Chaining CAS middleware and httprouter() routing

I'm deep in the weeds on what's probably a simple problem. I need wrap a func with a call to a third-party CAS authenication service. I'm using go-cas to do that, and it worked until I started adding routing requirements. I chose Julien Schmidt's httprouter, and somehow I need to get that to work with go-cas too.

If I'm not mistaken, I need to use some kind of custom-designed middleware to go from handler to handler. I think the chain needs to go something like this:

http.Handler -> func(http.ResponseWriter, *http.Request, httprouter.Params)

...the first being what CAS wants, and the second being what httprouter wants. But I'm so lost now that I can't make heads or tails of what to do.

Thanks for any advice!

In the code below, the call to ...

router.Handler("GET", "/", client.HandleFunc(defaultHandler))

... produces this error:

"cannot use defaultHandler (type func(http.ResponseWriter, *http.Request, httprouter.Params)) as type func(http.ResponseWriter, *http.Request) in argument to client.HandleFunc"

Here's the non-working code:

package main

import (
    "fmt"
    "log"
    "net/http"
    "strings"
    "time"

    "github.com/go-cas/cas"
    "github.com/julienschmidt/httprouter"
)

func defaultHandler(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
    if !cas.IsAuthenticated(r) {
        cas.RedirectToLogin(w, r)
    }

    pageID := ps.ByName("pageID")

    type pageModel struct {
        Title    string
        PageID   string
    }

    model := pageModel{
        Title:    "Seminars",
        PageID:    pageID,
    }
    render.ToBrowser(w, "views/index.html", &model)
}


func main() {

    u, _ := url.Parse("https://cas_example_server.com")

    client := cas.NewClient(&cas.Options{
        URL: u,
    })

    router := httprouter.New()

    //This line fails with the message:

    //"Cannot use defaultHandler (type func(http.ResponseWriter, *http.Request, httprouter.Params)) 
    //as type func(http.ResponseWriter, *http.Request) in argument to client.HandleFunc"

    router.Handler("GET", "/", client.HandleFunc(defaultHandler))

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        panic(err)
    }

}

Solution

Your middleware may use request context to pass the data to the handler with different signature:

import (
    "net/http"
    "net/url"

    "github.com/go-cas/cas"
    "github.com/julienschmidt/httprouter"
    "golang.org/x/net/context"
)

func defaultHandler(w http.ResponseWriter, r *http.Request) {
    if !cas.IsAuthenticated(r) {
        cas.RedirectToLogin(w, r)
    }

    ps := r.Context().Value("params").(httprouter.Params)

    // business logic
}


func main() {

    u, _ := url.Parse("https://cas_example_server.com")

    client := cas.NewClient(&cas.Options{
        URL: u,
    })

    router := httprouter.New()

    //This line fails with the message:

    //"Cannot use defaultHandler (type func(http.ResponseWriter, *http.Request, httprouter.Params))
    //as type func(http.ResponseWriter, *http.Request) in argument to client.HandleFunc"

    router.Handler("GET", "/", func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
        newContext := context.WithValue(r.Context(), "params", ps)
        r.WithContext(newContext)
        client.HandleFunc(defaultHandler)(w, r)
    })

    err := http.ListenAndServe(":8080", router)
    if err != nil {
        panic(err)
    }

}

UPDATE: There are a number of useful libraries to hold your http handlers stack like this https://github.com/urfave/negroni