Logging Responses to Incoming HTTP Requests in http.HandleFunc

In the previous article titled "In go, how to inspect the HTTP response that is written to http.ResponseWriter?" we explored a method for inspecting server responses in a unit testing environment. However, this approach may not be suitable for live servers.

Middleware Chaining

An alternative solution is middleware chaining, a commonly used technique for modifying and logging HTTP responses and requests while preserving the original request-response flow.

Functional Handler Combinators

Instead of using a library like negroni, we can create our own functional handler combinators:

<code class="go">func NewFooHandler(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        // do something before
        next(w, r)
        // do something after
    }
}</code>

Creating a Chain of Handlers

We can chain multiple handlers together using the combinators:

<code class="go">h := NewFooHandler(NewBarHandler(NewBazHandler(Sink)))</code>

In this example, Sink is an empty handler that does nothing.

Implementing Response Logging

Using the handler combinator approach, we can create a handler that logs the response:

<code class="go">func NewResponseLoggingHandler(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        // Replace the response writer with a recorder
        c := httptest.NewRecorder()
        next(c, r)

        // Copy the response from the recorder to the actual writer
        for k, v := range c.HeaderMap {
            w.Header()[k] = v
        }
        w.WriteHeader(c.Code)
        c.Body.WriteTo(w)
    }
}</code>

Applying the Response Logging Handler

We can apply the response logging handler to all HTTP routes by creating a default handler combinator:

<code class="go">func NewDefaultHandler(next http.HandlerFunc) http.HandlerFunc {
    return NewResponseLoggingHandler(NewOtherStuffHandler(next))
}</code>

This way, whenever we start a chain like:

<code class="go">h := NewDefaultHandler(...)</code>

It will automatically include response logging and any other default handlers.

The above is the detailed content of How can you log HTTP responses in Go's `http.HandleFunc` using middleware chaining and functional handler combinators?. For more information, please follow other related articles on the PHP Chinese website!