Unable to get data from PostgreSQL using mod_lua - apache

Question

This is my setup:
OS: Linux Ubuntu 14.04 64bit
DB: Postgres 9.4 (installed from official Postgres repo)
Apache: 2.4.7 with mod_lua manually compiled from source in Apache 2.4.20 and installed
Database init script is as follows:
CREATE TABLE users (
id SERIAL PRIMARY KEY,
client VARCHAR(20) NOT NULL UNIQUE,
secret VARCHAR(20) NOT NULL
);
INSERT INTO users(client, secret) VALUES('john' , 'john' );
INSERT INTO users(client, secret) VALUES('apple', 'orange');
INSERT INTO users(client, secret) VALUES('kiwi' , 'pear' );
INSERT INTO users(client, secret) VALUES('peach', 'berry' );
Apache has enabled mod_dbd that is configured as follows:
<IfModule dbd_module>
DBDriver pgsql
DBDPersist on
DBDMax 20
DBDParams "host='localhost' port='5432' dbname='demousers' user='postgres' password='postgres'"
DBDPrepareSQL 'SELECT u.secret FROM users u WHERE u.client=%s' client_secret
</IfModule>
There is also mod_lua which is configured like this:
<IfModule lua_module>
LuaRoot /vagrant/luatest
LuaScope thread
LuaCodeCache stat
LuaHookAccessChecker /vagrant/luatest/cookie_handler.lua handler early
LuaHookAccessChecker /vagrant/luatest/handler.lua handler late
</IfModule>
This is the sample code that I'm trying to execute in handler.lua that fails:
require "string"
require "apache2"
local inspect = require "inspect"
function handler(r)
local db, err = r:dbacquire()
if not db then
r:debug("[500] DB Error: " .. err)
return 500
end
r:debug("Acquired database")
local statement, errmsg = db:prepared(r, "client_secret")
if not statement then
r:debug("[500] DB Error: " .. errmsg)
db:close()
return 500
end
r:info("Acquired prepared statement")
local secret
local result, emsg = statement:select("john")
if not emsg then
r:info("Fetch rows")
local rows = result(0, true)
r:debug("Rows " .. inspect(rows))
for k, row in pairs(rows) do
r:info("Pass " .. k .. inspect(row))
if row[1] then
secret = string.format("%s", row[1])
end
end
else
r:debug( "Error : " .. emsg)
end
db:close()
return 403
end
Looking at the postgres sql log I see that the query was correctly executed and parameter passed. The issue is that I get the record that has no values just nil placeholders in lua table - rows is like this
{ {} }
So, is this a bug or my mistake?

Answer 1

Unfortunately it is a bug. For details see:
https://bz.apache.org/bugzilla/show_bug.cgi?id=56379

Answer 2

This is the solution that fixes the problem
# Install Apache 2.4.10 from backports repo that has working mod_lua
sudo apt-get install -y -t trusty-backports apache2 apache2-dev apache2-utils
sudo apt-get install -y libaprutil1-dbd-pgsql
# Install lua dependencies
sudo apt-get build-dep -y lua5.1
sudo apt-get install -y lua5.1
sudo apt-get install -y liblua5.1-0-dev
# Get the source code
APACHEVER='2.4.10'
cd /tmp/
apt-get source -y apache2="$APACHEVER"
mv "apache2-$APACHEVER/modules/lua/lua_dbd.c" "apache2-$APACHEVER/modules/lua/lua_dbd.c_original"
# Applying the patch for https://bz.apache.org/bugzilla/show_bug.cgi?id=56379
# without it dbd + lua + postgres do not work - you need to previously prepare the patched c file
cp -u /vagrant/lua_dbd.c "apache2-$APACHEVER/modules/lua/"
cd "apache2-$APACHEVER/modules/lua"
# Build and install patched lua module
sudo apxs -I/usr/include/lua5.1 -cia mod_lua.c lua_*.c -lm -llua5.1
sudo service apache2 restart