为什么我无法从 tcp 服务器得到响应？

Question

I have (ESP32 based) device that among other things implements TCP server. I can send to it messages in JSON format to change some controls in it.

I want to be able to control this device from my Android phone. I wrote an app for it, but I have a problem - my Android app doe not get any response from ESP32 device. I wrote for tests simple scripts in Python. First one is a client, that sends messages to ESP32. Second one implements tcp server, so that I can connect my Android app to it and check if response arrives. Both tests works fine.

Is there anything wrong in my Android code? I cannot be sure if it is not ESP32 device fault, but please first check my Android code - it is harder to make MCVE from C code for ESP32.

Here is my Android app's MCVE:

MainActivity.java:

package com.example.tcpclienttest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;

public class MainActivity extends AppCompatActivity {

    String TAG = "******** INFO ********";

    Socket tcpSocket;
    InetAddress IP;
    int tcpPort = 12345;
    PrintWriter mBufferOut;
    BufferedReader mBufferIn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button = this.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new Thread(new Runnable() {
                    public void run() {
                        // try twice in case of tcp error
                        if (SendSetStateCommandTaskFunction()) {
                            Log.i(TAG, "Retrying SendSetStateCommandTask function");
                            SendSetStateCommandTaskFunction();
                        }
                    }
                }).start();

            }
        });
    }

    boolean SendSetStateCommandTaskFunction() {

        boolean retry = false;



        String request_data = "'{\"cmd\":\"set_controls\", \"data\":{\"controls\":{\"name1\":5}}}'";

        try {
            IP = InetAddress.getByName("192.168.1.66");
            if (tcpSocket == null) {
                Log.i(TAG, "Creating new tcp socket");
                tcpSocket = new Socket(IP, tcpPort);
                tcpSocket.setSoTimeout(3000);
                //sends the message to the server
                mBufferOut =
                        new PrintWriter(
                                new BufferedWriter(
                                        new OutputStreamWriter(tcpSocket.getOutputStream())), true);

                //receives the message which the server sends back
                mBufferIn =
                        new BufferedReader(
                                new InputStreamReader(tcpSocket.getInputStream()));
            } else
                Log.i(TAG, "Tcp socket already created");
            if (!tcpSocket.isConnected()) {
                Log.i(TAG, "Connecting to ip addr");
                SocketAddress sockaddr = new InetSocketAddress(IP, tcpPort);
                tcpSocket.connect(sockaddr);
            } else
                Log.i(TAG, "Already connected");

            String in_message;

            mBufferOut.println(request_data);
            mBufferOut.flush();

            in_message = mBufferIn.readLine();

            if (in_message == null) {
                Log.i(TAG, "Received empty message");
                return false;
            }

            Log.i(TAG, in_message);
        } catch (IOException e) {
            Log.e(TAG, "ERROR: " + e.getMessage());
            e.printStackTrace();
            tcpSocket = null;
            retry = true;
        }

        Log.i(TAG, "Finishing SendSetStateCommandTask function");
        return retry;
    }
}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.tcpclienttest">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

main_activity.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Send"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Python client:

import socket
import json

TCP_IP = "192.168.1.66"
TCP_PORT = 12345

print("TCP target IP:", TCP_IP)
print("TCP target port:", TCP_PORT)

sock = socket.socket(socket.AF_INET, # Internet
                     socket.SOCK_STREAM) # TCP
sock.connect((TCP_IP, TCP_PORT))

MESSAGE = str.encode('{"cmd":"set_controls", "data":{"controls":{"name1":6}}}')

print("message:", MESSAGE)

sock.send(MESSAGE)

data = sock.recv(1024)  # buffer size is 1024 bytes
json_data = json.loads(data.decode("ascii"))
print("received message:")
print(json.dumps(json_data, indent=4))

Python server:

#!/usr/bin/env python

import socket

TCP_IP = ''
TCP_PORT = 12345
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(1)

conn, addr = s.accept()
print('Connection address:', addr)
while 1:
    data = conn.recv(BUFFER_SIZE)
    if not data:
        break
    print("received data:", data)
    conn.send(data)  # echo
conn.close()

Console log from the app lanuch, after clicking SEND button:

I/ViewRootImpl: jank_removeInvalidNode all the node in jank list is out of time
V/AudioManager: playSoundEffect   effectType: 0
    querySoundEffectsEnabled...
I/******** INFO ********: Creating new tcp socket
I/******** INFO ********: Already connected
E/******** INFO ********: ERROR: Read timed out
W/System.err: java.net.SocketTimeoutException: Read timed out
W/System.err:     at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.socketRead(SocketInputStream.java:119)
W/System.err:     at java.net.SocketInputStream.read(SocketInputStream.java:176)
        at java.net.SocketInputStream.read(SocketInputStream.java:144)
        at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:288)
W/System.err:     at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:351)
        at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:180)
W/System.err:     at java.io.InputStreamReader.read(InputStreamReader.java:184)
        at java.io.BufferedReader.fill(BufferedReader.java:172)
W/System.err:     at java.io.BufferedReader.readLine(BufferedReader.java:335)
        at java.io.BufferedReader.readLine(BufferedReader.java:400)
        at com.example.tcpclienttest.MainActivity.SendSetStateCommandTaskFunction(MainActivity.java:93)
W/System.err:     at com.example.tcpclienttest.MainActivity$1$1.run(MainActivity.java:44)
        at java.lang.Thread.run(Thread.java:784)
I/******** INFO ********: Finishing SendSetStateCommandTask function
I/******** INFO ********: Retrying SendSetStateCommandTask function
    Creating new tcp socket
I/******** INFO ********: Already connected
E/******** INFO ********: ERROR: Read timed out
W/System.err: java.net.SocketTimeoutException: Read timed out
W/System.err:     at java.net.SocketInputStream.socketRead0(Native Method)
W/System.err:     at java.net.SocketInputStream.socketRead(SocketInputStream.java:119)
        at java.net.SocketInputStream.read(SocketInputStream.java:176)
W/System.err:     at java.net.SocketInputStream.read(SocketInputStream.java:144)
        at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:288)
        at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:351)
W/System.err:     at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:180)
        at java.io.InputStreamReader.read(InputStreamReader.java:184)
W/System.err:     at java.io.BufferedReader.fill(BufferedReader.java:172)
        at java.io.BufferedReader.readLine(BufferedReader.java:335)
W/System.err:     at java.io.BufferedReader.readLine(BufferedReader.java:400)
        at com.example.tcpclienttest.MainActivity.SendSetStateCommandTaskFunction(MainActivity.java:93)
        at com.example.tcpclienttest.MainActivity$1$1.run(MainActivity.java:46)
W/System.err:     at java.lang.Thread.run(Thread.java:784)
I/******** INFO ********: Finishing SendSetStateCommandTask function

Answer 1

The problem was probably related to lack of new line character at the end of the response. Adding it didn't help instantly, but after some more changes in the server, Android app started to be able to get the response. I cannot tell what exactly was the problem after adding the new line character.