internal/http/request.go: replace GetReason() with GetReasonFromBody()

Update tests to inject the required JSON error body with reason.

internal/client/route_remove_test.go

@@ -43,12 +43,13 @@ func TestRemoveRouteErrorNonExistent(t *testing.T) {
 	defer gock.Off()
 	gock.New("http://localhost:8080").
 		Delete("/routes/ROUTE_BAD").
-		Reply(http.StatusNotFound)
+		Reply(http.StatusNotFound).
+		BodyString(`{"reason": "Route Not Found"}`)
 
 	err := RemoveRoute("http://localhost:8080", "ROUTE_BAD")
 	if err == nil {
 		t.Errorf("Error not reported for nonexistent route")
-	} else if err.Error() != "Not Found" {
+	} else if err.Error() != "Route Not Found" {
 		t.Errorf(`Error mismatch: got %q, want "Not Found"`, err)
 	}
 

internal/client/set_test.go

@@ -52,7 +52,8 @@ func TestSetDataErrIfBadHandlerID(t *testing.T) {
 	defer gock.Off()
 	gock.New("http://localhost:8080").
 		Put("/HANDLER_BAD/response/status/code").
-		Reply(http.StatusNotFound)
+		Reply(http.StatusNotFound).
+		BodyString(`{"reason": "Handler ID Not Found"}`)
 
 	if err := client.SetData(
 		"http://localhost:8080",
@@ -61,8 +62,8 @@ func TestSetDataErrIfBadHandlerID(t *testing.T) {
 		strings.NewReader("200"),
 	); err == nil {
 		t.Error("Expected error not present")
-	} else if err.Error() != "Not Found" {
+	} else if err.Error() != "Handler ID Not Found" {
-		t.Errorf(`Error mismatch: expected "Not Found", got %q`, err)
+		t.Errorf(`Error mismatch: expected "Handler ID Not Found", got %q`, err)
 	}
 
 	if !gock.IsDone() {

internal/http/request.go

@@ -66,7 +66,11 @@ func Request(method string, url string, contentType string, r io.Reader, w io.Wr
 	defer res.Body.Close()
 
 	if res.StatusCode < 200 || res.StatusCode >= 300 {
-		return errors.New(GetReason(res))
+		reason, err := GetReasonFromBody(res)
+		if err != nil {
+			return err
+		}
+		return errors.New(reason)
 	}
 
 	if w == nil {

internal/http/request_test.go

@@ -72,7 +72,9 @@ func TestReturnHTTPErrorAsIs(t *testing.T) {
 
 func TestReturnHTTPReasonAsErrorWhenUnsuccessful(t *testing.T) {
 	defer gock.Off()
-	gock.New("http://localhost").Reply(http.StatusTeapot)
+	gock.New("http://localhost").
+		Reply(http.StatusTeapot).
+		BodyString(`{"reason": "I'm a teapot"}`)
 
 	err := Request("GET", "http://localhost", "", nil, nil)
 	if err == nil || err.Error() != http.StatusText(http.StatusTeapot) {