无法从Java套接字服务器接收数据到C套接字客户端

Question

My Socket client is written in C and sends the values in the format below:

x00\x2C\x02\x00\xE0\x00

Now I would like to read the hex values from the TCP/IP socket server which is written in Java.

What should be a approach to read the stream values in Java Socket?

I'm trying to read in the following way, but it does not work:

InputStream ins = sock.getInputStream();
int byteRead;

while((byteRead = ins.read()) != -1) {
  System.out.println(Integer.toHexString(byteRead & 0xFF));
}

Answer 1

If you dont know the length of the message you will need to read each byte reperesentation into a String buffer and use Byte#parseByte(buffer, 16) to make a signed byte [-127, 127] out of it.

If you know the length of the whole String that the client is sending you could read it all and then String#split(regex) it using a delimiter whicht seems to be in your case \\x . and again make use of Byte#parseByte(buffer, 16) to convert.

If you need unsigned values [0, 255] then you have to go with Integer.html#parseInt(buffer, 16) .

Answer 2

First stating the obvious, "\\x41" is one byte with hex 41 aka ASCII 'A'. C strings also have a terminating \\x00 following it. So you are writing

\x00\x2C\x02\x00\xE0\x00

as char array with size 6. Writing it as string would write an empty string, as the first byte is \\x00 .

On the java side there is no problem with \\x00 , that is just a regular byte/char.

The java code is okay. A variation might be:

try (InputStream ins = new BufferedInputStream(sock.getInputStream())) {
    int byteRead;
    while ((byteRead = ins.read()) != -1) {
        System.out.printf("%02X%n", byteRead & 0xFF);
    }
} // Closes

Here capital X causes capitalized hex, and %na line break. String.format would be the alternative.

My first guess would be that the C writing is erroneously done with puts , using strlen or so.