I have created few types including interface as:
// GetProfileHandlerFunc turns a function with the right signature into a get profile handler
type GetProfileHandlerFunc func(GetProfileParams, interface{}) middleware.Responder
// Handle executing the request and returning a response
func (fn GetProfileHandlerFunc) Handle(params GetProfileParams, principal interface{}) middleware.Responder {
return fn(params, principal)
}
// GetProfileHandler interface for that can handle valid get profile params
type GetProfileHandler interface {
Handle(GetProfileParams, interface{}) middleware.Responder
}
Now in my api implementation package. I am using a logic to handle the request parameters. I am trying to assign GetProfileHandlerFunc to another type since it implements GetProfileHandler interface as you can see above.
api.ProfileGetProfileHandler = profile.GetProfileHandlerFunc(func(params profile.GetProfileParams, principal *models.User) middleware.Responder {
// contains logic to handle the request
}
Now I think I can do above logic. But I am getting type mismatch error.
cannot convert func literal (type func(profile.GetProfileParams,
*"userproj/models".User)
middleware.Responder) to type profile.GetProfileHandlerFuncgo
the point is:
if you have a function like
func A(param interface{}) {}
you can pass anything to param when you make a call to function A. like
A(10)
A(true)
A(nil)
Because interface{} means everything. So your handle func definition:
type GetProfileHandlerFunc func(GetProfileParams, interface{}) middleware.Responder
means a function GetProfileHandlerFunc which takes two params, the first is of type GetProfileParams, the second is of type interface{}. That means second param canbe anything.
But
func(params profile.GetProfileParams, principal *models.User) middleware.Responder
means a function which takes two params, the first is of type GetProfileParams, the second is of type *models.User. So, do you think they are the same? No.
I need a function can take anything as second param,not a function who can only take User as second function.
When you call your handle
GetProfileHandlerFunc(params, 10) // this is ok
So is that ok for
func(params profile.GetProfileParams, principal *models.User) middleware.Responder
No.
The right way to do this is :
api.ProfileGetProfileHandler = profile.GetProfileHandlerFunc(func(params profile.GetProfileParams, principal interface) middleware.Responder {
user:=principal.(*model.User) // watch this.
}
Related
I'm coding a communication protocol. It sends tokens, which I need to use to authenticate.
I have created a type, "AuthToken" that encodes/decodes the token for me.
In the package "utils", I declare it and some of the functions like this (this is like a pseudo-code):
package utils
type AuthToken struct{
// vars
}
func (token *AuthToken) Decode(encoded string){
// Decodes the token and fills internal fields
}
func (token AuthToken) GetField() string{
return field
}
In my main package, I want to create a map of AuthTokens to store them, but I can't use the function Decode in a member of the map, while I can use GetField:
package main
type TokenList map[string]utils.AuthToken
func main(){
tokenList := make(TokenList)
// To init one member I do:
tokenList["1"] = utils.AuthToken{} // This works
tokenList["2"] = make(utils.AuthToken) // This doesn't
// Then I need to call the function above, so I tried:
tokenList["1"].Decode("encoded") // Returns cannot call pointer method
I have tried searching for it, but either I don't know where to search, or there is no info about how to do this.
tokenList["2"] = make(utils.AuthToken) // This doesn't
You cannot use make keyword to instantiate an object from struct. That's the reason why above statement wont work.
tokenList["1"] = utils.AuthToken{}
tokenList["1"].Decode("encoded") // Returns cannot call pointer method
The tokenList["1"] returns non pointer object. You will need to store it into a variable, then from there do access the pointer, only then you will be able to call .Decode() method.
obj := tokenList["1"]
objPointer := &obj
objPointer.Decode("encoded")
Short premise:
I try to design a package which holds several types fullfilling the same set of interfaces and another package working with these interfaces. Now I'm puzzled how to fulfill an interface returning another interface type.
longer:
To be more specific: I've got two protocol / message types (broadcast / direct) which I want to be able to package to be transported by http/json and amqp/rabbit. My "transport"-packages (json and amqp) require my message-packages (dm/broadcast) to fulfill / present some information: e.g. GetAddress or NewResponse. For NewResponse my message format generates, out of it's metainformation,a ResponseMessage. My transporter knows how to translate GetAddress to a useful routing information. There is my interface problem: Now I'm puzzled how to fulfill an interface returning another interface type.
type Addresser interface {
GetRecipientAddress() string
}
type Responder interface {
NewResponse() (Responder, error)
}
type DM struct {
}
func (dm *DM) GetRecipientAddress() string {
return ""
}
func (dm *DM) NewResponse() (*DM, error) {
return dm, nil
}
As long as my (dm *DM) NewResponse returns Responder the Responder interface is fulfilled. When I return *DM, which fulfills Responder, *DM doesn't fulfill Responder.
I kind of see that this seems to be an chicken or the egg problem, as long as I return *DM, *DM doesn't fulfill Responder, but "de facto" it fulfills it.
That leeds my to my assumption: I try to implement a bad design for the use of interfaces. Can somebody point me in the direction golang-gurus would solve this problem?
I thought maybe this could be a solution, but it seems to be just as flawed
type AddressResponder interface {
Addresser
Responder
}
func (dm *DM) NewResponse() (AddressResponder, error) {
return dm, nil
}
See Type identity:
Two interface types are identical if they have the same set of methods with the same names and identical function types. Non-exported method names from different packages are always different. The order of the methods is irrelevant.
Two function types are identical if they have the same number of parameters and result values, corresponding parameter and result types are identical, and either both functions are variadic or neither is. Parameter and result names are not required to match.
Try this:
// NewResponse returns (Responder, error)
func (dm *DM) NewResponse() (Responder, error) {
return dm, nil
}
type DM can only fill Responder if and only if it has the methods described in Responder. I understand what you are saying, but this is how Golang works!
In other words, DM must have the method of signature NewResponse() (Responder, error) or else it does NOT implement Responder.
Thus perhaps you must change the definition to:
type DM struct {
}
func (dm *DM) NewResponse() (Responder, error) {
return dm, nil
}
I am using a package that has a Router interface, and I have created my own app-specific Router interface that wraps the third party package.
Everything is working well, however one of the methods is throwing a compilation error:
controllers/auth.go:52:17: cannot use func literal (type func(router.Router)) as type func(chi.Router) in argument to c.router.Group
This is the interface of the third party package (chi):
type Router interface {
// ...
// Group adds a new inline-Router along the current routing
// path, with a fresh middleware stack for the inline-Router.
Group(fn func(r Router)) Router
// ...
}
This is my wrapper interface:
type Router interface {
chi.Router
// Custom methods...
}
My usage of the Group function is like so:
type AuthController struct {
router router.Router
// ...
}
func (c *AuthController) SetRoutes() {
c.router.Group(func(r router.Router) {
r.Use(middleware.Anyone)
r.Post("/auth/register", c.Register)
r.Post("/auth/login", c.Authenticate)
r.Post("/auth/token/refresh", c.RefreshToken)
})
c.router.Group(func(r router.Router) {
r.Use(middleware.Authorized)
r.Get("/auth/ping", c.Ping)
r.Post("/auth/logout", c.Logout)
})
}
Why is it screaming at my function callbacks argument type? My wrapper router.Router implements the chi.Router interface, so it should work fine shouldn't it? Am I misunderstanding how Go works here?
I can see how this can be confusing so I will try to break it down. You have this method:
Group(fn func(r Router)) Router
This method takes a function as a parameter. That function must have a specific signature:
func(r Router)
That is, it takes a single argument of type chi.Router and has no return values. However, when you call it:
c.router.Group(func(r router.Router) { /***/ }
You're passing in a function of the wrong signature; your function signature is:
func(r router.Router)
That's not the signature required by the method you're calling, so it won't compile. It doesn't matter if router.Router implements chi.Router; the parameter (a func(router.Router)) passed is not of the expected type (a func(chi.Router)).
This may seem silly at first - after all, any router.Router must implement chi.Router. But, think about it: that method, Group, is expecting to receive a function, to which it can pass any chi.Router. That means it can pass a chi.Router which does not implement router.Router. If it were to accept your function, it would break type safety, and what in Go is meant to be a compile-time error (the error you're getting, in fact) would become a run-time error. Basically, by passing a function with a different (and more strict) argument type, you're expecting a guarantee which that method never offered.
The parameter types aren't the same, so the function type doesn't match what's expected, even though your interface includes the interface from the other package (the type has to match exactly). You need to have your functions take a chi.router and then use a type assertion, i.e., myRouter := r.(Router), to convert to your type.
So I've been trying to modify the request structure in golang using middleware, i tried creating a custom structure and embedding the request object and some more data but i can't type assert it to *http.Request, can anybody please help, thanks in advance.
Edit: so here is what my structure looks like
type CustomRequest struct {
*http.Request
*profile.User // This is the data i want to embed into the request
}
// then my middlware will be something like
func Middleware(next http.HandlerFunc) http.HandlerFunc {
return http.HandleFunc(func (w http.ResponseWriter, r *http.Request)) {
user := &User{
// User Details Are Here
}
customRequest := &CustomRequest{
r,
&user,
}
req := customRequest.(*http.Request)
next.ServeHttp(w, req)
}
That isn't how type assertion works.
For an expression x of interface type and a type T, the primary
expression
x.(T) asserts that x is not nil and that the value stored in x is of
type T. The notation x.(T) is called a type assertion.
You type assert interfaces to their underlying type.
You can't type assert one type to another, that would be type conversion, but in this case you can't convert between the two. You can only convert two types that are convertible according to the description in the spec above.
If you want to modify the *http.Request just do it directly, the fields are exported. If you want the request to hold extra data just write it in the request body as JSON or in the url.
EDIT: For passing data around you can also use a context, but I am not sure of what you're doing. There is also github.com/gorilla/context
I have several different structures.
Here show two:
type AdsResponse struct {
Body struct {
Docs []struct {
ID int `json:"ID"`
// others
} `json:"docs"`
} `json:"response"`
Header `json:"responseHeader"`
}
type OtherResponse struct {
Body struct {
Docs []struct {
ID int `json:"ID"`
// others
} `json:"docs"`
} `json:"response"`
Header `json:"responseHeader"`
}
but i don't know how i can do for this method accepts and return both.
func Get(url string, response Response) (Response, bool) {
res, err := goreq.Request{
Uri: url,
}.Do()
// several validations
res.Body.FromJsonTo(&response)
return response, true
}
And use like this:
var struct1 AdsResponse
var struct2 OtherResponse
Get("someURL", struct1)
Get("someURL", struct2)
There are any form?
Your code example is somewhat confusing since both structs appear to be identical. I'll assume that they differ somewhere in "others".
First, I generally recommend creating a wrapper around these kinds of JSON deserializations. Working directly on the JSON structure is fragile. Most of your program should not be aware of the fact that the data comes down in JSON. So for instance, you can wrap this in an Ads struct that contains an AdsResponse, or just copies the pieces it cares about out of it. Doing that will also make some of the below slightly easier to implement and less fragile.
The most common solution is probably to create an interface:
type Response interface {
ID() int
}
You make both Ads and Others conform to Response. Then you can return Response. If necessary, you can type-switch later to figure out which one you have and unload other data.
switch response := response.(type) {
case Ads:
...
case Other:
...
}
I don't quite get why you have the reponse as a parameter and as a return. I think you dont need to return it. You should pass a pointer to the reponse and fill it with the data. Also, I'd return an Error instead of a boolean, but that is another topic.
Anyway, the solution is to use interface{} (empty interface).
You are lucky because the function you are using (FromJsonTo) accepts an empty interface as a parameter, so you can safely change your parameter type to interface{} and just pass it to FromJsonTo. Like this:
func Get(url string, response interface{}) bool {
res, err := goreq.Request{
Uri: url,
}.Do()
// several validations
res.Body.FromJsonTo(response)
return true
}
Warning: I did not compile the code.
Then you would call this function with the url and a pointer to one of the reponse structs like this:
var struct1 AdsResponse
var struct2 OtherResponse
Get("someURL", &struct1)
Get("someURL", &struct2)
The way to achieve this is through Go's interfaces.
Two options:
empty interface
Get(url string, response interface{}) (Response, bool)
This option allows any value to be given to this function.
custom interface
Creating a custom interface will allow you to narrow down the types that can be provided as arguments to your function.
In this case you'll have to create an interface that all your Response structs will need to abide by. Any struct really that abides by that interface will be able to be used as an argument of your function.
Something like this:
type MyResponse interface {
SomeFunction()
}
Then your function signature could look like
Get(url string, response MyResponse) (MyResponse, bool)
As long as AdsResponse and OtherResponse abide by the MyResponse interface, they will be allowed to be used as arguments to the function.
Follow the solution working at Go Playground
Go has no polymorphic or any other OO like behaviour, so, when you try to pass a AdsResponse or OtherResponse struct as an Response (or any interface{}), these values becomes an Response (or other param type specified), and is not possible to Go to infer the real type that originate these interface{} and correctly decode your json to these struct types as expected.
This kind of thing should works perfectly in OO languages, like Java, C# etc. There is no hierarchy generalization/specialization on structs/interfaces in Go.
You would need to do a type assertion in your Rest executor, or a switch case, but it seems that you need a generic REST executor, like a generic lib some thing like that. Would not reasonable create a switch case for each struct in your program. Maybe you have dozens or hundreds of structs soon.
I think that a reasonable solution is the rest client pass a lambda function to do the last step for your, that is just create a correct struct destination type and call json decode.
As i say above, the return type of executeRest() in my example will became an interface{}, but the rest client can securely do the type assertion of returned value after executeRest() call.