How Can I Specifically Catch 'Connection Lost' or 'Connection Refused' Errors in Go?

Catching Specific Errors in Go

Go offers flexible error handling, allowing developers to address specific error types in their code. Suppose you're working with the rpc.Dial function and want to handle only "connection lost" or "connection refused" errors.

Using errors.Is and errors.As

Modern Go versions provide the errors.Is and errors.As functions for efficient error handling. In your case:

if errors.Is(err, syscall.ECONNREFUSED) {
  // Handle connection refused error
} else if errors.As(err, &net.OpError{}) {
  // Handle other network errors (e.g., connection lost)
}

Checking Error Types

Another approach is to check error types directly. As mentioned in your question, the net package defines various error types, including net.Error for network errors:

if _, ok := err.(net.Error); ok {
  // Handle net.Error instance
}

Reading Error Documentation

To understand all possible errors returned by a function, you can consult the documentation. For example, the godoc for rpc.Dial provides details on the different errors it can return.

Legacy Approach

As a last resort, you can compare the error string to the expected errors:

if strings.Contains(err.Error(), "connection lost") {
  // Handle connection lost error
}

However, this approach is not recommended as it's prone to false positives or negatives.

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