golang传递http.ResponseWriter

Question

I am trying to figure out if its possible to not have to pass along the http.ResponseWriter everywhere i go when programming a web application. I am setting up a simple mvc web framework and i find myself having to pass the http.ResponseWriter through various functions when its only used in lets say the last function.

Routes package

// Struct containing http requests and variables
type UrlInfo struct {
    Res http.ResponseWriter
    Req *http.Request
    Vars map[string]string
}

func HandleFunc(handlepath string, runfunc func(*UrlInfo)) {
    // Set handler and setup struct
    http.HandleFunc(getHandlePath(handlepath), func(w http.ResponseWriter, r *http.Request) {
        url := new(UrlInfo)
        url.Res = w
        url.Req = r
        url.Vars = parsePathVars(r.URL.Path, handlepath)

        runfunc(url)
    })
}

// Parse file and send to responsewriter
func View(w http.ResponseWriter, path string, data interface{}) {
    // Go grab file from views folder
    temp, err := template.ParseFiles(path+".html")
    if err != nil {
        // Couldnt find html file send error
        http.Error(w, err.Error(), http.StatusInternalServerError)
    } else {
        temp.ExecuteTemplate(w, temp.Name(), data)
    }
}

Controller package

import (
    "routes"
)

func init() {
    // Build handlefunc
    routes.HandleFunc("/home/", home)
}

func home(urlinfo *routes.UrlInfo) {
    info := make(map[string]string)
    info["Title"] = urlinfo.Vars["title"]
    info["Body"] = "Body Info"

    gi.View(urlinfo.Res, "pages/about", info)
}

I would like to not have to pass anything in the home function just so i can pass it again to the view function to spit out. Would be nice to be able to set it in one place and pull from it whenever needed. This would also nice in regard to multiple packages that communicate to the routes package in the same regard.

Any and all thoughts, tips or tricks are welcome. Thanks.

Answer 1

There are a number of ways you can do this. The trick is to figure out what is you actually need from the ResponseWriter you are passing through. It sounds like you just need to exercise a little function composition.

Change your design so that the View returns an io.Reader, and an error that you can then pipe into the ResponseWriter. Here's a completely untested example:

func View(path string, data interface{}) (io.Reader, error) {
    // Go grab file from views folder
    temp, err := template.ParseFiles(path+".html")
    if err != nil {
        // Couldnt find html file send error
       return nil, err
    } else {
        buf := bytes.Buffer()
        temp.ExecuteTemplate(buf, temp.Name(), data)
        return buf
    }
}

func HandleFunc(handlepath string, runfunc func(*UrlInfo) (io.Reader, error)) {
    // Set handler and setup struct
    http.HandleFunc(getHandlePath(handlepath),
                    func(w http.ResponseWriter, r *http.Request) {
        url := new(UrlInfo)
        url.Res = w
        url.Req = r
        url.Vars = parsePathVars(r.URL.Path, handlepath)

        rdr, err := runfunc(url)
        io.Copy(w, rdr);
    })
}

With this the only thing that has to worry about the http ResponseWriter is your HandleFunc function.