聊天服务的服务端代码如下：
```golang
type client chan<- string // an outgoing message channel
var (
entering = make(chan client)
leaving = make(chan client)
messages = make(chan string) // all incoming client messages
)
func broadcaster() {
clients := make(map[client]bool) // all connected clients
for {
select {
case msg := <-messages:
// Broadcast incoming message to all
// clients' outgoing message channels.
for cli := range clients {
cli <- msg
}
case cli := <-entering:
clients[cli] = true
case cli := <-leaving:
delete(clients, cli)
close(cli)
}
}
}
//!-broadcaster
//!+handleConn
func handleConn(conn net.Conn) {
ch := make(chan string) // outgoing client messages
go clientWriter(conn, ch)
who := conn.RemoteAddr().String()
ch <- "You are " + who
messages <- who + " has arrived"
entering <- ch
input := bufio.NewScanner(conn)
for input.Scan() {
messages <- who + ": " + input.Text()
}
// NOTE: ignoring potential errors from input.Err()
leaving <- ch
messages <- who + " has left"
conn.Close()
}
func clientWriter(conn net.Conn, ch <-chan string) {
for msg := range ch {
fmt.Fprintln(conn, msg) // NOTE: ignoring network errors
}
}
//!-handleConn
//!+main
func main() {
listener, err := net.Listen("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
go broadcaster()
for {
conn, err := listener.Accept()
if err != nil {
log.Print(err)
continue
}
go handleConn(conn)
}
}
```
客户端代码如下：
```golang
func main() {
conn, err := net.Dial("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
done := make(chan struct{})
go func() {
io.Copy(os.Stdout, conn) // NOTE: ignoring errors
log.Println("done")
done <- struct{}{} // signal the main goroutine
}()
mustCopy(conn, os.Stdin)
conn.Close()
<-done // wait for background goroutine to finish
}
//!-
func mustCopy(dst io.Writer, src io.Reader) {
if _, err := io.Copy(dst, src); err != nil {
log.Fatal(err)
}
}
```
我的疑问有如下两个：
1、在服务端代码的**handleConn**方法中，`entering <- ch`这句代码不会阻塞吗？我理解的是clientWriter方法已经消费了ch中的值，ch中已经没有值了，那么entering接收的值是什么呢？
2、在服务端代码的**handleConn**方法中，它调用了`go clientWriter(conn, ch)`方法将消息写入客户端的网络连接，但是广播消息都由**messages**这个channel接收，但是这个变量并没有传给clientWriter方法，那么messages中的消息是如何广播给其他客户端的呢？ 在**broadcaster**方法中，messages中的消息传递给了client，这部分代码的作用又是什么呢？
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