.bson file format: GraphViz block diagram (.dot) source

BSON, short for Binary JSON, is a binary-encoded serialization of JSON-like documents. Like JSON, BSON supports the embedding of documents and arrays within other documents and arrays. BSON also contains extensions that allow representation of data types that are not part of the JSON spec. For example, BSON has a Date type and a BinData type. BSON can be compared to binary interchange formats, like Protocol Buffers. BSON is more "schemaless" than Protocol Buffers, which can give it an advantage in flexibility but also a slight disadvantage in space efficiency (BSON has overhead for field names within the serialized data). BSON was designed to have the following three characteristics:

  • Lightweight. Keeping spatial overhead to a minimum is important for any data representation format, especially when used over the network.
  • Traversable. BSON is designed to be traversed easily. This is a vital property in its role as the primary data representation for MongoDB.
  • Efficient. Encoding data to BSON and decoding from BSON can be performed very quickly in most languages due to the use of C data types.

File extension

bson

KS implementation details

License: CC0-1.0

This page hosts a formal specification of .bson file format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

GraphViz block diagram source

bson.dot

digraph {
	rankdir=LR;
	node [shape=plaintext];
	subgraph cluster__bson {
		label="Bson";
		graph[style=dotted];

		bson__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
			<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
			<TR><TD PORT="len_pos">0</TD><TD PORT="len_size">4</TD><TD>s4le</TD><TD PORT="len_type">len</TD></TR>
			<TR><TD PORT="fields_pos">4</TD><TD PORT="fields_size">(len - 5)</TD><TD>ElementsList</TD><TD PORT="fields_type">fields</TD></TR>
			<TR><TD PORT="terminator_pos">...</TD><TD PORT="terminator_size">1</TD><TD>00</TD><TD PORT="terminator_type">terminator</TD></TR>
		</TABLE>>];
		subgraph cluster__timestamp {
			label="Bson::Timestamp";
			graph[style=dotted];

			timestamp__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="increment_pos">0</TD><TD PORT="increment_size">4</TD><TD>u4le</TD><TD PORT="increment_type">increment</TD></TR>
				<TR><TD PORT="timestamp_pos">4</TD><TD PORT="timestamp_size">4</TD><TD>u4le</TD><TD PORT="timestamp_type">timestamp</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__bin_data {
			label="Bson::BinData";
			graph[style=dotted];

			bin_data__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="len_pos">0</TD><TD PORT="len_size">4</TD><TD>s4le</TD><TD PORT="len_type">len</TD></TR>
				<TR><TD PORT="subtype_pos">4</TD><TD PORT="subtype_size">1</TD><TD>u1→Subtype</TD><TD PORT="subtype_type">subtype</TD></TR>
				<TR><TD PORT="content_pos">5</TD><TD PORT="content_size">...</TD><TD>switch (subtype)</TD><TD PORT="content_type">content</TD></TR>
			</TABLE>>];
bin_data__seq_content_switch [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
	<TR><TD BGCOLOR="#F0F2E4">case</TD><TD BGCOLOR="#F0F2E4">type</TD></TR>
	<TR><TD>:subtype_byte_array_deprecated</TD><TD PORT="case0">ByteArrayDeprecated</TD></TR>
</TABLE>>];
			subgraph cluster__byte_array_deprecated {
				label="Bson::BinData::ByteArrayDeprecated";
				graph[style=dotted];

				byte_array_deprecated__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
					<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
					<TR><TD PORT="len_pos">0</TD><TD PORT="len_size">4</TD><TD>s4le</TD><TD PORT="len_type">len</TD></TR>
					<TR><TD PORT="content_pos">4</TD><TD PORT="content_size">len</TD><TD></TD><TD PORT="content_type">content</TD></TR>
				</TABLE>>];
			}
		}
		subgraph cluster__elements_list {
			label="Bson::ElementsList";
			graph[style=dotted];

			elements_list__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="elements_pos">0</TD><TD PORT="elements_size">...</TD><TD>Element</TD><TD PORT="elements_type">elements</TD></TR>
				<TR><TD COLSPAN="4" PORT="elements__repeat">repeat to end of stream</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__cstring {
			label="Bson::Cstring";
			graph[style=dotted];

			cstring__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="str_pos">0</TD><TD PORT="str_size">...</TD><TD>str(UTF-8)</TD><TD PORT="str_type">str</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__string {
			label="Bson::String";
			graph[style=dotted];

			string__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="len_pos">0</TD><TD PORT="len_size">4</TD><TD>s4le</TD><TD PORT="len_type">len</TD></TR>
				<TR><TD PORT="str_pos">4</TD><TD PORT="str_size">(len - 1)</TD><TD>str(UTF-8)</TD><TD PORT="str_type">str</TD></TR>
				<TR><TD PORT="terminator_pos">...</TD><TD PORT="terminator_size">1</TD><TD>00</TD><TD PORT="terminator_type">terminator</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__element {
			label="Bson::Element";
			graph[style=dotted];

			element__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="type_byte_pos">0</TD><TD PORT="type_byte_size">1</TD><TD>u1→BsonType</TD><TD PORT="type_byte_type">type_byte</TD></TR>
				<TR><TD PORT="name_pos">1</TD><TD PORT="name_size">...</TD><TD>Cstring</TD><TD PORT="name_type">name</TD></TR>
				<TR><TD PORT="content_pos">...</TD><TD PORT="content_size">...</TD><TD>switch (type_byte)</TD><TD PORT="content_type">content</TD></TR>
			</TABLE>>];
element__seq_content_switch [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
	<TR><TD BGCOLOR="#F0F2E4">case</TD><TD BGCOLOR="#F0F2E4">type</TD></TR>
	<TR><TD>:bson_type_code_with_scope</TD><TD PORT="case0">CodeWithScope</TD></TR>
	<TR><TD>:bson_type_object_id</TD><TD PORT="case1">ObjectId</TD></TR>
	<TR><TD>:bson_type_string</TD><TD PORT="case2">String</TD></TR>
	<TR><TD>:bson_type_reg_ex</TD><TD PORT="case3">RegEx</TD></TR>
	<TR><TD>:bson_type_number_decimal</TD><TD PORT="case4">F16</TD></TR>
	<TR><TD>:bson_type_timestamp</TD><TD PORT="case5">Timestamp</TD></TR>
	<TR><TD>:bson_type_db_pointer</TD><TD PORT="case6">DbPointer</TD></TR>
	<TR><TD>:bson_type_array</TD><TD PORT="case7">Bson</TD></TR>
	<TR><TD>:bson_type_javascript</TD><TD PORT="case8">String</TD></TR>
	<TR><TD>:bson_type_document</TD><TD PORT="case9">Bson</TD></TR>
	<TR><TD>:bson_type_symbol</TD><TD PORT="case10">String</TD></TR>
	<TR><TD>:bson_type_bin_data</TD><TD PORT="case11">BinData</TD></TR>
</TABLE>>];
		}
		subgraph cluster__db_pointer {
			label="Bson::DbPointer";
			graph[style=dotted];

			db_pointer__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="namespace_pos">0</TD><TD PORT="namespace_size">...</TD><TD>String</TD><TD PORT="namespace_type">namespace</TD></TR>
				<TR><TD PORT="id_pos">...</TD><TD PORT="id_size">12</TD><TD>ObjectId</TD><TD PORT="id_type">id</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__u3 {
			label="Bson::U3";
			graph[style=dotted];

			u3__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="b1_pos">0</TD><TD PORT="b1_size">1</TD><TD>u1</TD><TD PORT="b1_type">b1</TD></TR>
				<TR><TD PORT="b2_pos">1</TD><TD PORT="b2_size">1</TD><TD>u1</TD><TD PORT="b2_type">b2</TD></TR>
				<TR><TD PORT="b3_pos">2</TD><TD PORT="b3_size">1</TD><TD>u1</TD><TD PORT="b3_type">b3</TD></TR>
			</TABLE>>];
			u3__inst__value [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">id</TD><TD BGCOLOR="#E0FFE0">value</TD></TR>
				<TR><TD>value</TD><TD>((b1 | (b2 &lt;&lt; 8)) | (b3 &lt;&lt; 16))</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__code_with_scope {
			label="Bson::CodeWithScope";
			graph[style=dotted];

			code_with_scope__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="id_pos">0</TD><TD PORT="id_size">4</TD><TD>s4le</TD><TD PORT="id_type">id</TD></TR>
				<TR><TD PORT="source_pos">4</TD><TD PORT="source_size">...</TD><TD>String</TD><TD PORT="source_type">source</TD></TR>
				<TR><TD PORT="scope_pos">...</TD><TD PORT="scope_size">...</TD><TD>Bson</TD><TD PORT="scope_type">scope</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__f16 {
			label="Bson::F16";
			graph[style=dotted];

			f16__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="str_pos">0</TD><TD PORT="str_size">1b</TD><TD>BitsType1</TD><TD PORT="str_type">str</TD></TR>
				<TR><TD PORT="exponent_pos">0:1</TD><TD PORT="exponent_size">15b</TD><TD>b15</TD><TD PORT="exponent_type">exponent</TD></TR>
				<TR><TD PORT="significand_hi_pos">2</TD><TD PORT="significand_hi_size">49b</TD><TD>b49</TD><TD PORT="significand_hi_type">significand_hi</TD></TR>
				<TR><TD PORT="significand_lo_pos">8:1</TD><TD PORT="significand_lo_size">8</TD><TD>u8le</TD><TD PORT="significand_lo_type">significand_lo</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__object_id {
			label="Bson::ObjectId";
			graph[style=dotted];

			object_id__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="epoch_time_pos">0</TD><TD PORT="epoch_time_size">4</TD><TD>u4le</TD><TD PORT="epoch_time_type">epoch_time</TD></TR>
				<TR><TD PORT="machine_id_pos">4</TD><TD PORT="machine_id_size">3</TD><TD>U3</TD><TD PORT="machine_id_type">machine_id</TD></TR>
				<TR><TD PORT="process_id_pos">7</TD><TD PORT="process_id_size">2</TD><TD>u2le</TD><TD PORT="process_id_type">process_id</TD></TR>
				<TR><TD PORT="counter_pos">9</TD><TD PORT="counter_size">3</TD><TD>U3</TD><TD PORT="counter_type">counter</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__reg_ex {
			label="Bson::RegEx";
			graph[style=dotted];

			reg_ex__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="pattern_pos">0</TD><TD PORT="pattern_size">...</TD><TD>Cstring</TD><TD PORT="pattern_type">pattern</TD></TR>
				<TR><TD PORT="options_pos">...</TD><TD PORT="options_size">...</TD><TD>Cstring</TD><TD PORT="options_type">options</TD></TR>
			</TABLE>>];
		}
	}
	bson__seq:len_type -> bson__seq:fields_size [color="#404040"];
	bson__seq:fields_type -> elements_list__seq [style=bold];
	bin_data__seq:content_type -> bin_data__seq_content_switch [style=bold];
	bin_data__seq_content_switch:case0 -> byte_array_deprecated__seq [style=bold];
	bin_data__seq:subtype_type -> bin_data__seq:content_type [color="#404040"];
	byte_array_deprecated__seq:len_type -> byte_array_deprecated__seq:content_size [color="#404040"];
	elements_list__seq:elements_type -> element__seq [style=bold];
	string__seq:len_type -> string__seq:str_size [color="#404040"];
	element__seq:name_type -> cstring__seq [style=bold];
	element__seq:content_type -> element__seq_content_switch [style=bold];
	element__seq_content_switch:case0 -> code_with_scope__seq [style=bold];
	element__seq_content_switch:case1 -> object_id__seq [style=bold];
	element__seq_content_switch:case2 -> string__seq [style=bold];
	element__seq_content_switch:case3 -> reg_ex__seq [style=bold];
	element__seq_content_switch:case4 -> f16__seq [style=bold];
	element__seq_content_switch:case5 -> timestamp__seq [style=bold];
	element__seq_content_switch:case6 -> db_pointer__seq [style=bold];
	element__seq_content_switch:case7 -> bson__seq [style=bold];
	element__seq_content_switch:case8 -> string__seq [style=bold];
	element__seq_content_switch:case9 -> bson__seq [style=bold];
	element__seq_content_switch:case10 -> string__seq [style=bold];
	element__seq_content_switch:case11 -> bin_data__seq [style=bold];
	element__seq:type_byte_type -> element__seq:content_type [color="#404040"];
	db_pointer__seq:namespace_type -> string__seq [style=bold];
	db_pointer__seq:id_type -> object_id__seq [style=bold];
	u3__seq:b1_type -> u3__inst__value [color="#404040"];
	u3__seq:b2_type -> u3__inst__value [color="#404040"];
	u3__seq:b3_type -> u3__inst__value [color="#404040"];
	code_with_scope__seq:source_type -> string__seq [style=bold];
	code_with_scope__seq:scope_type -> bson__seq [style=bold];
	object_id__seq:machine_id_type -> u3__seq [style=bold];
	object_id__seq:counter_type -> u3__seq [style=bold];
	reg_ex__seq:pattern_type -> cstring__seq [style=bold];
	reg_ex__seq:options_type -> cstring__seq [style=bold];
}