BSON parser

The project

A simple BSON (Binary Json) parser in C++. Bson is a binary version of JSON, frequenlty used in web apps. only partially reversed.

The programm provided parses the BSON into a class architechture detailled below. It then calls the dump() method to pretty print the BSON file content in a human readable way.

Specification

http://bsonspec.org/spec.html

Requirements

• A compiler supporting c++17. (gcc >= 7.0 or clang >= 4.0)

Architechture of the project

AST class

• base-element: The base class for all elements. Also used as default for elements without value.
• element: Inherits from base-element, templated to simplify treatment.
• binary: Represents the element of the same name frome the BSON grammar.
• binstring: Same.
• codew: Same.
• document: Representation of a document. The object returned by the parsing is a document.

All the AST class have a dump() method that displays their content.

Parser

You can find the parser in the parser.* files.

Main class

The main function is in the bson-parser.cc file.

Utils

Utils are only containing the operations on stream to manage the indentation.

Build the project

You can build the project with the simple Makefile provided at the root of the repository. There are three rules in the Makefile:

• all: builds the project
• debug: compiles with debug flags
• clean: clean everything created by the rules above.

Test it with provided samples

After building the project the binary is in the src folder and is called:

• bson-parser

The usage is:

./bson-parser file.bson

Some bson files are provided in the samples folder. You can use them to test the program.

Todo

• Synthetize all types in a global header to make them easily adaptable
• Use a real build system (cmake)
• Refactor into multiple folders (ast, parser, utils)
• Improve the pretty printing by removing useless lines
• Fix endianness for timestamp and counter fields
• Do not print the key when the element type is an array (to match other BSON parser)

Improvements

Make the bson parser portable

This bson parser was implemented on an x86-64 architechture. It probably won't work on an other architechture because of the size of basic types. To solve this issue an improvement could be to have an adaptable header with the corresponding using to the data types. To make it work on other architechture the only thing to do would be to replace with the adequate types in this header.

Improve memory management

Most of the complex data types parsed are stored in a std::shared_ptr. An improvement could be to store them in the more restricive std::unique_ptr. This improvement however has to take into account the moment when the memory is allocated. The code has to be refactored to allocate in the class constructors. I am not sure this improvement is really usefull.

Author

• Loic Banet [[email protected]]