Added docs for using EnableHTTPStatusErrors

README.md

@@ -234,7 +234,10 @@ simplerr.Formatter = func(e *simplerr.SimpleError) string {
 ## HTTP Status Codes
 
 HTTP status codes can be set automatically by using the [ecosystem/http](https://github.com/lobocv/simplerr/tree/master/ecosystem/http)
-package to translate `simplerr` error codes to HTTP status codes. To do so, you must use the `simplehttp.Handler` or 
+package to translate `simplerr` error codes to HTTP status codes and vice versa.
+
+### Converting SimpleError to HTTP status codes
+To do so, you must use the `simplehttp.Handler` or 
 `simplehttp.HandlerFunc`instead of the ones defined in the `http` package. The only difference between the two is that
 the `simplehttp` ones return an error. 
 Adapters are provided in order to interface with the `http` package. These adapters call `simplehttp.SetStatus()` on the returned
@@ -282,6 +285,15 @@ func main() {
 }
 ```
 
+### Converting HTTP status codes to SimpleError
+
+The standard library `http.DefaultTransport` will return all successfully transported request/responses without error.
+However, most applications will react to those responses by looking at the HTTP status code. From the application's point 
+of view, `4XX` and `5XX` series statuses **are errors**.
+
+In order to get your HTTP clients to return `SimpleError` for `4XX` and `5XX` series errors, you can wrap their `http.RoundTripper`
+using `simplehttp.EnableHTTPStatusErrors(rt http.RoundTripper)`.
+
 ## GRPC Status Codes
 
 Since GRPC functions return an error, it is even convenient to integrate error code translation using an interceptor (middleware).

ecosystem/http/roundtripper.go

@@ -16,6 +16,7 @@ type roundTripper struct {
 	rt http.RoundTripper
 }
 
+// RoundTrip calls the underlying RoundTripper and converts any 4XX or 5XX series errors to SimpleErrors
 func (s roundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
 	resp, err := s.rt.RoundTrip(request)
 	if err != nil {