Add GetReasonFromBody() that extracts reason from JSON

internal/http/reason.go

@@ -17,8 +17,13 @@
 package http
 
 import (
+	"encoding/json"
+	"errors"
+	"io/ioutil"
 	"net/http"
 	"strings"
+
+	"github.com/BBVA/kapow/internal/server/srverrors"
 )
 
 // GetReason returns the reason phrase part of an HTTP response
@@ -28,3 +33,22 @@ func GetReason(r *http.Response) string {
 	}
 	return ""
 }
+
+func GetReasonFromBody(r *http.Response) (string, error) {
+	body, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		return "", errors.New("error reading response's body")
+	}
+
+	reason := &srverrors.ServerErrMessage{}
+	err = json.Unmarshal(body, reason)
+	if err != nil {
+		return "", errors.New("error unmarshaling JSON")
+	}
+
+	if reason.Reason == "" {
+		return "", errors.New("no reason")
+	}
+
+	return reason.Reason, nil
+}

internal/http/reason_test.go

@@ -17,7 +17,9 @@
 package http
 
 import (
+	"io/ioutil"
 	nethttp "net/http"
+	"strings"
 	"testing"
 )
 
@@ -62,3 +64,83 @@ func TestBehaveWithOddSizeStatusCode(t *testing.T) {
 		t.Errorf("Unexpected reason found")
 	}
 }
+
+func TestGetReasonFromBodyExtractsReasonFromJSON(t *testing.T) {
+	r := &nethttp.Response{
+		Status: "200 OK",
+		Body: ioutil.NopCloser(
+			strings.NewReader(
+				`{"reason": "Because reasons", "foo": "bar"}`,
+			),
+		),
+	}
+
+	reason, _ := GetReasonFromBody(r)
+
+	if reason != "Because reasons" {
+		t.Errorf(`reason mismatch, want "Because reasons", got %q`, reason)
+	}
+}
+
+func TestGetReasonFromBodyErrorsOnJSONWithNoReason(t *testing.T) {
+	r := &nethttp.Response{
+		Status: "200 OK",
+		Body: ioutil.NopCloser(
+			strings.NewReader(
+				`{"madness": "Because madness", "foo": "bar"}`,
+			),
+		),
+	}
+
+	_, err := GetReasonFromBody(r)
+
+	if err == nil {
+		t.Error("error not reported")
+	}
+}
+
+func TestGetReasonFromBodyErrorsOnJSONWithEmptyReason(t *testing.T) {
+	r := &nethttp.Response{
+		Body: ioutil.NopCloser(
+			strings.NewReader(
+				`{"reason": "", "foo": "bar"}`,
+			),
+		),
+	}
+
+	_, err := GetReasonFromBody(r)
+
+	if err == nil {
+		t.Error("error not reported")
+	}
+}
+
+func TestGetReasonFromBodyErrorsOnNoJSON(t *testing.T) {
+	r := &nethttp.Response{
+		Body: ioutil.NopCloser(
+			strings.NewReader(""),
+		),
+	}
+
+	_, err := GetReasonFromBody(r)
+
+	if err == nil {
+		t.Error("error not reported")
+	}
+}
+
+func TestGetReasonFromBodyErrorsOnInvalidJSON(t *testing.T) {
+	r := &nethttp.Response{
+		Body: ioutil.NopCloser(
+			strings.NewReader(
+				`{"reason": "Because reasons", "cliffhanger...`,
+			),
+		),
+	}
+
+	_, err := GetReasonFromBody(r)
+
+	if err == nil {
+		t.Error("error not reported")
+	}
+}