server.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  /*
     6  	Package rpc provides access to the exported methods of an object across a
     7  	network or other I/O connection.  A server registers an object, making it visible
     8  	as a service with the name of the type of the object.  After registration, exported
     9  	methods of the object will be accessible remotely.  A server may register multiple
    10  	objects (services) of different types but it is an error to register multiple
    11  	objects of the same type.
    12  
    13  	Only methods that satisfy these criteria will be made available for remote access;
    14  	other methods will be ignored:
    15  
    16  		- the method's type is exported.
    17  		- the method is exported.
    18  		- the method has two arguments, both exported (or builtin) types.
    19  		- the method's second argument is a pointer.
    20  		- the method has return type error.
    21  
    22  	In effect, the method must look schematically like
    23  
    24  		func (t *T) MethodName(argType T1, replyType *T2) error
    25  
    26  	where T1 and T2 can be marshaled by encoding/gob.
    27  	These requirements apply even if a different codec is used.
    28  	(In the future, these requirements may soften for custom codecs.)
    29  
    30  	The method's first argument represents the arguments provided by the caller; the
    31  	second argument represents the result parameters to be returned to the caller.
    32  	The method's return value, if non-nil, is passed back as a string that the client
    33  	sees as if created by errors.New.  If an error is returned, the reply parameter
    34  	will not be sent back to the client.
    35  
    36  	The server may handle requests on a single connection by calling ServeConn.  More
    37  	typically it will create a network listener and call Accept or, for an HTTP
    38  	listener, HandleHTTP and http.Serve.
    39  
    40  	A client wishing to use the service establishes a connection and then invokes
    41  	NewClient on the connection.  The convenience function Dial (DialHTTP) performs
    42  	both steps for a raw network connection (an HTTP connection).  The resulting
    43  	Client object has two methods, Call and Go, that specify the service and method to
    44  	call, a pointer containing the arguments, and a pointer to receive the result
    45  	parameters.
    46  
    47  	The Call method waits for the remote call to complete while the Go method
    48  	launches the call asynchronously and signals completion using the Call
    49  	structure's Done channel.
    50  
    51  	Unless an explicit codec is set up, package encoding/gob is used to
    52  	transport the data.
    53  
    54  	Here is a simple example.  A server wishes to export an object of type Arith:
    55  
    56  		package server
    57  
    58  		import "errors"
    59  
    60  		type Args struct {
    61  			A, B int
    62  		}
    63  
    64  		type Quotient struct {
    65  			Quo, Rem int
    66  		}
    67  
    68  		type Arith int
    69  
    70  		func (t *Arith) Multiply(args *Args, reply *int) error {
    71  			*reply = args.A * args.B
    72  			return nil
    73  		}
    74  
    75  		func (t *Arith) Divide(args *Args, quo *Quotient) error {
    76  			if args.B == 0 {
    77  				return errors.New("divide by zero")
    78  			}
    79  			quo.Quo = args.A / args.B
    80  			quo.Rem = args.A % args.B
    81  			return nil
    82  		}
    83  
    84  	The server calls (for HTTP service):
    85  
    86  		arith := new(Arith)
    87  		rpc.Register(arith)
    88  		rpc.HandleHTTP()
    89  		l, e := net.Listen("tcp", ":1234")
    90  		if e != nil {
    91  			log.Fatal("listen error:", e)
    92  		}
    93  		go http.Serve(l, nil)
    94  
    95  	At this point, clients can see a service "Arith" with methods "Arith.Multiply" and
    96  	"Arith.Divide".  To invoke one, a client first dials the server:
    97  
    98  		client, err := rpc.DialHTTP("tcp", serverAddress + ":1234")
    99  		if err != nil {
   100  			log.Fatal("dialing:", err)
   101  		}
   102  
   103  	Then it can make a remote call:
   104  
   105  		// Synchronous call
   106  		args := &server.Args{7,8}
   107  		var reply int
   108  		err = client.Call("Arith.Multiply", args, &reply)
   109  		if err != nil {
   110  			log.Fatal("arith error:", err)
   111  		}
   112  		fmt.Printf("Arith: %d*%d=%d", args.A, args.B, reply)
   113  
   114  	or
   115  
   116  		// Asynchronous call
   117  		quotient := new(Quotient)
   118  		divCall := client.Go("Arith.Divide", args, quotient, nil)
   119  		replyCall := <-divCall.Done	// will be equal to divCall
   120  		// check errors, print, etc.
   121  
   122  	A server implementation will often provide a simple, type-safe wrapper for the
   123  	client.
   124  
   125  	The net/rpc package is frozen and is not accepting new features.
   126  */
   127  package rpc
   128  
   129  import (
   130  	"bufio"
   131  	"encoding/gob"
   132  	"errors"
   133  	"go/token"
   134  	"io"
   135  	"log"
   136  	"net"
   137  	"net/http"
   138  	"reflect"
   139  	"strings"
   140  	"sync"
   141  )
   142  
   143  const (
   144  	// Defaults used by HandleHTTP
   145  	DefaultRPCPath   = "/_goRPC_"
   146  	DefaultDebugPath = "/debug/rpc"
   147  )
   148  
   149  // Precompute the reflect type for error. Can't use error directly
   150  // because Typeof takes an empty interface value. This is annoying.
   151  var typeOfError = reflect.TypeOf((*error)(nil)).Elem()
   152  
   153  type methodType struct {
   154  	sync.Mutex // protects counters
   155  	method     reflect.Method
   156  	ArgType    reflect.Type
   157  	ReplyType  reflect.Type
   158  	numCalls   uint
   159  }
   160  
   161  type service struct {
   162  	name   string                 // name of service
   163  	rcvr   reflect.Value          // receiver of methods for the service
   164  	typ    reflect.Type           // type of the receiver
   165  	method map[string]*methodType // registered methods
   166  }
   167  
   168  // Request is a header written before every RPC call. It is used internally
   169  // but documented here as an aid to debugging, such as when analyzing
   170  // network traffic.
   171  type Request struct {
   172  	ServiceMethod string   // format: "Service.Method"
   173  	Seq           uint64   // sequence number chosen by client
   174  	next          *Request // for free list in Server
   175  }
   176  
   177  // Response is a header written before every RPC return. It is used internally
   178  // but documented here as an aid to debugging, such as when analyzing
   179  // network traffic.
   180  type Response struct {
   181  	ServiceMethod string    // echoes that of the Request
   182  	Seq           uint64    // echoes that of the request
   183  	Error         string    // error, if any.
   184  	next          *Response // for free list in Server
   185  }
   186  
   187  // Server represents an RPC Server.
   188  type Server struct {
   189  	serviceMap sync.Map   // map[string]*service
   190  	reqLock    sync.Mutex // protects freeReq
   191  	freeReq    *Request
   192  	respLock   sync.Mutex // protects freeResp
   193  	freeResp   *Response
   194  }
   195  
   196  // NewServer returns a new Server.
   197  func NewServer() *Server {
   198  	return &Server{}
   199  }
   200  
   201  // DefaultServer is the default instance of *Server.
   202  var DefaultServer = NewServer()
   203  
   204  // Is this type exported or a builtin?
   205  func isExportedOrBuiltinType(t reflect.Type) bool {
   206  	for t.Kind() == reflect.Pointer {
   207  		t = t.Elem()
   208  	}
   209  	// PkgPath will be non-empty even for an exported type,
   210  	// so we need to check the type name as well.
   211  	return token.IsExported(t.Name()) || t.PkgPath() == ""
   212  }
   213  
   214  // Register publishes in the server the set of methods of the
   215  // receiver value that satisfy the following conditions:
   216  //	- exported method of exported type
   217  //	- two arguments, both of exported type
   218  //	- the second argument is a pointer
   219  //	- one return value, of type error
   220  // It returns an error if the receiver is not an exported type or has
   221  // no suitable methods. It also logs the error using package log.
   222  // The client accesses each method using a string of the form "Type.Method",
   223  // where Type is the receiver's concrete type.
   224  func (server *Server) Register(rcvr any) error {
   225  	return server.register(rcvr, "", false)
   226  }
   227  
   228  // RegisterName is like Register but uses the provided name for the type
   229  // instead of the receiver's concrete type.
   230  func (server *Server) RegisterName(name string, rcvr any) error {
   231  	return server.register(rcvr, name, true)
   232  }
   233  
   234  // logRegisterError specifies whether to log problems during method registration.
   235  // To debug registration, recompile the package with this set to true.
   236  const logRegisterError = false
   237  
   238  func (server *Server) register(rcvr any, name string, useName bool) error {
   239  	s := new(service)
   240  	s.typ = reflect.TypeOf(rcvr)
   241  	s.rcvr = reflect.ValueOf(rcvr)
   242  	sname := reflect.Indirect(s.rcvr).Type().Name()
   243  	if useName {
   244  		sname = name
   245  	}
   246  	if sname == "" {
   247  		s := "rpc.Register: no service name for type " + s.typ.String()
   248  		log.Print(s)
   249  		return errors.New(s)
   250  	}
   251  	if !token.IsExported(sname) && !useName {
   252  		s := "rpc.Register: type " + sname + " is not exported"
   253  		log.Print(s)
   254  		return errors.New(s)
   255  	}
   256  	s.name = sname
   257  
   258  	// Install the methods
   259  	s.method = suitableMethods(s.typ, logRegisterError)
   260  
   261  	if len(s.method) == 0 {
   262  		str := ""
   263  
   264  		// To help the user, see if a pointer receiver would work.
   265  		method := suitableMethods(reflect.PointerTo(s.typ), false)
   266  		if len(method) != 0 {
   267  			str = "rpc.Register: type " + sname + " has no exported methods of suitable type (hint: pass a pointer to value of that type)"
   268  		} else {
   269  			str = "rpc.Register: type " + sname + " has no exported methods of suitable type"
   270  		}
   271  		log.Print(str)
   272  		return errors.New(str)
   273  	}
   274  
   275  	if _, dup := server.serviceMap.LoadOrStore(sname, s); dup {
   276  		return errors.New("rpc: service already defined: " + sname)
   277  	}
   278  	return nil
   279  }
   280  
   281  // suitableMethods returns suitable Rpc methods of typ. It will log
   282  // errors if logErr is true.
   283  func suitableMethods(typ reflect.Type, logErr bool) map[string]*methodType {
   284  	methods := make(map[string]*methodType)
   285  	for m := 0; m < typ.NumMethod(); m++ {
   286  		method := typ.Method(m)
   287  		mtype := method.Type
   288  		mname := method.Name
   289  		// Method must be exported.
   290  		if !method.IsExported() {
   291  			continue
   292  		}
   293  		// Method needs three ins: receiver, *args, *reply.
   294  		if mtype.NumIn() != 3 {
   295  			if logErr {
   296  				log.Printf("rpc.Register: method %q has %d input parameters; needs exactly three\n", mname, mtype.NumIn())
   297  			}
   298  			continue
   299  		}
   300  		// First arg need not be a pointer.
   301  		argType := mtype.In(1)
   302  		if !isExportedOrBuiltinType(argType) {
   303  			if logErr {
   304  				log.Printf("rpc.Register: argument type of method %q is not exported: %q\n", mname, argType)
   305  			}
   306  			continue
   307  		}
   308  		// Second arg must be a pointer.
   309  		replyType := mtype.In(2)
   310  		if replyType.Kind() != reflect.Pointer {
   311  			if logErr {
   312  				log.Printf("rpc.Register: reply type of method %q is not a pointer: %q\n", mname, replyType)
   313  			}
   314  			continue
   315  		}
   316  		// Reply type must be exported.
   317  		if !isExportedOrBuiltinType(replyType) {
   318  			if logErr {
   319  				log.Printf("rpc.Register: reply type of method %q is not exported: %q\n", mname, replyType)
   320  			}
   321  			continue
   322  		}
   323  		// Method needs one out.
   324  		if mtype.NumOut() != 1 {
   325  			if logErr {
   326  				log.Printf("rpc.Register: method %q has %d output parameters; needs exactly one\n", mname, mtype.NumOut())
   327  			}
   328  			continue
   329  		}
   330  		// The return type of the method must be error.
   331  		if returnType := mtype.Out(0); returnType != typeOfError {
   332  			if logErr {
   333  				log.Printf("rpc.Register: return type of method %q is %q, must be error\n", mname, returnType)
   334  			}
   335  			continue
   336  		}
   337  		methods[mname] = &methodType{method: method, ArgType: argType, ReplyType: replyType}
   338  	}
   339  	return methods
   340  }
   341  
   342  // A value sent as a placeholder for the server's response value when the server
   343  // receives an invalid request. It is never decoded by the client since the Response
   344  // contains an error when it is used.
   345  var invalidRequest = struct{}{}
   346  
   347  func (server *Server) sendResponse(sending *sync.Mutex, req *Request, reply any, codec ServerCodec, errmsg string) {
   348  	resp := server.getResponse()
   349  	// Encode the response header
   350  	resp.ServiceMethod = req.ServiceMethod
   351  	if errmsg != "" {
   352  		resp.Error = errmsg
   353  		reply = invalidRequest
   354  	}
   355  	resp.Seq = req.Seq
   356  	sending.Lock()
   357  	err := codec.WriteResponse(resp, reply)
   358  	if debugLog && err != nil {
   359  		log.Println("rpc: writing response:", err)
   360  	}
   361  	sending.Unlock()
   362  	server.freeResponse(resp)
   363  }
   364  
   365  func (m *methodType) NumCalls() (n uint) {
   366  	m.Lock()
   367  	n = m.numCalls
   368  	m.Unlock()
   369  	return n
   370  }
   371  
   372  func (s *service) call(server *Server, sending *sync.Mutex, wg *sync.WaitGroup, mtype *methodType, req *Request, argv, replyv reflect.Value, codec ServerCodec) {
   373  	if wg != nil {
   374  		defer wg.Done()
   375  	}
   376  	mtype.Lock()
   377  	mtype.numCalls++
   378  	mtype.Unlock()
   379  	function := mtype.method.Func
   380  	// Invoke the method, providing a new value for the reply.
   381  	returnValues := function.Call([]reflect.Value{s.rcvr, argv, replyv})
   382  	// The return value for the method is an error.
   383  	errInter := returnValues[0].Interface()
   384  	errmsg := ""
   385  	if errInter != nil {
   386  		errmsg = errInter.(error).Error()
   387  	}
   388  	server.sendResponse(sending, req, replyv.Interface(), codec, errmsg)
   389  	server.freeRequest(req)
   390  }
   391  
   392  type gobServerCodec struct {
   393  	rwc    io.ReadWriteCloser
   394  	dec    *gob.Decoder
   395  	enc    *gob.Encoder
   396  	encBuf *bufio.Writer
   397  	closed bool
   398  }
   399  
   400  func (c *gobServerCodec) ReadRequestHeader(r *Request) error {
   401  	return c.dec.Decode(r)
   402  }
   403  
   404  func (c *gobServerCodec) ReadRequestBody(body any) error {
   405  	return c.dec.Decode(body)
   406  }
   407  
   408  func (c *gobServerCodec) WriteResponse(r *Response, body any) (err error) {
   409  	if err = c.enc.Encode(r); err != nil {
   410  		if c.encBuf.Flush() == nil {
   411  			// Gob couldn't encode the header. Should not happen, so if it does,
   412  			// shut down the connection to signal that the connection is broken.
   413  			log.Println("rpc: gob error encoding response:", err)
   414  			c.Close()
   415  		}
   416  		return
   417  	}
   418  	if err = c.enc.Encode(body); err != nil {
   419  		if c.encBuf.Flush() == nil {
   420  			// Was a gob problem encoding the body but the header has been written.
   421  			// Shut down the connection to signal that the connection is broken.
   422  			log.Println("rpc: gob error encoding body:", err)
   423  			c.Close()
   424  		}
   425  		return
   426  	}
   427  	return c.encBuf.Flush()
   428  }
   429  
   430  func (c *gobServerCodec) Close() error {
   431  	if c.closed {
   432  		// Only call c.rwc.Close once; otherwise the semantics are undefined.
   433  		return nil
   434  	}
   435  	c.closed = true
   436  	return c.rwc.Close()
   437  }
   438  
   439  // ServeConn runs the server on a single connection.
   440  // ServeConn blocks, serving the connection until the client hangs up.
   441  // The caller typically invokes ServeConn in a go statement.
   442  // ServeConn uses the gob wire format (see package gob) on the
   443  // connection. To use an alternate codec, use ServeCodec.
   444  // See NewClient's comment for information about concurrent access.
   445  func (server *Server) ServeConn(conn io.ReadWriteCloser) {
   446  	buf := bufio.NewWriter(conn)
   447  	srv := &gobServerCodec{
   448  		rwc:    conn,
   449  		dec:    gob.NewDecoder(conn),
   450  		enc:    gob.NewEncoder(buf),
   451  		encBuf: buf,
   452  	}
   453  	server.ServeCodec(srv)
   454  }
   455  
   456  // ServeCodec is like ServeConn but uses the specified codec to
   457  // decode requests and encode responses.
   458  func (server *Server) ServeCodec(codec ServerCodec) {
   459  	sending := new(sync.Mutex)
   460  	wg := new(sync.WaitGroup)
   461  	for {
   462  		service, mtype, req, argv, replyv, keepReading, err := server.readRequest(codec)
   463  		if err != nil {
   464  			if debugLog && err != io.EOF {
   465  				log.Println("rpc:", err)
   466  			}
   467  			if !keepReading {
   468  				break
   469  			}
   470  			// send a response if we actually managed to read a header.
   471  			if req != nil {
   472  				server.sendResponse(sending, req, invalidRequest, codec, err.Error())
   473  				server.freeRequest(req)
   474  			}
   475  			continue
   476  		}
   477  		wg.Add(1)
   478  		go service.call(server, sending, wg, mtype, req, argv, replyv, codec)
   479  	}
   480  	// We've seen that there are no more requests.
   481  	// Wait for responses to be sent before closing codec.
   482  	wg.Wait()
   483  	codec.Close()
   484  }
   485  
   486  // ServeRequest is like ServeCodec but synchronously serves a single request.
   487  // It does not close the codec upon completion.
   488  func (server *Server) ServeRequest(codec ServerCodec) error {
   489  	sending := new(sync.Mutex)
   490  	service, mtype, req, argv, replyv, keepReading, err := server.readRequest(codec)
   491  	if err != nil {
   492  		if !keepReading {
   493  			return err
   494  		}
   495  		// send a response if we actually managed to read a header.
   496  		if req != nil {
   497  			server.sendResponse(sending, req, invalidRequest, codec, err.Error())
   498  			server.freeRequest(req)
   499  		}
   500  		return err
   501  	}
   502  	service.call(server, sending, nil, mtype, req, argv, replyv, codec)
   503  	return nil
   504  }
   505  
   506  func (server *Server) getRequest() *Request {
   507  	server.reqLock.Lock()
   508  	req := server.freeReq
   509  	if req == nil {
   510  		req = new(Request)
   511  	} else {
   512  		server.freeReq = req.next
   513  		*req = Request{}
   514  	}
   515  	server.reqLock.Unlock()
   516  	return req
   517  }
   518  
   519  func (server *Server) freeRequest(req *Request) {
   520  	server.reqLock.Lock()
   521  	req.next = server.freeReq
   522  	server.freeReq = req
   523  	server.reqLock.Unlock()
   524  }
   525  
   526  func (server *Server) getResponse() *Response {
   527  	server.respLock.Lock()
   528  	resp := server.freeResp
   529  	if resp == nil {
   530  		resp = new(Response)
   531  	} else {
   532  		server.freeResp = resp.next
   533  		*resp = Response{}
   534  	}
   535  	server.respLock.Unlock()
   536  	return resp
   537  }
   538  
   539  func (server *Server) freeResponse(resp *Response) {
   540  	server.respLock.Lock()
   541  	resp.next = server.freeResp
   542  	server.freeResp = resp
   543  	server.respLock.Unlock()
   544  }
   545  
   546  func (server *Server) readRequest(codec ServerCodec) (service *service, mtype *methodType, req *Request, argv, replyv reflect.Value, keepReading bool, err error) {
   547  	service, mtype, req, keepReading, err = server.readRequestHeader(codec)
   548  	if err != nil {
   549  		if !keepReading {
   550  			return
   551  		}
   552  		// discard body
   553  		codec.ReadRequestBody(nil)
   554  		return
   555  	}
   556  
   557  	// Decode the argument value.
   558  	argIsValue := false // if true, need to indirect before calling.
   559  	if mtype.ArgType.Kind() == reflect.Pointer {
   560  		argv = reflect.New(mtype.ArgType.Elem())
   561  	} else {
   562  		argv = reflect.New(mtype.ArgType)
   563  		argIsValue = true
   564  	}
   565  	// argv guaranteed to be a pointer now.
   566  	if err = codec.ReadRequestBody(argv.Interface()); err != nil {
   567  		return
   568  	}
   569  	if argIsValue {
   570  		argv = argv.Elem()
   571  	}
   572  
   573  	replyv = reflect.New(mtype.ReplyType.Elem())
   574  
   575  	switch mtype.ReplyType.Elem().Kind() {
   576  	case reflect.Map:
   577  		replyv.Elem().Set(reflect.MakeMap(mtype.ReplyType.Elem()))
   578  	case reflect.Slice:
   579  		replyv.Elem().Set(reflect.MakeSlice(mtype.ReplyType.Elem(), 0, 0))
   580  	}
   581  	return
   582  }
   583  
   584  func (server *Server) readRequestHeader(codec ServerCodec) (svc *service, mtype *methodType, req *Request, keepReading bool, err error) {
   585  	// Grab the request header.
   586  	req = server.getRequest()
   587  	err = codec.ReadRequestHeader(req)
   588  	if err != nil {
   589  		req = nil
   590  		if err == io.EOF || err == io.ErrUnexpectedEOF {
   591  			return
   592  		}
   593  		err = errors.New("rpc: server cannot decode request: " + err.Error())
   594  		return
   595  	}
   596  
   597  	// We read the header successfully. If we see an error now,
   598  	// we can still recover and move on to the next request.
   599  	keepReading = true
   600  
   601  	dot := strings.LastIndex(req.ServiceMethod, ".")
   602  	if dot < 0 {
   603  		err = errors.New("rpc: service/method request ill-formed: " + req.ServiceMethod)
   604  		return
   605  	}
   606  	serviceName := req.ServiceMethod[:dot]
   607  	methodName := req.ServiceMethod[dot+1:]
   608  
   609  	// Look up the request.
   610  	svci, ok := server.serviceMap.Load(serviceName)
   611  	if !ok {
   612  		err = errors.New("rpc: can't find service " + req.ServiceMethod)
   613  		return
   614  	}
   615  	svc = svci.(*service)
   616  	mtype = svc.method[methodName]
   617  	if mtype == nil {
   618  		err = errors.New("rpc: can't find method " + req.ServiceMethod)
   619  	}
   620  	return
   621  }
   622  
   623  // Accept accepts connections on the listener and serves requests
   624  // for each incoming connection. Accept blocks until the listener
   625  // returns a non-nil error. The caller typically invokes Accept in a
   626  // go statement.
   627  func (server *Server) Accept(lis net.Listener) {
   628  	for {
   629  		conn, err := lis.Accept()
   630  		if err != nil {
   631  			log.Print("rpc.Serve: accept:", err.Error())
   632  			return
   633  		}
   634  		go server.ServeConn(conn)
   635  	}
   636  }
   637  
   638  // Register publishes the receiver's methods in the DefaultServer.
   639  func Register(rcvr any) error { return DefaultServer.Register(rcvr) }
   640  
   641  // RegisterName is like Register but uses the provided name for the type
   642  // instead of the receiver's concrete type.
   643  func RegisterName(name string, rcvr any) error {
   644  	return DefaultServer.RegisterName(name, rcvr)
   645  }
   646  
   647  // A ServerCodec implements reading of RPC requests and writing of
   648  // RPC responses for the server side of an RPC session.
   649  // The server calls ReadRequestHeader and ReadRequestBody in pairs
   650  // to read requests from the connection, and it calls WriteResponse to
   651  // write a response back. The server calls Close when finished with the
   652  // connection. ReadRequestBody may be called with a nil
   653  // argument to force the body of the request to be read and discarded.
   654  // See NewClient's comment for information about concurrent access.
   655  type ServerCodec interface {
   656  	ReadRequestHeader(*Request) error
   657  	ReadRequestBody(any) error
   658  	WriteResponse(*Response, any) error
   659  
   660  	// Close can be called multiple times and must be idempotent.
   661  	Close() error
   662  }
   663  
   664  // ServeConn runs the DefaultServer on a single connection.
   665  // ServeConn blocks, serving the connection until the client hangs up.
   666  // The caller typically invokes ServeConn in a go statement.
   667  // ServeConn uses the gob wire format (see package gob) on the
   668  // connection. To use an alternate codec, use ServeCodec.
   669  // See NewClient's comment for information about concurrent access.
   670  func ServeConn(conn io.ReadWriteCloser) {
   671  	DefaultServer.ServeConn(conn)
   672  }
   673  
   674  // ServeCodec is like ServeConn but uses the specified codec to
   675  // decode requests and encode responses.
   676  func ServeCodec(codec ServerCodec) {
   677  	DefaultServer.ServeCodec(codec)
   678  }
   679  
   680  // ServeRequest is like ServeCodec but synchronously serves a single request.
   681  // It does not close the codec upon completion.
   682  func ServeRequest(codec ServerCodec) error {
   683  	return DefaultServer.ServeRequest(codec)
   684  }
   685  
   686  // Accept accepts connections on the listener and serves requests
   687  // to DefaultServer for each incoming connection.
   688  // Accept blocks; the caller typically invokes it in a go statement.
   689  func Accept(lis net.Listener) { DefaultServer.Accept(lis) }
   690  
   691  // Can connect to RPC service using HTTP CONNECT to rpcPath.
   692  var connected = "200 Connected to Go RPC"
   693  
   694  // ServeHTTP implements an http.Handler that answers RPC requests.
   695  func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
   696  	if req.Method != "CONNECT" {
   697  		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
   698  		w.WriteHeader(http.StatusMethodNotAllowed)
   699  		io.WriteString(w, "405 must CONNECT\n")
   700  		return
   701  	}
   702  	conn, _, err := w.(http.Hijacker).Hijack()
   703  	if err != nil {
   704  		log.Print("rpc hijacking ", req.RemoteAddr, ": ", err.Error())
   705  		return
   706  	}
   707  	io.WriteString(conn, "HTTP/1.0 "+connected+"\n\n")
   708  	server.ServeConn(conn)
   709  }
   710  
   711  // HandleHTTP registers an HTTP handler for RPC messages on rpcPath,
   712  // and a debugging handler on debugPath.
   713  // It is still necessary to invoke http.Serve(), typically in a go statement.
   714  func (server *Server) HandleHTTP(rpcPath, debugPath string) {
   715  	http.Handle(rpcPath, server)
   716  	http.Handle(debugPath, debugHTTP{server})
   717  }
   718  
   719  // HandleHTTP registers an HTTP handler for RPC messages to DefaultServer
   720  // on DefaultRPCPath and a debugging handler on DefaultDebugPath.
   721  // It is still necessary to invoke http.Serve(), typically in a go statement.
   722  func HandleHTTP() {
   723  	DefaultServer.HandleHTTP(DefaultRPCPath, DefaultDebugPath)
   724  }
   725
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