JSON TS

JSON-TS is a protocol for communication between server and agent. It uses JSON for message representation, and runs over raw TCP (no HTTP is needed).

Message format

Each message is obviously represented in JSON format, and has one mandatory field: id. For commands it is sequence number of invoked command.

There are three types of messages:

• Commands:

{   
   "id": ...  
   "cmd": name of the command  
   "msg": { "arg1": { value of arg1 },  
            "arg2": { value of arg2 } ... }  
  } 

• Responses:

{   
   "id": ...   
   "response": { "arg1": { value of arg1 },   
                "arg2": { value of arg2 } ... }   
} 

• Errors:

{ 
   "id": ...
   "error": "Error message"
   "code": ERROR_CODE (integer)
} 

Error codes:

code	agent_errcode	TSClient exception	comment
100	AE_COMMAND_NOT_FOUND	TSClientCommandNotFound	Name of command in "cmd" is invalid
101	AE_MESSAGE_FORMAT	TSClientMessageFormatError	Invalid format of "msg" field
102	AE_INVALID_DATA	TSClientInvalidData	Invalid data provided in message (internal checks)
103	AE_INVALID_STATE	TSClientInvalidState	Invalid state of object that used in agent operation
200	AE_INTERNAL_ERROR	TSClientError	Internal error occured while processing message

All messages are null-terminated!

Structure of clients

Because of nature of multi-agent environment of vPerfGenerator, traditional RPC protocols are not fit, because they can send requests only in one direction. In JSON-TS, every node may send requests and respond to them, but there is small difference in server and agent behaviour: server listens on socket and accepts connection from everybody, while agent only connects to one dedicated server.

Here is dataflow diagram for JSON-TS client/server/agent:

Command invocation is synchronious, so it will block invoking thread until response or error message arrive, while incoming commands, response and error to invoked commands are processed in separate threads - receiver (that reads it from socket) and processor (that notifies invoking thread or executes incoming command). Also, processor on server will spawn separate actor for each processing message to avoid deadlock between agent and server.

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