CppCon 2023-10-03 1tc::json::parser Extract some JSON members tc nlohmann RapidJSON Boost.JSON simdjson 0 10 20 30 40 Library Time in ms fully validating pull parser fast, O(1) memory usage implicitly y Jonathan Müller — @foonathan Express your expectations CppCon 2023-10-03 2(JSON) Parser design What is a parser? Jonathan Müller — @foonathan Express your expectations CppCon 2023-10-03 3Javascript "talks": [ { "title": "Express your expectations", "subtitle": "A fast, compliant JSON pull parser..." } ] } Jonathan Müller — @foonathan Express your expectations CppCon 2023-10-03 7JSON grammar

In a compiler: tokens -> parser -> syntax tree In a web browser: text -> JSON parser -> JS object parse(text or tokens) -> value or errorParser Combinators Create a parser by combining existing parsers parse_int(text, pos) parse_string_or_int -> parse_string | parse_int Simplified syntax:Parser Generators Create a parser from a grammar. Popular parsing algorithms used in generators are LL, LL(k), LR, LR(k) Example – Boost Spirit Boost Spirit library has a DSL for creating parsers. Example code from XML parser: text %= lexeme[+(char_ - '<')]; node %= xml | text; start_tag %= '<' >> !lit('/') >> lexeme[+(char_

Required Arguments Multiple Values & Lists Other Destinations Argument Locations Multiple Locations Parser Inheritance Error Handling Error Messages Output Fields Basic Usage Renaming Attributes Default from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) Data Formatting By default, all fields in your return iterable

from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note: Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) 1.2.5 Data Formatting By default, all fields in your return todo_id not in TODOS: abort(404, message="Todo {} doesn't exist".format(todo_id)) parser = reqparse.RequestParser() parser.add_argument('task') # Todo # shows a single todo item and lets you delete a todo

Required Arguments Multiple Values & Lists Other Destinations Argument Locations Multiple Locations Parser Inheritance Error Handling Error Messages Output Fields Basic Usage Renaming Attributes Default from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) Data Formatting By default, all fields in your return iterable

Required Arguments Multiple Values & Lists Other Destinations Argument Locations Multiple Locations Parser Inheritance Error Handling Error Messages Output Fields Basic Usage Renaming Attributes Default from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) Data Formatting By default, all fields in your return iterable

Required Arguments Multiple Values & Lists Other Destinations Argument Locations Multiple Locations Parser Inheritance Error Handling Error Messages Output Fields Basic Usage Renaming Attributes Default from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) Data Formatting By default, all fields in your return iterable

from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note: Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) 1.2.5 Data Formatting By default, all fields in your return todo_id not in TODOS: abort(404, message="Todo {} doesn't exist".format(todo_id)) parser = reqparse.RequestParser() parser.add_argument('task') # Todo # shows a single todo item and lets you delete a todo

from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note: Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) 1.2.5 Data Formatting By default, all fields in your return todo_id not in TODOS: abort(404, message="Todo {} doesn't exist".format(todo_id)) parser = reqparse.RequestParser() parser.add_argument('task') # Todo # shows a single todo item and lets you delete a todo

from flask_restful import reqparse parser = reqparse.RequestParser() parser.add_argument('rate', type=int, help='Rate to charge for this resource') args = parser.parse_args() Note: Unlike the argparse strict=True ensures that an error is thrown if the request includes arguments your parser does not define. args = parser.parse_args(strict=True) 1.2.5 Data Formatting By default, all fields in your return todo_id not in TODOS: abort(404, message="Todo {} doesn't exist".format(todo_id)) parser = reqparse.RequestParser() parser.add_argument('task') # Todo # shows a single todo item and lets you delete a todo