watchtower/wtwire/error: add generic error message

watchtower/wtwire/error.go

@@ -0,0 +1,62 @@
+package wtwire
+
+import "io"
+
+// Error is a generic error message that can be sent to a client if a request
+// fails outside of prescribed protocol errors. Typically this would be followed
+// by the server disconnecting the client, and so can be useful to transfering
+// the exact reason.
+type Error struct {
+	// Code specifies the error code encountered by the server.
+	Code ErrorCode
+
+	// Data encodes a payload whose contents can be interpreted by the
+	// client in response to the error code.
+	Data []byte
+}
+
+// NewError returns an freshly-initialized Error message.
+func NewError() *Error {
+	return &Error{}
+}
+
+// A compile time check to ensure Error implements the wtwire.Message interface.
+var _ Message = (*Error)(nil)
+
+// Decode deserializes a serialized Error message stored in the passed io.Reader
+// observing the specified protocol version.
+//
+// This is part of the wtwire.Message interface.
+func (e *Error) Decode(r io.Reader, pver uint32) error {
+	return ReadElements(r,
+		&e.Code,
+		&e.Data,
+	)
+}
+
+// Encode serializes the target Error into the passed io.Writer observing the
+// protocol version specified.
+//
+// This is part of the wtwire.Message interface.
+func (e *Error) Encode(w io.Writer, prver uint32) error {
+	return WriteElements(w,
+		e.Code,
+		e.Data,
+	)
+}
+
+// MsgType returns the integer uniquely identifying this message type on the
+// wire.
+//
+// This is part of the wtwire.Message interface.
+func (e *Error) MsgType() MessageType {
+	return MsgError
+}
+
+// MaxPayloadLength returns the maximum allowed payload size for a Error
+// complete message observing the specified protocol version.
+//
+// This is part of the wtwire.Message interface.
+func (e *Error) MaxPayloadLength(uint32) uint32 {
+	return MaxMessagePayload
+}