There are a number of internal structures within the scripting element of MySQL Proxy. The primary structure is proxy and this provides an interface to the many common structures used throughout the script, such as connection lists and configured backend servers. Other structures, such as the incoming packet from the client and result sets are only available within the context of one of the scriptable functions.

proxy.connection

The proxy.connection object is read only, and provides information about the current connection, and is split into a client and server tables. This allows you to examine information about both the incoming client connections to the proxy (client), and to the backend servers (server).

proxy.global.backends

The proxy.global.backends table is partially writable and contains an array of all the configured backend servers and the server metadata (IP address, status, etc.). You can determine the array index of the current connection using proxy.connection["backend_ndx"] which is the index into this table of the backend server being used by the active connection.

The attributes for each entry within the proxy.global.backends table are shown in this table.

proxy.queries

The proxy.queries object is a queue representing the list of queries to be sent to the server. The queue is not populated automatically, but if you do not explicitly populate the queue then queries are passed on to the backend server verbatim. Also, if you do not populate the query queue by hand, then the read_query_result() function is not triggered.

The following methods are supported for populating the proxy.queries object.

For example, you could append a query packet to the proxy.queries queue by using the append():

proxy.queries:append(1,packet)

The optional third argument to append() should contain the options for the packet. If you want to have access to the result set through the read_query_result() function, you must set the resultset_is_needed flag to true:

proxy.queries:append( 1, packet, { resultset_is_needed = true } )

If that flag is false (the default), proxy will:

The default mode is therefore quicker and useful if you only want to monitor the queries sent, and the basic statistics.

If, however, you want to perform any kind of manipulation on the returned data, you must set the flag to true, which will:

proxy.response

The proxy.response structure is used when you want to return your own MySQL response, instead of forwarding a packet that you have received a backend server. The structure holds the response type information, an optional error message, and the result set (rows/columns) that you want to return.

When using proxy.response you either set proxy.response.type to proxy.MYSQLD_PACKET_OK and then build resultset to contain the results that you want to return, or set proxy.response.type to proxy.MYSQLD_PACKET_ERR and set the proxy.response.errmsg to a string with the error message. To send the completed resultset or error message, you should return the proxy.PROXY_SEND_RESULT to trigger the return of the packet information.

An example of this can be seen in the tutorial-resultset.lua script within the MySQL Proxy package:

if string.lower(command) == "show" and string.lower(option) == "querycounter" then
        ---
        -- proxy.PROXY_SEND_RESULT requires
        --
        -- proxy.response.type to be either
        -- * proxy.MYSQLD_PACKET_OK or
        -- * proxy.MYSQLD_PACKET_ERR
        --
        -- for proxy.MYSQLD_PACKET_OK you need a resultset
        -- * fields
        -- * rows
        --
        -- for proxy.MYSQLD_PACKET_ERR
        -- * errmsg
        proxy.response.type = proxy.MYSQLD_PACKET_OK
        proxy.response.resultset = {
                fields = {
                        { type = proxy.MYSQL_TYPE_LONG, name = "global_query_counter", },
                        { type = proxy.MYSQL_TYPE_LONG, name = "query_counter", },
                },
                rows = {
                        { proxy.global.query_counter, query_counter }
                }
        }

        -- we have our result, send it back
        return proxy.PROXY_SEND_RESULT
elseif string.lower(command) == "show" and string.lower(option) == "myerror" then
        proxy.response.type = proxy.MYSQLD_PACKET_ERR
        proxy.response.errmsg = "my first error"

        return proxy.PROXY_SEND_RESULT

proxy.response.resultset

The proxy.response.resultset structure should be populated with the rows and columns of data that you want to return. The structure contains the information about the entire result set, with the individual elements of the data shown in the table below.

For an example of the population of this table, see Section 14.6.4.2, “Internal Structures”.

Proxy Return State Constants

The following constants are used internally by the proxy to specify the response to send to the client or server. All constants are exposed as values within the main proxy table.

As constants, these entities are available without qualification in the Lua scripts. For example, at the end of the read_query_result() you might return PROXY_IGNORE_RESULT:

return proxy.PROXY_IGNORE_RESULT

Packet State Constants

The following states describe the status of a network packet. These items are entries within the main proxy table.

Backend State/Type Constants

The following constants are used either to define the status of the backend server (the MySQL server to which the proxy is connected) or the type of backend server. These items are entries within the main proxy table.

Server Command Constants

The following values are used in the packets exchanged between the client and server to identify the information in the rest of the packet. These items are entries within the main proxy table. The packet type is defined as the first character in the sent packet. For example, when intercepting packets from the client to edit or monitor a query you would check that the first byte of the packet was of type proxy.COM_QUERY.

MySQL Type Constants

These constants are used to identify the field types in the query result data returned to clients from the result of a query. These items are entries within the main proxy table.