How to Effectively Pass Context to Middleware and Handlers in Golang?

Passing Context in Golang Request to Middleware

Understanding the context mechanism introduced in Golang 1.7 can be challenging. This article aims to clarify how to effectively pass context to middleware and handler functions.

Deriving Contexts

As mentioned in the Go Concurrency Patterns blog post, you can derive contexts from the background context. The Request object also provides Context and WithContext methods. This allows you to create customized contexts for specific purposes.

Implementing Timeout

Within your request handler, you can specify a timeout using the WithTimeout method. This creates a derived context with a set timeout.

ctx, cancel := context.WithTimeout(r.Context(), time.Duration(60*time.Second))
defer cancel()
r = r.WithContext(ctx)

Adding User Information to Context

In your authorization checker, you can add user information to the context before calling ServeHTTP.

type ContextKey string

const ContextUserKey ContextKey = "user"

// ...

ctx := context.WithValue(r.Context(), ContextUserKey, "theuser")
h.ServeHTTP(w, r.WithContext(ctx))

Retrieving User Information from Context

From within the handler, you can access the user information from the context.

user := r.Context().Value(ContextUserKey)
doSomethingForThisUser(user.(string))

Chaining Middleware with Context

In your main function, you can chain middleware handlers using util.UseMiddleware, passing context across each handler.

router.Handle("/hello", util.UseMiddleware(authCheck, HandlerW, ...))

Conclusion

By following these steps, you can effectively pass context in Golang requests to middleware and handler functions, enhancing flexibility and maintaining thread safety within your code.

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