upb: implement IsExactlyEqual() for proto messages

PiperOrigin-RevId: 543780133

upb/message/accessors.c

@@ -66,3 +66,27 @@ upb_MapInsertStatus upb_Message_InsertMapEntry(upb_Map* map,
                         &map_entry_value);
   return upb_Map_Insert(map, map_entry_key, map_entry_value, arena);
 }
+
+bool upb_Message_IsExactlyEqual(const upb_Message* m1, const upb_Message* m2,
+                                const upb_MiniTable* layout) {
+  if (m1 == m2) return true;
+
+  int opts = kUpb_EncodeOption_SkipUnknown | kUpb_EncodeOption_Deterministic;
+  upb_Arena* a = upb_Arena_New();
+
+  // Compare deterministically serialized payloads with no unknown fields.
+  size_t size1, size2;
+  char *data1, *data2;
+  upb_EncodeStatus status1 = upb_Encode(m1, layout, opts, a, &data1, &size1);
+  upb_EncodeStatus status2 = upb_Encode(m2, layout, opts, a, &data2, &size2);
+
+  if (status1 != kUpb_EncodeStatus_Ok || status2 != kUpb_EncodeStatus_Ok) {
+    // TODO(salo): How should we fail here? (In Ruby we throw an exception.)
+    upb_Arena_Free(a);
+    return false;
+  }
+
+  const bool ret = (size1 == size2) && (memcmp(data1, data2, size1) == 0);
+  upb_Arena_Free(a);
+  return ret;
+}

upb/message/accessors.h

@@ -387,6 +387,10 @@ upb_MapInsertStatus upb_Message_InsertMapEntry(upb_Map* map,
                                                upb_Message* map_entry_message,
                                                upb_Arena* arena);
 
+// Compares two messages by serializing them and calling memcmp().
+bool upb_Message_IsExactlyEqual(const upb_Message* m1, const upb_Message* m2,
+                                const upb_MiniTable* layout);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif