Add convert image to webp support for nginx

cwebp.lua

---------------------------  Function  ---------------------------------

function file_exists(name)
    local f=io.open(name,"r")
    if f~=nil then io.close(f) return true else return false end
end

------------------------------------------------------------------------

if ngx ~= nil then
    local reqpath = ngx.var.request_filename;
    local requri = ngx.var.uri;
    local originalFile = reqpath:sub(1, #reqpath - 13);
    local originalFile_uri = requri:sub(1, #requri - 13);

    if not file_exists(originalFile) then
        ngx.exit(404);
        return;
    end

    local newFile_md5 = ngx.md5(originalFile_uri);
    local newFile = ngx.var.document_root .. "/wp-content/webp/" .. newFile_md5 ..".webp";
    local newFile_uri = "/wp-content/webp/" .. newFile_md5 .. ".webp";

    if file_exists(newFile) then
        ngx.req.set_uri(newFile_uri);
        ngx.exec(ngx.var.uri);
        return;
    end

    os.execute("cwebp -quiet " .. originalFile  .. " -o " .. newFile);

    if file_exists(newFile) then
        ngx.req.set_uri(newFile_uri);
    else
        ngx.req.set_uri(originalFile_uri);
    end

    ngx.exec(ngx.var.uri);
end

https://kn007.net/topics/add-convert-image-to-webp-support-for-nginx/