将上下文传递给接口方法

上周这篇文章受到了一些启发,我正在重构一个应用程序,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,ServeHTTP我的自定义处理程序类型(满足http.Handler)上的方法将无法再访问映射以呈现模板.

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目标？

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
}

是否有更简洁的方法将context实例传递给ServeHTTP？

请注意,go build -gcflags=-m在堆分配的组中,两个选项似乎都没有变得更糟:&appContext在两种情况下,文字都转义到堆(如预期的那样),尽管我的解释是基于结构的选项确实context在每个上传递了第二个指针(to )请求 - 纠正我,如果我在这里错了,因为我希望能够更好地理解这一点.

我并不完全相信全局包在主包中是坏的(即不是lib)只要它们以这种方式安全使用(只读/互斥/池),但我确实喜欢明确传递上下文提供的清晰度.