Overview ?
Overview ?
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 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.
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)
rpc.Register(arith)
rpc.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 := rpc.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, "ient, 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.
- Constants
- Variables
- func Accept(lis net.Listener)
- func HandleHTTP()
- func Register(rcvr interface{}) error
- func RegisterName(name string, rcvr interface{}) error
- func ServeCodec(codec ServerCodec)
- func ServeConn(conn io.ReadWriteCloser)
- func ServeRequest(codec ServerCodec) error
- type Call
- type Client
- func Dial(network, address string) (*Client, error)
- func DialHTTP(network, address string) (*Client, error)
- func DialHTTPPath(network, address, path string) (*Client, error)
- func NewClient(conn io.ReadWriteCloser) *Client
- func NewClientWithCodec(codec ClientCodec) *Client
- func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error
- func (client *Client) Close() error
- func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call
- type ClientCodec
- type Request
- type Response
- type Server
- func NewServer() *Server
- func (server *Server) Accept(lis net.Listener)
- func (server *Server) HandleHTTP(rpcPath, debugPath string)
- func (server *Server) Register(rcvr interface{}) error
- func (server *Server) RegisterName(name string, rcvr interface{}) error
- func (server *Server) ServeCodec(codec ServerCodec)
- func (server *Server) ServeConn(conn io.ReadWriteCloser)
- func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request)
- func (server *Server) ServeRequest(codec ServerCodec) error
- type ServerCodec
- type ServerError
- func (e ServerError) Error() string
Package files
client.go
debug.go
server.go
Constants
const (
// Defaults used by HandleHTTP
DefaultRPCPath = "/_goRPC_"
DefaultDebugPath = "/debug/rpc"
)
Variables
var DefaultServer = NewServer()
DefaultServer is the default instance of *Server.
var ErrShutdown = errors.New("connection is shut down")
func Accept(lis net.Listener)
Accept accepts connections on the listener and serves requests
to DefaultServer for each incoming connection.
Accept blocks; the caller typically invokes it in a go statement.
func HandleHTTP()
HandleHTTP registers an HTTP handler for RPC messages to DefaultServer
on DefaultRPCPath and a debugging handler on DefaultDebugPath.
It is still necessary to invoke http.Serve(), typically in a go statement.
func Register(rcvr interface{}) error
Register publishes the receiver's methods in the DefaultServer.
func RegisterName(name string, rcvr interface{}) error
RegisterName is like Register but uses the provided name for the type
instead of the receiver's concrete type.
func ServeCodec(codec ServerCodec)
ServeCodec is like ServeConn but uses the specified codec to
decode requests and encode responses.
func ServeConn(conn io.ReadWriteCloser)
ServeConn runs the DefaultServer on a single connection.
ServeConn blocks, serving the connection until the client hangs up.
The caller typically invokes ServeConn in a go statement.
ServeConn uses the gob wire format (see package gob) on the
connection. To use an alternate codec, use ServeCodec.
func ServeRequest(codec ServerCodec) error
ServeRequest is like ServeCodec but synchronously serves a single request.
It does not close the codec upon completion.
type Call struct {
ServiceMethod string // The name of the service and method to call.
Args interface{} // The argument to the function (*struct).
Reply interface{} // The reply from the function (*struct).
Error error // After completion, the error status.
Done chan *Call // Strobes when call is complete.
}
Call represents an active RPC.
type Client struct {
// contains filtered or unexported fields
}
Client represents an RPC Client.
There may be multiple outstanding Calls associated
with a single Client, and a Client may be used by
multiple goroutines simultaneously.
func Dial(network, address string) (*Client, error)
Dial connects to an RPC server at the specified network address.
func DialHTTP(network, address string) (*Client, error)
DialHTTP connects to an HTTP RPC server at the specified network address
listening on the default HTTP RPC path.
func DialHTTPPath(network, address, path string) (*Client, error)
DialHTTPPath connects to an HTTP RPC server
at the specified network address and path.
func NewClient(conn io.ReadWriteCloser) *Client
NewClient returns a new Client to handle requests to the
set of services at the other end of the connection.
It adds a buffer to the write side of the connection so
the header and payload are sent as a unit.
func NewClientWithCodec(codec ClientCodec) *Client
NewClientWithCodec is like NewClient but uses the specified
codec to encode requests and decode responses.
func (*Client) Call
func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error
Call invokes the named function, waits for it to complete, and returns its error status.
func (*Client) Close
func (client *Client) Close() error
func (*Client) Go
func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call
Go invokes the function asynchronously. It returns the Call structure representing
the invocation. The done channel will signal when the call is complete by returning
the same Call object. If done is nil, Go will allocate a new channel.
If non-nil, done must be buffered or Go will deliberately crash.
type ClientCodec interface {
WriteRequest(*Request, interface{}) error
ReadResponseHeader(*Response) error
ReadResponseBody(interface{}) error
Close() error
}
A ClientCodec implements writing of RPC requests and
reading of RPC responses for the client side of an RPC session.
The client calls WriteRequest to write a request to the connection
and calls ReadResponseHeader and ReadResponseBody in pairs
to read responses. The client calls Close when finished with the
connection. ReadResponseBody may be called with a nil
argument to force the body of the response to be read and then
discarded.
type Request struct {
ServiceMethod string // format: "Service.Method"
Seq uint64 // sequence number chosen by client
// contains filtered or unexported fields
}
Request is a header written before every RPC call. It is used internally
but documented here as an aid to debugging, such as when analyzing
network traffic.
type Response struct {
ServiceMethod string // echoes that of the Request
Seq uint64 // echoes that of the request
Error string // error, if any.
// contains filtered or unexported fields
}
Response is a header written before every RPC return. It is used internally
but documented here as an aid to debugging, such as when analyzing
network traffic.
type Server struct {
// contains filtered or unexported fields
}
Server represents an RPC Server.
func NewServer() *Server
NewServer returns a new Server.
func (*Server) Accept
func (server *Server) Accept(lis net.Listener)
Accept accepts connections on the listener and serves requests
for each incoming connection. Accept blocks; the caller typically
invokes it in a go statement.
func (server *Server) HandleHTTP(rpcPath, debugPath string)
HandleHTTP registers an HTTP handler for RPC messages on rpcPath,
and a debugging handler on debugPath.
It is still necessary to invoke http.Serve(), typically in a go statement.
func (server *Server) Register(rcvr interface{}) error
Register publishes in the server the set of methods of the
receiver value that satisfy the following conditions:
- exported method
- two arguments, both pointers to exported structs
- one return value, of type error
It returns an error if the receiver is not an exported type or has no
suitable methods.
The client accesses each method using a string of the form "Type.Method",
where Type is the receiver's concrete type.
func (server *Server) RegisterName(name string, rcvr interface{}) error
RegisterName is like Register but uses the provided name for the type
instead of the receiver's concrete type.
func (server *Server) ServeCodec(codec ServerCodec)
ServeCodec is like ServeConn but uses the specified codec to
decode requests and encode responses.
func (server *Server) ServeConn(conn io.ReadWriteCloser)
ServeConn runs the server on a single connection.
ServeConn blocks, serving the connection until the client hangs up.
The caller typically invokes ServeConn in a go statement.
ServeConn uses the gob wire format (see package gob) on the
connection. To use an alternate codec, use ServeCodec.
func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request)
ServeHTTP implements an http.Handler that answers RPC requests.
func (server *Server) ServeRequest(codec ServerCodec) error
ServeRequest is like ServeCodec but synchronously serves a single request.
It does not close the codec upon completion.
type ServerCodec interface {
ReadRequestHeader(*Request) error
ReadRequestBody(interface{}) error
WriteResponse(*Response, interface{}) error
Close() error
}
A ServerCodec implements reading of RPC requests and writing of
RPC responses for the server side of an RPC session.
The server calls ReadRequestHeader and ReadRequestBody in pairs
to read requests from the connection, and it calls WriteResponse to
write a response back. The server calls Close when finished with the
connection. ReadRequestBody may be called with a nil
argument to force the body of the request to be read and discarded.
type ServerError string
ServerError represents an error that has been returned from
the remote side of the RPC connection.
func (ServerError) Error
func (e ServerError) Error() string