> For the complete documentation index, see [llms.txt](https://go.netdpi.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://go.netdpi.net/13-the-core-packages/pkg_serv.md).
# 13.07-伺服器
使用 Go 語言來設計網路伺服器是很簡單的，我們先看如何建立一個 TCP 伺服器：
```go
package main
import (
"encoding/gob"
"fmt"
"net"
)
func server() {
// listen on a port
ln, err := net.Listen("tcp", ":9999")
if err != nil {
fmt.Println(err)
return
}
for {
// accept a connection
c, err := ln.Accept()
if err != nil {
fmt.Println(err)
continue
}
// handle the connection
go handleServerConnection(c)
}
}
func handleServerConnection(c net.Conn) {
// receive the message
var msg string
err := gob.NewDecoder(c).Decode(&msg)
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Received", msg)
}
c.Close()
}
func client() {
// connect to the server
c, err := net.Dial("tcp", "127.0.0.1:9999")
if err != nil {
fmt.Println(err)
return
}
// send the message
msg := "Hello World"
fmt.Println("Sending", msg)
err = gob.NewEncoder(c).Encode(msg)
if err != nil {
fmt.Println(err)
}
c.Close()
}
func main() {
go server()
go client()
var input string
fmt.Scanln(&input)
}
```
這個範例使用了 `encoding/gob` package，這個 package 可以很容易的對 Go 值進行編碼，使得其它 Go 程式（或是本例中的 Go 程式）可以讀值。其它的編碼方式可取自 `encoding` （如 `encoding/json`）以及第三方的 packages（例如：我們可以使用 `labix.org/v2/mgo/bson` 取得 bson 的支援）。
#### HTTP
HTTP 伺服器更易設定於與使用：
```go
package main
import ("net/http" ; "io")
func hello(res http.ResponseWriter, req *http.Request) {
res.Header().Set(
"Content-Type",
"text/html",
)
io.WriteString(
res,
`
Hello World
Hello World!
`,
)
}
func main() {
http.HandleFunc("/hello", hello)
http.ListenAndServe(":9000", nil)
}
```
`HandleFunc` 透過呼叫提供的函式來處理一個 URL route (`/hello`)，我們也可以使用 `FileServer` 處理靜態檔案：
```
http.Handle(
"/assets/",
http.StripPrefix(
"/assets/",
http.FileServer(http.Dir("assets")),
),
)
```
#### RPC
`net/rpc`（remote procedure call）以及 `net/rpc/jsonrpc` packages 提供了一個簡單的方式可以揭露 methods 的存在，使得能夠透過網路執行呼叫（並非只是在呼叫它們的程式中執行）
```go
package main
import (
"fmt"
"net"
"net/rpc"
)
type Server struct {}
func (this *Server) Negate(i int64, reply *int64) error {
*reply = -i
return nil
}
func server() {
rpc.Register(new(Server))
ln, err := net.Listen("tcp", ":9999")
if err != nil {
fmt.Println(err)
return
}
for {
c, err := ln.Accept()
if err != nil {
continue
}
go rpc.ServeConn(c)
}
}
func client() {
c, err := rpc.Dial("tcp", "127.0.0.1:9999")
if err != nil {
fmt.Println(err)
return
}
var result int64
err = c.Call("Server.Negate", int64(999), &result)
if err != nil {
fmt.Println(err)
} else {
fmt.Println("Server.Negate(999) =", result)
}
}
func main() {
go server()
go client()
var input string
fmt.Scanln(&input)
}
```
此程式與 TCP 範例類似，只是我們現在有建立一個物件（object）來承載我們想要揭露的每個 method 與在客戶端（client）呼叫的 `Negate` method，細節請參考 `net/rpc` 中的文件。
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