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Transport

Jet heavily relies on JSON-RPC 2.0 semantics for all of its messages. There are some minor changes to the spec, however. To be able to follow the protocol details, the reader must be familiar with the (JSON-RPC 2.0) terms: Request, Response, Notification, Error Object and Batch.

As a reminder: Don't be confused by the term Notification. A Notification is simply a Request without an id specified, thus indicating no Response to the Request is expected.

There are two categories of Requests to distinguish:

  • Active: The Peer sends a Request to the Daemon
  • Passive: The Daemon sends a Request to the Peer

The Active Request always originate from Peers and are send to the Daemon. As a result of adding States/Methods or Fetching, the Daemon may send Passive Requests to Peers. For instance: If a Peer adds a State, another fetching Peer with matching fetch rules is informed by means of a Passive Request.

The Passive Requests are:

  • Fetch based messages
  • (Routed) Requests to set (change) a State
  • (Routed) Requests to call a Method

The method field of Passive Requests are Peer defined (via add and fetch), whereas the method name field of Active Requests is always either add, remove, fetch, unfetch, set, call, change or config.

Note: Batches can contain Active and/or Passive Requests.

Example for Active Message

In this example a Peer fetches all persons (all states and methods, where the path starts with "person"). The side-effect of this message is that, the Daemon may send a Passive message with "method":"personFetcher" to the peer whenever appropriate.

{
  "method": "fetch",
  "params": {
    "id": "personFetcher",
    "path": {
      "startsWith": "person"
    }
  },
  "id": 762
}

Example for Passive Message

This is a Passive message which is issued based on the fetch rule defined above. Note the method name, which has been specified earlier in the fetch call.

{
  "method": "personFetcher",
  "params": {
    "path": "person/asdlkjasdk92",
    "value": {
      "name": "Paul",
      "age": 63
    },
    "event": "add"
  }
}

Differences to JSON-RPC 2.0

In opposite to the JSON-RPC 2.0 spec the "jsonrpc": "2.0" field is considered optional and can be simply ignored.

Further Batch Messages are not subject of any order requirements are may be processed and send at any time. This allows to minimize message framing overhead (e.g. Websockets).

Messages

This chapter lists an overview of all active messsages by example.

add

Use the add message for adding States or Methods to the Daemon. The Daemon will route all set/call messages to the Peer, changing the method to the respective path.

// add a simple state
{
  "method": "add",
  "params": {
    "path": "foo/bar", //unique path
    "value": 123 // any non-function value
  }
  "id": 41
}
// add a more complicate state
{
  "method": "add",
  "params": {
    "path": "person/Xop",
    "value": {
      "name": "Bob",
      "age": 26,
      "hobbies": ["Hiking", "Swimming"]
    }
  }
  // Note that this is a Notification as there is no "id"
}
// add a method (just leave-out the value)
{
  "method": "add",
  "params": {
    "path": "addNumbers"
  }
  // Note that this is a Notification as there is no "id"
}

remove

Use the remove message for removing States or Methods from the Daemon. The Daemon will stop to route set/call messages for the respective path.

// remove a method or state
{
  "method": "remove",
  "params": {
    "path": "addNumbers"
  }
  // Note that this is a Notification as there is no "id"
}

// remove a method or state
{
  "method": "remove",
  "params": {
    "path": "persons/xyz"
  }
  "id": "ajsykw"
}

set

Use the set message for (trying) to set a State to a new value. The Daemon will route the Request to the responsible Peer. Accepting the new value is solely up to the Peer. In case of an error-less dispatching / assigning, the Peer posts a change Notification, thus informing all fetching Peers about the actual new value.

// set a state to a new value
{
  "method": "set",
  "params": {
    "path": "foo/bar",
    "value": 920
  }
  // Note that this is a Notification as there is no "id"
}

// set a state to a new value
{
  "method": "set",
  "params": {
    "path": "foo/bar",
    "value": { // the value can be any non-function type
      age: 22,
      gender: "female"
    }
  }
  "id": "92s"
}

call

Use the call message for calling a Method. The Daemon will route the Request to the responsible Peer.

// call a method
{
  "method": "call",
  "params": {
    "path": "logStuff",
    "args": ["WARN",{
      "system": "cpu",
      "category": "epicFail"
    }]
  }
  // Note that this is a Notification as there is no "id"
}

// call a method
{
  "method": "call",
  "params": {
    "path": "addNumbers",
    "args": [1,2]
  }
  "id": "91s"
}

// call a method with object args
{
  "method": "call",
  "params": {
    "path": "createPerson",
    "args": {
      "name": "Jefferson",
      "age": 22,
      "hobbies": ["soccer","stamps"]
    }
  }
  "id": "911s"
}

change

Use the change message to make a State value change public.

{
  "method": "change",
  "params": {
    "path": "foo/bar",
    "value": false // yes, state values may change type
  }
  "id": 41
}
{
  "method": "change",
  "params": {
    "path": "person/Xop",
    "value": {
      "name": "Bob",
      "age": 27,
      "hobbies": ["Computer Games", "Climbing"]
    }
  }
  // Note that this is a Notification as there is no "id"
}

fetch

Use the fetch message to create a new fetch rule. The Daemon sends fetch Notifications with the specified fetch id as method, whenever appropriate.

// some path based case insensitive fetch
{
  "method": "fetch",
  "params": {
    "id": "f1000",  // a peer defined fetch id
    "path": {
      "startsWith": "abc",
      "contains": "foo"
    },
    "caseInsensitive": true
  },
  "id": 3412
}

// some path based fetch (setup as Notification)
{
  "method": "fetch",
  "params": {
    "id": "__321_f",  // a peer defined fetch id
    "path": {
      "endsWith": "abc"
    }  
  }
  // no id -> Notification, no Response if fetch setup is ok
}

// some path / value based fetch
{
  "method": "fetch",
  "params": {
    "id": "f123",  // a peer defined fetch id
    "path": {
      "endsWith": "/temperature"
    },
    "value": {
      "lessThan": 7
    }
  }
  "id": "pasdp3"
}

// some path / valuefield based fetch
{
  "method": "fetch",
  "params": {
    "id": "f1pq23",  // a peer defined fetch id
    "path": {
      "startsWith": "persons/"
    },
    "valueField": {
      "age": {
        "greaterThan": 20
      },
      "name.first": {
        "equals": "Micheal"
      }
    }  
  }
  "id": "pa223"
}

// some path based sorted fetch
{
  "method": "fetch",
  "params": {
    "id": "f1pq23",  // a peer defined fetch id
    "path": {
      "startsWith": "persons/"
    },
    "sort": {
      "from": 20, // paginating
      "to": 40,
      "byPath": true // this is default
    }
  }
  "id": "pa223"
}

// some path based sorted (byValueField) fetch
{
  "method": "fetch",
  "params": {
    "id": "f1pq23",  // a peer defined fetch id
    "path": {
      "startsWith": "persons/"
    },
    "sort": {
      "from": 1, // paginating
      "to": 10,
      "byValueField": {
        "age": "number" // type is required for sorting: "number", "string" or "boolean"
      },
      "descending": true
    }
  }
  "id": "pa123"
}