Add typed error response to error object returned by helper

err.go

@@ -1,6 +1,7 @@
 package easclient
 
 import (
+	"encoding/json"
 	"fmt"
 
 	"gopkg.in/resty.v1"
@@ -10,10 +11,30 @@ const (
 	HeaderKeyOtrisErr = "X-Otris-Eas-Error"
 )
 
+// errorResponse is the response body of an eas response where
+// the HeaderKeyOtrisErr is set. It contains details about why something failed.
+type errorResponse struct {
+	Message string `json:"message"`
+	Code    int    `json:"code"`
+}
+
 type ResponseErr struct {
 	msg string
 
 	Body []byte
+
+	// Response is the original error response from the EAS. This may contain
+	// zero values if the EAS did not return a valid error response.
+	Response errorResponse
+}
+
+func NewResponseErr(msg string, body []byte) *ResponseErr {
+	err := &ResponseErr{msg: msg, Body: body}
+
+	// try to parse EAS response. If it fails, we ignore it.
+	_ = json.Unmarshal(body, &err.Response)
+
+	return err
 }
 
 func (r *ResponseErr) Error() string {
@@ -23,16 +44,10 @@ func (r *ResponseErr) Error() string {
 // isErrorResponse checks if the given response is an error.
 func isErrorResponse(res *resty.Response) (bool, *ResponseErr) {
 	if status := res.StatusCode(); status > 300 {
-		return true, &ResponseErr{
-			msg:  fmt.Sprintf("unexpected response status %v, expected value < 300", status),
-			Body: res.Body(),
-		}
+		return true, NewResponseErr(fmt.Sprintf("unexpected response status %v, expected value < 300", status), res.Body())
 	}
 	if hasErrHeader(res) {
-		return true, &ResponseErr{
-			msg:  fmt.Sprintf("eas responded with error header. status %v is considered an error in that case", res.StatusCode()),
-			Body: res.Body(),
-		}
+		return true, NewResponseErr(fmt.Sprintf("eas responded with error header. status %v is considered an error in that case", res.StatusCode()), res.Body())
 	}
 
 	return false, nil