Emit an error if user tries to iterate arrays out of order

include/simdjson/error.h

@@ -35,6 +35,7 @@ enum error_code {
   INVALID_URI_FRAGMENT,     ///< Invalid URI fragment
   UNEXPECTED_ERROR,         ///< indicative of a bug in simdjson
   PARSER_IN_USE,            ///< parser is already in use.
+  OUT_OF_ORDER_ITERATION,   ///< tried to iterate an array or object out of order
   /** @private Number of error codes */
   NUM_ERROR_CODES
 };

include/simdjson/generic/ondemand/object-inl.h

@@ -52,6 +52,7 @@ simdjson_really_inline object::object(const value_iterator &_iter) noexcept
 }
 
 simdjson_really_inline object_iterator object::begin() noexcept {
+  // TODO make it a runtime error if this is violated
   // Expanded version of SIMDJSON_ASSUME( iter.at_field_start() || !iter.is_open() )
   SIMDJSON_ASSUME( (iter._json_iter->token.index == iter._start_position + 1) || (iter._json_iter->_depth < iter._depth) );
   return iter;

include/simdjson/generic/ondemand/value_iterator-inl.h

@@ -10,7 +10,9 @@ simdjson_really_inline value_iterator::value_iterator(json_iterator *json_iter,
 }
 
 simdjson_warn_unused simdjson_really_inline simdjson_result<bool> value_iterator::start_object() noexcept {
-  if (*advance_container_start("object") != '{') { return incorrect_type_error("Not an object"); }
+  const uint8_t *json;
+  SIMDJSON_TRY( advance_container_start("object", json) );
+  if (*json != '{') { return incorrect_type_error("Not an object"); }
   return started_object();
 }
 
@@ -248,7 +250,9 @@ simdjson_warn_unused simdjson_really_inline error_code value_iterator::field_val
 }
 
 simdjson_warn_unused simdjson_really_inline simdjson_result<bool> value_iterator::start_array() noexcept {
-  if (*advance_container_start("array") != '[') { return incorrect_type_error("Not an array"); }
+  const uint8_t *json;
+  SIMDJSON_TRY( advance_container_start("array", json) );
+  if (*json != '[') { return incorrect_type_error("Not an array"); }
   return started_array();
 }
 
@@ -428,15 +432,20 @@ simdjson_really_inline const uint8_t *value_iterator::advance_start(const char *
   _json_iter->ascend_to(depth()-1);
   return result;
 }
-simdjson_really_inline const uint8_t *value_iterator::advance_container_start(const char *type) const noexcept {
-  // If we're not at the position anymore, we don't want to advance the cursor.
-  if (is_at_container_start()) { return peek_start(); }
-
+simdjson_really_inline error_code value_iterator::advance_container_start(const char *type, const uint8_t *&json) const noexcept {
   logger::log_start_value(*_json_iter, _start_position, depth(), type);
 
+  // If we're not at the position anymore, we don't want to advance the cursor.
+  if (!is_at_start()) {
+    if (!is_at_container_start()) { return OUT_OF_ORDER_ITERATION; }
+    json = peek_start();
+    return SUCCESS;
+  }
+
   // Get the JSON and advance the cursor, decreasing depth to signify that we have retrieved the value.
   assert_at_start();
-  return _json_iter->advance();
+  json = _json_iter->advance();
+  return SUCCESS;
 }
 simdjson_really_inline const uint8_t *value_iterator::advance_root_scalar(const char *type) const noexcept {
   logger::log_value(*_json_iter, _start_position, depth(), type);

include/simdjson/generic/ondemand/value_iterator.h

@@ -274,7 +274,7 @@ protected:
   simdjson_really_inline const uint8_t *peek_start() const noexcept;
   simdjson_really_inline uint32_t peek_start_length() const noexcept;
   simdjson_really_inline const uint8_t *advance_start(const char *type) const noexcept;
-  simdjson_really_inline const uint8_t *advance_container_start(const char *type) const noexcept;
+  simdjson_really_inline error_code advance_container_start(const char *type, const uint8_t *&json) const noexcept;
   simdjson_really_inline const uint8_t *advance_root_scalar(const char *type) const noexcept;
   simdjson_really_inline const uint8_t *advance_non_root_scalar(const char *type) const noexcept;
 

src/internal/error_tables.cpp

@@ -28,7 +28,8 @@ namespace internal {
     { INVALID_JSON_POINTER, "Invalid JSON pointer syntax." },
     { INVALID_URI_FRAGMENT, "Invalid URI fragment syntax." },
     { UNEXPECTED_ERROR, "Unexpected error, consider reporting this problem as you may have found a bug in simdjson" },
-    { PARSER_IN_USE, "Cannot parse a new document while a document is still in use." }
+    { PARSER_IN_USE, "Cannot parse a new document while a document is still in use." },
+    { OUT_OF_ORDER_ITERATION, "Objects and arrays can only be iterated when they are first encountered." }
   }; // error_messages[]
 
 } // namespace internal