Refactoring: unify upb_msg.

The cost is that a upb_msg will now always have an overhead
of 2*sizeof(void*).  This is comparable to proto2 overhead.
The benefit is that upb_msg is now self-describing, and
read-only algorithms can now operate on a upb_msg regardless
of the memory-management scheme.

Also, upb_array and upb_string now know inherently if they
own their associated memory, and upb_array has a generic
pointer for memory management purposes like upb_msg does.

1 files changed, 57 insertions, 21 deletions

diff --git a/src/upb_string.h b/src/upb_string.h
index 528c8c8..7b63f1c 100644
--- a/src/upb_string.h
+++ b/src/upb_string.h
@@ -37,6 +37,7 @@ extern "C" {
 #define INLINE static inline
 #endif
 
+#define UPB_MAX(x, y) ((x) > (y) ? (x) : (y))
 #define UPB_MIN(x, y) ((x) < (y) ? (x) : (y))
 
 struct upb_string {
@@ -44,45 +45,80 @@ struct upb_string {
    * ingrained convention that we follow it. */
   char *ptr;
   uint32_t byte_len;
+  uint32_t byte_size;  /* How many bytes of ptr we own. */
 };
 
+INLINE void upb_strinit(struct upb_string *str)
+{
+  str->ptr = NULL;
+  str->byte_len = 0;
+  str->byte_size = 0;
+}
+
+INLINE void upb_struninit(struct upb_string *str)
+{
+  if(str->byte_size) free(str->ptr);
+}
+
+INLINE struct upb_string *upb_strnew()
+{
+  struct upb_string *str = (struct upb_string*)malloc(sizeof(*str));
+  upb_strinit(str);
+  return str;
+}
+
+INLINE void upb_strfree(struct upb_string *str)
+{
+  upb_struninit(str);
+  free(str);
+}
+
+INLINE void upb_stralloc(struct upb_string *str, uint32_t size)
+{
+  if(str->byte_size < size) {
+    /* Need to resize. */
+    str->byte_size = size;
+    void *oldptr = str->byte_size == 0 ? NULL : str->ptr;
+    str->ptr = (char*)realloc(oldptr, str->byte_size);
+  }
+}
+
+INLINE void upb_strdrop(struct upb_string *str)
+{
+  upb_struninit(str);
+}
+
 INLINE bool upb_streql(struct upb_string *s1, struct upb_string *s2) {
   return s1->byte_len == s2->byte_len &&
          memcmp(s1->ptr, s2->ptr, s1->byte_len) == 0;
 }
 
-INLINE int upb_strcmp(struct upb_string s1, struct upb_string s2) {
-  size_t common_length = UPB_MIN(s1.byte_len, s2.byte_len);
-  int common_diff = memcmp(s1.ptr, s2.ptr, common_length);
-  if(common_diff == 0) return s1.byte_len - s2.byte_len;
-  else return common_diff;
+INLINE int upb_strcmp(struct upb_string *s1, struct upb_string *s2) {
+  size_t common_length = UPB_MIN(s1->byte_len, s2->byte_len);
+  int common_diff = memcmp(s1->ptr, s2->ptr, common_length);
+  return common_diff == 0 ? (int)s1->byte_len - (int)s2->byte_len : common_diff;
 }
 
 INLINE void upb_strcpy(struct upb_string *dest, struct upb_string *src) {
-  memcpy(dest->ptr, src->ptr, src->byte_len);
   dest->byte_len = src->byte_len;
+  upb_stralloc(dest, dest->byte_len);
+  memcpy(dest->ptr, src->ptr, src->byte_len);
 }
 
-INLINE struct upb_string upb_strdup(struct upb_string s) {
-  struct upb_string copy;
-  copy.ptr = (char*)malloc(s.byte_len);
-  copy.byte_len = s.byte_len;
-  memcpy(copy.ptr, s.ptr, s.byte_len);
+INLINE struct upb_string *upb_strdup(struct upb_string *s) {
+  struct upb_string *copy = upb_strnew();
+  upb_strcpy(copy, s);
   return copy;
 }
 
-INLINE struct upb_string upb_strdupc(char *s) {
-  struct upb_string copy;
-  copy.byte_len = strlen(s);
-  copy.ptr = (char*)malloc(copy.byte_len);
-  memcpy(copy.ptr, s, copy.byte_len);
+INLINE struct upb_string *upb_strdupc(char *s) {
+  struct upb_string *copy = upb_strnew();
+  copy->byte_len = strlen(s);
+  upb_stralloc(copy, copy->byte_len);
+  memcpy(copy->ptr, s, copy->byte_len);
   return copy;
 }
 
-INLINE void upb_strfree(struct upb_string s) {
-  free(s.ptr);
-}
-
 /* Reads an entire file into a newly-allocated string. */
 bool upb_strreadfile(const char *filename, struct upb_string *data);
 
@@ -95,7 +131,7 @@ bool upb_strreadfile(const char *filename, struct upb_string *data);
 /* Allows using upb_strings in printf, ie:
  *   struct upb_string str = UPB_STRLIT("Hello, World!\n");
  *   printf("String is: " UPB_STRFMT, UPB_STRARG(str)); */
-#define UPB_STRARG(str) (str).byte_len, (str).ptr
+#define UPB_STRARG(str) (str)->byte_len, (str)->ptr
 #define UPB_STRFMT "%.*s"
 
 #ifdef __cplusplus