Serves webp as png for Firefox and Safari

webp2png.lua

--[[
 * @Author: esterTion
 * requirement: nginx-lua-module, working ffmpeg
 * explaination: webp decode and png encode speed should be quick enough to serve on the fly. 
 * use under {location ~ .+\.webp$}
 * Currently deployed under https://redive.estertion.win/
]]

local ua=string.lower(ngx.var.http_user_agent)
local file=ngx.var.document_root..ngx.var.uri
if ( (string.match(ua, "safari") and not string.match(ua, 'chrome')) or string.match(ua, "firefox") ) and (os.rename(file, file) and true or false) then
	ngx.header.content_type="image/png"
	local p=io.popen("/usr/local/bin/ffmpeg -hide_banner -loglevel quiet -i \""..file.."\" -f image2 -c:v png -", "r")
	local buf = p:read('*a')
	p:close()
	ngx.header.content_length = string.len(buf)
	ngx.print(buf)
	ngx.exit(200)
end