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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 (
"errors"
"io"
"log"
"net"
"reflect"
"sync"
"time"
)
// 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
chanLock sync.Mutex // protects access to channel map
names map[string]*netChan
chans map[int]*netChan
errors chan error
maxId int
mu sync.Mutex // protects remaining fields
unacked int64 // number of unacknowledged sends.
seqLock sync.Mutex // guarantees messages are in sequence, only locked under mu
}
// NewImporter creates a new Importer object to import a set of channels
// from the given connection. The Exporter must be available and serving when
// the Importer is created.
func NewImporter(conn io.ReadWriter) *Importer {
imp := new(Importer)
imp.encDec = newEncDec(conn)
imp.chans = make(map[int]*netChan)
imp.names = make(map[string]*netChan)
imp.errors = make(chan error, 10)
imp.unacked = 0
go imp.run()
return imp
}
// Import imports a set of channels from the given network and address.
func Import(network, remoteaddr string) (*Importer, error) {
conn, err := net.Dial(network, remoteaddr)
if err != nil {
return nil, err
}
return NewImporter(conn), 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.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.ValueOf(hdr)
ackHdr := new(header)
err := new(error_)
errValue := reflect.ValueOf(err)
for {
*hdr = header{}
if e := imp.decode(hdrValue); e != nil {
if e != io.EOF {
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)
select {
case imp.errors <- errors.New(err.Error):
continue // errors are not acknowledged
default:
imp.shutdown()
return
}
}
case payClosed:
nch := imp.getChan(hdr.Id, false)
if nch != nil {
nch.close()
}
continue // closes are not acknowledged.
case payAckSend:
// we can receive spurious acks if the channel is
// hung up, so we ask getChan to ignore any errors.
nch := imp.getChan(hdr.Id, true)
if nch != nil {
nch.acked()
imp.mu.Lock()
imp.unacked--
imp.mu.Unlock()
}
continue
default:
impLog("unexpected payload type:", hdr.PayloadType)
return
}
nch := imp.getChan(hdr.Id, false)
if nch == nil {
continue
}
if nch.dir != Recv {
impLog("cannot happen: receive from non-Recv channel")
return
}
// Acknowledge receipt
ackHdr.Id = hdr.Id
ackHdr.SeqNum = hdr.SeqNum
imp.encode(ackHdr, payAck, nil)
// Create a new value for each received item.
value := reflect.New(nch.ch.Type().Elem()).Elem()
if e := imp.decode(value); e != nil {
impLog("importer value decode:", e)
return
}
nch.send(value)
}
}
func (imp *Importer) getChan(id int, errOk bool) *netChan {
imp.chanLock.Lock()
ich := imp.chans[id]
imp.chanLock.Unlock()
if ich == nil {
if !errOk {
impLog("unknown id in netchan request: ", id)
}
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 error {
return imp.errors
}
// Import imports a channel of the given type, size 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, size int) error {
return imp.ImportNValues(name, chT, dir, size, -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 will have buffer space for size values, or 1 value if size < 1.
// 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, size, n int) error
// Example usage:
// imp, err := NewImporter("tcp", "netchanserver.mydomain.com:1234")
// if err != nil { log.Fatal(err) }
// ch := make(chan myType)
// err = imp.ImportNValues("name", ch, Recv, 1, 1)
// if err != nil { log.Fatal(err) }
// fmt.Printf("%+v\n", <-ch)
func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, size, n int) error {
ch, err := checkChan(chT, dir)
if err != nil {
return err
}
imp.chanLock.Lock()
defer imp.chanLock.Unlock()
_, present := imp.names[name]
if present {
return errors.New("channel name already being imported:" + name)
}
if size < 1 {
size = 1
}
id := imp.maxId
imp.maxId++
nch := newNetChan(name, id, &chanDir{ch, dir}, imp.encDec, size, int64(n))
imp.names[name] = nch
imp.chans[id] = nch
// Tell the other side about this channel.
hdr := &header{Id: id}
req := &request{Name: name, Count: int64(n), Dir: dir, Size: size}
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, ok := nch.recv()
if !ok {
if err = imp.encode(hdr, payClosed, nil); err != nil {
impLog("error encoding client closed message:", err)
}
return
}
// We hold the lock during transmission to guarantee messages are
// sent in order.
imp.mu.Lock()
imp.unacked++
imp.seqLock.Lock()
imp.mu.Unlock()
if err = imp.encode(hdr, payData, val.Interface()); err != nil {
impLog("error encoding client send:", err)
return
}
imp.seqLock.Unlock()
}
}()
}
return nil
}
// Hangup disassociates the named channel from the Importer and closes
// the channel. Messages in flight for the channel may be dropped.
func (imp *Importer) Hangup(name string) error {
imp.chanLock.Lock()
defer imp.chanLock.Unlock()
nc := imp.names[name]
if nc == nil {
return errors.New("netchan import: hangup: no such channel: " + name)
}
delete(imp.names, name)
delete(imp.chans, nc.id)
nc.close()
return nil
}
func (imp *Importer) unackedCount() int64 {
imp.mu.Lock()
n := imp.unacked
imp.mu.Unlock()
return n
}
// Drain waits until all messages sent from this exporter/importer, including
// those not yet sent to any server and possibly including those sent while
// Drain was executing, have been received by the exporter. In short, it
// waits until all the importer's messages have been received.
// If the timeout (measured in nanoseconds) is positive and Drain takes
// longer than that to complete, an error is returned.
func (imp *Importer) Drain(timeout int64) error {
deadline := time.Now().Add(time.Duration(timeout))
for imp.unackedCount() > 0 {
if timeout > 0 && time.Now().After(deadline) {
return errors.New("timeout")
}
time.Sleep(100 * time.Millisecond)
}
return nil
}