Resolve "Cater for errors being nil and update checks for retryable errors"

Related to #34

errors/error.go

@@ -9,6 +9,7 @@ import (
 )
 
 // CustomError implements the following interfaces:
+//
 //	error
 //	github.com/pkg/errors: Cause
 type CustomError struct {
@@ -264,3 +265,34 @@ func IsRetryableError(err error) bool {
 
 	return false
 }
+
+func IsRetryableErrorOrShouldFail(err error) (shouldRetry bool, shouldFail bool) {
+	if err == nil {
+		return false, false
+	}
+
+	// Check for retryable
+	if IsRetryableError(err) {
+		return true, false
+	}
+
+	code := HTTPCode(err)
+
+	// If no HTTP code in the error, just fail but don't retry
+	if code == 0 {
+		return false, true
+	}
+
+	// Explicitly check for 400s, and don't retry or fail
+	if code >= 400 && code < 500 {
+		return false, false
+	}
+
+	// Explicitly check for 200s, for a fail-safe
+	if code >= 200 && code < 300 {
+		return false, false
+	}
+
+	// If we got here, we should fail normally
+	return false, true
+}