语法: data, err = udpsock:receive(size?)
环境: rewrite_by_lua, access_by_lua*, content_by_lua*, ngx.timer.**
使用一个可选的接收缓冲区大小参数 size ，从 UDP 或 unix 域数据报 socket 对象中读取数据。
该方法是异步操作并且 100% 非阻塞。
成功情况，返回已经接收的数据；错误情况，返回 nil 和错误描述信息。
如果指定了 size 参数，该方法将使用它作为缓冲区大小。但是当该值比 8192 大时，将继续使用 8192 这个大小。
如果没有参数指定，那么最大的缓冲区大小，将假定 8192 。
读操作超时控制，是由 lua_socket_read_timeout 配置指令和 settimeout 方法设置的。而后者有更高的优先级，例如：
sock:settimeout(1000) -- one second timeout
local data, err = sock:receive()
if not data then
ngx.say("failed to read a packet: ", data)
return
end
ngx.say("successfully read a packet: ", data)调用这个方法 之前 调用 settimeout 方法设置超时时间，是非常重要的。
该特性是在 v0.5.7 版本首次引入的。
English source:
syntax: data, err = udpsock:receive(size?)
context: rewrite_by_lua, access_by_lua*, content_by_lua*, ngx.timer.**
Receives data from the UDP or datagram unix domain socket object with an optional receive buffer size argument, size.
This method is a synchronous operation and is 100% nonblocking.
In case of success, it returns the data received; in case of error, it returns nil with a string describing the error.
If the size argument is specified, then this method will use this size as the receive buffer size. But when this size is greater than 8192, then 8192 will be used instead.
If no argument is specified, then the maximal buffer size, 8192 is assumed.
Timeout for the reading operation is controlled by the lua_socket_read_timeout config directive and the settimeout method. And the latter takes priority. For example:
sock:settimeout(1000) -- one second timeout
local data, err = sock:receive()
if not data then
ngx.say("failed to read a packet: ", data)
return
end
ngx.say("successfully read a packet: ", data)It is important here to call the settimeout method before calling this method.
This feature was first introduced in the v0.5.7 release.