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Parse LiveQuery Protocol Specification

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Antonio Davi Macedo Coelho de Castro edited this page Apr 23, 2020 · 3 revisions

Overview

Parse LiveQuery server has its own protocol. It is built on top of standard WebSocket connections. A client should follow this protocol to interact with the LiveQuery server. This protocol defines the messages to connect to the LiveQuery server, subscribe/unsubscribe a ParseQuery and get updates from the LiveQuery server. The clients and the server communicate with each other in messages. Each message is a compacted JSON object.

Connect message

The connect message is sent from a client to the LiveQuery server. It should be the first message sent from a client after the WebSocket connection is established. The connect message's format is:

{
  "op": "connect",
  "applicationId": "",
  "restAPIKey": "",  // Optional 
  "javascriptKey": "", // Optional
  "clientKey": "", //Optional
  "windowsKey": "", //Optional
  "masterKey": "", // Optional
  "sessionToken": "", // Optional
  "installationId": "" // Optional
}
  • The op field must be connect.
  • The key field is optional. When you initialize the LiveQuery server with key pairs, the LiveQuery server will try to match the key field in the connect message with the given key pairs. If no key pair is provided when the LiveQuery server is initialized, the key field will be ignored.
  • The sessionToken field is optional. If you provide the sessionToken, when the LiveQuery get ParseObject's updates from parse server, it will try to check whether the sessionToken fulfills the ParseObject's ACL. The LiveQuery server will only send updates to clients whose sessionToken is fit for the ParseObject's ACL.
  • The installationId field is optional. InstallationId is a identifier for a device. It can be used for monitoring.

If a client connects to the LiveQuery server successfully, it will receive a response like

{
  "op": "connected"
}

Subscribe message

After a client connects to the LiveQuery server, it can send a subscribe message to subscribe a ParseQuery. The message's format is:

{
  "op": "subscribe",
  "requestId": 1,
  "query": {
      "className": "Player",
      "where": {"name": "test"},
      "fields": ["name"] // Optional
  },
  "sessionToken": "" // Optional
}
  • The op field must be subscribe.
  • The requestId field is mandatory. It is a number which is unique for each LiveQuery subscription. The LiveQuery server will use this to distinguish between the different subscriptions from the same client.
  • The query.className field is mandatory. It represents the className of the ParseQuery the client subscribes to.
  • The query.where field is mandatory. It represents the condition of the ParseQuery the client subscribes to. The format of the where field is the same with ParseQuery's REST API format. You can check the detail here. Right now we support $lt, $lte, $gt, $gte, $ne, $in, $nin, $exists, $all, $regex, $nearSphere, $within and normal equal condition. Any unsupported conditions will be ignored.
  • The query.fields field is optional. It is an array of field names of a ParseObject. Suppose the ParseObject Player contains three fields name, id and age. If you are only interested in the change of the name field, you can set query.fields to [name]. In this situation, when the change of a Player ParseObject fulfills the subscription, only the name field will be sent to the clients instead of the full Player ParseObject.
  • The sessionToken field is optional. It is similar to the sessionToken field in the connect message. The sessionToken field in subscribe message has higher priority than the sessionToken field in connect message. This means the LiveQuery server will try to use the sessionToken in subscribe message to check a ParseObject's ACL first.

If a client subscribes a ParseQuery to the LiveQuery server successfully, it will receive a response like:

{
  "op": "subscribed",
  "requestId":1
}

Once a client get this response from the LiveQuery server, it will start to receive ParseObjects whose changes fulfill the ParseQuery.

Event message

After a client subscribes to a ParseQuery, the LiveQuery server will send event messages to the client. We support 5 types of events. Suppose you subscribe to a ParseQuery like:

{
  "op": "subscribe",
  "requestId": 1,
  "query": {
      "className": "Player",
      "where": {"name": "test"}
  }
}

Create event

This event means a ParseObject is created and it fulfills the ParseQuery the client subscribes. When a new Player ParseObject whose name is "test" is created, the LiveQuery server will send a create event message to the client. The create event message's format is:

{
  "op": "create",
  "requestId": 1,
  "object": {
    "className": "Player",
    "objectId": "",
    "createdAt": "",
    "updatedAt": "",
    ...
  }
}
  • The op field is create.
  • The requestId field is a numebr. It is same as the requestId when the client subscribes the ParseQuery to the LiveQuery server.
  • The object is the ParseObject in JSON format.

Enter event

This event means a ParseObject's old value does not fulfill the ParseQuery but its new value fulfills the ParseQuery. When an existing Player ParseObject's name is changed from unknown to test, the LiveQuery server will send an enter event message to the client. The enter event message's format is:

{
  "op": "enter",
  "requestId": 1,
  "object": {
    "className": "Player",
    "objectId": "",
    "createdAt": "",
    "updatedAt": "",
    ...
  }
}

Update event

This event means a ParseObject's old value and its new value fulfill the ParseQuery at the same time. For an existing Player ParseObject' whose name is "test", when its age changes from 20 to 21, the LiveQuery server will send an update event message to the client. The update event message's format is:

{
  "op": "update",
  "requestId": 1,
  "object": {
    "className": "Player",
    "objectId": "",
    "createdAt": "",
    "updatedAt": "",
    ...
  }
}

Leave event

This event means a ParseObject's old value fulfills the ParseQuery but its new value does not. When an existing Player ParseObject's name is changed from test to unknown, the LiveQuery server will send a leave event message to the client. The leave event message's format is:

{
  "op": "leave",
  "requestId": 1,
  "object": {
    "className": "Player",
    "objectId": "",
    "createdAt": "",
    "updatedAt": "",
    ...
  }
}

Delete event

This event means a ParseObject's whose value fulfills the ParseQuery is deleted. When an existing Player ParseObject's whose name is "test" is deleted, the LiveQuery server will send an delete event message to the client. The delete event message's format is:

{
  "op": "delete",
  "requestId": 1,
  "object": {
    "className": "Player",
    "objectId": "",
    "createdAt": "",
    "updatedAt": "",
    ...
  }
}

Unsubscribe message

The unsubscribe message is sent from clients to the LiveQuery server. It should be sent after a client successfully unsubscribes some ParseQuery. The format of the unsubscribe message is:

{
  "op": "unsubscribe",
  "requestId":1
}
  • The op field is unsubscribe.
  • The requestId field is mandatory. It is a number which is unique for each LiveQuery subscription. It is the same requestId when the client subscribes the ParseQuery to the LiveQuery server.

If a client unsubscribes a ParseQuery to the LiveQuery server successfully, it will receive a response like:

{
  "op": "unsubscribed",
  "requestId":1
}

Error message

When a client sends unknown or error messages to the LiveQuery server, the server will respond with an error message to the client. The format of the error message is:

{
  "op": "error",
  "code": 1,
  "error": "",
  "reconnect": true
}
  • The op field is error.
  • The code field is a number which represents the type of the error.
  • The error field is the error message.
  • The reconnect field is a boolean which indicates whether a client can reconnect to the LiveQuery server after this error. Most of the cases it is true. But if the LiveQuery server has some internal errors, it can be false. If it is false, a client should not try to reconnect to the LiveQuery server.

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