Lua Trigger Functions » History » Revision 2
Revision 1 (gstrauss, 2022-05-11 20:39) → Revision 2/3 (gstrauss, 2022-05-11 21:42)
h1. Lua Trigger Functions
lighttpd [[Docs_ModMagnet|mod_magnet]] can be configured to send a trigger to another process when a specific event occurs.
h3. lua trigger functions
h4. trigger_sock: send trigger to socket
<pre>
function trigger_sock (addr, port, msg)
-- connect and send msg to socket
-- note: *blocking* connect() (and blocking send() unless msg is short)
-- (caller should prefer addr "127.0.0.1" to succeed or fail fast)
local socket = require("socket")
local s = socket.tcp4()
if (not s) then return false end
s:settimeout(1)
local rc = false
if (s:connect(addr, port)) then
local wr = s:send(msg)
if (wr and wr == msg:len()) msg.len) then rc = true end
end
s:close()
return rc
end
</pre>
h4. trigger_fifo: send trigger to FIFO
<pre>
function trigger_fifo (path, msg)
-- write msg to fifo; non-blocking; tries once or fails
-- (requires luaposix)
-- (lua-posix package or see https://github.com/luaposix/luaposix)
local P = require "posix.fcntl"
local fd = P.open(path, P.O_WRONLY | P.O_NONBLOCK | P.O_CLOEXEC)
if (not fd) then return false end
local unistd = require "posix.unistd"
local wr = unistd.write(fd, msg);
unistd.close(fd)
return (wr and wr == msg:len()) msg.len)
-- lua 5.3+ supports bitwise operations (used above)
--local fd = P.open(path, P.O_WRONLY | P.O_NONBLOCK | P.O_CLOEXEC)
-- lua 5.2 provides bit32 table of functions
--local fd = P.open(path, bit32.bor(P.O_WRONLY, P.O_NONBLOCK, P.O_CLOEXEC))
-- luaJIT
--local bit = require("bit")
--local fd = P.open(path, bit.bor(P.O_WRONLY, P.O_NONBLOCK, P.O_CLOEXEC))
-- lua 5.1 needs an alternative bit operator implementation
-- (if running lua 5.1 from before bit32 was backported to the lua 5.1 series)
-- https://lua-users.org/wiki/BitwiseOperators
--(not implemented here for lua 5.1)
end
</pre>
h4. trigger_execp_bg: trigger command execution in background
<pre>
function trigger_execp_bg (path, argt)
-- execute command in background (fork(), setsid(), fork(), execp())
-- (requires luaposix)
-- (lua-posix package or see https://github.com/luaposix/luaposix)
local unistd = require "posix.unistd"
-- fork()
local pid, _ = unistd.fork()
if pid == nil then -- error
return -1
elseif pid ~= 0 then -- parent
local syswait = require "posix.sys.wait"
local reaped, _, status = syswait.wait(pid)
return reaped == pid and status or -1
end -- child (pid == 0)
-- setsid()
if (not unistd.setpid('s', 0)) then -- setsid
unistd._exit(-1)
end
-- fork()
pid, _ = unistd.fork()
if pid == nil then -- error
unistd._exit(-1)
elseif pid ~= 0 then -- parent
unistd._exit(0)
end -- child (pid == 0)
-- execp()
unistd.execp(path, argt)
unistd._exit(-1)
end
</pre>
h3. lua trigger examples
h4. thumbnail-trigger.lua
The example below triggers thumbnail creation (by an external process) following successful upload of an image file.
<pre>
-- thumbnail-trigger.lua for lighttpd mod_magnet
--
-- trigger a script to generate a thumbnail after successful PUT of an image file
--
-- lighttpd.conf
-- server.modules += ("mod_magnet")
-- $HTTP["method"] == "PUT" {
-- magnet.attract-response-start-to = ("/path/to/thumbnail-trigger.lua")
-- }
local r = lighty.r
local req_attr = r.req_attr
-- check for successful PUT request with HTTP status 201 or 204
-- lighttpd 1.4.60 - 1.4.65 (to be removed in 1.4.66)
--local http_status = req_attr["response.http-status"]
-- lighttpd 1.4.65+
local http_status = r.req_item.http_status
if (not http_status == 201 and not http_status == 204) then return 0 end
-- (method is checked in lighttpd.conf sample in comment at top)
--if (not req_attr["request.method"] == "PUT") then return 0 end
-- get file path components
local path = req_attr["physical.path"]
local dir, file, ext = string.match(path, "^(.*/)([^/]+)([.][%a%d]+)$")
if (not ext) then return 0 end
-- check for .jpg (or list of extensions for which to trigger)
-- TODO: (as needed)
if (not ext == ".jpg") then return 0 end
-- string manipulation on path to get path to thumbnail
-- TODO: (as needed)
local thumb = dir .. "thumbs/" .. file .. ext
-- trigger thumbnail update
-- TODO: fill in and call chosen trigger method
-- (Functions must be defined before being called)
-- (e.g. copy reference code implementation into script)
--trigger_sock("127.0.0.1", 8888, path .. " " .. thumb .. "\n")
--trigger_fifo("/path/to/thumbnail.fifo", path .. " " .. thumb .. "\n")
--trigger_execp_bg("/path/to/thumbnail.py, { path, thumb })
return 0
</pre>