Develop Reference

Converting Java byte array to Buffer in Node.js

In an Android app I have a byte array containing data in the following format:
In another Node.js server, the same data is stored in a Buffer which looks like this:
I am looking for a way to convert both data to the same format so I can compare the two and check if they are equal. What would be the best way to approach this?

[B#cbf1911 is not a format. That is the result of invoking the .toString() method on a java object which doesn't have a custom toString implementation (thus, you get the default implementation written in java.lang.Object itself. The format of that string is:
binary-style-class-name#system-identity-hashcode.
[B is the binary style class name. That's JVM-ese for byte[].
cbf1911 is the system identity hashcode, which is (highly oversimplified and not truly something you can use to look stuff up) basically the memory address.
It is not the content of that byte array.
Lots of java APIs allow you to pass in any object and will just invoke the toString for you. Where-ever you're doing this, you wrote a bug; you need to write some explicit code to turn that byte array into data.
Note that converting bytes into characters, which you'll have to do whenever you need to put that byte array onto a character-based comms channel (such as JSON or email), is tricky.
<Buffer 6a 61 ...>
This is listing each byte as an unsigned hex nibble. This is an incredibly inefficient format, but it gets the job done.
A better option is base64. That is merely highly inefficient (but not incredibly inefficient); it spends 4 characters to encode 3 bytes (vs the node.js thing which spends 3 characters to encode 1 byte). Base64 is a widely supported standard.
When encoding, you need to explicitly write that. When decoding, same story.
In java, to encode:
import android.util.Base64;
class Foo {
void example() {
byte[] array = ....;
String base64 = Base64.encodeToString(array, Base64.DEFAULT);
System.out.println(base64);
}
}
That string is generally 'safe' - it has no characters in it that could end up being interpreted as control flow (so no <, no ", etc), and is 100% ASCII which tends to survive broken charset encoding transitions, which are common when tossing strings about the interwebs.
How do you decode base64 in node? I don't know, but I'm sure a web search for 'node base64 decode' will provide hundreds of tutorials.
Good luck!

C# - Writing strings to a stream using two bytes for length, not one

I am creating an easy to use server-client model with an extensible protocol, where the server is in Java and clients can be Java, C#, what-have-you.
I ran into this issue: Java data streams write strings with a short designating the length, followed by the data.
C# lets me specify the encoding I want, but it only reads one byte for the length. (actually, it says '7 bits at a time'...this is odd. This might be part of my problem?)
Here is my setup: The server sends a string to the client once it connects. It's a short string, so the first byte is 0 and the second byte is 9; the string is 9 bytes long.
//...
_socket.Connect(host, port);
var stream = new NetworkStream(_socket);
_in = new BinaryReader(stream, Encoding.UTF8);
Console.WriteLine(_in.ReadString()); //outputs nothing
Reading a single byte before reading the string of course outputs the expected string. But, how can I set up my stream reader to read a string using two bytes as the length, not one? Do I need to subclass BinaryReader and override ReadString()?

The C# BinaryWriter/Reader behavior uses, if I recall correctly, the 8th bit to signify where the last byte of the count is. This allows for counts up to 127 to fit in a single byte while still allowing for actual count values much larger (i.e. up to 2^31-1); it's a bit like UTF8 in that respect.
For your own purposes, note that you are writing the whole protocol (presumably), so you have complete control over both ends. Both behaviors you describe, in C# and Java, are implemented by what are essentially helper classes in each language. There's nothing saying that you have to use them, and both languages offer a way to simply encode text directly into an array of bytes which you can send however you like.
If you do want to stick with the Java-based protocol, you can use BitConverter to convert between a short to a byte[] so that you can send and receive those two bytes explicitly. For example:
_in = new BinaryReader(stream, Encoding.UTF8);
byte[] header = _in.ReadBytes(2);
short count = BitConverter.ToInt16(header, 0);
byte[] data = _in.ReadBytes(count);
string text = Encoding.UTF8.GetString(data);
Console.WriteLine(text); // outputs something

Can I add a binary file to a String based server message queue?

I have a multi-threaded client-server application that uses Vector<String> as a queue of messages to send.
I need, however, to send a file using this application. In C++ I would not really worry, but in Java I'm a little confused when converting anything to string.
Java has 2 byte characters. When you see Java string in HEX, it's usually like:
00XX 00XX 00XX 00XX
Unless some Unicode characters are present.
Java also uses Big endian.
These facts make me unsure, whether - and eventually how - to add the file into the queue. Preferred format of the file would be:
-- Headers --
2 bytes Size of the block (excluding header, which means first four bytes)
2 bytes Data type (text message/file)
-- End of headers --
2 bytes Internal file ID (to avoid referring by filenames)
2 bytes Length of filename
X bytes Filename
X bytes Data
You can see I'm already using 2 bytes for all numbers to avoid some horrible operations required when getting 2 numbers out of one char.
But I have really no idea how to add the file data correctly. For numbers, I assume this would do:
StringBuilder packetData = new StringBuilder();
packetData.append((char) packetSize);
packetData.append((char) PacketType.BINARY.ordinal()); //Just convert enum constant to number
But file is really a problem. If I have also described anything wrongly regarding the Java data types please correct me - I'm a beginner.

Does it have to send only Strings? I think if it does then you really need to encode it using base64 or similar. The best approach overall would probably be to send it as raw bytes. Depending on how difficult it would be to refactor your code to support byte arrays instead of just Strings, that may be worth doing.
To answer your String question I just saw pop up in the comments, there's a getBytes method on a String.
For the socket question, see:
Java sending and receiving file (byte[]) over sockets

Extract first valid line of string from byte array

I am writing a utility in Java that reads a stream which may contain both text and binary data. I want to avoid having I/O wait. To do that I create a thread to keep reading the data (and wait for it) putting it into a buffer, so the clients can check avialability and terminate the waiting whenever they want (by closing the input stream which will generate IOException and stop waiting). This works every well as far as reading bytes out of it; as binary is concerned.
Now, I also want to make it easy for the client to read line out of it like '.hasNextLine()' and '.readLine()'. Without using an I/O-wait stream like buffered stream, (Q1) How can I check if a binary (byte[]) contain a valid unicode line (in the form of the length of the first line)? I look around the String/CharSet API but could not find it (or I miss it?). (NOTE: If possible I don't want to use non-build-in library).
Since I could not find one, I try to create one. Without being so complicated, here is my algorithm.
1). I look from the start of the byte array until I find '\n' or '\r' without '\n'.
2). Then, I cut the byte array from the start to that point and using it to create a string (with CharSet if specified) using 'new String(byte[])' or 'new String(byte[], CharSet)'.
3). If that success without exception, we found the first valid line and return it.
4). Otherwise, these bytes may not be a string, so I look further to another '\n' or '\r' w/o '\n'. and this process repeat.
5. If the search ends at the end of available bytes I stop and return null (no valid line found).
My question is (Q2)Is the following algorithm adequate?
Just when I was about to implement it, I searched on Google and found that there are many other codes for new line, for example U+2424, U+0085, U+000C, U+2028 and U+2029.
So my last question is (Q3), Do I really need to detect these code? If I do, Will it increase the chance of false alarm?
I am well aware that recognize something from binary is not absolute. I am just trying to find the best balance.
To sum up, I have an array of byte and I want to extract a first valid string line from it with/without specific CharSet. This must be done in Java and avoid using any non-build-in library.
Thanks you all in advance.

I am afraid your problem is not well-defined. You write that you want to extract the "first valid string line" from your data. But whether somet byte sequence is a "valid string" depends on the encoding. So you must decide which encoding(s) you want to use in testing.
Sensible choices would be:
the platform default encoding (Java property "file.encoding")
UTF-8 (as it is most common)
a list of encodings you know your clients will use (such as several Russian or Chinese encodings)
What makes sense will depend on the data, there's no general answer.
Once you have your encodings, the problem of line termination should follow, as most encodings have rules on what terminates a line. In ASCII or Latin-1, LF,CR-LF and LF-CR would suffice. On Unicode, you need all the ones you listed above.
But again, there's no general answer, as new line codes are not strictly regulated. Again, it would depend on your data.

First of all let me ask you a question, is the data you are trying to process a legacy data? In other words, are you responsible for the input stream format that you are trying to consume here?
If you are indeed controlling the input format, then you probably want to take a decision Binary vs. Text out of the Q1 algorithm. For me this algorithm has one troubling part.
`4). Otherwise, these bytes may not be a string, so I look further to
another '\n' or '\r' w/o '\n'. and this process repeat.`
Are you dismissing input prior to line terminator and take the bytes that start immediately after, or try to reevaluate the string with now 2 line terminators? If former, you may have broken binary data interface, if latter you may still not parse the text correctly.
I think having well defined markers for binary data and text data in your stream will simplify your algorithm a lot.
Couple of words on String constructor. new String(byte[], CharSet) will not generate any exception if the byte array is not in particular CharSet, instead it will create a string full of question marks ( probably not what you want ). If you want to generate an exception you should use CharsetDecoder.
Also note that in Java 6 there are 2 constructors that take charset
String(byte[] bytes, String charsetName) and String(byte[] bytes, Charset charset). I did some simple performance test a while ago, and constructor with String charsetName is magnitudes faster than the one that takes Charset object ( Question to Sun: bug, feature? ).

I would try this:
make the IO reader put strings/lines into a thread safe collection (for example some implementation of BlockingQueue)
the main code has only reference to the synced collection and checks for new data when needed, like queue.peek(). It doesn't need to know about the io thread nor the stream.
Some pseudo java code (missing exception & io handling, generics, imports++) :
class IORunner extends Thread {
IORunner(InputStream in, BlockingQueue outputQueue) {
this.reader = new BufferedReader(new InputStreamReader(in, "utf-8"));
this.outputQueue = outputQueue;
}
public void run() {
String line;
while((line=reader.readLine())!=null)
this.outputQueue.put(line);
}
}
class Main {
public static void main(String args[]) {
...
BlockingQueue dataQueue = new LinkedBlockingQueue();
new IORunner(myStreamFromSomewhere, dataQueue).start();
while(true) {
if(!dataQueue.isEmpty()) { // can also use .peek() != null
System.out.println(dataQueue.take());
}
Thread.sleep(1000);
}
}
}
The collection decouples the input(stream) more from the main code. You can also limit the number of lines stored/mem used by creating the queue with a limited capacity (see blockingqueue doc).
The BufferedReader handles the checking of new lines for you :) The InputStreamReader handles the charset (recommend setting one yourself since the default one changes depending on OS etc.).

The java.text namespace is designed for this sort of natural language operation. The BreakIterator.getLineInstance() static method returns an iterator that detects line breaks. You do need to know the locale and encoding for best results, though.

Q2: The method you use seems reasonable enough to work.
Q1: Can't think of something better than the algorithm that you are using
Q3: I believe it will be enough to test for \r and \n. The others are too exotic for usual text files.

I just solved this to get test stubb working for Datagram - I did byte[] varName= String.getBytes(); then final int len = varName.length; then send the int as DataOutputStream and then the byte array and just do readInt() on the rcv then read bytes(count) using the readInt.
Not a lib, not hard to do either. Just read up on readUTF and do what they did for the bytes.
The string should construct from the byte array recovered that way, if not you have other problems. If the string can be reconstructed, it can be buffered ... no?
May be able to just use read / write UTF() in DataStream - why not?
{ edit: per OP's request }
//Sending end
String data = new String("fdsfjal;sajssaafe8e88e88aa");// fingers pounding keyboard
DataOutputStream dataOutputStream = new DataOutputStream();//
final Integer length = new Integer(data.length());
dataOutputStream.writeInt(length.intValue());//
dataOutputStream.write(data.getBytes());//
dataOutputStream.flush();//
dataOutputStream.close();//
// rcv end
DataInputStream dataInputStream = new DataInputStream(source);
final int sizeToRead = dataInputStream.readInt();
byte[] datasink = new byte[sizeToRead.intValue()];
dataInputStream.read(datasink,sizeToRead);
dataInputStream.close;
try
{
// constructor
// String(byte[] bytes, int offset, int length)
final String result = new String(datasink,0x00000000,sizeToRead);//
// continue coding here
Do me a favor, keep the heat off of me. This is very fast right in the posting tool - code probably contains substantial errors - it's faster for me just to explain it writing Java ~ there will be others who can translate it to other code language ( s ) which you can too if you wish it in another codebase. You will need exception trapping an so on, just do a compile and start fixing errors. When you get a clean compile, start over from the beginnning and look for blunders. ( that's what a blunder is called in engineering - a blunder )

In Java, what's the fastest way to "build" and use a string, character by character?

I have a Java socket connection that is receiving data intermittently. The number of bytes of data received with each burst varies. The data may or may not be terminated by a well-known character (such as CR or LF). The length of each burst of data is variable.
I'm attempting to build a string out of each burst of data. What is the fastest way (speed, not memory), to build a string that would later need to be parsed?
I began by using a byte array to store the incoming bytes, then converting them to a String with each burst, like so:
byte[] message = new byte[1024];
...
message[i] = //byte from socket
i++;
...
String messageStr = new String(message);
...
//parse the string here
The obvious disadvantage of this is that some bursts may be longer than 1024. I don't want to arbitrarily create a larger byte array (what if my burst is larger?).
What is the best way of doing this? Should I create a StringBuilder object and append() to it? That way I don't have to convert from StringBuilder to String (since the former has most of the methods I need).
Again, speed of execution is my biggest concern.
TIA.

I would probably use an InputStreamReader wrapped around a BufferedInputStream, which in turn wraps the socket. And write code that processes a message at a time, potentially blocking for input. If the input is bursty, I might run on a background thread and use a concurrent queue to hold the messages.
Reading a buffer at a time and trying to convert it to characters is exactly what BufferedInputStream/InputStreamReader does. And it does so while paying attention to encoding, something that (as other people have noted) your solution does not.
I don't know why you're focused on speed, but you'll find that the time to process data coming off a socket is far less than the time it takes to transmit over that socket.

Note that as you're transmitting across network layers, your speed of conversion may not be the bottleneck. It would be worth measuring, if you believe this to be important.
Note (also) that you're not specifying a character encoding in your conversion from bytes to String (via characters). I would enforce that somehow, otherwise your client/server communication can become corrupted if/when your client/server run in different environments. You can enforce that via JVM runtime args, but it's not a particularly safe option.
Given the above, you may want to consider StringBuilder(int capacity) to configure it in advance with an appropriate size, such that it doesn't have to reallocate on the fly.

First of all, you are making a lot of assumptions about charachter encoding that you receive from your client. Is it US-ASCII, ISO-8859-1, UTF-8?
Because in Java string is not a sequence of bytes, when it comes to building portable String serialization code you should make explicit decisions about character encoding. For this reason you should NEVER use StringBuilder to convert bytes to String. If you look at StringBuilder interface you will notice that it does not even have an append( byte ) method, and that's not because designers just overlooked it.
In your case you should definetly use a ByteArrayOutputStream. The only drawback of using straight implementation of ByteArrayOutputStream is that its toByteArray() method returns a copy of the array held by the object internaly. For this reason you may create your own subclass of ByteArrayOutputStream and provide direct access to the protected buf member.
Note that if you don't use default implementation, remember to specify byte array bounds in your String constructor. Your code should look something like this:
MyByteArrayOutputStream message = new MyByteArrayOutputStream( 1024 );
...
message.write( //byte from socket );
...
String messageStr = new String(message.buf, 0, message.size(), "ISO-8859-1");
Substitute ISO-8859-1 for the character set that's suitable for your needs.

StringBuilder is your friend. Add as many characters as needed, then call toString() to obtain the String.

I would create a "small" array of characters and append characters to it.
When the array is full (or transmission ends), use the StringBuilder.append(char[] str) method to append the content of the array to your string.
Now for the "small" size of the array - you will need to try various sizes and see which one is fastest for your production environment (performance "may" depend on the JVM, OS, processor type and speed and so on)
EDIT: Other people mentioned ByteArrayOutputStream, I agree it is another option as well.

You may wish to look at ByteArrayOutputStream depending if you are dealing with Bytes instead of Characters.
I generally will use a ByteArrayOutputStream to assemble a message then use toString/toByteArray to retrive it when the message is finished.
Edit: ByteArrayOutputStream can handle various Character set encoding through the toString call.

Personally, independent of language, I would send all characters to an in-memory data stream and once I need the string, I would read all characters from this stream into a string.
As an alternative, you could use a dynamic array, making it bigger whenever you need to add more characters. Even better, keep track of the actual length and increase the array with additional blocks instead of single characters. Thus, you would start with 1 character in an array of 1000 chars. Once you get at 1001, the array needs to be resized to 2000, then 3000, 4000, etc...
Fortunately, several languages including Java have a special build-in class that specializes in this. These are the stringbuilder classes. Whatever technique they use isn't that important but they have been created to boost performance so they should be your fastest option.

Have a look at the Text class. It's faster (for the operations you perform) and more deterministic than StringBuilder.
Note: the project containing the class is aimed at RTSJ VMs. It is perfectly usable in standard SE/EE environments though.