Unable to get data from PostgreSQL using mod_lua

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

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