jrpc2

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 Go to latest Published: Dec 19, 2021 License: BSD-3-Clause Imports: 17 Imported by: 98

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jrpc2

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This repository provides a Go module that implements a JSON-RPC 2.0 client and server. There is also a working example in the Go playground.

Packages

  • Package jrpc2 implements the base client and server.

  • Package channel defines the communication channel abstraction used by the server & client.

  • Package code defines standard error codes as defined by the JSON-RPC 2.0 protocol.

  • Package handler defines support for adapting functions to service methods.

  • Package jctx implements an encoder and decoder for request context values, allowing context metadata to be propagated through JSON-RPC requests.

  • Package jhttp allows clients and servers to use HTTP as a transport.

  • Package metrics defines a server metrics collector.

  • Package server provides support for running a server to handle multiple connections, and an in-memory implementation for testing.

Versioning

This module is currently still at v0 and subject to change. To the extent practical, I try to avoid breaking changes to the API, but when I do make a breaking change I will update the minor version. For bug fixes and non-breaking minor changes I update only the patch. Hence, when going from (say) v0.11.3 to v0.12.0, be advised that some API changes may occur.

I am planning to commit to a stable v1 at some point. If you have opinions about what that should mean, please feel free to comment on https://github.com/creachadair/jrpc2/issues/46.

Implementation Notes

The following describes some of the implementation choices made by this module.

Batch requests and error reporting

The JSON-RPC 2.0 spec is ambiguous about the semantics of batch requests. Specifically, the definition of notifications says:

A Notification is a Request object without an "id" member. ... 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").

This conflicts with the definition of batch requests, which asserts:

A Response object SHOULD exist for each Request object, except that there SHOULD NOT be any Response objects for notifications. ... The Response objects being returned from a batch call MAY be returned in any order within the Array. ... If the batch rpc call itself fails to be recognized as an valid JSON or as an Array with at least one value, the response from the Server MUST be a single Response object.

and includes examples that contain request values with no ID (which are, perforce, notifications) and report errors back to the client. Since order may not be relied upon, and there are no IDs, the client cannot correctly match such responses back to their originating requests.

This implementation resolves the conflict in favour of the notification rules. Specifically:

  • If a batch is empty or not valid JSON, the server reports error -32700 (Invalid JSON) as a single error Response object.

  • Otherwise, parse or validation errors resulting from any batch member without an ID are mapped to error objects with a null ID, in the same position in the reply as the corresponding request. Preservation of order is not required by the specification, but it ensures the server has stable behaviour.

Because a server is allowed to reorder the results, a client should not depend on this implementation detail.

Non-standard server push

The specification defines client and server as follows:

The Client is defined as the origin of Request objects and the handler of Response objects. The Server is defined as the origin of Response objects and the handler of Request objects.

Although a client may also be a server, and vice versa, the specification does not require them to do so. The server notification support defined in the jrpc2 package is thus "non-standard" in that it allows the server to act as a client, and the client as a server, in the narrow context of "push" notifications and server callbacks. Otherwise the feature is not special: Requests sent by *jrpc2.Server.Notify and *jrpc2.Server.Callbackare standard Request objects.

Documentation

Overview

Package jrpc2 implements a server and a client for the JSON-RPC 2.0 protocol defined by http://www.jsonrpc.org/specification.

Servers

The *Server type implements a JSON-RPC server. A server communicates with a client over a channel.Channel, and dispatches client requests to user-defined method handlers. Handlers satisfy the jrpc2.Handler interface by exporting a Handle method with this signature: 

Handle(ctx Context.Context, req *jrpc2.Request) (interface{}, error)

A server finds the handler for a request by looking up its method name in a jrpc2.Assigner provided when the server is set up.

For example, suppose we want to export this Add function via JSON-RPC: 

// Add returns the sum of a slice of integers.
func Add(ctx context.Context, values []int) int {
   sum := 0
   for _, v := range values {
      sum += v
   }
   return sum
}

The handler package helps adapt existing functions to the Handler interface. To convert Add to a jrpc2.Handler, call handler.New, which uses reflection to lift its argument into the jrpc2.Handler interface: 

h := handler.New(Add)  // h is now a jrpc2.Handler that calls Add

The handler package also provides handler.Map, which implements the Assigner interface with a Go map. To advertise this function under the name "Add": 

assigner := handler.Map{
   "Add": handler.New(Add),
}

Equipped with an Assigner we can now construct a Server: 

srv := jrpc2.NewServer(assigner, nil)  // nil for default options

To start the server, we need a channel.Channel. Implementations of the Channel interface handle the framing, transmission, and receipt of JSON messages. The channel package implements some common framing disciplines for byte streams like pipes and sockets. For this example, we'll use a channel that communicates over stdin and stdout, with messages delimited by newlines: 

ch := channel.Line(os.Stdin, os.Stdout)

Now we can start the server: 

srv.Start(ch)

The Start method does not block. The server runs until the channel closes, or until it is stopped explicitly by calling srv.Stop(). To wait for the server to finish, call: 

err := srv.Wait()

This will report the error that led to the server exiting. The code for this example is available from tools/examples/adder/adder.go: 

$ go run tools/examples/adder/adder.go

Interact with the server by sending JSON-RPC requests on stdin, such as for example: 

{"jsonrpc":"2.0", "id":1, "method":"Add", "params":[1, 3, 5, 7]}

Clients

The *Client type implements a JSON-RPC client. A client communicates with a server over a channel.Channel, and is safe for concurrent use by multiple goroutines. It supports batched requests and may have arbitrarily many pending requests in flight simultaneously.

To create a client we need a channel: 

import "net"

conn, err := net.Dial("tcp", "localhost:8080")
...
ch := channel.Line(conn, conn)
cli := jrpc2.NewClient(ch, nil)  // nil for default options

To send a single RPC, use the Call method: 

rsp, err := cli.Call(ctx, "Math.Add", []int{1, 3, 5, 7})

Call blocks until the response is received. Errors returned by the server have concrete type *jrpc2.Error.

To issue a batch of concurrent requests, use the Batch method: 

rsps, err := cli.Batch(ctx, []jrpc2.Spec{
   {Method: "Math.Add", Params: []int{1, 2, 3}},
   {Method: "Math.Mul", Params: []int{4, 5, 6}},
   {Method: "Math.Max", Params: []int{-1, 5, 3, 0, 1}},
})

Batch blocks until all the responses are received. An error from the Batch call reflects an error in sending the request: The caller must check each response separately for errors from the server. Responses are returned in the same order as the Spec values, save that notifications are omitted.

To decode the result from a successful response, use its UnmarshalResult method: 

var result int
if err := rsp.UnmarshalResult(&result); err != nil {
   log.Fatalln("UnmarshalResult:", err)
}

To close a client and discard all its pending work, call cli.Close().

Notifications

A JSON-RPC notification is a one-way request: The client sends the request to the server, but the server does not reply. Use the Notify method of a client to send a notification: 

note := handler.Obj{"message": "A fire is burning!"}
err := cli.Notify(ctx, "Alert", note)

A notification is complete once it has been sent. Notifications can also be sent as part of a batch request: 

rsps, err := cli.Batch(ctx, []jrpc2.Spec{
   {Method: "Alert", Params: note, Notify: true},  // this is a notification
   {Method: "Math.Add": Params: []int{1, 2}},      // this is a normal call
   // ...
})

On the server, notifications are handled just like other requests, except that the return value is discarded once the handler returns. If a handler does not want to do anything for a notification, it can query the request: 

if req.IsNotification() {
   return 0, nil  // ignore notifications
}

Services with Multiple Methods

The example above shows a server with one method. A handler.Map works for any number of distinctly-named methods: 

mathService := handler.Map{
   "Add": handler.New(Add),
   "Mul": handler.New(Mul),
}

Maps may be further combined with the handler.ServiceMap type to allow multiple services to be exported from the same server: 

func getStatus(context.Context) string { return "all is well" }

assigner := handler.ServiceMap{
   "Math":   mathService,
   "Status": handler.Map{
     "Get": handler.New(Status),
   },
}

This assigner dispatches "Math.Add" and "Math.Mul" to the arithmetic functions, and "Status.Get" to the getStatus function. A ServiceMap splits the method name on the first period ("."), and you may nest ServiceMaps more deeply if you require a more complex hierarchy.

Concurrency

A Server issues concurrent requests to handlers in parallel, up to the limit given by the Concurrency field in ServerOptions.

Two requests (either calls or notifications) are concurrent if they arrive as part of the same batch. In addition, two calls are concurrent if the time intervals between the arrival of the request objects and delivery of the response objects overlap.

The server may issue concurrent requests to their handlers in any order. Non-concurrent requests are processed in order of arrival. Notifications, in particular, can only be concurrent with other requests in the same batch. This ensures a client that sends a notification can be sure its notification will be fully processed before any subsequent calls are issued to their handlers.

These rules imply that the client cannot rely on the execution order of calls that overlap in time: If the caller needs to ensure that call A completes before call B starts, it must wait for A to return before invoking B.

Built-in Methods

Per the JSON-RPC 2.0 spec, method names beginning with "rpc." are reserved by the implementation. By default, a server does not dispatch these methods to its assigner. In this configuration, the server exports a "rpc.serverInfo" method taking no parameters and returning a jrpc2.ServerInfo value.

Setting the DisableBuiltin server option to true removes special treatment of "rpc." method names, and disables the rpc.serverInfo handler. When this option is true, method names beginning with "rpc." will be dispatched to the assigner like any other method.

Server Push

The AllowPush server option allows handlers to "push" requests back to the client. This is a non-standard extension of JSON-RPC used by some applications such as the Language Server Protocol (LSP). When this option is enabled, the server's Notify and Callback methods send requests back to the client. Otherwise, those methods will report an error: 

if err := s.Notify(ctx, "methodName", params); err == jrpc2.ErrPushUnsupported {
  // server push is not enabled
}
if rsp, err := s.Callback(ctx, "methodName", params); err == jrpc2.ErrPushUnsupported {
  // server push is not enabled
}

A method handler may use jrpc2.ServerFromContext to access the server from its context, and then invoke these methods on it. On the client side, the OnNotify and OnCallback options in jrpc2.ClientOptions provide hooks to which any server requests are delivered, if they are set.

Since not all clients support server push, handlers should set a timeout when using the server Callback method; otherwise the callback may block forever for a client response that will never arrive.

Index

Examples

Constants

View Source 
const Version = "2.0"

Version is the version string for the JSON-RPC protocol understood by this implementation, defined at http://www.jsonrpc.org/specification.

Variables

View Source 
var ErrConnClosed = errors.New("client connection is closed")

ErrConnClosed is returned by a server's push-to-client methods if they are called after the client connection is closed.

View Source 
var ErrInvalidVersion error = &Error{Code: code.InvalidRequest, Message: "incorrect version marker"}

ErrInvalidVersion is returned by ParseRequests if one or more of the requests in the input has a missing or invalid version marker.

View Source 
var ErrPushUnsupported = errors.New("server push is not enabled")

ErrPushUnsupported is returned by the Notify and Call methods if server pushes are not enabled.

Functions

func Network added in v0.2.2 

func Network(s string) (network, address string)

Network guesses a network type for the specified address and returns a tuple of that type and the address.

The assignment of a network type uses the following heuristics:

If s does not have the form [host]:port, the network is assigned as "unix". The network "unix" is also assigned if port == "", port contains characters other than ASCII letters, digits, and "-", or if host contains a "/".

Otherwise, the network is assigned as "tcp". Note that this function does not verify whether the address is lexically valid.

func StrictFields added in v0.11.0 

func StrictFields(v interface{}) interface{}

StrictFields wraps a value v to implement the DisallowUnknownFields method, requiring unknown fields to be rejected when unmarshaling from JSON.

For example: 

var obj RequestType
err := req.UnmarshalParams(jrpc2.StrictFields(&obj))`

Types

type Assigner 

type Assigner interface {
	// Assign returns the handler for the named method, or nil.
	// The implementation can obtain the complete request from ctx using the
	// jrpc2.InboundRequest function.
	Assign(ctx context.Context, method string) Handler
}

An Assigner assigns a Handler to handle the specified method name, or nil if no method is available to handle the request.

type Client 

type Client struct {
	// contains filtered or unexported fields
}

A Client is a JSON-RPC 2.0 client. The client sends requests and receives responses on a channel.Channel provided by the caller.

func ClientFromContext added in v0.31.0 

func ClientFromContext(ctx context.Context) *Client

ClientFromContext returns the client associated with the given context. This will be populated on the context passed to callback handlers.

A callback handler must not close the client, as the close will deadlock waiting for the callback to return.

func NewClient 

func NewClient(ch channel.Channel, opts *ClientOptions) *Client

NewClient returns a new client that communicates with the server via ch.

func (*Client) Batch 

func (c *Client) Batch(ctx context.Context, specs []Spec) ([]*Response, error)

Batch initiates a batch of concurrent requests, and blocks until all the responses return. The responses are returned in the same order as the original specs, omitting notifications.

Any error reported by Batch represents an error in encoding or sending the batch to the server. Errors reported by the server in response to requests must be recovered from the responses.

Example 
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/creachadair/jrpc2"
	"github.com/creachadair/jrpc2/handler"
	"github.com/creachadair/jrpc2/server"
)

var ctx = context.Background()

type Msg struct {
	Text string `json:"msg"`
}

func startServer() server.Local {
	return server.NewLocal(handler.Map{
		"Hello": handler.New(func(ctx context.Context) string {
			return "Hello, world!"
		}),
		"Echo": handler.New(func(_ context.Context, args []json.RawMessage) []json.RawMessage {
			return args
		}),
		"Log": handler.New(func(ctx context.Context, msg Msg) (bool, error) {
			fmt.Println("Log:", msg.Text)
			return true, nil
		}),
	}, nil)
}

func main() {
	loc := startServer()
	defer loc.Close()

	rsps, err := loc.Client.Batch(ctx, []jrpc2.Spec{
		{Method: "Hello"},
		{Method: "Log", Params: Msg{"Sing it!"}, Notify: true},
	})
	if err != nil {
		log.Fatalf("Batch: %v", err)
	}

	fmt.Printf("len(rsps) = %d\n", len(rsps))
	for i, rsp := range rsps {
		var msg string
		if err := rsp.UnmarshalResult(&msg); err != nil {
			log.Fatalf("Invalid result: %v", err)
		}
		fmt.Printf("Response #%d: %s\n", i+1, msg)
	}
}

Output:

Log: Sing it!
len(rsps) = 1
Response #1: Hello, world!

func (*Client) Call 

func (c *Client) Call(ctx context.Context, method string, params interface{}) (*Response, error)

Call initiates a single request and blocks until the response returns. A successful call reports a nil error and a non-nil response. Errors from the server have concrete type *jrpc2.Error. 

rsp, err := c.Call(ctx, method, params)
if e, ok := err.(*jrpc2.Error); ok {
   log.Fatalf("Error from server: %v", err)
} else if err != nil {
   log.Fatalf("Call failed: %v", err)
}
handleValidResponse(rsp)
Example 
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/creachadair/jrpc2/handler"
	"github.com/creachadair/jrpc2/server"
)

var ctx = context.Background()

type Msg struct {
	Text string `json:"msg"`
}

func startServer() server.Local {
	return server.NewLocal(handler.Map{
		"Hello": handler.New(func(ctx context.Context) string {
			return "Hello, world!"
		}),
		"Echo": handler.New(func(_ context.Context, args []json.RawMessage) []json.RawMessage {
			return args
		}),
		"Log": handler.New(func(ctx context.Context, msg Msg) (bool, error) {
			fmt.Println("Log:", msg.Text)
			return true, nil
		}),
	}, nil)
}

func main() {
	loc := startServer()
	defer loc.Close()

	rsp, err := loc.Client.Call(ctx, "Hello", nil)
	if err != nil {
		log.Fatalf("Call: %v", err)
	}
	var msg string
	if err := rsp.UnmarshalResult(&msg); err != nil {
		log.Fatalf("Decoding result: %v", err)
	}
	fmt.Println(msg)
}

Output:

Hello, world!

func (*Client) CallResult 

func (c *Client) CallResult(ctx context.Context, method string, params, result interface{}) error

CallResult invokes Call with the given method and params. If it succeeds, the result is decoded into result. This is a convenient shorthand for Call followed by UnmarshalResult. It will panic if result == nil.

Example 
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/creachadair/jrpc2/handler"
	"github.com/creachadair/jrpc2/server"
)

var ctx = context.Background()

type Msg struct {
	Text string `json:"msg"`
}

func startServer() server.Local {
	return server.NewLocal(handler.Map{
		"Hello": handler.New(func(ctx context.Context) string {
			return "Hello, world!"
		}),
		"Echo": handler.New(func(_ context.Context, args []json.RawMessage) []json.RawMessage {
			return args
		}),
		"Log": handler.New(func(ctx context.Context, msg Msg) (bool, error) {
			fmt.Println("Log:", msg.Text)
			return true, nil
		}),
	}, nil)
}

func main() {
	loc := startServer()
	defer loc.Close()

	var msg string
	if err := loc.Client.CallResult(ctx, "Hello", nil, &msg); err != nil {
		log.Fatalf("CallResult: %v", err)
	}
	fmt.Println(msg)
}

Output:

Hello, world!

func (*Client) Close 

func (c *Client) Close() error

Close shuts down the client, terminating any pending in-flight requests.

func (*Client) Notify 

func (c *Client) Notify(ctx context.Context, method string, params interface{}) error

Notify transmits a notification to the specified method and parameters. It blocks until the notification has been sent.

type ClientOptions 

type ClientOptions struct {
	// If not nil, send debug text logs here.
	Logger Logger

	// If set, this function is called with the context, method name, and
	// encoded request parameters before the request is sent to the server.
	// Its return value replaces the request parameters. This allows the client
	// to send context metadata along with the request. If unset, the parameters
	// are unchanged.
	EncodeContext func(context.Context, string, json.RawMessage) (json.RawMessage, error)

	// If set, this function is called if a notification is received from the
	// server. If unset, server notifications are logged and discarded.  At
	// most one invocation of the callback will be active at a time.
	// Server notifications are a non-standard extension of JSON-RPC.
	OnNotify func(*Request)

	// If set, this function is called if a request is received from the server.
	// If unset, server requests are logged and discarded. Multiple invocations
	// of the callback handler may be active concurrently.
	//
	// The callback handler can retrieve the client from its context using the
	// jrpc2.ClientFromContext function. The context terminates when the client
	// is closed.
	//
	// If a callback handler panics, the client will recover the panic and
	// report a system error back to the server describing the error.
	//
	// Server callbacks are a non-standard extension of JSON-RPC.
	OnCallback func(context.Context, *Request) (interface{}, error)

	// If set, this function is called when the context for a request terminates.
	// The function receives the client and the response that was cancelled.
	// The hook can obtain the ID and error value from rsp.
	//
	// Note that the hook does not receive the request context, which has
	// already ended by the time the hook is called.
	OnCancel func(cli *Client, rsp *Response)
}

ClientOptions control the behaviour of a client created by NewClient. A nil *ClientOptions provides sensible defaults.

type Error 

type Error struct {
	Code    code.Code       `json:"code"`              // the machine-readable error code
	Message string          `json:"message,omitempty"` // the human-readable error message
	Data    json.RawMessage `json:"data,omitempty"`    // optional ancillary error data
}

Error is the concrete type of errors returned from RPC calls.

func Errorf 

func Errorf(code code.Code, msg string, args ...interface{}) *Error

Errorf returns an error value of concrete type *Error having the specified code and formatted message string.

func (Error) ErrCode added in v0.17.0 

func (e Error) ErrCode() code.Code

ErrCode trivially satisfies the code.ErrCoder interface for an *Error.

func (Error) Error 

func (e Error) Error() string

Error renders e to a human-readable string for the error interface.

func (*Error) WithData added in v0.28.0 

func (e *Error) WithData(v interface{}) *Error

WithData marshals v as JSON and constructs a copy of e whose Data field includes the result. If v == nil or if marshaling v fails, e is returned without modification.

type Handler 

type Handler interface {
	// Handle invokes the method with the specified request. The response value
	// must be JSON-marshalable or nil. In case of error, the handler can
	// return a value of type *jrpc2.Error to control the response code sent
	// back to the caller; otherwise the server will wrap the resulting value.
	//
	// The context passed to the handler by a *jrpc2.Server includes two special
	// values that the handler may extract.
	//
	// To obtain the server instance running the handler, write:
	//
	//    srv := jrpc2.ServerFromContext(ctx)
	//
	// To obtain the inbound request message, write:
	//
	//    req := jrpc2.InboundRequest(ctx)
	//
	// The latter is primarily useful for handlers generated by handler.New,
	// which do not receive the request directly. For a handler that implements
	// the Handle method directly, req is the same value passed as a parameter
	// to Handle.
	Handle(context.Context, *Request) (interface{}, error)
}

A Handler handles a single request.

type Logger added in v0.30.0 

type Logger func(text string)

A Logger records text logs from a server or a client. A nil logger discards text log input.

func StdLogger added in v0.30.0 

func StdLogger(logger *log.Logger) Logger

StdLogger adapts a *log.Logger to a Logger. If logger == nil, the returned function sends logs to the default logger.

func (Logger) Printf added in v0.30.0 

func (lg Logger) Printf(msg string, args ...interface{})

Printf writes a formatted message to the logger. If lg == nil, the message is discarded.

type Namer added in v0.34.2 

type Namer interface {
	// Names returns all known method names in lexicographic order.
	Names() []string
}

Namer is an optional interface that an Assigner may implement to expose the names of its methods to the ServerInfo method.

type RPCLogger added in v0.6.1 

type RPCLogger interface {
	// Called for each request received prior to invoking its handler.
	LogRequest(ctx context.Context, req *Request)

	// Called for each response produced by a handler, immediately prior to
	// sending it back to the client. The inbound request can be recovered from
	// the context using jrpc2.InboundRequest.
	LogResponse(ctx context.Context, rsp *Response)
}

An RPCLogger receives callbacks from a server to record the receipt of requests and the delivery of responses. These callbacks are invoked synchronously with the processing of the request.

type Request 

type Request struct {
	// contains filtered or unexported fields
}

A Request is a request message from a client to a server.

func InboundRequest 

func InboundRequest(ctx context.Context) *Request

InboundRequest returns the inbound request associated with the given context, or nil if ctx does not have an inbound request. The context passed to the handler by *jrpc2.Server will include this value.

This is mainly useful to wrapped server methods that do not have the request as an explicit parameter; for direct implementations of Handler.Handle the request value returned by InboundRequest will be the same value as was passed explicitly.

func ParseRequests 

func ParseRequests(msg []byte) ([]*Request, error)

ParseRequests parses a single request or a batch of requests from JSON.

If msg is syntactically valid apart from one or more of the requests having a missing or invalid JSON-RPC version, ParseRequests returns ErrInvalidVersion along with the parsed results.

func (*Request) HasParams 

func (r *Request) HasParams() bool

HasParams reports whether the request has non-empty parameters.

func (*Request) ID 

func (r *Request) ID() string

ID returns the request identifier for r, or "" if r is a notification.

func (*Request) IsNotification 

func (r *Request) IsNotification() bool

IsNotification reports whether the request is a notification, and thus does not require a value response.

func (*Request) Method 

func (r *Request) Method() string

Method reports the method name for the request.

func (*Request) ParamString added in v0.6.2 

func (r *Request) ParamString() string

ParamString returns the encoded request parameters of r as a string. If r has no parameters, it returns "".

func (*Request) UnmarshalParams 

func (r *Request) UnmarshalParams(v interface{}) error

UnmarshalParams decodes the request parameters of r into v. If r has empty parameters, it returns nil without modifying v. If the parameters are invalid, UnmarshalParams returns an InvalidParams error.

By default, unknown object keys are ignored and discarded when unmarshaling into a v of struct type. If the type of v implements a DisallowUnknownFields method, unknown fields will instead generate an InvalidParams error. The jrpc2.StrictFields helper adapts existing struct values to this interface. For more specific behaviour, implement a custom json.Unmarshaler.

If v has type *json.RawMessage, unmarshaling will never report an error.

Example 
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"log"

	"github.com/creachadair/jrpc2"
	"github.com/creachadair/jrpc2/code"
)

func main() {
	const msg = `{"jsonrpc":"2.0", "id":101, "method":"M", "params":{"a":1, "b":2, "c":3}}`

	reqs, err := jrpc2.ParseRequests([]byte(msg))
	if err != nil {
		log.Fatalf("ParseRequests: %v", err)
	}

	var t, u struct {
		A int `json:"a"`
		B int `json:"b"`
	}

	// By default, unmarshaling ignores unknown fields (here, "c").
	if err := reqs[0].UnmarshalParams(&t); err != nil {
		log.Fatalf("UnmarshalParams: %v", err)
	}
	fmt.Printf("t.A=%d, t.B=%d\n", t.A, t.B)

	// To implement strict field checking, there are several options:
	//
	// Solution 1: Use the jrpc2.StrictFields helper.
	err = reqs[0].UnmarshalParams(jrpc2.StrictFields(&t))
	if code.FromError(err) != code.InvalidParams {
		log.Fatalf("UnmarshalParams strict: %v", err)
	}

	// Solution 2: Implement a DisallowUnknownFields method.
	var p strictParams
	err = reqs[0].UnmarshalParams(&p)
	if code.FromError(err) != code.InvalidParams {
		log.Fatalf("UnmarshalParams strict: %v", err)
	}

	// Solution 3: Decode the raw message separately.
	var tmp json.RawMessage
	reqs[0].UnmarshalParams(&tmp) // cannot fail
	dec := json.NewDecoder(bytes.NewReader(tmp))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&u); err == nil {
		log.Fatal("Decode should have failed for an unknown field")
	}

}

type strictParams struct {
	A int `json:"a"`
	B int `json:"b"`
}

func (strictParams) DisallowUnknownFields() {}

Output:

t.A=1, t.B=2

type Response 

type Response struct {
	// contains filtered or unexported fields
}

A Response is a response message from a server to a client.

func (*Response) Error 

func (r *Response) Error() *Error

Error returns a non-nil *Error if the response contains an error.

func (*Response) ID 

func (r *Response) ID() string

ID returns the request identifier for r.

func (*Response) MarshalJSON 

func (r *Response) MarshalJSON() ([]byte, error)

MarshalJSON converts the response to equivalent JSON.

func (*Response) ResultString added in v0.6.2 

func (r *Response) ResultString() string

ResultString returns the encoded result message of r as a string. If r has no result, for example if r is an error response, it returns "".

func (*Response) SetID 

func (r *Response) SetID(s string)

SetID sets the ID of r to s, for use in proxies.

func (*Response) UnmarshalResult 

func (r *Response) UnmarshalResult(v interface{}) error

UnmarshalResult decodes the result message into v. If the request failed, UnmarshalResult returns the same *Error value that is returned by r.Error(), and v is unmodified.

By default, unknown object keys are ignored and discarded when unmarshaling into a v of struct type. If the type of v implements a DisallowUnknownFields method, unknown fields will instead generate an error. The jrpc2.StrictFields helper adapts existing struct values to this interface. For more specific behaviour, implement a custom json.Unmarshaler.

If v has type *json.RawMessage, unmarshaling will never report an error.

Example 
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/creachadair/jrpc2/handler"
	"github.com/creachadair/jrpc2/server"
)

var ctx = context.Background()

type Msg struct {
	Text string `json:"msg"`
}

func startServer() server.Local {
	return server.NewLocal(handler.Map{
		"Hello": handler.New(func(ctx context.Context) string {
			return "Hello, world!"
		}),
		"Echo": handler.New(func(_ context.Context, args []json.RawMessage) []json.RawMessage {
			return args
		}),
		"Log": handler.New(func(ctx context.Context, msg Msg) (bool, error) {
			fmt.Println("Log:", msg.Text)
			return true, nil
		}),
	}, nil)
}

func main() {
	loc := startServer()
	defer loc.Close()

	rsp, err := loc.Client.Call(ctx, "Echo", []string{"alpha", "oscar", "kilo"})
	if err != nil {
		log.Fatalf("Call: %v", err)
	}
	var r1, r3 string

	// Note the nil, which tells the decoder to skip that argument.
	if err := rsp.UnmarshalResult(&handler.Args{&r1, nil, &r3}); err != nil {
		log.Fatalf("Decoding result: %v", err)
	}
	fmt.Println(r1, r3)
}

Output:

alpha kilo

type Server 

type Server struct {
	// contains filtered or unexported fields
}

A Server is a JSON-RPC 2.0 server. The server receives requests and sends responses on a channel.Channel provided by the caller, and dispatches requests to user-defined Handlers.

func NewServer 

func NewServer(mux Assigner, opts *ServerOptions) *Server

NewServer returns a new unstarted server that will dispatch incoming JSON-RPC requests according to mux. To start serving, call Start.

N.B. It is only safe to modify mux after the server has been started if mux itself is safe for concurrent use by multiple goroutines.

This function will panic if mux == nil.

Example 
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"

	"github.com/creachadair/jrpc2/handler"
	"github.com/creachadair/jrpc2/server"
)

type Msg struct {
	Text string `json:"msg"`
}

func startServer() server.Local {
	return server.NewLocal(handler.Map{
		"Hello": handler.New(func(ctx context.Context) string {
			return "Hello, world!"
		}),
		"Echo": handler.New(func(_ context.Context, args []json.RawMessage) []json.RawMessage {
			return args
		}),
		"Log": handler.New(func(ctx context.Context, msg Msg) (bool, error) {
			fmt.Println("Log:", msg.Text)
			return true, nil
		}),
	}, nil)
}

func main() {
	// Construct a new server with methods "Hello" and "Log".
	loc := startServer()
	defer loc.Close()

	// We can query the server for its current status information, including a
	// list of its methods.
	si := loc.Server.ServerInfo()

	fmt.Println(strings.Join(si.Methods, "\n"))
}

Output:

Echo
Hello
Log

func ServerFromContext added in v0.12.0 

func ServerFromContext(ctx context.Context) *Server

ServerFromContext returns the server associated with the given context. This will be populated on the context passed to request handlers. This function is for use by handlers, and will panic for a non-handler context.

It is safe to retain the server and invoke its methods beyond the lifetime of the context from which it was extracted; however, a handler must not block on the Wait or WaitStatus methods of the server, as the server will deadlock waiting for the handler to return.

func (*Server) Callback added in v0.10.0 

func (s *Server) Callback(ctx context.Context, method string, params interface{}) (*Response, error)

Callback posts a single server-side call to the client. It blocks until a reply is received, ctx ends, or the client connection terminates. A successful callback reports a nil error and a non-nil response. Errors returned by the client have concrete type *jrpc2.Error.

This is a non-standard extension of JSON-RPC, and may not be supported by all clients. If you are not sure whether the client supports push calls, you should set a deadline on ctx, otherwise the callback may block forever for a client response that will never arrive.

Unless s was constructed with the AllowPush option set true, this method will always report an error (ErrPushUnsupported) without sending anything. If Callback is called after the client connection is closed, it returns ErrConnClosed.

func (*Server) CancelRequest added in v0.12.0 

func (s *Server) CancelRequest(id string)

CancelRequest instructs s to cancel the pending or in-flight request with the specified ID. If no request exists with that ID, this is a no-op.

func (*Server) Metrics added in v0.15.0 

func (s *Server) Metrics() *metrics.M

Metrics returns the server metrics collector for s. If s does not define a collector, this method returns nil, which is ready for use but discards all metrics.

func (*Server) Notify added in v0.10.0 

func (s *Server) Notify(ctx context.Context, method string, params interface{}) error

Notify posts a single server-side notification to the client.

This is a non-standard extension of JSON-RPC, and may not be supported by all clients. Unless s was constructed with the AllowPush option set true, this method will always report an error (ErrPushUnsupported) without sending anything. If Notify is called after the client connection is closed, it returns ErrConnClosed.

func (*Server) ServerInfo 

func (s *Server) ServerInfo() *ServerInfo

ServerInfo returns an atomic snapshot of the current server info for s.

func (*Server) Start 

func (s *Server) Start(c channel.Channel) *Server

Start enables processing of requests from c and returns. Start does not block while the server runs. This function will panic if the server is already running. It returns s to allow chaining with construction.

func (*Server) Stop 

func (s *Server) Stop()

Stop shuts down the server. It is safe to call this method multiple times or from concurrent goroutines; it will only take effect once.

func (*Server) Wait 

func (s *Server) Wait() error

Wait blocks until the server terminates and returns the resulting error. It is equivalent to s.WaitStatus().Err.

func (*Server) WaitStatus added in v0.6.3 

func (s *Server) WaitStatus() ServerStatus

WaitStatus blocks until the server terminates, and returns the resulting status. After WaitStatus returns, whether or not there was an error, it is safe to call s.Start again to restart the server with a fresh channel.

type ServerInfo 

type ServerInfo struct {
	// The list of method names exported by this server.
	Methods []string `json:"methods,omitempty"`

	// Metric values defined by the evaluation of methods.
	Counter  map[string]int64       `json:"counters,omitempty"`
	MaxValue map[string]int64       `json:"maxValue,omitempty"`
	Label    map[string]interface{} `json:"labels,omitempty"`

	// When the server started.
	StartTime time.Time `json:"startTime,omitempty"`
}

ServerInfo is the concrete type of responses from the rpc.serverInfo method.

func RPCServerInfo 

func RPCServerInfo(ctx context.Context, cli *Client) (result *ServerInfo, err error)

RPCServerInfo calls the built-in rpc.serverInfo method exported by servers. It is a convenience wrapper for an invocation of cli.CallResult.

type ServerOptions 

type ServerOptions struct {
	// If not nil, send debug text logs here.
	Logger Logger

	// If not nil, the methods of this value are called to log each request
	// received and each response or error returned.
	RPCLog RPCLogger

	// Instructs the server to allow server callbacks and notifications, a
	// non-standard extension to the JSON-RPC protocol. If AllowPush is false,
	// the Notify and Callback methods of the server report errors if called.
	AllowPush bool

	// Instructs the server to disable the built-in rpc.* handler methods.
	//
	// By default, a server reserves all rpc.* methods, even if the given
	// assigner maps them. When this option is true, rpc.* methods are passed
	// along to the given assigner.
	DisableBuiltin bool

	// Allows up to the specified number of goroutines to execute in parallel in
	// request handlers. A value less than 1 uses runtime.NumCPU().  Note that
	// this setting does not constrain order of issue.
	Concurrency int

	// If set, this function is called to create a new base request context.
	// If unset, the server uses a background context.
	NewContext func() context.Context

	// If set, this function is called with the method name and encoded request
	// parameters received from the client, before they are delivered to the
	// handler. Its return value replaces the context and argument values. This
	// allows the server to decode context metadata sent by the client.
	// If unset, context and parameters are used as given.
	DecodeContext func(context.Context, string, json.RawMessage) (context.Context, json.RawMessage, error)

	// If set, use this value to record server metrics. All servers created
	// from the same options will share the same metrics collector.  If none is
	// set, an empty collector will be created for each new server.
	Metrics *metrics.M

	// If nonzero this value as the server start time; otherwise, use the
	// current time when Start is called. All servers created from the same
	// options will share the same start time if one is set.
	StartTime time.Time
}

ServerOptions control the behaviour of a server created by NewServer. A nil *ServerOptions provides sensible defaults. It is safe to share server options among multiple server instances.

type ServerStatus added in v0.6.3 

type ServerStatus struct {
	Err error // the error that caused the server to stop (nil on success)

	// On success, these flags explain the reason why the server stopped.
	// At most one of these fields will be true.
	Stopped bool // server exited because Stop was called
	Closed  bool // server exited because the client channel closed
}

ServerStatus describes the status of a stopped server.

A server is said to have succeeded if it stopped because the client channel closed or because its Stop method was called. On success, Err == nil, and the flag fields indicate the reason why the server exited. Otherwise, Err != nil is the error value that caused the server to exit.

func (ServerStatus) Success added in v0.6.3 

func (s ServerStatus) Success() bool

Success reports whether the server exited without error.

type Spec 

type Spec struct {
	Method string
	Params interface{}
	Notify bool
}

A Spec combines a method name and parameter value as part of a Batch. If the Notify field is true, the request is sent as a notification.

Source Files

View all Source files

Directories

Path Synopsis
Package channel defines a basic communications channel.
 Package channel defines a basic communications channel.
Package code defines error code values used by the jrpc2 package.
 Package code defines error code values used by the jrpc2 package.
Package handler provides implementations of the jrpc2.Assigner interface, and support for adapting functions to the jrpc2.Handler interface.
 Package handler provides implementations of the jrpc2.Assigner interface, and support for adapting functions to the jrpc2.Handler interface.
Package jctx implements an encoder and decoder for request context values, allowing context metadata to be propagated through JSON-RPC.
 Package jctx implements an encoder and decoder for request context values, allowing context metadata to be propagated through JSON-RPC.
Package jhttp implements a bridge from HTTP to JSON-RPC.
 Package jhttp implements a bridge from HTTP to JSON-RPC.
Package metrics defines a concurrently-accessible metrics collector.
 Package metrics defines a concurrently-accessible metrics collector.
Package server provides support routines for running jrpc2 servers.
 Package server provides support routines for running jrpc2 servers.
tools module

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