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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>BSON (Binary JSON): Specification</title>
<link rel="stylesheet" href="css/spec.css" type="text/css">
</head>
<body>
<h2 class="nojs">Specification Version 1.1</h2>
<p>BSON is a binary format in which zero or more ordered key/value
pairs are stored as a single entity. We call this entity
a <em>document</em>.</p>
<p>The following grammar specifies version 1.1 of the
BSON standard. We've written the grammar using a
pseudo-<a href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">BNF</a>
syntax. Valid BSON data is represented by
the <code>document</code> non-terminal.</p>
<div id="grammar">
<h3>Basic Types</h3>
<p>The following basic types are used as terminals in
the rest of the grammar. Each type must be serialized in
little-endian format.</p>
<div class="tb">
<table>
<tr>
<td class="t">byte</td>
<td>1 byte (8-bits)</td>
</tr>
<tr>
<td class="t">signed_byte(n)</td>
<td>8-bit, two's complement signed integer for which the value is <code>n</code></td>
</tr>
<tr>
<td class="t">unsigned_byte(n)</td>
<td>8-bit unsigned integer for which the value is <code>n</code></td>
</tr>
<tr>
<td class="t">int32</td>
<td>4 bytes (32-bit signed integer, two's complement)</td>
</tr>
<tr>
<td class="t">int64</td>
<td>8 bytes (64-bit signed integer, two's complement)</td>
</tr>
<tr>
<td class="t">uint64</td>
<td>8 bytes (64-bit unsigned integer)</td>
</tr>
<tr>
<td class="t">double</td>
<td>8 bytes (64-bit IEEE 754-2008 binary floating point)</td>
</tr>
<tr>
<td class="t">decimal128</td>
<td>16 bytes (128-bit IEEE 754-2008 decimal floating point)</td>
</tr>
</table>
</div>
<h3>Non-terminals</h3>
<p>The following specifies the rest of the BSON
grammar. Note that we use the <code>*</code> operator as
shorthand for repetition (e.g. <code>(byte*2)</code>
is <code>byte byte</code>). When used as a unary
operator, <code>*</code> means that the repetition can
occur 0 or more times.</p>
<div class="tb">
<table>
<tr>
<td class="fix nt">document</td>
<td class="fix op">::=</td>
<td class="fix ex">int32 e_list unsigned_byte(0)</td>
<td>BSON Document. int32 is the total number of bytes comprising the document.</td>
</tr>
<tr class="section">
<td class="fix nt">e_list</td>
<td class="fix op">::=</td>
<td class="fix ex">element e_list</td>
<td></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">""</td>
<td></td>
</tr>
<tr class="section">
<td class="fix nt">element</td>
<td class="fix op">::=</td>
<td style="width:35%" class="fix ex">signed_byte(1) e_name double</td>
<td>64-bit binary floating point</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(2) e_name string</td>
<td>UTF-8 string</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(3) e_name document</td>
<td>Embedded document</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(4) e_name document</td>
<td>Array</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(5) e_name binary</td>
<td>Binary data</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(6) e_name</td>
<td>Undefined (value) — <em>Deprecated</em></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(7) e_name (byte*12)</td>
<td><a href="https://www.mongodb.com/docs/manual/reference/bson-types/#objectid">ObjectId</a></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(8) e_name unsigned_byte(0)</td>
<td>Boolean - false</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(8) e_name unsigned_byte(1)</td>
<td>Boolean - true</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(9) e_name int64</td>
<td>UTC datetime</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(10) e_name</td>
<td>Null value</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(11) e_name cstring cstring</td>
<td>Regular expression - The first cstring is the regex
pattern, the second is the regex options string.
Options are identified by characters, which must be stored in
alphabetical order. Valid option characters are <code>i</code> for
case insensitive matching, <code>m</code> for multiline
matching, <code>s</code> for <i>dotall</i> mode ("." matches
everything), <code>x</code> for verbose mode, and
<code>u</code> to make "\w", "\W", etc. match Unicode.
</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(12) e_name string (byte*12)</td>
<td>DBPointer — <em>Deprecated</em></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(13) e_name string</td>
<td>JavaScript code</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(14) e_name string</td>
<td> Symbol — <em>Deprecated</em></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(15) e_name code_w_s</td>
<td>JavaScript code with scope — <em>Deprecated</em></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(16) e_name int32</td>
<td>32-bit integer</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(17) e_name uint64</td>
<td>Timestamp</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(18) e_name int64</td>
<td>64-bit integer</td>
</tr>
<tr class="section">
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(19) e_name decimal128</td>
<td><a
href="https://github.com/mongodb/specifications/blob/master/source/bson-decimal128/decimal128.rst">128-bit
decimal floating point</a></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(-1) e_name</td>
<td>Min key</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">signed_byte(127) e_name</td>
<td>Max key</td>
</tr>
<tr class="section">
<td class="fix nt">e_name</td>
<td class="fix op">::=</td>
<td class="fix ex">cstring</td>
<td>Key name</td>
</tr>
<tr class="section">
<td class="fix nt">string</td>
<td class="fix op">::=</td>
<td class="fix ex">int32 (byte*) unsigned_byte(0)</td>
<td>String - The int32 is the number of bytes in the
(byte*) plus one for the trailing null byte. The (byte*) is
zero or more UTF-8 encoded characters.</td>
</tr>
<tr class="section">
<td class="fix nt">cstring</td>
<td class="fix op">::=</td>
<td class="fix ex">(byte*) unsigned_byte(0)</td>
<td>Zero or more modified UTF-8 encoded characters
followed by the null byte. The (byte*) MUST NOT contain
<code>unsigned_byte(0)</code>, hence it is not full UTF-8.
</td>
</tr>
<tr class="section">
<td class="fix nt">binary</td>
<td class="fix op">::=</td>
<td class="fix ex">int32 subtype (byte*)</td>
<td>Binary - The int32 is the number of bytes in the (byte*).</td>
</tr>
<tr class="section">
<td class="fix nt">subtype</td>
<td class="fix op">::=</td>
<td class="fix ex">unsigned_byte(0)</td>
<td>Generic binary subtype</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(1)</td>
<td>Function</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(2)</td>
<td>Binary (Old)</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(3)</td>
<td>UUID (Old)</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(4)</td>
<td>UUID</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(5)</td>
<td>MD5</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(6)</td>
<td><a
href="https://github.com/mongodb/specifications/blob/master/source/client-side-encryption/subtype6.rst">Encrypted
BSON value</a></td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(7)</td>
<td>Compressed BSON column</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(8)</td>
<td>Sensitive</td>
</tr>
<tr>
<td class="fix nt"></td>
<td class="fix op">|</td>
<td class="fix ex">unsigned_byte(128)—unsigned_byte(255)</td>
<td>User defined</td>
</tr>
<tr class="section">
<td class="fix nt">code_w_s</td>
<td class="fix op">::=</td>
<td class="fix ex">int32 string document</td>
<td>Code with scope — <em>Deprecated</em></td>
</tr>
</table>
</div>
</div>
<h3>Notes</h3>
<ul>
<li>Array - The document for an array is a normal BSON document with integer values for the keys, starting with 0
and continuing sequentially. For example, the array ['red', 'blue'] would be encoded as the document {'0': 'red',
'1': 'blue'}. The keys must be in ascending numerical order.</li>
<li>UTC datetime - The int64 is UTC milliseconds since the Unix epoch.</li>
<li>Timestamp - Special internal type used by MongoDB replication and sharding. First 4 bytes are an increment,
second 4 are a timestamp.</li>
<li>Min key - Special type which compares lower than all other possible BSON element values.</li>
<li>Max key - Special type which compares higher than all other possible BSON element values.</li>
<li>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers
and tools.</li>
<li>Compressed BSON Column - Compact storage of BSON data. This data
type uses delta and delta-of-delta compression and
run-length-encoding for efficient element storage. Also has an
encoding for sparse arrays containing missing values.</li>
<li>The BSON "binary" or "BinData" datatype is used to represent
arrays of bytes. It is somewhat analogous to the Java notion of a
ByteArray. BSON binary values have a <em>subtype</em>. This is used to
indicate what kind of data is in the byte array. Subtypes from 0 to
127 are predefined or reserved. Subtypes from 128 to 255 are
user-defined.</li>
<ul>
<li><code>unsigned_byte(2)</code> Binary (Old) - This used to be the default
subtype, but was deprecated in favor of subtype 0.
Drivers and tools should be sure to handle subtype 2
appropriately. The structure of the binary data (the byte* array in
the binary non-terminal) must be an int32 followed by a (byte*). The
int32 is the number of bytes in the repetition.</li>
<li><code>unsigned_byte(3)</code> UUID (Old) - This used to be the UUID subtype,
but was deprecated in favor of subtype 4. Drivers
and tools for languages with a native UUID type should handle
subtype 3 appropriately.</li>
<li><code>unsigned_byte(128)—unsigned_byte(255)</code> User defined subtypes. The binary data can be
anything.</li>
</ul>
<li>Code with scope - <em>Deprecated.</em> The int32 is the length in bytes of the entire code_w_s value. The string
is JavaScript code. The document is a mapping from identifiers to values, representing the scope in which the
string should be evaluated.</li>
</ul>
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