RexPro Messages

Communication over RexPro is achieved by sending and receiving messages that adhere to the format specified on this page. There are several clients that communicate via RexPro that would serve as good examples for how communication over RexPro works:

• Rexster Console
• RexsterClient – A Java language binding
• rexpro-python – A Python languge binding

Basic Message Structure

Evern RexPro message consists of the following segments:

[protocol version][message type][message size][message body]

segment	type(bytes)	description
protocol version	byte(1)	The version of RexPro. Currently, this value should be set to zero.
message type	byte(1)	The type of message as described below.
message size	int(4)	The length of the message body
message body	byte(n)	The body of the message itself containing the instructions for the RexPro Server. This portion of the message is serialized using MsgPack.

Message Definitions

RexPro messages are divided into those that deal with requests made from the client and those that involved a response from the server. The following table represents an overview of the basic message set:

message	type	description
session	request	A request to open or close the session with the RexPro Server.
session	response	The response from the RexPro Server to a session request containing session information.
script	request	A request to process a Gremlin script on the RexPro Server.
script	response	A response to a script request. Script response messages actually refer to a set of response messages that are unique to each serialization channel (i.e. MsgPack, GraphSON, and Console).
error	response	A response from the RexPro Server indicating a problem has occurred.

NOTE – The following sections describe the individual RexPro Messages in greater detail. It is important to note that the messages are defined in terms of MsgPack serialization, so data types defined must adhere to MsgPack expectations.

Request Messages

The request class of messages are those that are sent by the client to the RexPro Server for processing.

Session

The Session Request Message is used to establish or destroy a session on the RexPro Server. When a session is opened, future Script Request Messages can be executed within this session and variable bindings established in previous scripts can be accessed.

Map<String, Object> Meta
byte[] Session
byte[] Request
byte Channel
String Username
String Password
 
Meta attributes:
  graphName: (String) not required, the name of the graph to open a session on
  graphObjName: (String) not required, the variable name of the graph object, defaults to 'g'
  killSession: (Boolean) not required, if true, the given session will be destroyed, otherwise, one will be created, defaults to false

Script

The Script Request Message is used to send Gremlin scripts to the RexPro Server. Script Requests can be made either in-session or sessionless. In-session requires that a session is already established with the RexPro Server via the Session Request Message. Sessionless Script Request Messages can be sent without the context of the session but come with the limitation that variable bindings established by a script are lost between requests.

```text
Map<String, Object> Meta
byte[] Session
byte[] Request
String LanguageName
String Script
byte[] Bindings
 
Meta attributes:
 inSession: (Boolean) not required, indicates this requests should be executed in the supplied session, defaults to false
 isolate: (Boolean) not required prevents variables defined in this request from being accessible in later requests, defaults to true
 transaction: (Boolean) not required executes script within a transaction, committing if successful, rolling back if not. Has no effect with non transactional graph. defaults to true
 graphName: (String) not required, the name of the graph to open a session on
 graphObjName: (String) not required, the variable name of the graph object, defaults to 'g'
 *note: supplying graphName or graphObjName for a session request which already has these values defined will raise an exception

Response Messages

The response class of messages are those that are sent by the RexPro Server back to the client, in response to a request message.

Session

The Session Response Message is used to send a response to a Session Request Message and is sent when the session is successfully created. The Session Response Message will contain information about the session like:

• Session Identifier – Used on future Script Request Messages that need to be made on the session.
• Languages – The list of Gremlin flavors that are [[configured|Rexster Configuration] for Rexster. By default the language list will just be gremlin-groovy.

Map<String, Object> Meta
byte[] Session
byte[] Request
String[] Languages
 
Meta attributes:
  None

Script

A Script Response Message contains the results of a Gremlin script sent in a Script Request Message.

ConsoleScriptResponse
  Map<String, Object> Meta
  byte[] Session
  byte[] Request
  String[] ConsoleLines
  byte[] Bindings
 
  Meta attributes:
    None
 
MsgPackScriptResponse
  Map<String, Object> Meta
  byte[] Session
  byte[] Request
  byte[] Results;
  byte[] Bindings;
 
  Meta attributes:
    None

Error

An Error Response Message may be returned by the RexPro Server for any request message sent.

Map<String, Object> Meta
byte[] Session
byte[] Request
String ErrorMessage
 
Meta attributes:
  flag: (Integer) error reason {INVALID_MESSAGE:0, INVALID_SESSION:1, SCRIPT_FAILURE:2, AUTH_FAILURE:3}