Develop Reference

Send ASCII Data to UART3 on Android Things with 3 Byes of 0xFF at the end

I am trying to interface a Nextion HMI Serial Screen to Android Things, specifically the PICO-PI-IMX6UL
I am using the sample-uartloopback template as a starting place.
What I need to do is send the following payload over serial (UART3) in a certain format and in ASCII
page 1
The instruction is ended with three bytes "0xff 0xff 0xff"
All the instructions and parameters are in ASCII
All the instructions are in lowercase letters
mLoopbackDevice.write(buffer, buffer.length);
Where buffer is the payload with the three terminating bytes.
The thing is the screen wants in in ASCII but I can only send in the bytearray...
I have tried multiple ways and I cant seem to get it to work.
What would be the proper way to format a string of "page 1" and then add the terminating bytes?
I have it working in a node app but java is blowing my mind right now...
I have tried:
String strCommand = "page 1";
byte b = (byte)0xFF;
byte[] endCommand = {b,b,b};
byte[] cmd = strCommand.getBytes();
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
outputStream.write(cmd);
outputStream.write(endCommand);
byte[] payload = outputStream.toByteArray();
Screen.write(payload, payload.length);
but that does not work.
I can read data (nothing useful at the moment) so I can confirm the communication is fine and It works in my Node app, but I need to port it to Android Things...
Can anyone point me in the right direction?
EDIT: This returns the correct format for me in JS
function hex(str) {
var arr = [];
for (var i = 0, l = str.length; i < l; i ++) {
var ascii = str.charCodeAt(i);
arr.push(ascii);
}
arr.push(255);
arr.push(255);
arr.push(255);
return new Buffer(arr);
}

Java DataOutputStream doesnt write all messages ( TCP Socket )

in my Client-Server application I found a strange error. I got the following Methods :
sendLoginResponse();
sendPlayerList();
sendCurrentLevelState();
Each Methods sends a byte array to the Client-Side
If I only call 2 of them, everything works fine and the Client-Side gets all the sent byte arrays. But if I call all 3 of them only the first and second one arrive the Client, the order of the following methods doesnt matter. but the Server says all of them were send. To write to the Client iam using the
write(byte[] b, int off, int len); method
all The lenghts within the packages make sense too.
Here comes the strange point:
if I add a Thread.sleep(1000); after the second Method, the third one does now arrive the Client after the sleep. I Have also tried to flush the DataOutputStream after every write call, but this didnt help.
EDIT:
So let's say I'd send 3 Login-Response
The Method's that gives me the byte[]:
public byte[] getLoginResponse(int playerID){
byte[] msg = new byte[4];
short shortMsgLength = 4;
byte[] msgLength = shortToBytes(shortMsgLength);
msg[0] = 2;
msg[1] = msgLength[0];
msg[2] = msgLength[1];
msg[3] = (byte) playerID;
return msg;
}
private byte[] shortToBytes(short value) {
byte[] returnByteArray = new byte[2];
returnByteArray[0] = (byte) (value & 0xff);
returnByteArray[1] = (byte) ((value >>> 8) & 0xff);
return returnByteArray;
}
And the Send Method:
private void sendLoginResponse() {
try{
byte[] msg = rfcObject.getLoginResponse(playerID);
out.write(msg,0,msg.length);
}catch(Exception e){
System.err.println(e.getMessage());
System.exit(0);
}
}
So if I call the sendLoginResponse(); three times in a row, the client only recieves 2 byte-arrays, but the server says it has been sent 3 times. If i add a
Thread.sleep(1000); `after the second Method-Call, everything works fine..`
The Client that reads the message runs in a Thread:
public void run(){
while(true){
try {
byte[] data = new byte[MAX_DATA_SIZE]; // MAX_DATA = 255
byteCount = in.read(data);
} catch (IOException ex) {
handleExceptionError(ex);
}
}
}
thank you!

if I call the sendLoginResponse(); three times in a row, the client only recieves 2 byte-arrays, but the server says it has been sent 3 times.
This is because TCP is a stream-oriented protocol. Meaning it doesn't know or care how your messages are delimited. There's no concept of individual messages in TCP, just a stream of bytes, with the guarantee that the order of bytes is preserved.
So when the sender calls three write, the three byte arrays are simply concatenated over the connection and arrives at the receiver in the same order, but the receiver doesn't necessarily need three read to get all the bytes, and even if it does take three read, the read doesn't necessarily gives you the same byte array passed to each corresponding write.
Your message already have the necessary information to get the individual message back from the byte stream:
// Client code for reading individual messages from a TCP connection
byte type = din.readByte();
// Read the message length, little-endian.
// We cannot use din.readShort because it's big-endian
int lenLo = din.read();
int lenHi = din.read();
short len = (short)(lenLo | (lenHi << 8));
byte [] body = new byte[len];
din.readFully(body);

DataOutputStream and TCP don't lose data.
As almost invariable seen in questions of this nature, the problem is at the receiving end. You are probably assuming that `read()' fills the buffer, and ignoring the count that it returns.
Based on your protocol description in comments, you should be using DataInputStream.readFully() in this circumstance:
byte type = din,readByte();
int length = din.readShort();
byte[] data = new byte[length];
din.readFully(data);

Converting pointer to string and send as char array not working properly

I have a problem with sending directory names over socket from my C++ client, to my Java server.
Sending ordinary messages like "hello world", works great , but the following doesn't and I can not figure out what the problem is:
char const * files = ffd.cFileName; // get directory name
string str(files, 0, strlen(files)); // convert pointer to string, right?
char mess[str.size()];
strcpy(mess, str.c_str()); // make char array :)
cout << "Send file: " << mess << " with strlen: " << strlen(mess) << " and sizeof: " << sizeof(mess) << endl;
int sent = 0;
if ((sent = send(connectSocket, mess, sizeof(mess), 0)) == SOCKET_ERROR)
{
closesocket(connectSocket);
WSACleanup();
connectToServer();
}
The java server just receives the directory names like this:
wam
p
Win
dow
s
Win
dow
s.o
ld
wxW
idg
ets
I can not understand what I'm missing because I have tried every possible way to do this and the C++ client prints like:
"Send file: windows with strlen: 7 and sizeof: 7"
I do not think that the java server is the problem since I can receive normal strings and messages perfectly, but anyway here is the JAVA code:
is = socket.getInputStream();
byteArray = new byteArray[1024];
while (true) {
c = is.read(byteArray, 0, byteArray.length);
String recv = new String(byteArray, 0, c);
System.out.println(recv);
if (recv.equals("<EOF>")){
break;
}
list.add(recv);
}
If you request something else or anything just leave a comment and I will fix it.

Question: are you sending via TCP or UDP? I'm guessing TCP, and if that is the case, you need to treat the socket as more of a stream. That stream may get broken up into a bunch of packets - you don't really control that. What I might do is to prefix the string length of each directory (ex, 3foo, 4barz, etc), read from the socket and determine what constitutes as a logical block or string, and then assemble / print the strings based on that. If you go with that route, you need to track how much you read each time until you think you are done.

I solved it, Just added byteArray = new byte[1024]; and now it works:
while (true) {
byteArray = new byte[1024]; // I ADDED THIS AND NOW THE JAVA SERVER RECEIVES IT CORRECTLY!
c = is.read(byteArray, 0, byteArray.length);
recv = new String(byteArray, 0, c);
System.out.println(recv);
if (recv.equals("<EOF>")){
break;
}
list.add(recv);
}

Integer to byte and byte to integer convertion - java

I'm developing an app based on Samsung Chord SDK. I need to send the video's current position in the sendDataToAll(), which accepts data in byte[][]. My problem is that when I try to send the current position (which is an int) type-casted into byte, I'm getting negative value (in byte) as returned. And when I try to convert the negative value in to int in the OnDataRecived(), it's still the same negative value. How do I solve this issue?
Sending code:
//for sending the message
int currPos = mVideoView.getCurrentPosition();
logView.append("Duration sent= " + currPos);
//Integer resume = -3;
Byte msgByte = new Byte("-3");
byte [] [] pay = new byte [1] [2];
pay[0] [0] = msgByte;
Byte msgByte2 = new Byte((byte) currPos);
logView.append("Duration sent= " + msgByte2);
pay[0] [1] = msgByte2;
mChordchannel.sendDataToAll("Integer", pay);
// im sending -3 so that im checking that the user pressed the resume .
Receiving code:
//on receiving
else if(intRec == -3) {
Byte pos = rec[0] [1];
int posn;
posn = pos.intValue();
logView.append("Duration received= " + posn);
mVideoView.seekTo(posn);
mVideoView.start();
}

I don't know anything about the Samsung Chord SDK, but you can't fit (most) ints in a byte. An int is 4 bytes wide.
To create a payload compatible with your current code, that sends all 4 bytes:
byte[][] payload = { {
-3,
(byte)(currPos >> 24),
(byte)(currPos >> 16),
(byte)(currPos >> 8),
(byte)(currPos >> 0),
} };
mChordchannel.sendDataToAll("Integer", payload);
To receive:
int position = new java.math.BigInteger(
Arrays.copyOfRange(rec[0], 1, 5)).intValue();
P.S. This is not pretty code! It is tolerable for basic ints, but if you later find you need to transmit more complicated data structures you will need a better way. Some ideas, in increasing order of sophistication:
Use data streams (wrap a DataOutputStream around a ByteArrayOutputStream; write values; when done writing, close the DataOutputStream and call toByteArray() on the ByteArrayOutputStream to get the payload).
Use serialization (wrap an ObjectOutputStream around a ByteArrayOutputStream; write values and/or objects; finish as above).
Use a JSON-encoder or XML-encoder. (E.g., encode the data as a String, then call getBytes("UTF-8") on the String and send that.)

How to send C char array to Java client over a socket

I'm writing a server program in c, and the client is on android platform which uses java language.Now I have a trouble to send char array from the server to the client,which means the client can get the data but can not decode it.I think it maybe because of the problem of data types or encoding differences.Can anyone give me some ideas,Thanks a lot!
Here is my code of server side:
char buf[MAXSIZE];
memset(buf, 0, MAXSIZE);
int n_write;
strcpy(buf, "0008200050005001");
n_write = Write(confd, buf, strlen(buf));
if (n_write <= 0)
{
fputs("Write error in send_matrix_and_position\n", stderr);
close(confd);
return -1;
}
And here is Java code:
mSocket = new Socket(HOST, PORT);
mIn = mSocket.getInputStream();
mOut = mSocket.getOutputStream();
byte[] lengthByte = new byte[4];
mIn.read(lengthByte);
for(byte b : lengthByte)
{
System.out.println(b + "");
}

You are sending 16 characters, but you read only four. Aren't you getting the data
48
48
48
56? These are the codes of the first four characters sent.

Try checking what values you get at the client when you read the char array, you might probably be doing br.readline(); see if this prints the characters??
You need to debug and check, then you might come up with some way.