Bolt Protocol Message Specification - Version 3

• Version 3

• Appendix - Bolt Message Exchange Examples

Note: Byte values are represented using hexadecimal notation unless otherwise specified.

Version 3

Deltas

The changes compared to Bolt protocol version 2 are listed below:

• The INIT request message has been replaced with HELLO message.
• The ACK_FAILUER request message has been removed. Use RESET message instead.
• Added extra::Dictionary field to RUN message.
• Added extra::Dictionary field to BEGIN message.
• New HELLO request message.
• New GOODBYE request message.
• New BEGIN request message.
• New COMMIT request message.
• New ROLLBACK request message.
• New RESET request message.

Overview of Major Version Changes

Several new messages have been introduced to support new features. The INIT message have been replaced with the HELLO message that have a more generic structure.

The new request message GOODBYE have been introduced to be able to tell the server that the connection have been closed.

In Bolt protocol version 3 the concept of Auto-commit Transaction and Explicit Transaction have been introduced. Auto-commit Transaction is the concept of being in the READY server state and transition to the STREAMING server state. A new Explicit Transaction is created with the request message BEGIN and closed with the request message COMMIT. See, Bolt Protocol Server State Specification Version 3

The request message ACK_FAILURE has been removed and to reset the connection the new request message RESET should be used. The RESET message will trigger an <INTERRUPT> signal on the server.

Bolt Protocol Server State Specification

For the server, each connection using the Bolt Protocol will occupy one of several states throughout its lifetime.

This state is used to determine what actions may be undertaken by the client.

See, Bolt Protocol Server State Specification Version 3

Server Signals

Jump ahead is that the signal will imediatly be available before any messages are processed in the message queue.

Server Signal	Jump Ahead	Description
<INTERRUPT>	x	an interrupt signal
<DISCONNECT>		a disconnect signal

Protocol Errors

If a server or client receives a message type that is unexpected, according to the transitions described in this document, it must treat that as a protocol error. Protocol errors are fatal and should immediately transition the server state to DEFUNCT, closing any open connections.

Message Exchange

Messages are exchanged in a request-response pattern between client and server.

Each request consists of exactly one message and each response consists of zero or more detail messages followed by exactly one summary message. The presence or absence of detail messages in a response is directly related to the type of request message that has been sent. In other words, some request message types elicit a response that may contain detail messages, others do not.

Messages may also be pipelined. In other words, clients may send multiple requests eagerly without first waiting for responses.

When a failure occurs in this scenario, the server must ignore all subsequent requests until the connection from the server side is in the READY state. This prevents inadvertent execution of queries that may not be valid.

Serialization

Messages and their contents are serialized into network streams using PackStream Specification Version 1.

Each message is represented as a PackStream structure, that contains a fixed number of fields.
Note: conceptually BOLT messages and PackStream structures are not the same. Even though they have the same encoded form, the tags used might overlap. It is recommended to model them separately when implementing the protocol.

The message type is denoted by the PackStream structure tag byte and each message is defined in the Bolt protocol.

Serialization is specified with PackStream Version 1.

Some messages that contain Dictionary fields, define default values for some of the keys. Bandwidth can be saved by omitting these entries if the value equals the default.

Chunking

A layer of chunking is also applied to message transmissions as a way to more predictably manage packets of data.

The chunking process allows the message to be broken into one or more pieces, each of an arbitrary size, and for those pieces to be transmitted within separate chunks.

Each chunk consists of a two-byte header, detailing the chunk size in bytes followed by the chunk data itself. Chunk headers are 16-bit unsigned integers, meaning that the maximum theoretical chunk size permitted is 65,535 bytes.

Each encoded message must be terminated with a chunk of zero size, i.e.

00 00

This is used to signal message boundaries to a receiving parties, allowing blocks of data to be fully received without requiring that the message is parsed immediately. This also allows for unknown message types to be received and handled without breaking the messaging chain.

The Bolt protocol encodes each message using a chunked transfer encoding.

• Each message is transferred as one or more chunks of data.
• Each chunk starts with a two-byte header, an unsigned big-endian 16-bit integer, representing the size of the chunk not including the header.
• A message can be divided across multiple chunks, allowing client and server alike to transfer large messages without having to determine the length of the entire message in advance.
• Chunking applies on each message individually.
• One chunk cannot contain more than one message.
• Each message ends with two bytes with the value 00 00, these are not counted towards the chunk size. (Or you can think they are individual chunks of size 0)

This section provides some examples to illustrate how Bolt chunks messages.

Example: A message in one chunk

Message data containing 16 bytes,

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F

The chunk,

00 10 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 00 00

chunk header: 00 10

end marker: 00 00

Example: A message split in two chunks

Message data containig 20 bytes:

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 01 02 03 04

chunk 1, chunk 2,

00 10 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
00 04 01 02 03 04 00 00

chunk 1 header: 00 10

chunk 1 end marker: no end marker, still message data

chunk 2 header: 00 04

chunk 2 end marker: 00 00

Example: Two messages

Message 1 data containing 16 bytes:

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F

Message 2 data containing 8 bytes:

0F 0E 0D 0C 0B 0A 09 08

The two messages encoded with chunking,

00 10 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 00 00
00 08 0F 0E 0D 0C 0B 0A 09 08 00 00

Pipelining

The client may send multiple requests eagerly without first waiting for responses.

Transaction

A transaction is the concept of atomic units of work.

An Auto-commit Transaction is a basic but limited form of transaction.

The concept of Auto-commit Transaction is when the server is in the READY state and the transaction is opened with the request message RUN and the response of a summary message SUCCESS.

The Auto-commit Transaction is successfully closed with the summary message SUCCESS for the request message PULL_ALL or the request message DISCARD_ALL. Thus the Auto-commit Transaction can only contain one RUN request message.

Example 1:

...
C: HELLO ...
S: SUCCESS ...  // Server is in READY state

C: RUN ...      // Open a new Auto-commit Transaction
S: SUCCESS ...  // Server is in STREAMING state

C: PULL_ALL ...
S: RECORD ...
   ...
S: RECORD ...
S: SUCCESS ... // Server is in READY state and this implies that the Auto-commit Transaction is closed.

See, Bolt Protocol Server State Specification Version 3

An Explicit Transaction is a more generic transaction that can contain several RUN request messages.

The concept of Explicit Transaction is when the server is in the READY state and the transaction is opened with the request message BEGIN and the response of a summary message SUCCESS (thus transition into the TX_READY server state).

The Explicit Transaction is successfully closed with the request message COMMIT and the response of a summary message SUCCESS. The result stream (detail messages) must be fully consumed or discarded by a client before the server can transition to the TX_READY state and thus be able to close the transaction with a COMMIT request message.

The Explicit Transaction can be gracefully discarded and set to the initial server state of READY with the request message ROLLBACK.

Example 2:

...
C: HELLO ...
S: SUCCESS ...  // Server is in READY state

C: BEGIN ...    // Open a new Explicit Transaction
S: SUCCESS ...  // Server is in TX_READY state

C: RUN ...
S: SUCCESS ... // Server is in TX_STREAMING state, first stream is open

C: PULL_ALL ...
S: RECORD ...
   ...
S: RECORD ...
S: SUCCESS ... // Server is in TX_READY state, first stream has been fully consumed

C: RUN ...
S: SUCCESS ... // Server is in TX_STREAMING state, second stream is open

C: PULL_ALL ...
S: RECORD ...
   ...
S: RECORD ...
S: SUCCESS ... // Server is in TX_READY state, second stream has been fully consumed

C: COMMIT   // Close the Explicit Transaction
S: SUCCESS  // Server is in READY state

See, Bolt Protocol Server State Specification Version 3

Messages

• Request Message, the client sends a message.
• Summary Message, the server will always respond with one summary message.
• Detail Message, the server will always repond with zero or more detail messages before sending a summary message.

Message	Signature	Request Message	Summary Message	Detail Message	Fields	Description
HELLO	01	x			extra::Dictionary(user_agent::String, scheme::String)	initialize connection
GOODBYE	02	x				close the connection, triggers a <DISCONNECT> signal
RESET	0F	x				reset the connection, triggers a <INTERRUPT> signal
RUN	10	x			query::String, parameters::Dictionary, extra::Dictionary(bookmarks::List<String>, tx_timeout::Integer, tx_metadata::Dictionary, mode::String)	execute a query
DISCARD_ALL	2F	x				discard all records
PULL_ALL	3F	x				fetch all records
BEGIN	11	x			extra::Dictionary(bookmarks::List<String>, tx_timeout::Integer, tx_metadata::Dictionary, mode::String)	begin a new transaction
COMMIT	12	x				commit a transaction
ROLLBACK	13	x				rollback a transaction
SUCCESS	70		x		metadata::Dictionary	request succeeded
IGNORED	7E		x			request was ignored
FAILURE	7F		x		metadata::Dictionary(code::String, message::String)	request failed
RECORD	71			x	data::List	data values

Request Message - HELLO

The HELLO message request the connection to be authorized for use with the remote database.

The server must be in the CONNECTED state to be able to process a HELLO message. For any other states, receipt of an HELLO request must be considered a protocol violation and lead to connection closure.

Clients should send HELLO message to the server immediately after connection and process the corresponding response before using that connection in any other way.

If authentication fails, the server must respond with a FAILURE message and immediately close the connection.

Clients wishing to retry initialization should establish a new connection.

Signature: 01

Fields:

extra::Dictionary(
  user_agent::String,
  scheme::String,
  …
)

• The user_agent should conform to "Name/Version" for example "Example/3.0.0". (see, developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent)
• The scheme is the authentication scheme. Predefined schemes are "none", "basic", "kerberos".
• Further entries in extra are passed to the implementation of the chosen authentication scheme. Their names, types, and defaults depend on that choice.
  The scheme "basic" requires a user name principal::String and a password credentials::String.

Detail Messages:

No detail messages should be returned.

Valid Summary Messages:

• SUCCESS
• FAILURE

Synopsis

HELLO {user_agent::String, scheme::String}

Example:

HELLO {"user_agent": "Example/3.0.0", "scheme": "basic", "principal": "user-id-1", "credentials": "user-password"}

Server Response SUCCESS

A SUCCESS message response indicates that the client is permitted to exchange further messages. Servers can include metadata that describes details of the server environment and/or the connection.

The following fields are defined for inclusion in the SUCCESS metadata.

• server::String, the server agent string. e.g. "Neo4j/3.5.0".
• connection_id::String, an unique identifier of the bolt connection used on the server side. e.g. "bolt-61".

Example:

SUCCESS {"server": "Neo4j/3.5.0", "connection_id": "bolt-61"}

Server Response FAILURE

A FAILURE message response indicates that the client is not permitted to exchange further messages. Servers may choose to include metadata describing the nature of the failure but must immediately close the connection after the failure has been sent.

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - GOODBYE

The GOODBYE message notifies the server that the connection is terminating gracefully.

On receipt of this message, the server should immediately shut down the socket on its side without sending a response.

A client may shut down the socket at any time after sending the GOODBYE message.

This message interrupts the server current work if there is any.

Signature: 02

Fields:

No fields.

Detail Messages:

No detail messages should be returned.

Valid Summary Messages:

No summary message should be returned.

Synopsis

GOODBYE

Example:

GOODBYE

Request Message - RESET

The RESET message requests that the connection should be set back to its initial state, as if a HELLO message had just been successfully completed.

The RESET message is unique in that it on arrival at the server, it jumps ahead in the message queue, stopping any unit of work that happens to be executing.

All the queued messages originally in front of the RESET message will then be IGNORED until the RESET position is reached. Then from this point, the server state is reset to a state that is ready for a new session.

Signature: 0F

Fields:

No fields.

Detail Messages:

No detail messages should be returned.

Valid Summary Messages:

No summary message should be returned.

Synopsis

RESET

Example:

RESET

Request Message - RUN

The RUN message requests that a Cypher query is executed with a set of parameters and additional extra data.

This message could both be used in an Explicit Transaction or an Auto-commit Transaction. The transaction type is implied by the order of message sequence.

Signature: 10

Fields:

query::String,
parameters::Dictionary,
extra::Dictionary(
  bookmarks::List<String>,
  tx_timeout::Integer,
  tx_metadata::Dictionary,
  mode::String,
)

• The query can be a Cypher syntax or a procedure call.
• The parameters is a dictionary of parameters to be used in the query string.

An Explicit Transaction (BEGIN+RUN) does not carry any data in the extra field.

For Auto-commit Transaction (RUN) the extra field carries:

• The bookmarks is a list of strings containing some kind of bookmark identification e.g ["neo4j-bookmark-transaction:1", "neo4j-bookmark-transaction:2"]. Default: [].
• The tx_timeout is an integer in that specifies a transaction timeout in ms. Default: server-side configured timeout.
• The tx_metadata is a dictionary that can contain some metadata information, mainly used for logging. Default: null.
• The mode specifies what kind of server the RUN message is targeting. For write access use "w" and for read access use "r". Default: "w".

Detail Messages:

No detail messages should be returned.

Valid Summary Messages:

• SUCCESS
• IGNORED
• FAILURE

Synopsis

RUN "query" {parameters} {extra}

Example 1:

RUN "RETURN $x AS x" {"x": 1} {bookmarks: [], "tx_timeout": 123, "tx_metadata": {"log": "example_message"}, mode: "r"}

Example 2:

RUN "RETURN $x AS x" {"x": 1} {}

Example 3:

RUN "CALL dbms.procedures()" {} {}

Server Response SUCCESS

A SUCCESS message response indicates that the client is permitted to exchange further messages.

The following fields are defined for inclusion in the SUCCESS metadata.

• fields::List<String>, the fields of the return result. e.g. [“name”, “age”, …]
• t_first::Integer, the time, specified in ms, which the first record in the result stream is available after.

Example 1:

SUCCESS {"fields": ["x"], "t_first": 123}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - DISCARD_ALL

The DISCARD_ALL message requests that all of the result stream should be thrown away.

Signature: 2F

Fields:

No fields.

Detail Messages:

No detail messages should be returned.

Valid Summary Messages:

• SUCCESS
• IGNORED
• FAILURE

Synopsis

DISCARD_ALL

Example 1:

DISCARD_ALL

Server Response SUCCESS

The following fields are defined for inclusion in the SUCCESS metadata.

• bookmark::String, the bookmark after committing this transaction. (Auto-commit Transaction only).

Example:

SUCCESS {"bookmark": "example-bookmark:1"}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - PULL_ALL

The PULL_ALL message requests all data of the result stream.

Signature: 3F

Fields:

No fields.

Detail Messages:

Zero or more RECORD

Valid Summary Messages:

• SUCCESS
• IGNORED
• FAILURE

Synopsis

PULL_ALL

Example:

PULL_ALL

Server Response SUCCESS

The following fields are defined for inclusion in the SUCCESS metadata.

• bookmark::String, the bookmark after committing this transaction. (Autocommit Transaction only).
• t_last::Integer, the time, specified in ms, which the last record in the result stream is consumed after.
• type::String, the type of the statement, e.g. "r" for read-only statement, "w" for write-only statement, "rw" for read-and-write, and "s" for schema only.
• stats::Dictionary, counter information, such as db-hits etc.
• plan::Dictionary, plan result.
• profile::Dictionary, profile result.
• notifications::Dictionary, any notification generated during execution of this statement.

Example:

SUCCESS {"bookmark": "example-bookmark:1", "t_last": 123}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - BEGIN

The BEGIN message request the creation of a new Explicit Transaction.

This message should then be followed by a RUN message.

The Explicit Transaction is closed with either the COMMIT message or ROLLBACK message.

Signature: 11

Fields:

extra::Dictionary(
  bookmarks::List<String>,
  tx_timeout::Integer,
  tx_metadata::Dictionary,
  mode::String,
)

• The bookmarks is a list of strings containg some kind of bookmark identification e.g ["neo4j-bookmark-transaction:1", "neo4j-bookmark-transaction:2"]. Default: [].
• The tx_timeout is an integer in that specifies a transaction timeout in ms. Default: server-side configured timeout.
• The tx_metadata is a dictionary that can contain some metadata information, mainly used for logging. Default: null.
• The mode specifies what kind of server the RUN message is targeting. For write access use "w" and for read access use "r". Default: "w".

Detail Messages:

No detail messages.

Valid Summary Messages:

• SUCCESS
• FAILURE

Synopsis

BEGIN {extra}

Example 1:

BEGIN {"tx_timeout": 123, "mode": "r", "tx_metadata": {"log": "example_log_data"}}

Example 2:

BEGIN {"tx_metadata": {"log": "example_log_data"}, "bookmarks": ["example-bookmark:1", "example-bookmark2"]}

Server Response SUCCESS

Example:

SUCCESS {}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - COMMIT

The COMMIT message request that the Explicit Transaction is done.

Signature: 12

Fields:

No fields.

Detail Messages:

No detail messages.

Valid Summary Messages:

• SUCCESS
• IGNORED
• FAILURE

Synopsis

COMMIT

Example:

COMMIT

Server Response SUCCESS

A SUCCESS message response indicates that the Explicit Transaction was completed.

• bookmark::String, the bookmark after committing this transaction.

Example:

SUCCESS {"bookmark": "example-bookmark:1"}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Request Message - ROLLBACK

The ROLLBACK message requests that the Explicit Transaction rolls back.

Signature: 13

Fields:

No fields.

Detail Messages:

No detail messages.

Valid Summary Messages:

• SUCCESS
• IGNORED
• FAILURE

Synopsis

ROLLBACK

Example:

ROLLBACK

Server Response SUCCESS

A SUCCESS message response indicates that the Explicit Transaction was rolled back.

SUCCESS {}

Server Response IGNORED

Example:

IGNORED

Server Response FAILURE

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Summary Message - SUCCESS

The SUCCESS message indicates that the corresponding request has succeeded as intended.

It may contain metadata relating to the outcome.

Metadata keys are described in the section of this document relating to the message that began the exchange.

Signature: 70

Fields:

metadata::Dictionary

Synopsis

SUCCESS {metadata}

Example:

SUCCESS {"example": "see specific message for server response metadata"}

Summary Message - IGNORED

The IGNORED message indicates that the corresponding request has not been carried out.

Signature: 7E

Fields:

No fields

Synopsis

IGNORED

Example:

IGNORED

Summary Message - FAILURE

Signature: 7F

Fields:

metadata::Dictionary(
  code::String,
  message::String,
)

• The code is a textual code that uniquely identifies the type of failure.
• The message is a textual description of the failure, intended for human consumption.

Synopsis

FAILURE {metadata}

Example:

FAILURE {"code": "Example.Failure.Code", "message": "example failure"}

Detail Message - RECORD

A RECORD message carries a sequence of values corresponding to a single entry in a result.

Signature: 71

These messages are currently only ever received in response to a PULL_ALL message and will always be followed by a summary message.

Fields:

data::List

Synopsis

RECORD [data]

Example 1:

RECORD ["1", "2", "3"]

Example 2:

RECORD [{"point": [1, 2]}, "example_data", 123]

Appendix - Message Exchange Examples

• The C: stands for client.
• The S: stands for server.

Example 1

C: 60 60 B0 17
C: 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00
S: 00 00 00 03
C: HELLO {"user_agent": "Example/3.0.0", "scheme": "basic", "principal": "user", "credentials": "password"}
S: SUCCESS {"server": "Neo4j/3.5.0", "connection_id": "example-connection-id:1"}
C: GOODBYE

Example 2

C: 60 60 B0 17
C: 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00
S: 00 00 00 03
C: HELLO {"user_agent": "Example/3.0.0", "scheme": "basic", "principal": "user", "credentials": "password"}
S: SUCCESS {"server": "Neo4j/3.5.0", "connection_id": "example-connection-id:1"}
C: RUN "RETURN $x AS example" {"x": 123} {"mode": "r"}
S: SUCCESS {"fields": ["example"]}
C: PULL_ALL
S: RECORD [123]
S: SUCCESS {"bookmark": "example-bookmark:1", "t_last": 300, "type": "r"}
C: GOODBYE

Example 3

C: 60 60 B0 17
C: 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00
S: 00 00 00 03
C: HELLO {"user_agent": "Example/3.0.0", "scheme": "basic", "principal": "user", "credentials": "password"}
S: SUCCESS {"server": "Neo4j/3.5.0", "connection_id": "example-connection-id:1"}
C: RUN "RETURN $x AS example" {"x": 123} {"mode": "r"}
S: SUCCESS {"fields": ["example"]}
C: DISCARD_ALL
S: SUCCESS {"bookmark": "example-bookmark:1", "t_last": 300, "type": "r"}
C: GOODBYE

Example 4

C: 60 60 B0 17
C: 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00
S: 00 00 00 03
C: HELLO {"user_agent": "Example/3.0.0", "scheme": "basic", "principal": "user", "credentials": "password"}
S: SUCCESS {"server": "Neo4j/3.5.0", "connection_id": "example-connection-id:1"}
C: BEGIN {"mode": "r"}
S: SUCCESS {}
C: RUN "RETURN $x AS example" {"x": 123} {}
S: SUCCESS {"fields": ["example"]}
C: PULL_ALL
S: RECORD [123]
S: SUCCESS {"t_last": 300, "type": "r"}
C: COMMIT
S: SUCCESS {"bookmark": "example-bookmark:1"}
C: GOODBYE