Revert "rpc: add method to test for subscription support (ethereum#25942

)"

This reverts commit e851e46.

rpc/client.go

@@ -538,13 +538,6 @@ func (c *Client) Subscribe(ctx context.Context, namespace string, channel interf
 	return op.sub, nil
 }
 
-// SupportsSubscriptions reports whether subscriptions are supported by the client
-// transport. When this returns false, Subscribe and related methods will return
-// ErrNotificationsUnsupported.
-func (c *Client) SupportsSubscriptions() bool {
-	return !c.isHTTP
-}
-
 func (c *Client) newMessage(method string, paramsIn ...interface{}) (*jsonrpcMessage, error) {
 	msg := &jsonrpcMessage{Version: vsn, ID: c.nextID(), Method: method}
 	if paramsIn != nil { // prevent sending "params":null

rpc/errors.go

@@ -58,13 +58,12 @@ var (
 )
 
 const (
-	errcodeDefault          = -32000
-	errcodeTimeout          = -32002
-	errcodeResponseTooLarge = -32003
-	errcodePanic            = -32603
-	errcodeMarshalError     = -32603
-
-	legacyErrcodeNotificationsUnsupported = -32001
+	errcodeDefault                  = -32000
+	errcodeNotificationsUnsupported = -32001
+	errcodeTimeout                  = -32002
+	errcodeResponseTooLarge         = -32003
+	errcodePanic                    = -32603
+	errcodeMarshalError             = -32603
 )
 
 const (
@@ -81,34 +80,6 @@ func (e *methodNotFoundError) Error() string {
 	return fmt.Sprintf("the method %s does not exist/is not available", e.method)
 }
 
-type notificationsUnsupportedError struct{}
-
-func (e notificationsUnsupportedError) Error() string {
-	return "notifications not supported"
-}
-
-func (e notificationsUnsupportedError) ErrorCode() int { return -32601 }
-
-// Is checks for equivalence to another error. Here we define that all errors with code
-// -32601 (method not found) are equivalent to notificationsUnsupportedError. This is
-// done to enable the following pattern:
-//
-//	sub, err := client.Subscribe(...)
-//	if errors.Is(err, rpc.ErrNotificationsUnsupported) {
-//		// server doesn't support subscriptions
-//	}
-func (e notificationsUnsupportedError) Is(other error) bool {
-	if other == (notificationsUnsupportedError{}) {
-		return true
-	}
-	rpcErr, ok := other.(Error)
-	if ok {
-		code := rpcErr.ErrorCode()
-		return code == -32601 || code == legacyErrcodeNotificationsUnsupported
-	}
-	return false
-}
-
 type subscriptionNotFoundError struct{ namespace, subscription string }
 
 func (e *subscriptionNotFoundError) ErrorCode() int { return -32601 }

rpc/handler.go

@@ -530,7 +530,10 @@ func (h *handler) handleCall(cp *callProc, msg *jsonrpcMessage) *jsonrpcMessage
 // handleSubscribe processes *_subscribe method calls.
 func (h *handler) handleSubscribe(cp *callProc, msg *jsonrpcMessage) *jsonrpcMessage {
 	if !h.allowSubscribe {
-		return msg.errorResponse(ErrNotificationsUnsupported)
+		return msg.errorResponse(&internalServerError{
+			code:    errcodeNotificationsUnsupported,
+			message: ErrNotificationsUnsupported.Error(),
+		})
 	}
 
 	// Subscription method name is first argument.

rpc/subscription.go

@@ -32,17 +32,8 @@ import (
 )
 
 var (
-	// ErrNotificationsUnsupported is returned by the client when the connection doesn't
-	// support notifications. You can use this error value to check for subscription
-	// support like this:
-	//
-	//	sub, err := client.EthSubscribe(ctx, channel, "newHeads", true)
-	//	if errors.Is(err, rpc.ErrNotificationsUnsupported) {
-	//		// Server does not support subscriptions, fall back to polling.
-	//	}
-	//
-	ErrNotificationsUnsupported = notificationsUnsupportedError{}
-
+	// ErrNotificationsUnsupported is returned when the connection doesn't support notifications
+	ErrNotificationsUnsupported = errors.New("notifications not supported")
 	// ErrSubscriptionNotFound is returned when the notification for the given id is not found
 	ErrSubscriptionNotFound = errors.New("subscription not found")
 )