add multiple params in http.HandlerFunc

hi i am trying tr write unit test for a post request using

"net/http"
"net/http/httptest"

if in my handler i have extra parameter other than w http.ResponseWriter, r *http.Request like db , kafka, etc

func ResponseHandler(w http.ResponseWriter, r *http.Request, db *dynamo.DB, p *Confluent.Producer)

how can i do

handler := http.HandlerFunc(handlername) any idea ?

I m getting
***cannot convert ResponseHandler (type func(http.ResponseWriter, http.Request, dynamo.DB, "github.com/confluentinc/confluent-kafka-go/kafka".Producer)) to type http.HandlerFunc

Your handler needs to implement the http.Handler signature, meaning it cannot have other arguments or return anything.

The way to provide it with other arguments is to have them come from an outer scope. So, assuming your not-really-a-Handler looks like:

func ResponseHandler(w http.ResponseWriter, r *http.Request, db *dynamo.DB, p *Confluent.Producer)

...you will need to generate an actual Handler calling your not-really-a-Handler. Supposing you already obtained the DB and Producer in your router initialization function, you can route like this:

var db *dynamo.DB = someDBFactory()
var p *Confluent.Producer = giveMeAProducer()

responseHandler := func(w http.ResponseWriter, r *http.Request) {
    return ResponseHandler(w, r, db, p)
})

http.HandleFunc(somePath, responseHandler)

You could also pass the parameters explicitly instead of relying on the outer scope, using a higher-order function:

var db *dynamo.DB := someDBFactory()
var p *Confluent.Producer := giveMeAProducer()

newResponseHandler := func(db *dynamo.DB, p *Confluent.Producer) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        return ResponseHandler(w, r, db, p)
    })
})

http.HandleFunc(somePath, newResponseHandler(db, p))

Wrap the HandlerFunc with your custom function as

func ResponseHandler(w http.ResponseWriter, r *http.Request, db *dynamo.DB, p *Confluent.Producer)func(http.ResponseWriter, *http.Request){
return func(http.ResponseWriter, *http.Request){
	// your code goes here
}}

I may wrong, but the two "extra" parameters (db *dynamo.DB and p *Confluent.Producer) don't seem request-specific. If the handler depends on them to handle requests, you could make those dependencies available to the handler in several ways. Seasoned Gophers tend to "inject" dependencies through a method receiver.

You could declare a custom struct type whose fields are the dependencies needed by your handler(s):

type API struct {
    db *dynamo.DB
    p  *Confluent.Producer
}

You can drop the extra two parameters and turn your ResponseHandler function into a method on your custom API type, thereby making it compatible with the http.HandlerFunc type:

func (api *API) ResponseHandler(w http.ResponseWriter, r *http.Request) {
    // ...
}

Finally, you only have to wire the dependencies in an API variable in main.