How Can I Pass Data from Middleware to Handlers in Golang?

Passing Data from Middleware to Handlers

In your design, you have middleware that processes an incoming request and handlers that return an http.Handler. You want to pass data from the middleware to the handlers, specifically a JSON web token parsed from the request body.

To achieve this, you can utilize Gorilla's context package:

import (
    "github.com/gorilla/context"
)

func Middleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Middleware operations
        // Parse body/get token.
        context.Set(r, "token", token)

        next.ServeHTTP(w, r)
    })
}

func Handler() http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := context.Get(r, "token")
    })
}

In the middleware, you parse the request body and store the JWT in the request context. Then, in the handler, you can retrieve the JWT from the context:

token := context.Get(r, "token")

This allows you to avoid parsing the JWT again in your handlers, which is more efficient.

Update:

The Gorilla context package is currently in maintenance mode.

func Middleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Middleware operations
        // Parse body/get token.
        ctx := context.WithValue(r.Context(), "token", token)

        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

func Handler() http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Context().Value("token")
    })
}

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