implement chainError to support go1.19

p2p/net/swarm/dial_error.go

@@ -49,15 +49,11 @@ func (e *DialError) Error() string {
 	return builder.String()
 }
 
-func (e *DialError) Unwrap() []error {
+func (e *DialError) Unwrap() error {
 	if e == nil || len(e.DialErrors) == 0 {
 		return nil
 	}
-	errs := make([]error, len(e.DialErrors))
-	for i := 0; i < len(e.DialErrors); i++ {
-		errs[i] = &e.DialErrors[i]
-	}
-	return errs
+	return chainError(e.DialErrors)
 }
 
 func (e *DialError) Is(target error) bool {
@@ -84,3 +80,32 @@ func (e *TransportError) Unwrap() error {
 }
 
 var _ error = (*TransportError)(nil)
+
+// chainError is used to implement Unwrap for DialError
+// errors.Is and errors.As only support `interface { Unwrap() []error }` from go1.20
+//
+// The implementation is a modified version of multierror.chain from:
+// https://github.com/hashicorp/go-multierror/blob/main/multierror.go#L96
+type chainError []TransportError
+
+func (c chainError) Error() string {
+	// The actual value is not important. Only want to implement error.
+	if len(c) == 0 {
+		return "chainError: []"
+	}
+	return c[0].Error()
+}
+
+func (c chainError) Unwrap() error {
+	if len(c) == 1 {
+		return nil
+	}
+	return c[1:]
+}
+
+func (c chainError) Is(target error) bool {
+	if len(c) == 0 {
+		return false
+	}
+	return errors.Is(&c[0], target)
+}