84 lines
3.0 KiB
Lua
84 lines
3.0 KiB
Lua
--[[ A telnet server T. Ellison, May 2018
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This version is more complex than the simple Lua example previously provided in our
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distro. The main reason is that a single Lua command can produce a LOT of output,
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and the server has to work within four constraints:
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- The SDK rules are that you can only issue one send per task invocation, so any
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overflow must be buffered, and the buffer emptied using an on:sent cb
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- Since the interpeter invokes a node.output cb per field, you have a double
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whammy that these fields are typically small, so using a simple array FIFO
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would rapidly exhaust RAM.
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- For network efficiency, you want to aggregate any FIFO buffered into sensible
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sized packet, say 1024 bytes, but you also need to handle the case when larger
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string span multiple packets. However, you must flush the buffer if necessary.
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- The overall buffering strategy needs to be reasonably memory efficient and avoid
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hitting the GC too hard, so where practical avoid aggregating small strings to
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more than 256 chars (as NodeMCU handles <256 using stack buffers), and avoid
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serial aggregation such as buf = buf .. str as this hammers the GC.
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So this server adopts a simple buffering scheme using a two level FIFO. The node.output
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cb adds cb records to the 1st level FIFO until the #recs is > 32 or the total size
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would exceed 256 bytes. Once over this threashold, the contents of the FIFO are
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concatenated into a 2nd level FIFO entry of upto 256 bytes, and the 1st level FIFO
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cleared down to any residue.
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]]
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local node, table, tmr, wifi, uwrite, tostring =
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node, table, tmr, wifi, uart.write, tostring
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local function telnet_listener(socket)
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local queueLine = (require "fifosock").wrap(socket)
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local function receiveLine(s, line)
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node.input(line)
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end
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local function disconnect(s)
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socket:on("disconnection", nil)
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socket:on("reconnection", nil)
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socket:on("connection", nil)
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socket:on("receive", nil)
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socket:on("sent", nil)
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node.output(nil)
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end
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socket:on("receive", receiveLine)
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socket:on("disconnection", disconnect)
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node.output(queueLine, 0)
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print(("Welcome to NodeMCU world (%d mem free, %s)"):format(node.heap(), wifi.sta.getip()))
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end
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local listenerSocket
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return {
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open = function(this, ssid, pwd, port)
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if ssid then
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wifi.setmode(wifi.STATION, false)
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wifi.sta.config { ssid = ssid, pwd = pwd, save = false }
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end
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local t = tmr.create()
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t:alarm(500, tmr.ALARM_AUTO, function()
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if (wifi.sta.status() == wifi.STA_GOTIP) then
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t:unregister()
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t=nil
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print(("Telnet server started (%d mem free, %s)"):format(node.heap(), wifi.sta.getip()))
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net.createServer(net.TCP, 180):listen(port or 23, telnet_listener)
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else
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uwrite(0,".")
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end
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end)
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end,
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close = function(this)
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if listenerSocket then
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listenerSocket:close()
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package.loaded.telnet = nil
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listenerSocket = nil
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collectgarbage()
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end
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end,
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}
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