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:

id: 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.
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 MariaDB 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 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.

The following example injects additional SELECT NOW() statements into the query queue, giving them a different ID to the ID of the original query. Within read_query_result(), if the ID for the injected queries is identified, we display the result row, and return the proxy.PROXY_IGNORE_RESULT from the function so that the result is not returned to the client. If the result is from any other query, we print out the query time information for the query and return the default, which passes on the result set unchanged. We could also have explicitly returned proxy.PROXY_IGNORE_RESULT to the MariaDB client.

function read_query( packet )
 if packet:byte() == proxy.COM_QUERY then
 proxy.queries:append(2, string.char(proxy.COM_QUERY) .. 'SELECT NOW()', {resultset_is_needed = true} )
 proxy.queries:append(1, packet, {resultset_is_needed = true})
 proxy.queries:append(2, string.char(proxy.COM_QUERY) .. 'SELECT NOW()', {resultset_is_needed = true} )
 return proxy.PROXY_SEND_QUERY
 end end function read_query_result(inj)
 if inj.id == 2 then
 for row in inj.resultset.rows do
 print('injected query returned: ' .. row[1])
 end
 return proxy.PROXY_IGNORE_RESULT
 else
 print('query-time: ' .. (inj.query_time / 1000) .. 'ms')
 print('response-time: ' .. (inj.response_time / 1000) .. 'ms')
 end end

For further examples, see , "Using MariaDB Proxy".

Manipulating Results with read_query_result()

Retornar

Manipulating Results with `read_query_result()`