box.iproto.override()

box.iproto.override(request_type, handler)¶

Since version 2.11.0. Set a new IPROTO request handler callback for the given request type.

Parameters:

request_type (number) – a request type code. Possible values: a type code from box.iproto.type (except box.iproto.type.UNKNOWN) – override the existing request type handler. box.iproto.type.UNKNOWN – override the handler of unknown request types. handler (function) – IPROTO request handler. The signature of a handler function: function(sid, header, body), where header (userdata): a request header encoded as a msgpack_object body (userdata): a request body encoded as a msgpack_object Returns true on success, otherwise false. On false, there is a fallback to the default handler. Also, you can indicate an error by throwing an exception. In this case, the return value is false, but this does not always mean a failure. To reset the request handler, set the handler parameter to nil.

Return:

none

Possible errors:

If a Lua handler throws an exception, the behavior is similar to that of a remote procedure call. The following errors are returned to the client over IPROTO (see src/lua/utils.h):

• ER_PROC_LUA – an exception is thrown from a Lua handler, diagnostic is not set.
• diagnostics from src/box/errcode.h – an exception is thrown, diagnostic is set.

For details, see src/box/errcode.h.

Warning

When using box.iproto.override(), it is important that you follow the wire protocol. That is, the server response should match the return value types of the corresponding request type. Otherwise, it could lead to peer breakdown or undefined behavior.

Example:

Define a handler function for the box.iproto.type.SELECT request type:

local function iproto_select_handler_lua(header, body)
    if body.space_id == 512 then
        box.iproto.send(box.session.id(),
                { request_type = box.iproto.type.OK,
                  sync = header.SYNC,
                  schema_version = box.info.schema_version },
                { data = { 1, 2, 3 } })
        return true
    end
    return false
end

Override box.iproto.type.SELECT handler:

box.iproto.override(box.iproto.type.SELECT, iproto_select_handler_lua)

Reset box.iproto.type.SELECT handler:

box.iproto.override(box.iproto.type.SELECT, nil)

Override a handler function for the unknown request type:

box.iproto.override(box.iproto.type.UNKNOWN, iproto_unknown_request_handler_lua)