mirror of
https://github.com/autc04/Retro68.git
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401 lines
12 KiB
Go
401 lines
12 KiB
Go
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// 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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/*
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Package netchan implements type-safe networked channels:
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it allows the two ends of a channel to appear on different
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computers connected by a network. It does this by transporting
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data sent to a channel on one machine so it can be recovered
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by a receive of a channel of the same type on the other.
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An exporter publishes a set of channels by name. An importer
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connects to the exporting machine and imports the channels
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by name. After importing the channels, the two machines can
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use the channels in the usual way.
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Networked channels are not synchronized; they always behave
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as if they are buffered channels of at least one element.
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*/
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package netchan
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// BUG: can't use range clause to receive when using ImportNValues to limit the count.
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import (
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"errors"
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"io"
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"log"
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"net"
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"reflect"
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"strconv"
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"sync"
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"time"
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)
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// Export
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// expLog is a logging convenience function. The first argument must be a string.
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func expLog(args ...interface{}) {
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args[0] = "netchan export: " + args[0].(string)
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log.Print(args...)
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}
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// An Exporter allows a set of channels to be published on a single
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// network port. A single machine may have multiple Exporters
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// but they must use different ports.
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type Exporter struct {
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*clientSet
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}
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type expClient struct {
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*encDec
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exp *Exporter
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chans map[int]*netChan // channels in use by client
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mu sync.Mutex // protects remaining fields
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errored bool // client has been sent an error
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seqNum int64 // sequences messages sent to client; has value of highest sent
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ackNum int64 // highest sequence number acknowledged
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seqLock sync.Mutex // guarantees messages are in sequence, only locked under mu
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}
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func newClient(exp *Exporter, conn io.ReadWriter) *expClient {
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client := new(expClient)
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client.exp = exp
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client.encDec = newEncDec(conn)
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client.seqNum = 0
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client.ackNum = 0
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client.chans = make(map[int]*netChan)
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return client
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}
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func (client *expClient) sendError(hdr *header, err string) {
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error := &error_{err}
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expLog("sending error to client:", error.Error)
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client.encode(hdr, payError, error) // ignore any encode error, hope client gets it
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client.mu.Lock()
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client.errored = true
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client.mu.Unlock()
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}
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func (client *expClient) newChan(hdr *header, dir Dir, name string, size int, count int64) *netChan {
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exp := client.exp
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exp.mu.Lock()
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ech, ok := exp.names[name]
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exp.mu.Unlock()
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if !ok {
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client.sendError(hdr, "no such channel: "+name)
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return nil
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}
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if ech.dir != dir {
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client.sendError(hdr, "wrong direction for channel: "+name)
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return nil
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}
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nch := newNetChan(name, hdr.Id, ech, client.encDec, size, count)
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client.chans[hdr.Id] = nch
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return nch
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}
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func (client *expClient) getChan(hdr *header, dir Dir) *netChan {
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nch := client.chans[hdr.Id]
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if nch == nil {
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return nil
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}
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if nch.dir != dir {
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client.sendError(hdr, "wrong direction for channel: "+nch.name)
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}
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return nch
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}
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// The function run manages sends and receives for a single client. For each
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// (client Recv) request, this will launch a serveRecv goroutine to deliver
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// the data for that channel, while (client Send) requests are handled as
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// data arrives from the client.
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func (client *expClient) run() {
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hdr := new(header)
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hdrValue := reflect.ValueOf(hdr)
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req := new(request)
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reqValue := reflect.ValueOf(req)
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error := new(error_)
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for {
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*hdr = header{}
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if err := client.decode(hdrValue); err != nil {
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if err != io.EOF {
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expLog("error decoding client header:", err)
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}
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break
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}
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switch hdr.PayloadType {
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case payRequest:
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*req = request{}
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if err := client.decode(reqValue); err != nil {
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expLog("error decoding client request:", err)
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break
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}
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if req.Size < 1 {
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panic("netchan: remote requested " + strconv.Itoa(req.Size) + " values")
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}
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switch req.Dir {
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case Recv:
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// look up channel before calling serveRecv to
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// avoid a lock around client.chans.
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if nch := client.newChan(hdr, Send, req.Name, req.Size, req.Count); nch != nil {
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go client.serveRecv(nch, *hdr, req.Count)
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}
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case Send:
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client.newChan(hdr, Recv, req.Name, req.Size, req.Count)
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// The actual sends will have payload type payData.
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// TODO: manage the count?
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default:
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error.Error = "request: can't handle channel direction"
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expLog(error.Error, req.Dir)
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client.encode(hdr, payError, error)
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}
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case payData:
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client.serveSend(*hdr)
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case payClosed:
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client.serveClosed(*hdr)
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case payAck:
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client.mu.Lock()
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if client.ackNum != hdr.SeqNum-1 {
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// Since the sequence number is incremented and the message is sent
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// in a single instance of locking client.mu, the messages are guaranteed
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// to be sent in order. Therefore receipt of acknowledgement N means
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// all messages <=N have been seen by the recipient. We check anyway.
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expLog("sequence out of order:", client.ackNum, hdr.SeqNum)
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}
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if client.ackNum < hdr.SeqNum { // If there has been an error, don't back up the count.
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client.ackNum = hdr.SeqNum
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}
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client.mu.Unlock()
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case payAckSend:
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if nch := client.getChan(hdr, Send); nch != nil {
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nch.acked()
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}
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default:
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log.Fatal("netchan export: unknown payload type", hdr.PayloadType)
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}
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}
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client.exp.delClient(client)
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}
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// Send all the data on a single channel to a client asking for a Recv.
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// The header is passed by value to avoid issues of overwriting.
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func (client *expClient) serveRecv(nch *netChan, hdr header, count int64) {
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for {
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val, ok := nch.recv()
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if !ok {
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if err := client.encode(&hdr, payClosed, nil); err != nil {
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expLog("error encoding server closed message:", err)
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}
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break
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}
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// We hold the lock during transmission to guarantee messages are
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// sent in sequence number order. Also, we increment first so the
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// value of client.SeqNum is the value of the highest used sequence
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// number, not one beyond.
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client.mu.Lock()
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client.seqNum++
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hdr.SeqNum = client.seqNum
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client.seqLock.Lock() // guarantee ordering of messages
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client.mu.Unlock()
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err := client.encode(&hdr, payData, val.Interface())
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client.seqLock.Unlock()
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if err != nil {
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expLog("error encoding client response:", err)
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client.sendError(&hdr, err.Error())
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break
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}
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// Negative count means run forever.
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if count >= 0 {
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if count--; count <= 0 {
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break
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}
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}
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}
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}
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// Receive and deliver locally one item from a client asking for a Send
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// The header is passed by value to avoid issues of overwriting.
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func (client *expClient) serveSend(hdr header) {
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nch := client.getChan(&hdr, Recv)
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if nch == nil {
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return
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}
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// Create a new value for each received item.
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val := reflect.New(nch.ch.Type().Elem()).Elem()
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if err := client.decode(val); err != nil {
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expLog("value decode:", err, "; type ", nch.ch.Type())
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return
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}
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nch.send(val)
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}
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// Report that client has closed the channel that is sending to us.
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// The header is passed by value to avoid issues of overwriting.
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func (client *expClient) serveClosed(hdr header) {
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nch := client.getChan(&hdr, Recv)
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if nch == nil {
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return
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}
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nch.close()
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}
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func (client *expClient) unackedCount() int64 {
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client.mu.Lock()
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n := client.seqNum - client.ackNum
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client.mu.Unlock()
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return n
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}
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func (client *expClient) seq() int64 {
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client.mu.Lock()
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n := client.seqNum
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client.mu.Unlock()
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return n
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}
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func (client *expClient) ack() int64 {
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client.mu.Lock()
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n := client.seqNum
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client.mu.Unlock()
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return n
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}
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// Serve waits for incoming connections on the listener
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// and serves the Exporter's channels on each.
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// It blocks until the listener is closed.
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func (exp *Exporter) Serve(listener net.Listener) {
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for {
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conn, err := listener.Accept()
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if err != nil {
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expLog("listen:", err)
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break
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}
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go exp.ServeConn(conn)
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}
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}
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// ServeConn exports the Exporter's channels on conn.
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// It blocks until the connection is terminated.
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func (exp *Exporter) ServeConn(conn io.ReadWriter) {
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exp.addClient(conn).run()
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}
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// NewExporter creates a new Exporter that exports a set of channels.
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func NewExporter() *Exporter {
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e := &Exporter{
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clientSet: &clientSet{
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names: make(map[string]*chanDir),
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clients: make(map[unackedCounter]bool),
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},
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}
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return e
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}
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// ListenAndServe exports the exporter's channels through the
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// given network and local address defined as in net.Listen.
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func (exp *Exporter) ListenAndServe(network, localaddr string) error {
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listener, err := net.Listen(network, localaddr)
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if err != nil {
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return err
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}
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go exp.Serve(listener)
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return nil
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}
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// addClient creates a new expClient and records its existence
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func (exp *Exporter) addClient(conn io.ReadWriter) *expClient {
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client := newClient(exp, conn)
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exp.mu.Lock()
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exp.clients[client] = true
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exp.mu.Unlock()
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return client
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}
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// delClient forgets the client existed
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func (exp *Exporter) delClient(client *expClient) {
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exp.mu.Lock()
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delete(exp.clients, client)
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exp.mu.Unlock()
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}
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// Drain waits until all messages sent from this exporter/importer, including
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// those not yet sent to any client and possibly including those sent while
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// Drain was executing, have been received by the importer. In short, it
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// waits until all the exporter's messages have been received by a client.
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// If the timeout is positive and Drain takes longer than that to complete,
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// an error is returned.
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func (exp *Exporter) Drain(timeout time.Duration) error {
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// This wrapper function is here so the method's comment will appear in godoc.
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return exp.clientSet.drain(timeout)
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}
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// Sync waits until all clients of the exporter have received the messages
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// that were sent at the time Sync was invoked. Unlike Drain, it does not
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// wait for messages sent while it is running or messages that have not been
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// dispatched to any client. If the timeout is positive and Sync takes longer
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// than that to complete, an error is returned.
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func (exp *Exporter) Sync(timeout time.Duration) error {
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// This wrapper function is here so the method's comment will appear in godoc.
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return exp.clientSet.sync(timeout)
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}
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func checkChan(chT interface{}, dir Dir) (reflect.Value, error) {
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chanType := reflect.TypeOf(chT)
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if chanType.Kind() != reflect.Chan {
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return reflect.Value{}, errors.New("not a channel")
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}
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if dir != Send && dir != Recv {
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return reflect.Value{}, errors.New("unknown channel direction")
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}
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switch chanType.ChanDir() {
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case reflect.BothDir:
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case reflect.SendDir:
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if dir != Recv {
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return reflect.Value{}, errors.New("to import/export with Send, must provide <-chan")
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}
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case reflect.RecvDir:
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if dir != Send {
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return reflect.Value{}, errors.New("to import/export with Recv, must provide chan<-")
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}
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}
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return reflect.ValueOf(chT), nil
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}
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// Export exports a channel of a given type and specified direction. The
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// channel to be exported 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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// Export(name string, chT chan T, dir Dir)
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func (exp *Exporter) Export(name string, chT interface{}, dir Dir) 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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exp.mu.Lock()
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defer exp.mu.Unlock()
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_, present := exp.names[name]
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if present {
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return errors.New("channel name already being exported:" + name)
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}
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exp.names[name] = &chanDir{ch, dir}
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return nil
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}
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// Hangup disassociates the named channel from the Exporter and closes
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// the channel. Messages in flight for the channel may be dropped.
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func (exp *Exporter) Hangup(name string) error {
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exp.mu.Lock()
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chDir, ok := exp.names[name]
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if ok {
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delete(exp.names, name)
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}
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// TODO drop all instances of channel from client sets
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exp.mu.Unlock()
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if !ok {
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return errors.New("netchan export: 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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