Android & NodeMCU，无法正常接收来自服务器的响应？

Question

我在Android上写了一个应用程序，它实现了向服务器发送简单的请求（使用Volley）。服务器架设在 NodeMCU (ESP8266) 微控制器上，用 Lua 编写。问题是，在发送请求后，应用程序并不总是能够打印响应。如果地址是例如“http://www.google.com”它正确发送请求并接收和显示响应，但如果它是来自下面代码的地址 - 它正确发送请求（服务器反应）但不（？）接收响应（不显示它, 显示："That didn't work!")。你有什么想法，我该如何解决它并能够打印回复？

Android（负责发送请求的部分）：

buttonSynchro.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {


        // Instantiate the RequestQueue.
        String url = "http://192.168.1.12/";


        // Request a string response from the provided URL.
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // Display the first 500 characters of the response string.
                        testTextView.setText("Response is: "+ response.substring(0,500));
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                testTextView.setText("That didn't work!");
            }
        });


        // Add the request to the RequestQueue.
        RequestQueue queue = Volley.newRequestQueue(SettingsActivity.this);
        queue.add(stringRequest);
    }
});

NodeMCU, Lua:

station_cfg={}
station_cfg.ssid="Dom"
station_cfg.pwd="lalala"
wifi.sta.config(station_cfg)
function receive(conn, request)
        print(request)
        print()
        local buf = "";
        buf = buf.."<!doctype html><html>";
        buf = buf.."<h1> ESP8266 Web Server</h1>";
        buf = buf.."</html>";

        conn:send(buf);
        conn:on("sent", function(sck) sck:close() end);     
        collectgarbage();

end

function connection(conn) 
    conn:on("receive", receive) 

end

srv=net.createServer(net.TCP, 30) 
srv:listen(80, connection)

Answer 1

我不是 Lua 专家，但我认为您是在 发送响应后 注册 "sent" 回调。

我认为你应该把它移到连接函数中：

station_cfg={}
station_cfg.ssid="Dom"
station_cfg.pwd="lalala"
wifi.sta.config(station_cfg)
function receive(conn, request)
        print(request)
        print()
        local buf = "";
        buf = buf.."<!doctype html><html>";
        buf = buf.."<h1> ESP8266 Web Server</h1>";
        buf = buf.."</html>";
        conn:send(buf);  
        collectgarbage();

end

function connection(conn) 
    conn:on("receive", receive) 
    conn:on("sent", function(sck) sck:close() end);   
end

srv=net.createServer(net.TCP, 30) 
srv:listen(80, connection)

Answer 2

nPn 的代码在某些用户代理（macOS 上的 Chrome/Firfox/curl/wget）中有效，但在其他用户代理中无效（macOS 上的 Safari 和 iOS，iOS 上的 Firefox Klar）。这可能是由于缺少 HTTP headers.

我建议您坚持使用我们在 https://nodemcu.readthedocs.io/en/latest/en/modules/net/#netsocketsend.

文档中的示例

srv = net.createServer(net.TCP)

function receiver(sck, data)
  print(data)
  print()

  -- if you're sending back HTML over HTTP you'll want something like this instead
  local response = {"HTTP/1.0 200 OK\r\nServer: NodeMCU on ESP8266\r\nContent-Type: text/html\r\n\r\n"}

  response[#response + 1] = "<!doctype html><html>"
  response[#response + 1] = "<h1> ESP8266 Web Server</h1>"
  response[#response + 1] = "</html>"

  -- sends and removes the first element from the 'response' table
  local function send(localSocket)
    if #response > 0 then
      localSocket:send(table.remove(response, 1))
    else
      localSocket:close()
      response = nil
    end
  end

  -- triggers the send() function again once the first chunk of data was sent
  sck:on("sent", send)

  send(sck)
end

srv:listen(80, function(conn)
  conn:on("receive", receiver)
end)

此外，您的代码（以及 nPn 的代码）假设 WiFi 在不可用的地方可用。

wifi.sta.config(station_cfg) (with auto-connect=true) and wifi.stat.connect are asynchronous and thus non-blocking - as are many other NodeMCU APIs. Hence, you should put the above code into a function and only call it once the device is connected to the AP and got an IP. You do that by e.g. registering a callback for the STA_GOT_IP event with the WiFi event monitor. You'll find a very elaborate example of a boot sequence that listens to all WiFi events at https://nodemcu.readthedocs.io/en/latest/en/upload/#initlua。对于初学者，您可能想要 trim 这个并且只听 got-IP.

Answer 3

根据您上面的评论和您发布的显示回溯的 link，您的 android 应用程序在 onResponse() 方法中崩溃，因为您要求的子字符串比实际字符串长长度。

您可以通过多种方式解决此问题，但一种方法是使结束索引为响应长度和 500 中的最小值（我假设这是您可以在 TextView 中使用的最大值？） .你可以尝试改变

testTextView.setText("Response is: "+ response.substring(0,500));

到

testTextView.setText("Response is: "+ response.substring(0, Math.min(response.length(), n)));

或您认为更合适的任何其他方式来限制不会导致 IndexOutOfBoundsException

的响应的长度

看子串方法here

public String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Examples:
 "hamburger".substring(4, 8) returns "urge"
 "smiles".substring(1, 5) returns "mile"
Parameters: beginIndex - the beginning index, inclusive. endIndex - the ending index, exclusive. Returns: the specified substring. Throws: IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

Android & NodeMCU，无法正常接收来自服务器的响应？

Android & NodeMCU, receiving response from server does not work properly?

java

lua

android

nodemcu

esp8266