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MySQL Proxy Scripting

1419

• Unless your client is designed to cope with more result sets than queries, you should ensure that the

number of queries from the client match the number of results sets returned to the client. Using the
unique ID and removing result sets you inserted will help.

Normally, the

read_query()

and

read_query_result()

function are used in conjunction

with each other to inject additional queries and remove the additional result sets. However,

read_query_result()

is only called if you populate the query queue within

read_query()

15.7.4.8. Manipulating Results with

read_query_result()

The

read_query_result()

is called for each result set returned by the server only if you have

manually injected queries into the query queue. If you have not manipulated the query queue, this
function is not called. The function supports a single argument, the result packet, which provides a
number of properties:

•

: The ID of the result set, which corresponds to the ID that was set when the query packet was

submitted to the server when using

append(id)

on the query queue. You must have set the

resultset_is_needed

flag to

append

to intercept the result set before it is returned to the client.

See

proxy.queries [1411]

•

query

: The text of the original query.

•

query_time

: The number of microseconds required to receive the first row of a result set since the

query was sent to the server.

•

response_time

: The number of microseconds required to receive the last row of the result set

since the query was sent to the server.

•

resultset

: The content of the result set data.

By accessing the result information from the MySQL server, you can extract the results that match the
queries that you injected, return different result sets (for example, from a modified query), and even
create your own result sets.

The following Lua script, for example, will output the query, followed by the query time and response
time (that is, the time to execute the query and the time to return the data for the query) for each query
sent to the server:

function read_query( packet )

if packet:byte() == proxy.COM_QUERY then

print("we got a normal query: " .. packet:sub(2))

proxy.queries:append(1, packet )

return proxy.PROXY_SEND_QUERY

end

function read_query_result(inj)

print("query-time: " .. (inj.query_time / 1000) .. "ms")

print("response-time: " .. (inj.response_time / 1000) .. "ms")

end

You can access the rows of returned results from the result set by accessing the

rows

property of the

resultset

property of the result that is exposed through

read_query_result()

. For example, you

can iterate over the results showing the first column from each row using this Lua fragment:

for row in inj.resultset.rows do

print("injected query returned: " .. row[1])

end

Just like

read_query()

read_query_result()

can return different values for each result

according to the result returned. If you have injected additional queries into the query queue, for
example, remove the results returned from those additional queries and return only the results from the
query originally submitted by the client.

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