Register Dependency from Context

When you want to create a middleware of iris.Handler form but you want to bind any input arguments of a potential (MVC) Controller's method or dependency-injection handlers.
The ctx.RegisterDependency is the method that allows you to build and add request-time dependencies.
// RegisterDependency registers a struct or slice
// or pointer to struct dependency at request-time
// for the next handler in the chain. One value per type.
// Note that it's highly recommended to register
// your dependencies before server ran
// through Party.ConfigureContainer or mvc.Application.Register
// in sake of minimum performance cost.
RegisterDependency(v interface{})
// UnregisterDependency removes a dependency based on its type.
// Reports whether a dependency with that type was
// found and removed successfully.
UnregisterDependency(typ reflect.Type) bool
Let's start by creating a custom middleware that we can use in our hypothetical app.
// Role struct value example.
type Role struct {
    Name string
}
​
const roleContextKey = "myapp.role"
​
// RoleMiddleware example of a custom middleware.
func RoleMiddleware(ctx iris.Context) {
    // [do it yourself: extract the role from the request...]
    if ctx.URLParam("name") != "kataras" {
        ctx.StopWithStatus(iris.StatusUnauthorized)
        return
    }
    //
​
    role := Role{Name: "admin"}
​
    // Share the role value to the next handler(s).
    ctx.Values().Set(roleContextKey, role)
When you have access to the middleware itself: Use the RegisterDependency to register struct type values as dependencies at request-time for any potential dependency injection-ed user handler. This way the user of your middleware can get rid of manually register a dependency for that Role type with calls of APIContainer.RegisterDependency (and mvc.Application.Register).
    ctx.RegisterDependency(role)
    ctx.Next()
}
// GetRole returns the role inside the context values,
// the `roleMiddleware` should be executed first.
func GetRole(ctx iris.Context) (Role, bool) {
    v := ctx.Values().Get(roleContextKey)
    if v != nil {
        if role, ok := v.(Role); ok {
            return role, true
        }
    }
​
    return Role{}, false
}
It's time to use our RoleMiddleware, in a common iris.Handler and a handler which accepts one or more dependencies. Create a main.go file and copy-paste the following code:
package main
​
import "github.com/kataras/iris/v12"
​
func main() {
    app := iris.New()
    app.Use(RoleMiddleware)
​
    app.Get("/", commonHandler)
    c := app.ConfigureContainer()
When you do NOT have access to the middleware code itself then you can register a request dependency which retrieves the value from the Context and returns it, so handler/function's input arguments with that Role type can be binded.
    c.RegisterDependency(func(ctx iris.Context) Role {
        role, ok := GetRole(ctx)
        if !ok {
            // This codeblock will never be executed here
            // but you can stop executing a handler which depends on
            // that dependency with
            // `ctx.StopExecution/ctx.StopWithXXX` methods
            // or by returning a second output argument of `error` type.
            ctx.StopExecution()
            return Role{}
        }
​
        return role
    })
    c.Get("/dep", handlerWithDependencies)
​
    // http://localhost:8080?name=kataras
    // http://localhost:8080/dep?name=kataras
    app.Listen(":8080")
}
​
func commonHandler(ctx iris.Context) {
    role, _ := GetRole(ctx)
    ctx.WriteString(role.Name)
}
​
func handlerWithDependencies(role Role) string {
    return role.Name
}
That's all.
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Last updated 1 year ago