BSON

Filename extension	.bson
Internet media type	application/bson[1]
Type of format	Data interchange
Extended from	JSON
Website	bsonspec.org

BSON (/ˈbiːsən/^[2]) is a computer data interchange format. The name "BSON" is based on the term JSON and stands for "Binary JSON".^[2] It is a binary form for representing simple or complex data structures including associative arrays (also known as name-value pairs), integer indexed arrays, and a suite of fundamental scalar types. BSON originated in 2009 at MongoDB. Several scalar data types are of specific interest to MongoDB and the format is used both as a data storage and network transfer format for the MongoDB database, but it can be used independently outside of MongoDB. Implementations are available in a variety of languages such as C, C++, C#, D, Delphi, Erlang, Go, Haskell, Java, JavaScript, Julia, Lua, OCaml, Perl, PHP, Python, Ruby, Rust, Scala, Smalltalk, and Swift.^[3]

Data types and syntax

BSON has a published specification.^[4][5] The topmost element in the structure must be of type BSON object and contains 1 or more elements, where an element consists of a field name, a type, and a value. Field names are strings. Types include:

• Unicode string (using the UTF-8 encoding)
• 32 bit integer
• 64 bit integer
• double (64-bit IEEE 754 floating point number)
• decimal128 (128-bit IEEE 754-2008 floating point number; Binary Integer Decimal (BID) variant), suitable as a carrier for decimal-place sensitive financial data and arbitrary precision numerics with 34 decimal digits of precision, a max value of approximately 10⁶¹⁴⁵
• datetime w/o time zone (long integer number of milliseconds since the Unix epoch)
• byte array (for arbitrary binary data)
• boolean (true and false)
• null
• BSON object
• BSON array
• JavaScript code
• MD5 binary data
• Regular expression (Perl compatible regular expressions ("PCRE") version 8.41 with UTF-8 support)^[6]

An important differentiator to JSON is that BSON contains types not present in JSON (e.g. datetime and byte array) and offers type-strict handling for several numeric types instead of a universal "number" type. For situations where these additional types need to be represented in a textual way, MongoDB's Extended JSON format^[7] can be used.

Efficiency

Compared to JSON, BSON is designed to be efficient both in storage space and scan-speed. Large elements in a BSON document are prefixed with a length field to facilitate scanning. In some cases, BSON will use more space than JSON due to the length prefixes and explicit array indices.^[2]

Example

A document such as {"hello": "world"} will be stored as:

\x16\x00\x00\x00          // total document size
\x02                      // 0x02 = type String
hello\x00                 // field name
\x06\x00\x00\x00world\x00 // field value (size of value, value, null terminator)
\x00                      // 0x00 = type EOO ('end of object')