+   * also.
    */
-  bool GetJsonName(char* buf) const;
+  size_t GetJsonName(char* buf, size_t len) const;
+
+  /* Convenience version of the above function which copies the JSON name
+   * into the given string, returning false if the name is not set. */
+  template <class T>
+  bool GetJsonName(T* str) {
+    str->resize(GetJsonName(NULL, 0));
+    GetJsonName(&(*str)[0], str->size());
+    return str->size() > 0;
+  }
 
   /* For UPB_TYPE_MESSAGE fields only where is_tag_delimited() == false,
    * indicates whether this field should have lazy parsing handlers that yield
@@ -552,7 +567,7 @@ const char *upb_fielddef_name(const upb_fielddef *f);
 bool upb_fielddef_isextension(const upb_fielddef *f);
 bool upb_fielddef_lazy(const upb_fielddef *f);
 bool upb_fielddef_packed(const upb_fielddef *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 upb_msgdef *upb_fielddef_containingtype(const upb_fielddef *f);
 const upb_oneofdef *upb_fielddef_containingoneof(const upb_fielddef *f);
 upb_msgdef *upb_fielddef_containingtype_mutable(upb_fielddef *f);
@@ -1335,6 +1350,9 @@ inline const char* FieldDef::name() const { return upb_fielddef_name(this); }
 inline bool FieldDef::is_extension() const {
   return upb_fielddef_isextension(this);
 }
+inline size_t FieldDef::GetJsonName(char* buf, size_t len) const {
+  return upb_fielddef_getjsonname(this, buf, len);
+}
 inline bool FieldDef::lazy() const {
   return upb_fielddef_lazy(this);
 }

upb/json/parser.c

@@ -1609,6 +1609,11 @@ static void add_jsonname_table(upb_json_parsermethod *m, const upb_msgdef* md) {
   upb_msg_field_iter i;
   upb_strtable *t;
 
+  /* It would be nice to stack-allocate this, but protobufs do not limit the
+   * length of fields to any reasonable limit. */
+  char *buf = NULL;
+  size_t len = 0;
+
   if (upb_inttable_lookupptr(&m->name_tables, md, NULL)) {
     return;
   }
@@ -1622,17 +1627,20 @@ static void add_jsonname_table(upb_json_parsermethod *m, const upb_msgdef* md) {
       !upb_msg_field_done(&i);
       upb_msg_field_next(&i)) {
     const upb_fielddef *f = upb_msg_iter_field(&i);
-    /* It would be nice to stack-allocate this, but protobufs do not limit the
-     * length of fields to any reasonable limit. */
-    char *buf = malloc(strlen(upb_fielddef_name(f)) + 1);
-    upb_fielddef_getjsonname(f, buf);
+    size_t field_len = upb_fielddef_getjsonname(f, buf, len);
+    if (field_len > len) {
+      buf = realloc(buf, field_len);
+      len = field_len;
+      upb_fielddef_getjsonname(f, buf, len);
+    }
     upb_strtable_insert(t, buf, upb_value_constptr(f));
-    free(buf);
 
     if (upb_fielddef_issubmsg(f)) {
       add_jsonname_table(m, upb_fielddef_msgsubdef(f));
     }
   }
+
+  free(buf);
 }
 
 /* Public API *****************************************************************/

upb/json/parser.rl

@@ -1344,6 +1344,11 @@ static void add_jsonname_table(upb_json_parsermethod *m, const upb_msgdef* md) {
   upb_msg_field_iter i;
   upb_strtable *t;
 
+  /* It would be nice to stack-allocate this, but protobufs do not limit the
+   * length of fields to any reasonable limit. */
+  char *buf = NULL;
+  size_t len = 0;
+
   if (upb_inttable_lookupptr(&m->name_tables, md, NULL)) {
     return;
   }
@@ -1357,17 +1362,20 @@ static void add_jsonname_table(upb_json_parsermethod *m, const upb_msgdef* md) {
       !upb_msg_field_done(&i);
       upb_msg_field_next(&i)) {
     const upb_fielddef *f = upb_msg_iter_field(&i);
-    /* It would be nice to stack-allocate this, but protobufs do not limit the
-     * length of fields to any reasonable limit. */
-    char *buf = malloc(strlen(upb_fielddef_name(f)) + 1);
-    upb_fielddef_getjsonname(f, buf);
+    size_t field_len = upb_fielddef_getjsonname(f, buf, len);
+    if (field_len > len) {
+      buf = realloc(buf, field_len);
+      len = field_len;
+      upb_fielddef_getjsonname(f, buf, len);
+    }
     upb_strtable_insert(t, buf, upb_value_constptr(f));
-    free(buf);
 
     if (upb_fielddef_issubmsg(f)) {
       add_jsonname_table(m, upb_fielddef_msgsubdef(f));
     }
   }
+
+  free(buf);
 }
 
 /* Public API *****************************************************************/

upb/json/printer.c

@@ -47,9 +47,10 @@ void freestrpc(void *ptr) {
 strpc *newstrpc(upb_handlers *h, const upb_fielddef *f) {
   /* TODO(haberman): handle malloc failure. */
   strpc *ret = malloc(sizeof(*ret));
-  ret->ptr = malloc(strlen(upb_fielddef_name(f)) + 1);
-  upb_fielddef_getjsonname(f, ret->ptr);
-  ret->len = strlen(ret->ptr);
+  ret->len = upb_fielddef_getjsonname(f, NULL, 0);
+  ret->ptr = malloc(ret->len);
+  upb_fielddef_getjsonname(f, ret->ptr, ret->len);
+  ret->len--;  /* NULL */
 
   upb_handlers_addcleanup(h, ret, freestrpc);
   return ret;