I pasted a section of code that was supposed to catch an AllTopologyNodesDownError error which doesn't work and I have no idea why.

func (sc *ServerConfig) addNodesToCluster(store *ravendb.DocumentStore) error {
        clusterTopology, err := sc.getClusterTopology(store)
        if errors.Is(err, &ravendb.AllTopologyNodesDownError{}) {
            for _, url := range sc.Url.List {
                    err = addNodeToCluster(store, url)
                    if err != nil {
                        return err
                    }
            }
        } else if err != nil {
            return err
        }

the structure of the ravendb.AllTopologyNodesDownError is

// AllTopologyNodesDownError represents "all topology nodes are down" error
type AllTopologyNodesDownError struct {
    errorBase
} 

type errorBase struct {
    wrapped  error
    ErrorStr string
}

screen shot of the error when debugging the code

CodePudding user response：

errors.Is() is used to tell if any error in the chain is the same instance as the provided error¹, that can never be the case here because you provided a literal of your error type, no other code could hold that instance or a reference to it.

Your error looks like a type, to tell if any error in the chain is a given type you should use errors.As():

clusterTopology, err := sc.getClusterTopology(store)
var errAllDown *AllTopologyNodesDownError
if errors.As(err, &errAllDown) {
    // err had an *AllTopologyNodesDownError in its
    // chain and errAllDown now contains it.
}

1. Can be overridden by implementing the Unwrap() interface which your error type does not.