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JSON-RPC

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JSON-RPC (JavaScript Object Notation-Remote Procedure Call) is a remote procedure call (RPC) protocol encoded in JSON. It is similar to the XML-RPC protocol, defining only a few data types and commands. JSON-RPC allows for notifications (data sent to the server that does not require a response) and for multiple calls to be sent to the server which may be answered asynchronously.

History

Version Description Dated
1.0 Original version 2005
1.1 WD Working draft. Adds named parameters, adds specific error codes, and adds introspection functions. 2006-08-07
1.1 Alt Suggestion for a simple JSON-RPC 1.1. Alternative proposal to 1.1 WD. 2007-05-06
1.1 Object Specification Object Specification. Alternative proposal to 1.1 WD/1.1ALT. 2007-07-30
1.2 Proposal. A later revision of this document was renamed to 2.0. 2007-12-27
2.0 Specification proposal 2009-05-24
2.0 (Revised-) Specification 2010-03-26

Usage

JSON-RPC works by sending a request to a server implementing this protocol. The client in that case is typically software intending to call a single method of a remote system. Multiple input parameters can be passed to the remote method as an array or object, whereas the method itself can return multiple output data as well. (This depends on the implemented version.)

All transfer types are single objects, serialized using JSON.[1] A request is a call to a specific method provided by a remote system. It can contain three members:

  • method - A string with the name of the method to be invoked. Method names that begin with "rpc." are reserved for rpc-internal methods.
  • params - An object or array of values to be passed as parameters to the defined method. This member may be omitted.
  • id - A string or non-fractional number used to match the response with the request that it is replying to.[2] This member may be omitted if no response should be returned.[3]

The receiver of the request must reply with a valid response to all received requests. A response can contain the members mentioned below.

  • result - The data returned by the invoked method. If an error occurred while invoking the method, this member must not exist.[4]
  • error - An error object if there was an error invoking the method, otherwise this member must not exist.[5] The object must contain members code (integer) and message (string).[6] An optional data member can contain further server-specific data. There are pre-defined error codes which follow those defined for XML-RPC.
  • id - The id of the request it is responding to.

Since there are situations where no response is needed or even desired, notifications were introduced. A notification is similar to a request except for the id, which is not needed because no response will be returned. In this case the id property should be omitted (Version 2.0) or be null (Version 1.0).

Examples

In these examples, --> denotes data sent to a service (request), while <-- denotes data coming from a service. Although <-- is often called a response in client–server computing, depending on the JSON-RPC version it does not necessarily imply an answer to a request.

Version 2.0

Request and response: 

--> {"jsonrpc": "2.0", "method": "subtract", "params": {"minuend": 42, "subtrahend": 23}, "id": 3}
<-- {"jsonrpc": "2.0", "result": 19, "id": 3}

Notification (no response): 

--> {"jsonrpc": "2.0", "method": "update", "params": [1,2,3,4,5]}

Version 1.1 (Working Draft)

Request and response: 

--> {"version": "1.1", "method": "confirmFruitPurchase", "params": [["apple", "orange", "mangoes"], 1.123], "id": "194521489"}
<-- {"version": "1.1", "result": "done", "error": null, "id": "194521489"}

Version 1.0

Request and response: 

--> {"method": "echo", "params": ["Hello JSON-RPC"], "id": 1}
<-- {"result": "Hello JSON-RPC", "error": null, "id": 1}

See also

  • gRPC
  • SOAP - a messaging protocol
  • JSON-WSP - a JSON-RPC inspired protocol with a service description specification

References

  1. ^ "specification - JSON-RPC - Trac". Archived from the original on 2008-05-17. Retrieved 2008-05-14.
  2. ^ "JSON-RPC 2.0 Specification". id: An identifier established by the Client that MUST contain a String, Number, or NULL value if included. If it is not included it is assumed to be a notification. The value SHOULD normally not be Null and Numbers SHOULD NOT contain fractional parts
  3. ^ "JSON-RPC 2.0 Specification". A Notification is a Request object without an "id" member. A Request object that is a Notification signifies the Client's lack of interest in the corresponding Response object, and as such no Response object needs to be returned to the client. The Server MUST NOT reply to a Notification, including those that are within a batch request. Notifications are not confirmable by definition, since they do not have a Response object to be returned. As such, the Client would not be aware of any errors (like e.g. "Invalid params", "Internal error").
  4. ^ "JSON-RPC 2.0 Specification". result: This member is REQUIRED on success. This member MUST NOT exist if there was an error invoking the method. The value of this member is determined by the method invoked on the Server.
  5. ^ "JSON-RPC 2.0 Specification". error: This member is REQUIRED on error. This member MUST NOT exist if there was no error triggered during invocation. The value for this member MUST be an Object as defined in section 5.1.
  6. ^ "JSON-RPC 2.0 Specification". Error object: When a rpc call encounters an error, the Response Object MUST contain the error member with a value that is a Object with the following members: (code) - A Number that indicates the error type that occurred. This MUST be an integer. (message) - A String providing a short description of the error. The message SHOULD be limited to a concise single sentence. (data) - A Primitive or Structured value that contains additional information about the error. This may be omitted. The value of this member is defined by the Server (e.g. detailed error information, nested errors etc.).
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