Python（Server）从Java（client）接收数据，在单独的行中..（TCP）

Question

Okay so I read many questions and couldn't figure it out. I am facing problem with the data which I receive from my Android App. Basically I want to control a servo. The code works, but the data sent by the app to the server is received in separate lines. Yes i know i need to use buffer, I researched a bit but couldn't find a way to add a buffer to my code. Also I don't think I need to show my Java Code because its just basic Commands (Strings like Up, Down, etc) Sending from the Button Clicks.

...Python Code(Server)...
  ctrCmd = ['Up','Down', 'ON', 'OFF']
  ...
  ...
  while True:
        print ("Waiting for connection")
        tcpCliSock,addr = tcpSerSock.accept()
        print ("...connected from :", addr)

    try:
            while True:
                    data = ''
                    data = tcpCliSock.recv(BUFSIZE).decode()
                    print("This",data)

                    if not data:
                            print ("No Data",data)
                            break
                    if data == ctrCmd[0]:
                            print("I am here")
                            Servomotor.ServoUp()
                            print ("Increase: ",Servomotor.cur_X)
                            #tcpCliSock.send("Servo Increases".encode())
                    if data == ctrCmd[1]:
                            Servomotor.ServoDown()
                            print ("Decrease: ",Servomotor.cur_X)
                            #tcpCliSock.send("Servo Decreases".encode())
                    if data == ctrCmd[2]:
                            Servomotor.ledOn()
                            print ("Led On")
                            #tcpCliSock.send("Led On".encode())
                    if data == ctrCmd[3]:
                            Servomotor.ledOff()
                            print ("Led Off")
                           # tcpCliSock.send("Led Off".encode())
    except KeyboardInterrupt:
            Servomotor.close()
            GPIO.cleanup()
tcpSerSock.close();

Also i dont understand why it says No data even when it shows recieved data? Please Help I'm really a noob and am trying to learn. THANKS!!

UPDATE!! After I changed the decode() Suggested,

    public class MainActivity extends AppCompatActivity {
    //UI Element
    Button btnUp;
    Button btnDown;
    Button btnLedOn;
    Button btnLedOff;
    EditText txtAddress;
    /*TextView message;*/
    Socket myAppSocket = null;
    public static String wifiModuleIp = "";
    public static int wifiModulePort = 0;
    public static String CMD = "0";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnUp = (Button) findViewById(R.id.btnUp);
        btnDown = (Button) findViewById(R.id.btnDown);
        btnLedOn = (Button) findViewById(R.id.btnLedOn);
        btnLedOff = (Button) findViewById(R.id.btnLedOff);
        txtAddress = (EditText) findViewById(R.id.ipAddress);
        /*message = (TextView) findViewById(R.id.message);*/

        btnUp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "Up";
                Socket_AsyncTask cmd_increase_servo = new Socket_AsyncTask();
                cmd_increase_servo.execute();
            }
        });
        btnDown.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "Down";
                Socket_AsyncTask cmd_increase_servo = new Socket_AsyncTask();
                cmd_increase_servo.execute();
            }
        });
        btnLedOn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();;
                CMD = "ON";
                Socket_AsyncTask cmd_led_on = new Socket_AsyncTask();
                cmd_led_on.execute();
            }
        });
        btnLedOff.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "OFF";
                Socket_AsyncTask cmd_led_off = new Socket_AsyncTask();
                cmd_led_off.execute();
            }
        });

    }
    public void getIPandPort()
    {
        String iPandPort = txtAddress.getText().toString();

        Log.d("MYTEST","IP String: "+ iPandPort);
        String temp[]= iPandPort.split(":");
        wifiModuleIp = temp[0];
        wifiModulePort = Integer.valueOf(temp[1]);
        Log.d("MY TEST","IP:" +wifiModuleIp);
        Log.d("MY TEST","PORT:"+wifiModulePort);
    }
    public class Socket_AsyncTask extends AsyncTask<Void,Void,Void>
    {
        Socket socket;

        @Override
        protected Void doInBackground(Void... params){

            try{

                InetAddress inetAddress = InetAddress.getByName(MainActivity.wifiModuleIp);
                socket = new java.net.Socket(inetAddress,MainActivity.wifiModulePort);
                //read input msg from server

                DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
                dataOutputStream.writeBytes(CMD);
                System.out.println(CMD);
                dataOutputStream.close();

                socket.close();
            }catch (UnknownHostException e){e.printStackTrace();}catch (IOException e){e.printStackTrace();}
            return null;
        }
    }
}

Output of the Android Code

UPDATED 17May I tried writeUTF it gives some null data before Up(See Image)

Answer 1

Give it a try:

socket = new java.net.Socket(inetAddress,MainActivity.wifiModulePort);
//read input msg from server
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
dataOutputStream.writeChars(CMD);
System.out.println(CMD);
dataOutputStream.close();

socket.close();

If this adds additional spaces then the simples solution would be to keep using writeutf and substring the data on the server side

socket = new java.net.Socket(inetAddress,MainActivity.wifiModulePort);

//read input msg from server
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
dataOutputStream.writeUTF(CMD);
System.out.println(CMD);
dataOutputStream.close();

socket.close();

and on the server side:

data = tcpCliSock.recv(BUFSIZE).decode()
data = data[2:]

Quote from Javadoc:

Writes a string to the underlying output stream using modified UTF-8 encoding in a machine-independent manner.

First, two bytes are written to the output stream as if by the writeShort method giving the number of bytes to follow. This value is the number of bytes actually written out, not the length of the string. Following the length, each character of the string is output, in sequence, using the modified UTF-8 encoding for the character. If no exception is thrown, the counter written is incremented by the total number of bytes written to the output stream. This will be at least two plus the length of str, and at most two plus thrice the length of str.

Answer 2

Please can you provide you Android code snippet (where you are sending the message) to the server.

When I run the code on my local machine (I don't have a raspberry controller so I commented out certain lines):

import sys
import socket
import select

ctrCmd = ['Up', 'Down', 'Left', 'Right', 'Stop', 'Connect']

HOST = ''
PORT = 21567
BUFSIZE = 1024
ADDR = (HOST, PORT)

tcpSerSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
tcpSerSock.bind(ADDR)

tcpSerSock.listen(1)
print('Waiting for connection')

sendInterval = 1.0  # interval(sec) for sending messages to connected clients

rxset = [tcpSerSock]
txset = []
while True:
    print("Waiting for connection")
    tcpCliSock, addr = tcpSerSock.accept()
    print("...connected from :", addr)

    try:
        while True:
            data = ''
            data = tcpCliSock.recv(BUFSIZE).decode()
            print("This", data)

            if not data:
                print("No Data", data)
                break
            if data == ctrCmd[0]:
                print("I am here")
                # Servomotor.ServoUp()
                print("Increase: ")
                #tcpCliSock.send("Servo Increases".encode())
            if data == ctrCmd[1]:
                # Servomotor.ServoDown()
                print("Decrease: ")
                #tcpCliSock.send("Servo Decreases".encode())
            if data == ctrCmd[2]:
                # Servomotor.ledOn()
                print("Led On")
                #tcpCliSock.send("Led On".encode())
            if data == ctrCmd[3]:
                # Servomotor.ledOff()
                print("Led Off")
               # tcpCliSock.send("Led Off".encode())
    except KeyboardInterrupt:
        # Servomotor.close()
        # GPIO.cleanup()
        print('Exception')
tcpSerSock.close()

And on the client side a run the following code:

import sys
import socket
import time

ctrCmd = [b'Up', b'Down', b'Left', b'Right', b'Stop', b'Connect']

HOST = '127.0.0.1'
PORT = 21567
BUFSIZE = 1024
ADDR = (HOST, PORT)

tcpCliSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

tcpCliSock.connect(ADDR)
time.sleep(1)
for i in range(len(ctrCmd)):
    tcpCliSock.send(ctrCmd[i])
    time.sleep(1)
data = tcpCliSock.recv(BUFSIZE)
print(data)
tcpCliSock.close()

What I finally receive is :

Waiting for connection
Waiting for connection
...connected from : ('127.0.0.1', 54430)
This Up
I am here
Increase:
This Down
Decrease:
This Left
Led On
This Right
Led Off
This Stop
This Connect

As you may have noticed the key is that on the client side instead of sending string I am sending a byte array (b'Up', instead of 'Up'). So as you see there is no problem on the server side.

Probably on your Android side yo will need something like:

String msg = "Up"
byte[] byteArr = msg.getBytes();

Update

Ok, I think I see what's happening there. Using the Socket's output stream you can only send byte data. And what it actually does is converting your message to an array of bytes (CMD.getBytes()). Not surprisingly your server is receiving everything step by step, byte by byte. What you need to do is:

    public class MainActivity extends AppCompatActivity {
    //UI Element
    Button btnUp;
    Button btnDown;
    Button btnLedOn;
    Button btnLedOff;
    EditText txtAddress;
    /*TextView message;*/
    Socket myAppSocket = null;
    public static String wifiModuleIp = "";
    public static int wifiModulePort = 0;
    public static String CMD = "0";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnUp = (Button) findViewById(R.id.btnUp);
        btnDown = (Button) findViewById(R.id.btnDown);
        btnLedOn = (Button) findViewById(R.id.btnLedOn);
        btnLedOff = (Button) findViewById(R.id.btnLedOff);
        txtAddress = (EditText) findViewById(R.id.ipAddress);
        /*message = (TextView) findViewById(R.id.message);*/

        btnUp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "Up";
                Socket_AsyncTask cmd_increase_servo = new Socket_AsyncTask();
                cmd_increase_servo.execute();
            }
        });
        btnDown.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "Down";
                Socket_AsyncTask cmd_increase_servo = new Socket_AsyncTask();
                cmd_increase_servo.execute();
            }
        });
        btnLedOn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();;
                CMD = "ON";
                Socket_AsyncTask cmd_led_on = new Socket_AsyncTask();
                cmd_led_on.execute();
            }
        });
        btnLedOff.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getIPandPort();
                CMD = "OFF";
                Socket_AsyncTask cmd_led_off = new Socket_AsyncTask();
                cmd_led_off.execute();
            }
        });

    }
    public void getIPandPort()
    {
        String iPandPort = txtAddress.getText().toString();

        Log.d("MYTEST","IP String: "+ iPandPort);
        String temp[]= iPandPort.split(":");
        wifiModuleIp = temp[0];
        wifiModulePort = Integer.valueOf(temp[1]);
        Log.d("MY TEST","IP:" +wifiModuleIp);
        Log.d("MY TEST","PORT:"+wifiModulePort);
    }
    public class Socket_AsyncTask extends AsyncTask<Void,Void,Void>
    {
        Socket socket;
        OutputStreamWriter osw;

        @Override
        protected Void doInBackground(Void... params){
            try{

                InetAddress inetAddress = InetAddress.getByName(MainActivity.wifiModuleIp);
                socket = new java.net.Socket(inetAddress,MainActivity.wifiModulePort);
                //read input msg from server
                osw = new OutputStreamWriter(socket.getOutputStream(), 'UTF-8');
                osw.write(CMD, 0, CMD.length());
                out.flush();
                socket.close();
            }catch (UnknownHostException e){e.printStackTrace();}catch (IOException e){e.printStackTrace();}
            return null;
        }
    }
}

Answer 3

if not "some string" won't be equal to True. You might want to change it to:

if data != "" :
    # process here
    pass

You received data in separate line, it might be because of sending separately. you can look at my code that i once written for TCP socket. TCP Socket

Also ctrCmd[0] is equal to 'Up' and your data content as i see in shell are characters like 'U' and 'P' . So the line

if data == ctrCmd[0]:
    print("I am here")

won't run, because 'Up' is not equal to 'U' .