Consolidate /sys/health error checks (#221)

* Consolidate /sys/health error checks

* Use switch instead of slices.Contains

Co-authored-by: Max Bowsher <maxbowsher@gmail.com>

* cleanup

* fix build

* PR feedback

* comment

---------

Co-authored-by: Max Bowsher <maxbowsher@gmail.com>

errors.go

@@ -55,16 +55,12 @@ func isResponseError(req *http.Request, resp *http.Response) *ResponseError {
 		return nil
 	}
 
-	// 429 is returned by standby instances for /sys/health requests and should
-	// not be treated as an error; for other paths the status code indicates
-	// that the quota limit has been reached.
-	if resp.StatusCode == http.StatusTooManyRequests /* 429 */ && req.URL.Path == "/v1/sys/health" {
-		return nil
-	}
-
-	// 472 & 473 are returned by (performance/secondary) standby instances for /sys/health requests and should
-	// not be treated as an error
-	if (resp.StatusCode == 472 || resp.StatusCode == 473) && req.URL.Path == "/v1/sys/health" {
+	// /v1/sys/health returns a few special 4xx and 5xx status codes that
+	// should not be treated as errors; the response body will contain valuable
+	// health status information.
+	//
+	// See: https://developer.hashicorp.com/vault/api-docs/system/health
+	if req.URL.Path == "/v1/sys/health" && resp != nil {
 		return nil
 	}