log http.ResponseWriter content - go

Question

Premise: I've found a similar issue but not working in my case, so please do not mark this as a duplicate.
I've a HTTP server in Go and I've created a middleware to log the request, the response time and I would like to log the response too.
I've used httputil.DumpRequest in a function called HTTPRequest under the package log.
How can I correctly get the response body and status and headers from the w http.ResponseWriter and log them together with the other data?
My ISSUE is: I would like to intercept the Response Headers, Status and Body and to log the together with the Request and Response Time
Here's the code:
log "core/logger"
...
func RequestLoggerMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
start := time.Now()
defer func() {
log.Info(
fmt.Sprintf(
"[Request: %s] [Execution time: %v] [Response: %s]",
log.HTTPRequest(r),
time.Since(start),
// RESPONSE DATA HERE !!!!!!!
))
}()
next.ServeHTTP(w, r)
})
}

Answer 1

Thanks, #Sivachandran for the response. It was almost perfect, only it didn't implement the http.ResponseWriter because of the pointers.
For the sake of completeness, I post here the correct solution code, because it's not easy to find any documentation on it, even if this question has been given a negative score.
Stackoverflow is a good place to exchange questions and this, in my opinion, was a very good and difficult question, either for a middle lever Golang programmer, so it didn't deserve a negative score at all!
That's the solution, enjoy:
// RequestLoggerMiddleware is the middleware layer to log all the HTTP requests
func RequestLoggerMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
start := time.Now()
rww := NewResponseWriterWrapper(w)
w.Header()
defer func() {
log.Info(
fmt.Sprintf(
"[Request: %s] [Execution time: %v] [Response: %s]",
log.HTTPRequest(r),
time.Since(start),
rww.String(),
))
}()
next.ServeHTTP(rww, r)
})
}
// ResponseWriterWrapper struct is used to log the response
type ResponseWriterWrapper struct {
w *http.ResponseWriter
body *bytes.Buffer
statusCode *int
}
// NewResponseWriterWrapper static function creates a wrapper for the http.ResponseWriter
func NewResponseWriterWrapper(w http.ResponseWriter) ResponseWriterWrapper {
var buf bytes.Buffer
var statusCode int = 200
return ResponseWriterWrapper{
w: &w,
body: &buf,
statusCode: &statusCode,
}
}
func (rww ResponseWriterWrapper) Write(buf []byte) (int, error) {
rww.body.Write(buf)
return (*rww.w).Write(buf)
}
// Header function overwrites the http.ResponseWriter Header() function
func (rww ResponseWriterWrapper) Header() http.Header {
return (*rww.w).Header()
}
// WriteHeader function overwrites the http.ResponseWriter WriteHeader() function
func (rww ResponseWriterWrapper) WriteHeader(statusCode int) {
(*rww.statusCode) = statusCode
(*rww.w).WriteHeader(statusCode)
}
func (rww ResponseWriterWrapper) String() string {
var buf bytes.Buffer
buf.WriteString("Response:")
buf.WriteString("Headers:")
for k, v := range (*rww.w).Header() {
buf.WriteString(fmt.Sprintf("%s: %v", k, v))
}
buf.WriteString(fmt.Sprintf(" Status Code: %d", *(rww.statusCode)))
buf.WriteString("Body")
buf.WriteString(rww.body.String())
return buf.String()
}

Answer 2

You need to wrap the ResponseWriter to capture the response data.
type ResponseWriterWrapper struct {
w http.ResponseWriter
body bytes.Buffer
statusCode int
}
func (i *ResponseWriterWrapper) Write(buf []byte) (int, error) {
i.body.Write(buf)
return i.w.Write(buf)
}
func (i *ResponseWriterWrapper) WriteHeader(statusCode int) {
i.statusCode = statusCode
i.w.WriteHeader(statusCode)
}
func (i *ResponseWriterWrapper) String() {
var buf bytes.Buffer
buf.WriteString("Response:")
buf.WriteString("Headers:")
for k, v := range i.w.Header() {
buf.WriteString(fmt.Sprintf("%s: %v", k, v))
}
buf.WriteString(fmt.Sprintf("Status Code: %d", i.statusCode))
buf.WriteString("Body")
buf.WriteString(i.body.String())
}
Pass the wrapper to ServeHTTP and log captured response data.
func RequestLoggerMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
start := time.Now()
rww := ResponseWriterWrapper{ w: w }
defer func() {
log.Info(
fmt.Sprintf(
"[Request: %s] [Execution time: %v] [Response: %s]",
log.HTTPRequest(r),
time.Since(start),
log.Info(rww.String())
))
}()
next.ServeHTTP(rww, r)
})
}