On Mon, 30 Nov 2015 08:37:00 +0100
joris dedieu <[email protected]> wrote:
> Hi all,
>
> I started to drive into haproxy's lua interface. I produced a few code
> that allows dnsbl lookup and it seems to work.
>
> First I have a C wrapper against the libc resolver..
>
> #include <netdb.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
> #include <arpa/inet.h>
>
> #include <lua53/lua.h>
> #include <lua53/lauxlib.h>
>
> static int gethostbyname_wrapper(lua_State *L)
> {
> const char* query = luaL_checkstring(L, 1);
> struct hostent *he;
> if ((he = gethostbyname(query)) != NULL) {
> const char *first_addr =
> inet_ntoa(*(struct in_addr*)he->h_addr_list[0]);
> lua_pushstring(L, first_addr);
> return 1;
> }
> return 0;
> }
>
> static const luaL_Reg sysdb_methods[] = {
> {"gethostbyname", gethostbyname_wrapper},
> {NULL, NULL}
> };
>
> LUALIB_API int luaopen_sysdb(lua_State *L) {
> luaL_newlib(L, sysdb_methods);
> return 1;
> }
>
> I have some doubts on the asyncness of libc operations but in other
> side I don't want to reinvent the wheel. Should I prefer a resolver
> implementation that uses lua socket ? As far as I tested libc seems to
> do the job.
Hello,
I confirm your doubts: gethostbyname is synchronous and it is a
blocking call. If your hostname resolution is in the /etc/hosts file,
it blocks while reading file. It it is from DNS server, it blocks
waiting for the server response (or worse: wainting for the timeout).
So, this code seems to run, but your HAProxy will be not efficient
because the entire haproxy process will be blocked during each
resolution. For example: if your DNS fails after 3s timeout, during 3s,
HAProxy doesn't process any data.
Otherwise, your code is the good way to perform fast Lua/C libraries.
There are no way to simulate blocking access out of the HAProxy core,
all the functions writed for Lua must be non block.
> Then the lua code
>
> local sysdb = require("sysdb")
>
> core.register_fetches("rbl", function(txn, rbl, ip)
> if (not ip) then
> ip = txn.sf:src()
> end
> if (not rbl) then
> rbl = "zen.spamhaus.org"
> end
> local query = rbl
> for x in string.gmatch(ip, "[^%.]+") do
> query = x .. '.' .. query
> end
> if(sysdb.gethostbyname(query)) then
> return 1
> else
> return 0
> end
> end)
>
> I want to use a sticky table as a local cache so my second question :
> is there a way to set a gpt0 value from lua ?
You can use the samples fetches mapper and use the sc_set_gpt0. The
syntax is like this:
For the read access:
txn.sf:sc_set_gpt0()
txn.sc:table_gpc0()
For the write access, I don't have direct solution. You must use an Lua
sample fetch and the following configuration directive:
http-request sc-set-gpt0 lua.my_sample_fetch
Maybe it will be a good idea to implement the stick table access in Lua.
If you want a other maneer to store shared data inhaproxy, you can use
maps. The maps are shared by all the HAProxy process including Lua with
a special API (see Map class)
Thierry
