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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
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 | int(n) | The body of the message itself containing the instructions for the RexPro Server. This portion of the message is serialized using MsgPack. |
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. |
The following sections define the request class of messages for RexPro. Request messages are those that are sent by the client to the RexPro Server for processing.
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.
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.
The following sections define the response class of messages for RexPro. Response messages are those that are sent by the RexPro Server back to the client, in response to a request message.
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.