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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package netchan
import (
"log"
"net"
"os"
"reflect"
"sync"
)
// Import
// impLog is a logging convenience function. The first argument must be a string.
func impLog(args ...interface{}) {
args[0] = "netchan import: " + args[0].(string)
log.Print(args...)
}
// An Importer allows a set of channels to be imported from a single
// remote machine/network port. A machine may have multiple
// importers, even from the same machine/network port.
type Importer struct {
*encDec
conn net.Conn
chanLock sync.Mutex // protects access to channel map
chans map[string]*chanDir
errors chan os.Error
}
// NewImporter creates a new Importer object to import channels
// from an Exporter at the network and remote address as defined in net.Dial.
// The Exporter must be available and serving when the Importer is
// created.
func NewImporter(network, remoteaddr string) (*Importer, os.Error) {
conn, err := net.Dial(network, "", remoteaddr)
if err != nil {
return nil, err
}
imp := new(Importer)
imp.encDec = newEncDec(conn)
imp.conn = conn
imp.chans = make(map[string]*chanDir)
imp.errors = make(chan os.Error, 10)
go imp.run()
return imp, nil
}
// shutdown closes all channels for which we are receiving data from the remote side.
func (imp *Importer) shutdown() {
imp.chanLock.Lock()
for _, ich := range imp.chans {
if ich.dir == Recv {
ich.ch.Close()
}
}
imp.chanLock.Unlock()
}
// Handle the data from a single imported data stream, which will
// have the form
// (response, data)*
// The response identifies by name which channel is transmitting data.
func (imp *Importer) run() {
// Loop on responses; requests are sent by ImportNValues()
hdr := new(header)
hdrValue := reflect.NewValue(hdr)
ackHdr := new(header)
err := new(error)
errValue := reflect.NewValue(err)
for {
*hdr = header{}
if e := imp.decode(hdrValue); e != nil {
impLog("header:", e)
imp.shutdown()
return
}
switch hdr.payloadType {
case payData:
// done lower in loop
case payError:
if e := imp.decode(errValue); e != nil {
impLog("error:", e)
return
}
if err.error != "" {
impLog("response error:", err.error)
if sent := imp.errors <- os.ErrorString(err.error); !sent {
imp.shutdown()
return
}
continue // errors are not acknowledged.
}
case payClosed:
ich := imp.getChan(hdr.name)
if ich != nil {
ich.ch.Close()
}
continue // closes are not acknowledged.
default:
impLog("unexpected payload type:", hdr.payloadType)
return
}
ich := imp.getChan(hdr.name)
if ich == nil {
continue
}
if ich.dir != Recv {
impLog("cannot happen: receive from non-Recv channel")
return
}
// Acknowledge receipt
ackHdr.name = hdr.name
ackHdr.seqNum = hdr.seqNum
imp.encode(ackHdr, payAck, nil)
// Create a new value for each received item.
value := reflect.MakeZero(ich.ch.Type().(*reflect.ChanType).Elem())
if e := imp.decode(value); e != nil {
impLog("importer value decode:", e)
return
}
ich.ch.Send(value)
}
}
func (imp *Importer) getChan(name string) *chanDir {
imp.chanLock.Lock()
ich := imp.chans[name]
imp.chanLock.Unlock()
if ich == nil {
impLog("unknown name in netchan request:", name)
return nil
}
return ich
}
// Errors returns a channel from which transmission and protocol errors
// can be read. Clients of the importer are not required to read the error
// channel for correct execution. However, if too many errors occur
// without being read from the error channel, the importer will shut down.
func (imp *Importer) Errors() chan os.Error {
return imp.errors
}
// Import imports a channel of the given type and specified direction.
// It is equivalent to ImportNValues with a count of -1, meaning unbounded.
func (imp *Importer) Import(name string, chT interface{}, dir Dir) os.Error {
return imp.ImportNValues(name, chT, dir, -1)
}
// ImportNValues imports a channel of the given type and specified direction
// and then receives or transmits up to n values on that channel. A value of
// n==-1 implies an unbounded number of values. The channel to be bound to
// the remote site's channel is provided in the call and may be of arbitrary
// channel type.
// Despite the literal signature, the effective signature is
// ImportNValues(name string, chT chan T, dir Dir, n int) os.Error
// Example usage:
// imp, err := NewImporter("tcp", "netchanserver.mydomain.com:1234")
// if err != nil { log.Exit(err) }
// ch := make(chan myType)
// err = imp.ImportNValues("name", ch, Recv, 1)
// if err != nil { log.Exit(err) }
// fmt.Printf("%+v\n", <-ch)
func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, n int) os.Error {
ch, err := checkChan(chT, dir)
if err != nil {
return err
}
imp.chanLock.Lock()
defer imp.chanLock.Unlock()
_, present := imp.chans[name]
if present {
return os.ErrorString("channel name already being imported:" + name)
}
imp.chans[name] = &chanDir{ch, dir}
// Tell the other side about this channel.
hdr := &header{name: name}
req := &request{count: int64(n), dir: dir}
if err = imp.encode(hdr, payRequest, req); err != nil {
impLog("request encode:", err)
return err
}
if dir == Send {
go func() {
for i := 0; n == -1 || i < n; i++ {
val := ch.Recv()
if ch.Closed() {
if err = imp.encode(hdr, payClosed, nil); err != nil {
impLog("error encoding client closed message:", err)
}
return
}
if err = imp.encode(hdr, payData, val.Interface()); err != nil {
impLog("error encoding client send:", err)
return
}
}
}()
}
return nil
}