我试图通过检查golang TCPConn.Write返回的错误来检测发送失败，但它没有。我也尝试使用TCPConn.SetWriteDeadline但没有成功。
事情就是这样：
问题：为什么只有第二封邮件发送给不存在的客户端会导致错误？如何正确处理案件？
代码如下：
package main
import (
"net"
"os"
"bufio"
"fmt"
"time"
)
func AcceptConnections(listener net.Listener, console <- chan string) {
msg := ""
for {
conn, err := listener.Accept()
if err != nil {
panic(err)
}
fmt.Printf("client connected\n")
for {
if msg == "" {
msg = <- console
fmt.Printf("read from console: %s", msg)
}
err = conn.SetWriteDeadline(time.Now().Add(time.Second))
if err != nil {
fmt.Printf("SetWriteDeadline failed: %v\n", err)
}
_, err = conn.Write([]byte(msg))
if err != nil {
// expecting an error after sending a message
// to a non-existing client endpoint
fmt.Printf("failed sending a message to network: %v\n", err)
break
} else {
fmt.Printf("msg sent: %s", msg)
msg = ""
}
}
}
}
func ReadConsole(network chan <- string) {
console := bufio.NewReader(os.Stdin)
for {
line, err := console.ReadString('\n')
if err != nil {
panic(err)
} else {
network <- line
}
}
}
func main() {
listener, err := net.Listen("tcp", "localhost:6666")
if err != nil {
panic(err)
}
println("listening on " + listener.Addr().String())
consoleToNetwork := make(chan string)
go AcceptConnections(listener, consoleToNetwork)
ReadConsole(consoleToNetwork)
}
服务器控制台如下所示：
listening on 127.0.0.1:6666
client connected
hi there!
read from console: hi there!
msg sent: hi there!
this one should fail
read from console: this one should fail
msg sent: this one should fail
this one actually fails
read from console: this one actually fails
failed sending a message to network: write tcp 127.0.0.1:51194: broken pipe
客户端看起来像这样：
package main
import (
"net"
"os"
"io"
//"bufio"
//"fmt"
)
func cp(dst io.Writer, src io.Reader, errc chan<- error) {
// -reads from src and writes to dst
// -blocks until EOF
// -EOF is not an error
_, err := io.Copy(dst, src)
// push err to the channel when io.Copy returns
errc <- err
}
func StartCommunication(conn net.Conn) {
//create a channel for errors
errc := make(chan error)
//read connection and print to console
go cp(os.Stdout, conn, errc)
//read user input and write to connection
go cp(conn, os.Stdin, errc)
//wait until nil or an error arrives
err := <- errc
if err != nil {
println("cp error: ", err.Error())
}
}
func main() {
servAddr := "localhost:6666"
tcpAddr, err := net.ResolveTCPAddr("tcp", servAddr)
if err != nil {
println("ResolveTCPAddr failed:", err.Error())
os.Exit(1)
}
conn, err := net.DialTCP("tcp", nil, tcpAddr)
if err != nil {
println("net.DialTCP failed:", err.Error())
os.Exit(1)
}
defer conn.Close()
StartCommunication(conn)
}
编辑：根据JimB的建议，我想出了一个有效的例子。消息不会再丢失，并在新连接中重新发送。我不太确定在不同的例程之间使用共享变量（connWrap.IsFaulted）有多安全。
package main
import (
"net"
"os"
"bufio"
"fmt"
)
type Connection struct {
IsFaulted bool
Conn net.Conn
}
func StartWritingToNetwork(connWrap * Connection, errChannel chan <- error, msgStack chan string) {
for {
msg := <- msgStack
if connWrap.IsFaulted {
//put it back for another connection
msgStack <- msg
return
}
_, err := connWrap.Conn.Write([]byte(msg))
if err != nil {
fmt.Printf("failed sending a message to network: %v\n", err)
connWrap.IsFaulted = true
msgStack <- msg
errChannel <- err
return
} else {
fmt.Printf("msg sent: %s", msg)
}
}
}
func StartReadingFromNetwork(connWrap * Connection, errChannel chan <- error){
network := bufio.NewReader(connWrap.Conn)
for (!connWrap.IsFaulted) {
line, err := network.ReadString('\n')
if err != nil {
fmt.Printf("failed reading from network: %v\n", err)
connWrap.IsFaulted = true
errChannel <- err
} else {
fmt.Printf("%s", line)
}
}
}
func AcceptConnections(listener net.Listener, console chan string) {
errChannel := make(chan error)
for {
conn, err := listener.Accept()
if err != nil {
panic(err)
}
fmt.Printf("client connected\n")
connWrap := Connection{false, conn}
go StartReadingFromNetwork(&connWrap, errChannel)
go StartWritingToNetwork(&connWrap, errChannel, console)
//block until an error occurs
<- errChannel
}
}
func ReadConsole(network chan <- string) {
console := bufio.NewReader(os.Stdin)
for {
line, err := console.ReadString('\n')
if err != nil {
panic(err)
} else {
network <- line
}
}
}
func main() {
listener, err := net.Listen("tcp", "localhost:6666")
if err != nil {
panic(err)
}
println("listening on " + listener.Addr().String())
consoleToNetwork := make(chan string)
go AcceptConnections(listener, consoleToNetwork)
ReadConsole(consoleToNetwork)
}
答案 0 :(得分：11)
这不是特定于Go的，并且是底层TCP套接字的工件。
TCP终止步骤的合适图表位于此页面的底部： http://www.tcpipguide.com/free/t_TCPConnectionTermination-2.htm
简单版本是当客户端关闭其套接字时，它发送FIN，并从服务器接收ACK。然后它等待服务器执行相同的操作。虽然不是发送FIN，而是发送更多数据，而这些数据被丢弃，而客户端套接字现在假定来自您的更多数据无效，因此下次发送时会获得RST，这就是冒泡你看到的错误。
回到你的程序，你需要以某种方式处理它。通常你可以想到谁负责发起一个发送，也负责启动发送，因此你的服务器应该假设它可以继续发送，直到它关闭连接，或遇到错误。如果需要更可靠地检测客户端关闭，则需要在协议中进行某种客户端响应。这样可以在套接字上调用recv并返回0，它会提醒您关闭连接。
在go中，这将从连接的Read方法（或在您的情况下从Copy中）返回EOF错误。 SetWriteDeadline不起作用，因为一个小的写入会通过并静默删除，或者客户端最终将使用RST响应，从而导致错误。