serial-port - 读取串行输入，直到控制字符指示消息结束

Question

我正在使用 knewter/erlang-serial使用 Elixir 并尝试读取一个 JSON 字符串(例如 {"temperature":20.40,"humidity":30.10} 在收到控制信号后通过串行输入从 Arduino 传入:

defmodule MyApp.SerialInput do
  require Logger


  def start_link do
    serial_pid = :serial.start [{:open, "/dev/cu.usbmodem1431"}, {:speed, 115200}]

    control_signal = "1"
    :timer.send_interval 5000, serial_pid, {:send, control_signal}

    wait_for_new_values serial_pid
  end


  defp wait_for_new_values(serial_pid) do
    receive do
      {:data, jsonString} when is_binary(jsonString) ->
        Logger.debug "received :data #{inspect jsonString}"

    wait_for_new_values serial_pid
  end
end

我现在的问题是，我将串行输入拆分成这样(有时它会立即通过):

[debug] received :data "{\"t"
[debug] received :data "emperature\":19.00,\"humidity\":42.00}\r\n"

[debug] received :data "{\"temperature\":19.60,\"humidity\":41"
[debug] received :data ".00}\r\n"

[debug] received :data "{\"temperature\":19.50,\"humidity\":40.90}\r\n"

[debug] received :data "{\"temperature\":19.50,\"humi"
[debug] received :data "dity\":40.90}\r\n"

[debug] received :data "{\"temperat"
[debug] received :data "ure\":19.50,\"humidity\":41.30}\r\n"

有没有办法告诉接收 block 等待直到\r\n出现在字符串的末尾或固定数量的字符或类似的东西那？如果不是，在 wait_for_new_values 之外保持状态的最佳方法是什么，直到 \r\n 出现然后连接这些？

Answer 1

receive block 是一个非常低级的函数，因此它不能做这样专门的事情。

Elixir 中的状态是显式的，可以通过可选参数累加器(在本例中为 acc)来实现。您可以稍后将累加值传递给递归调用，并且仅在它以 "\r\n" 结尾时打印它。

defp wait_for_new_values(serial_pid, acc \\ "") do
  receive do
    {:data, chunk} when is_binary(chunk) ->
      acc = acc + chunk
  end

  if String.ends_with? acc, "\r\n"
    Logger.debug "received :data #{inspect acc}"
    acc = ""
  end

  wait_for_new_values serial_pid, acc
end