Documentation
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Overview ¶
Package rpc provides access to the exported methods of an object across a network or other I/O connection. After creating a server instance objects can be registered, making it visible from the outside. Exported methods that follow specific conventions can be called remotely. It also has support for the publish/subscribe pattern.
Methods that satisfy the following criteria are made available for remote access:
- object must be exported
- method must be exported
- method returns 0, 1 (response or error) or 2 (response and error) values
- method argument(s) must be exported or builtin types
- method returned value(s) must be exported or builtin types
An example method:
func (s *CalcService) Add(a, b int) (int, error)
When the returned error isn't nil the returned integer is ignored and the error is send back to the client. Otherwise the returned integer is send back to the client.
Optional arguments are supported by accepting pointer values as arguments. E.g. if we want to do the addition in an optional finite field we can accept a mod argument as pointer value.
func (s *CalService) Add(a, b int, mod *int) (int, error)
This RPC method can be called with 2 integers and a null value as third argument. In that case the mod argument will be nil. Or it can be called with 3 integers, in that case mod will be pointing to the given third argument. Since the optional argument is the last argument the RPC package will also accept 2 integers as arguments. It will pass the mod argument as nil to the RPC method.
The server offers the ServeCodec method which accepts a ServerCodec instance. It will read requests from the codec, process the request and sends the response back to the client using the codec. The server can execute requests concurrently. Responses can be send back to the client out of order.
An example server which uses the JSON codec:
type CalculatorService struct {} func (s *CalculatorService) Add(a, b int) int { return a + b } func (s *CalculatorService Div(a, b int) (int, error) { if b == 0 { return 0, errors.New("divide by zero") } return a/b, nil } calculator := new(CalculatorService) server := NewServer() server.RegisterName("calculator", calculator") l, _ := net.ListenUnix("unix", &net.UnixAddr{Net: "unix", Name: "/tmp/calculator.sock"}) for { c, _ := l.AcceptUnix() codec := v2.NewJSONCodec(c) go server.ServeCodec(codec) }
The package also supports the publish subscribe pattern through the use of subscriptions. A method that is considered eligible for notifications must satisfy the following criteria:
- object must be exported
- method must be exported
- first method argument type must be context.Context
- method argument(s) must be exported or builtin types
- method must return the tuple Subscription, error
An example method:
func (s *BlockChainService) NewBlocks(ctx context.Context) (Subscription, error) { ... }
Subscriptions are deleted when:
- the user sends an unsubscribe request
- the connection which was used to create the subscription is closed. This can be initiated by the client and server. The server will close the connection on an write error or when the queue of buffered notifications gets too big.
Index ¶
- Constants
- Variables
- func CreateIPCListener(endpoint string) (net.Listener, error)
- func NewHTTPServer(corsString string, srv *Server) *http.Server
- func NewWSServer(allowedOrigins string, handler *Server) *http.Server
- func SupportedModules(client Client) (map[string]string, error)
- type API
- type BlockNumber
- type Client
- type CodecOption
- type HexNumber
- type JSONErrResponse
- type JSONError
- type JSONRequest
- type JSONSuccessResponse
- type Notifier
- type RPCError
- type RPCService
- type Server
- type ServerCodec
- type Subscription
- type UnsubscribeCallback
Constants ¶
const ( MetadataApi = "rpc" DefaultIPCApis = "admin,debug,eth,miner,net,personal,shh,txpool,web3" DefaultHTTPApis = "eth,net,web3" )
const ( PendingBlockNumber = BlockNumber(-2) LatestBlockNumber = BlockNumber(-1) )
const (
JSONRPCVersion = "2.0"
)
Variables ¶
var ( // ErrNotificationsUnsupported is returned when the connection doesn't support notifications ErrNotificationsUnsupported = errors.New("notifications not supported") // ErrNotificationNotFound is returned when the notification for the given id is not found ErrNotificationNotFound = errors.New("notification not found") )
Functions ¶
func CreateIPCListener ¶ added in v1.4.0
CreateIPCListener creates an listener, on Unix platforms this is a unix socket, on Windows this is a named pipe
func NewHTTPServer ¶
NewHTTPServer creates a new HTTP RPC server around an API provider.
func NewWSServer ¶
NewWSServer creates a new websocket RPC server around an API provider.
Types ¶
type API ¶
type API struct { Namespace string // namespace under which the rpc methods of Service are exposed Version string // api version for DApp's Service interface{} // receiver instance which holds the methods Public bool // indication if the methods must be considered safe for public use }
API describes the set of methods offered over the RPC interface
type BlockNumber ¶
type BlockNumber int64
func (*BlockNumber) Int64 ¶
func (bn *BlockNumber) Int64() int64
func (*BlockNumber) UnmarshalJSON ¶
func (bn *BlockNumber) UnmarshalJSON(data []byte) error
UnmarshalJSON parses the given JSON fragement into a BlockNumber. It supports: - "latest", "earliest" or "pending" as string arguments - the block number Returned errors: - an invalid block number error when the given argument isn't a known strings - an out of range error when the given block number is either too little or too large
type Client ¶
type Client interface { // SupportedModules returns the collection of API's the server offers SupportedModules() (map[string]string, error) Send(req interface{}) error Recv(msg interface{}) error Close() }
Client defines the interface for go client that wants to connect to a geth RPC endpoint
func NewHTTPClient ¶ added in v1.4.0
NewHTTPClient create a new RPC clients that connection to a geth RPC server over HTTP.
func NewIPCClient ¶ added in v1.4.0
NewIPCClient create a new IPC client that will connect on the given endpoint. Messages are JSON encoded and encoded. On Unix it assumes the endpoint is the full path to a unix socket, and Windows the endpoint is an identifier for a named pipe.
func NewInProcRPCClient ¶ added in v1.4.0
NewInProcRPCClient creates an in-process buffer stream attachment to a given RPC server.
func NewWSClient ¶ added in v1.4.0
NewWSClientj creates a new RPC client that communicates with a RPC server that is listening on the given endpoint using JSON encoding.
type CodecOption ¶
type CodecOption int
CodecOption specifies which type of messages this codec supports
const ( // OptionMethodInvocation is an indication that the codec supports RPC method calls OptionMethodInvocation CodecOption = 1 << iota // OptionSubscriptions is an indication that the codec suports RPC notifications OptionSubscriptions = 1 << iota // support pub sub )
type HexNumber ¶ added in v1.4.0
HexNumber serializes a number to hex format using the "%#x" format
func NewHexNumber ¶ added in v1.4.0
func NewHexNumber(val interface{}) *HexNumber
NewHexNumber creates a new hex number instance which will serialize the given val with `%#x` on marshal.
func (*HexNumber) MarshalJSON ¶ added in v1.4.0
MarshalJSON serialize the hex number instance to a hex representation.
func (*HexNumber) UnmarshalJSON ¶ added in v1.4.0
type JSONErrResponse ¶ added in v1.4.0
type JSONErrResponse struct { Version string `json:"jsonrpc"` Id interface{} `json:"id,omitempty"` Error JSONError `json:"error"` }
JSON-RPC error response
type JSONError ¶ added in v1.4.0
type JSONError struct { Code int `json:"code"` Message string `json:"message"` Data interface{} `json:"data,omitempty"` }
JSON-RPC error object
type JSONRequest ¶ added in v1.4.0
type JSONRequest struct { Method string `json:"method"` Version string `json:"jsonrpc"` Id json.RawMessage `json:"id,omitempty"` Payload json.RawMessage `json:"params,omitempty"` }
JSON-RPC request
type JSONSuccessResponse ¶ added in v1.4.0
type JSONSuccessResponse struct { Version string `json:"jsonrpc"` Id interface{} `json:"id,omitempty"` Result interface{} `json:"result"` }
JSON-RPC response
type Notifier ¶
type Notifier interface { // Create a new subscription. The given callback is called when this subscription // is cancelled (e.g. client send an unsubscribe, connection closed). NewSubscription(UnsubscribeCallback) (Subscription, error) // Cancel subscription Unsubscribe(id string) error }
A Notifier type describes the interface for objects that can send create subscriptions
type RPCError ¶ added in v1.4.0
RPCError implements RPC error, is add support for error codec over regular go errors
type RPCService ¶
type RPCService struct {
// contains filtered or unexported fields
}
RPCService gives meta information about the server. e.g. gives information about the loaded modules.
func (*RPCService) Modules ¶
func (s *RPCService) Modules() map[string]string
Modules returns the list of RPC services with their version number
type Server ¶
type Server struct {
// contains filtered or unexported fields
}
Server represents a RPC server
func NewServer ¶
func NewServer() *Server
NewServer will create a new server instance with no registered handlers.
func (*Server) RegisterName ¶
RegisterName will create an service for the given rcvr type under the given name. When no methods on the given rcvr match the criteria to be either a RPC method or a subscription an error is returned. Otherwise a new service is created and added to the service collection this server instance serves.
func (*Server) ServeCodec ¶
func (s *Server) ServeCodec(codec ServerCodec, options CodecOption)
ServeCodec reads incoming requests from codec, calls the appropriate callback and writes the response back using the given codec. It will block until the codec is closed or the server is stopped. In either case the codec is closed.
func (*Server) ServeSingleRequest ¶
func (s *Server) ServeSingleRequest(codec ServerCodec, options CodecOption)
ServeSingleRequest reads and processes a single RPC request from the given codec. It will not close the codec unless a non-recoverable error has occurred. Note, this method will return after a single request has been processed!
type ServerCodec ¶
type ServerCodec interface { // Read next request ReadRequestHeaders() ([]rpcRequest, bool, RPCError) // Parse request argument to the given types ParseRequestArguments([]reflect.Type, interface{}) ([]reflect.Value, RPCError) // Assemble success response, expects response id and payload CreateResponse(interface{}, interface{}) interface{} // Assemble error response, expects response id and error CreateErrorResponse(interface{}, RPCError) interface{} // Assemble error response with extra information about the error through info CreateErrorResponseWithInfo(id interface{}, err RPCError, info interface{}) interface{} // Create notification response CreateNotification(string, interface{}) interface{} // Write msg to client. Write(interface{}) error // Close underlying data stream Close() // Closed when underlying connection is closed Closed() <-chan interface{} }
ServerCodec implements reading, parsing and writing RPC messages for the server side of a RPC session. Implementations must be go-routine safe since the codec can be called in multiple go-routines concurrently.
func NewJSONCodec ¶
func NewJSONCodec(rwc io.ReadWriteCloser) ServerCodec
NewJSONCodec creates a new RPC server codec with support for JSON-RPC 2.0
type Subscription ¶
type Subscription interface { // Inform client of an event Notify(data interface{}) error // Unique identifier ID() string // Cancel subscription Cancel() error }
Subscription defines the interface for objects that can notify subscribers
type UnsubscribeCallback ¶ added in v1.4.0
type UnsubscribeCallback func(id string)
UnsubscribeCallback defines a callback that is called when a subcription ends. It receives the subscription id as argument.