【发布时间】：2014-07-12 15:51:34
【问题描述】：
上周受到this article 的启发，我正在尝试重构一个应用程序，我必须更明确地将上下文（数据库池、会话存储等）传递给我的处理程序。
但是，我遇到的一个问题是，如果没有全局模板映射，我的自定义处理程序类型上的 ServeHTTP 方法（为了满足 http.Handler）不能再访问映射来呈现模板。
我需要保留全局 templates 变量，或者将我的自定义处理程序类型重新定义为结构。
有没有更好的方法来实现这一点？
func.go
package main
import (
"fmt"
"log"
"net/http"
"html/template"
"github.com/gorilla/sessions"
"github.com/jmoiron/sqlx"
"github.com/zenazn/goji/graceful"
"github.com/zenazn/goji/web"
)
var templates map[string]*template.Template
type appContext struct {
db *sqlx.DB
store *sessions.CookieStore
}
type appHandler func(w http.ResponseWriter, r *http.Request) (int, error)
func (ah appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// templates must be global for us to use it here
status, err := ah(w, r)
if err != nil {
log.Printf("HTTP %d: %q", status, err)
switch status {
case http.StatusNotFound:
// Would actually render a "http_404.tmpl" here...
http.NotFound(w, r)
case http.StatusInternalServerError:
// Would actually render a "http_500.tmpl" here
// (as above)
http.Error(w, http.StatusText(status), status)
default:
// Would actually render a "http_error.tmpl" here
// (as above)
http.Error(w, http.StatusText(status), status)
}
}
}
func main() {
// Both are 'nil' just for this example
context := &appContext{db: nil, store: nil}
r := web.New()
r.Get("/", appHandler(context.IndexHandler))
graceful.ListenAndServe(":8000", r)
}
func (app *appContext) IndexHandler(w http.ResponseWriter, r *http.Request) (int, error) {
fmt.Fprintf(w, "db is %q and store is %q", app.db, app.store)
return 200, nil
}
struct.go
package main
import (
"fmt"
"log"
"net/http"
"html/template"
"github.com/gorilla/sessions"
"github.com/jmoiron/sqlx"
"github.com/zenazn/goji/graceful"
"github.com/zenazn/goji/web"
)
type appContext struct {
db *sqlx.DB
store *sessions.CookieStore
templates map[string]*template.Template
}
// We need to define our custom handler type as a struct
type appHandler struct {
handler func(w http.ResponseWriter, r *http.Request) (int, error)
c *appContext
}
func (ah appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
status, err := ah.handler(w, r)
if err != nil {
log.Printf("HTTP %d: %q", status, err)
switch status {
case http.StatusNotFound:
// Would actually render a "http_404.tmpl" here...
http.NotFound(w, r)
case http.StatusInternalServerError:
// Would actually render a "http_500.tmpl" here
// (as above)
http.Error(w, http.StatusText(status), status)
default:
// Would actually render a "http_error.tmpl" here
// (as above)
http.Error(w, http.StatusText(status), status)
}
}
}
func main() {
// Both are 'nil' just for this example
context := &appContext{db: nil, store: nil}
r := web.New()
// A little ugly, but it works.
r.Get("/", appHandler{context.IndexHandler, context})
graceful.ListenAndServe(":8000", r)
}
func (app *appContext) IndexHandler(w http.ResponseWriter, r *http.Request) (int, error) {
fmt.Fprintf(w, "db is %q and store is %q", app.db, app.store)
return 200, nil
}
有没有更简洁的方法将context 实例传递给ServeHTTP？
请注意，go build -gcflags=-m 表明在堆分配团队中这两个选项似乎都没有更糟：&appContext 在这两种情况下都会逃逸到堆中（如预期的那样），尽管我的解释是基于结构的选项确实如此在每个请求上传递第二个指针（指向context）——如果我在这里错了，请纠正我，因为我很想更好地理解这一点。
我并不完全相信全局变量在 main 包（即不是 lib）中是不好的，前提是它们可以安全地以这种方式使用（只读/互斥体/池），但我确实希望明确通过上下文提供。
【问题讨论】：
标签： go