Get bytes sent to client

Hello.
I'd like to collect some statistics in my application (using JDBC). In
Oracle I could collect data, sent to client, using the following query:

SELECT S.value FROM V$MYSTAT S,SYS.V_$STATNAME NAMES
WHERE NAMES.STATISTIC#=S.STATISTIC#
AND NAMES.NAME='bytes sent via SQL*Net to client';

Can I do something like this in PostgreSQL? I'd like to estimate query
result size, to be more precise, amount of network traffic, which is
generated in response to a query.

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Best regards,
Alexander Pyhalov,
system administrator of Computer Center of South Federal University