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