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connect_server()
read_handshake()
read_auth()
read_auth_result()
read_query()
read_query_result()
You can control how MySQL Proxy manipulates and works with the queries and results that are passed on to the MySQL server through the use of the embedded Lua scripting language. You can find out more about the Lua programming language from the Lua Website.
The primary interaction between MySQL Proxy and the server is provided by defining one or more functions through an Lua script. A number of functions are supported, according to different events and operations in the communication sequence between a client and one or more backend MySQL servers:
connect_server()
— this function is
called each time a connection is made to MySQL Proxy from a
client. You can use this function during load-balancing to
intercept the original connection and decide which server the
client should ultimately be attached to. If you do not define
a special solution, then a simple round-robin style
distribution is used by default.
read_handshake()
— this function is
called when the initial handshake information is returned by
the server. You can capture the handshake information returned
and provide additional checks before the authorization
exchange takes place.
read_auth()
— this function is
called when the authorization packet (user name, password,
default database) are submitted by the client to the server
for authentication.
read_auth_result()
— this function
is called when the server returns an authorization packet to
the client indicating whether the authorization succeeded.
read_query()
— this function is
called each time a query is sent by the client to the server.
You can use this to edit and manipulate the original query,
including adding new queries before and after the original
statement. You can also use this function to return
information directly to the client, bypassing the server,
which can be useful to filter unwanted queries or queries that
exceed known limits.
read_query_result()
— this function
is called each time a result is returned from the server,
providing you have manually injected queries into the query
queue. If you have not explicitly inject queries within the
read_query()
function then this function
is not triggered. You can use this to edit the result set, or
to remove or filter the result sets generated from additional
queries you injected into the queue when using
read_query()
.
The table below describes the direction of flow of information at the point when the function is triggered.
Function | Supplied Information | Direction |
---|---|---|
connect_server() |
None | Client to Server |
read_handshake() |
None | Server to Client |
read_auth() |
None | Client to Server |
read_auth_result() |
None | Server to Client |
read_query() |
Query | Client to Server |
read_query_result() |
Query result | Server to Client |
By default, all functions return a result that indicates that the
data should be passed on to the client or server (depending on the
direction of the information being transferred). This return value
can be overridden by explicitly returning a constant indicating
that a particular response should be sent. For example, it is
possible to construct result set information by hand within
read_query()
and to return the resultset
directly to the client without ever sending the original query to
the server.
In addition to these functions, a number of built-in structures provide control over how MySQL Proxy forwards on queries and returns the results by providing a simplified interface to elements such as the list of queries and the groups of result sets that are returned.
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