Arduino (c++), How to read bytes from Sockets (WiFiClient)? - c++

Question

A server in java, sends from a Server socket a byte array, this byte array contains text (utf-8) with the next format:
first 4 bytes: an int with the number of bytes of the text
next n
bytes: each byte represents a char.
So i am using "WiFiClient" from the "ESP8266WiFi.h" library (it should be the same as "WiFi.h" library), WifiClient has a method to receive a byte using the read() method, the problem is that i am unable to read correctly the int (first four bytes) or transform the bytes into int value. So i will be very gratefull if you help me with that:
Java (Server) simplified code:
String respuestaServer="RESPUESTAS DEL SERVER";
DataOutputStream out=new DataOutputStream(sock.getOutputStream());
out.writeInt(respuestaServer.getBytes(StandardCharsets.UTF_8).length);
out.write(respuestaServer.getBytes(StandardCharsets.UTF_8));
out.flush();
Arduino (Client) code to receive and interpret the byte array (the objective of this code is transform the bytes into a String):
String recibirInfo() {
//TRYING TO READ FIRST FOUR BYTES
byte bytesSizeMsj[4];
for (int i = 0; i < sizeof(bytesSizeMsj); i++) {
bytesSizeMsj[i] = client.read();
Serial.print("BYTE: "+bytesSizeMsj[i]);
}
//TRYING TO TRANSFORM THE FOUR BYTES INTO AN INT
int sizeMsj = int((unsigned char)(bytesSizeMsj[0]) |
(unsigned char)(bytesSizeMsj[1]) |
(unsigned char)(bytesSizeMsj[2])|
(unsigned char)(bytesSizeMsj[3]));
Serial.println(sizeMsj);
char charArray[sizeMsj];
//TRYING TO READ THE REST OF THE MESSAGE
for (int i = 0; i < sizeof(charArray); i++) {
charArray[i] = client.read();
}
//TRYING TO TRANSFORM THE BYTE ARRAY INTO A STRING
String msj=charArray;
return msj;
}

Answer 1

I fix it, i had problems with the way I read from the socket, the way I transform the 4 bytes into an Int datatype and with the way I transoform the bytes into a String, I figure out why i was not receiving all the bytes when trying to read from the socket, the reason was that when I call the method "client.read()" the server was not fast enought to send the information so it did not read anything, so I did a loop and with help of the method "client.available()" I checked that there was a byte ready to be read, so the loop ends when the first 4 bytes were read. Then I transform the 4 bytes readed into an Int, read the rest of the bytes in a similar way than before, and I tranformed the bytes into a String.
Here is my functional code:
String recibirInfo(bool* error) {
String msj = "";
byte bytesSizeMsj[4];
for (int i = 0; i < sizeof(bytesSizeMsj); i++) {
if (client.connected()) {
if (client.available()) {
bytesSizeMsj[i] = client.read();
} else {
delay(10);
i--;
}
} else {
*error = true;
return "";
}
}
//TRANSFORMAR LOS 4 BYTES A INT
int sizeMsj = 0;
sizeMsj = ((int)bytesSizeMsj[3]) | sizeMsj;
sizeMsj = ((int)bytesSizeMsj[2]) << 8 | sizeMsj;
sizeMsj = ((int)bytesSizeMsj[1]) << 16 | sizeMsj;
sizeMsj = ((int)bytesSizeMsj[0]) << 24 | sizeMsj;
char charArray[sizeMsj];
//LEER EL TEXTO
for (int i = 0; i < sizeof(charArray); i++) {
if (client.connected()) {
if (client.available()) {
charArray[i] = client.read();
} else {
delay(250);
i--;
}
} else {
*error = true;
return "";
}
}
//TRANSFORMAR BYTES A STRING
msj = charArrayToString(charArray, sizeMsj);
Serial.print("RECIBIDO: ");
Serial.println(msj);
return msj;
}
String charArrayToString(char arrChar[], int tam) {
String s = "";
for (int i = 0; i < tam; i++) {
s = s + arrChar[i];
}
return s;
}

Answer 2

It's kinda of hard to trouble shoot like this do you actually receive data ? Can you show the output you get ? Maybe you aren't even connected.
Also what i've done in the past is convert every int or "letter" into a char. Since i usually send a message of known lenght with a starting char i read every byte of my message and convert it to a char and then add it to my received message string. I dont know if this helps... Basically i do the conversion on the arrival of the byte.