jsonrpc2

Overview ¶

Package jsonrpc implements a JSON-RPC ClientCodec and ServerCodec for the rpc package.

Package rpc provides access to the exported methods of an object across a
network or other I/O connection.  A server registers an object, making it visible
as a service with the name of the type of the object.  After registration, exported
methods of the object will be accessible remotely.  A server may register multiple
objects (services) of different types but it is an error to register multiple
objects of the same type.

Only methods that satisfy these criteria will be made available for remote access;
other methods will be ignored:

	- the method is exported.
	- the method has two arguments, both exported (or builtin) types.
	- the method's second argument is a pointer.
	- the method has return type error.

In effect, the method must look schematically like

	func (t *T) MethodName(argType T1, replyType *T2) error

where T, T1 and T2 can be marshaled by encoding/gob.
These requirements apply even if a different codec is used.
(In the future, these requirements may soften for custom codecs.)

The method's first argument represents the arguments provided by the caller; the
second argument represents the result parameters to be returned to the caller.
The method's return value, if non-nil, is passed back as a string that the client
sees as if created by errors.New.  If an error is returned, the reply parameter
will not be sent back to the client.

The server may handle requests on a single connection by calling ServeConn.  More
typically it will create a network listener and call Accept or, for an HTTP
listener, HandleHTTP and http.Serve.

A client wishing to use the service establishes a connection and then invokes
NewClient on the connection.  The convenience function Dial (DialHTTP) performs
both steps for a raw network connection (an HTTP connection).  The resulting
Client object has two methods, Call and Go, that specify the service and method to
call, a pointer containing the arguments, and a pointer to receive the result
parameters.

The Call method waits for the remote call to complete while the Go method
launches the call asynchronously and signals completion using the Call
structure's Done channel.

Unless an explicit codec is set up, package encoding/gob is used to
transport the data.

Here is a simple example.  A server wishes to export an object of type Arith:

	package server

	type Args struct {
		A, B int
	}

	type Quotient struct {
		Quo, Rem int
	}

	type Arith int

	func (t *Arith) Multiply(args *Args, reply *int) error {
		*reply = args.A * args.B
		return nil
	}

	func (t *Arith) Divide(args *Args, quo *Quotient) error {
		if args.B == 0 {
			return errors.New("divide by zero")
		}
		quo.Quo = args.A / args.B
		quo.Rem = args.A % args.B
		return nil
	}

The server calls (for HTTP service):

	arith := new(Arith)
	jsonrpc2.Register(arith)
	jsonrpc2.HandleHTTP()
	l, e := net.Listen("tcp", ":1234")
	if e != nil {
		log.Fatal("listen error:", e)
	}
	go http.Serve(l, nil)

At this point, clients can see a service "Arith" with methods "Arith.Multiply" and
"Arith.Divide".  To invoke one, a client first dials the server:

	client, err := jsonrpc2.DialHTTP("tcp", serverAddress + ":1234")
	if err != nil {
		log.Fatal("dialing:", err)
	}

Then it can make a remote call:

	// Synchronous call
	args := &server.Args{7,8}
	var reply int
	err = client.Call("Arith.Multiply", args, &reply)
	if err != nil {
		log.Fatal("arith error:", err)
	}
	fmt.Printf("Arith: %d*%d=%d", args.A, args.B, reply)

or

	// Asynchronous call
	quotient := new(Quotient)
	divCall := client.Go("Arith.Divide", args, quotient, nil)
	replyCall := <-divCall.Done	// will be equal to divCall
	// check errors, print, etc.

A server implementation will often provide a simple, type-safe wrapper for the
client.