## 中間件
### 怎樣自己寫一個中間件？
比如有以下需求
- 通過該中間件去統計請求數目、狀態和時間。
- 中間件把寫過寫回響應。
#### Server
`server.go`
```go
package main
import (
"net/http"
"strconv"
"sync"
"time"
"github.com/labstack/echo"
)
type (
Stats struct {
Uptime time.Time `json:"uptime"`
RequestCount uint64 `json:"requestCount"`
Statuses map[string]int `json:"statuses"`
mutex sync.RWMutex
}
)
func NewStats() *Stats {
return &Stats{
Uptime: time.Now(),
Statuses: make(map[string]int),
}
}
// Process is the middleware function.
func (s *Stats) Process(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) error {
if err := next(c); err != nil {
c.Error(err)
}
s.mutex.Lock()
defer s.mutex.Unlock()
s.RequestCount++
status := strconv.Itoa(c.Response().Status)
s.Statuses[status]++
return nil
}
}
// Handle is the endpoint to get stats.
func (s *Stats) Handle(c echo.Context) error {
s.mutex.RLock()
defer s.mutex.RUnlock()
return c.JSON(http.StatusOK, s)
}
// ServerHeader middleware adds a `Server` header to the response.
func ServerHeader(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) error {
c.Response().Header().Set(echo.HeaderServer, "Echo/3.0")
return next(c)
}
}
func main() {
e := echo.New()
// Debug mode
e.Debug = true
//-------------------
// Custom middleware
//-------------------
// Stats
s := NewStats()
e.Use(s.Process)
e.GET("/stats", s.Handle) // Endpoint to get stats
// Server header
e.Use(ServerHeader)
// Handler
e.GET("/", func(c echo.Context) error {
return c.String(http.StatusOK, "Hello, World!")
})
// Start server
e.Logger.Fatal(e.Start(":1323"))
}
```
#### 響應
*響應頭*
```sh
Content-Length:122
Content-Type:application/json; charset=utf-8
Date:Thu, 14 Apr 2016 20:31:46 GMT
Server:Echo/2.0
```
*響應體*
```js
{
"uptime": "2016-04-14T13:28:48.486548936-07:00",
"requestCount": 5,
"statuses": {
"200": 4,
"404": 1
}
}
```
