outputStream.write has has buffer overflow?

Question

I'm trying to send a byte[] to a serial port. However outputstream.write(byte[]); only works when byte[].length contains less then about 100 bytes.

Just to know:

using spring source tool suite (Eclipse)

JDK 1.7

DEFAULTBAUDRATE is set to 9600

the byte[] never contains more then 476 bytes

NRSerial is a library offering a platform in-depended version of the 'deceased' vaxx.comm library

there is no hardware connected to the serial port

I'm sniffing the serial port with an application (a bit like wireshark)

I'm still a student so the code may suck :P

This code works:

 NRSerialPort port = new NRSerialPort(portname, DEFAULTBAUDRATE); port.connect(); OutputStream outputStream = port.getOutputStream(); for(int i = 0; i<bytes.length; i++){ if(i%10==0){ Thread.sleep(1); } outputStream.write(bytes[i]); } outputStream.flush(); outputStream.close(); port.disconnect(); 

Advantage: works on all systems
Disadvantage: may sleep unnecessarily

And so does this:

 NRSerialPort port = new NRSerialPort(portname, DEFAULTBAUDRATE); port.connect(); OutputStream outputStream = port.getOutputStream(); for(byte b : bytes){ outputStream.write(b); } outputStream.flush(); outputStream.close(); port.disconnect(); 

Advantage: no unnecessarily sleeping
Disadvantage: may not work on fast systems because they can process the for each much faster

But the code below will fail if bytes contains more then about 100 bytes:

 NRSerialPort port = new NRSerialPort(portname, DEFAULTBAUDRATE); port.connect(); OutputStream outputStream = port.getOutputStream(); outputStream.write(bytes); outputStream.flush(); outputStream.close(); port.disconnect(); 

Although write(byte[]) is a valid method in the sun library

I have some ideas about this:

• I overflow the output buffer, the baudrate is to low to send this data at once
• write(byte[]) does not cut the byte[] to smaller pieces

You might wonder why I ask this question if I got a working solution. Well:

I want to know which one of my solutions is better and/or if there is a other/better way to do this. besides why make a method write(byte[]) if its processing capability's depend on hardware (at least say so in the JavaDoc?)

Answer 1

Assuming I've googled the correct code, this does not look like a problem with Java but with the implementation of the NRSerialPort library.

Diving into the code, I can see that SerialOutputStream provides the implementation of the OutputStream and it calls two different methods depending on whether the write(byte) or write(byte[]) method is used:

see here

protected native void writeByte( int b, boolean i ) throws IOException;
protected native void writeArray( byte b[], int off, int len, boolean i ) 
    throws IOException;

Without digging into the native code, I would surmise that there may be a bug in the implementation of the writeArray method.