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Ruby base 64 decoding for Java base 64 encoding

I having a string that is encoded in java using
data = new String(Base64.getEncoder().encode(encVal), StandardCharsets.UTF_8);
I am receiving this encoded data as an API response. I want to base64 decode this in ruby. I am using
Base64.strict_decode64(data)
for this. but this is not working. Can anyone help me with this?

Your Java code is correct:
byte[] encVal = "Hello World".getBytes();
String data = new String(Base64.getEncoder().encode(encVal), StandardCharsets.UTF_8);
System.out.println(data); // SGVsbG8gV29ybGQ=
The SGVsbG8gV29ybGQ= decodes correctly using multiple tools, e.g. https://www.base64decode.org/.
You are observing garbage characters decoding your value most likely due to an error in creating byte[]. Possibly you have to specify the correct encoding when creating byte[].

Java equivalent of perl unpack function

I have a perl code (say client) which sends packed data as HTTP POST to another perl code running on apache mod_perl module (say server).
In client side, I have the pack function like this,
$postData = pack("N a*", length($metaData), $metaData);
From perl pack document, it seems,
N -> An unsigned long (32-bit) in "network" (big-endian) order.
a -> A string with arbitrary binary data, will be null padded.
Now the $postData will be sent to server using perl LWP User Agent.
In the server side perl, we used to unpack like this,
# first reading the metaData Length
my $buf;
$request->read($buf, 4); #$request is apache request handler
my $metaDataLength = unpack("N", $buf);
# now read the metaData itself
$request->read($buf, $metaDataLength);
Now I have to do this server side data parsing in java (moving away from perl for some reasons). I have searched google for this and it seems to be not a single line solution as in perl. Some suggested to write our own unpack function. I am using java 1.7 version.
Is there any simple solution available in java for the above server side data parsing ?
Edit: Thanks Elliot for 'ByteBuffer' idea. The following code works fine for me,
InputStream is = request.getInputStream(); //request is HTTPServletRequest
byte[] bArr = new byte[4]; //reading first 4 bytes to get metaDataLength
int bytesRead = is.read(bArr);
ByteBuffer buf = ByteBuffer.wrap(bArr);
int metaDataLength = buf.getInt(); //shows value matches with clientside perl code.

potentially JBBP can be such one
final int value = JBBPParser.prepare("int;").parse(theInputStream).findFieldForType(JBBPFieldInt.class).getAsInt();

XStream not sent via sockets

I used already working code for save/load game for sending a player state via sockets. And I encountered a problem that game save is correct, but server is not receiving client's player state.
Here is the base code that is tested and working:
int retval = fc.showSaveDialog(givenComponent);
if (retval == JFileChooser.APPROVE_OPTION) {
File file = fc.getSelectedFile();
try {
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), "UTF-8"));
XStream xs = new XStream();
GameSave gs = new GameSave();
ArrayList<PlayerSerialize> listps = new ArrayList<PlayerSerialize>();
for (Player tempplayer : Players.players) {
PlayerSerialize ps = new PlayerSerialize();
ps.getPlayerData(tempplayer);
listps.add(ps);
}
gs.playersSerialize = listps;
gs.gamedate = Dateutils.gamedate;
String s = xs.toXML(gs);
bw.write(s);
bw.close();
} catch (IOException ex) {
Logger.getLogger(DialogMainField.class.getName()).log(Level.SEVERE, null, ex);
}
}
Here is the client side code that is not sending anything to server:
XStream xs = new XStream();
GameSave gs = new GameSave();
ArrayList<PlayerSerialize> listps = new ArrayList<PlayerSerialize>();
PlayerSerialize ps = new PlayerSerialize();
ps.getPlayerData(Players.players.get(1));
listps.add(ps);
gs.playersSerialize = listps;
gs.gamedate = Dateutils.gamedate;
String s = xs.toXML(gs);
out.println("clientplayertoserver");
out.println(s);
Here is the server side just in case:
if (strIn.contains("clientplayertoserver")) {
strIn = in.readLine();
XStream xs = new XStream();
GameSave gs = (GameSave) xs.fromXML(strIn);
Players.players.get(1).getPlayerSerializeData(gs.playersSerialize.get(0));
}
I need some kind of clue because I'm stuck investigating the problem. Are there any XStream limitations? Or the error is in the working with sockets? The same code is working in one place and is not working in another - I greatly thank in advance for any help with this weird situation.

Well, you are doing two different things here:
1) Saving the data to a file, which is ok.
2) Sending data via a socket. You seem to assume that all your data (the XStream serialized object) is actually in one line. This will usually not be the case. Even if you configure XStream to serialize all data without identation, you still cannot be sure you won't have linebreaks in the serialized data (your variables).
So solve your issue, you should separate your concerns here.
1st serialize / deserialize your objects to String and back (that seems to be working for you.
2nd send this data to a medium, like a file (which you already have) or to a server.
For sending string data to a server, you'll need some kind of protocol. Either you can reuse an existing protocol, like HTTP (POST request to a server), Web Service, Rest Call or whatever else your server is running.
If you want to implement your own protocol (as you have tried above), you must ensure that the server knows what to expect and how to treat it properly. Usually you should split your request in a header and a payload section or something like that.
Include in your header what you want to do (e.g save player state) and the meta information of that (e.g how many bytes payload you are sending).
After the header, send the payload.
The server must now read the header 1st (like everything until the first newline), parse the header to understand what is going on (e.g save player state, 543 bytes data) and act on it (read the data, transform it to a string, deserialize the XStream object and store it in a local database or whatever the server should do with that).
So and after all this information, please adapt your question. As you have seen you do not really have a question about XStream, but about how to send some data from client to a custom server.

Getting an object into a ChannelBuffer

I've written a small http server using Netty by following the example http server and now i'm trying to adapt it to my needs (a small app that should send json). I began by manually encoding my POJOs to json using jackson and then using the StringEncoder to get a ChannelBuffer. Now i'm trying to generalize it slightly by extracting the bit that encodes the POJOs to json by adding a HttpContentEncoder and I've managed to implement that more or less.
The part that i can't figure out is how to set the content on the HttpResponse. It expects a ChannelBuffer but how do i get my object into a ChannelBuffer?
Edit
Say i have a handler with code like below and have a HttpContentEncoder that knows how to serialize SomeSerializableObject. Then how do i get my content (SomeSerializableObject) to the HttpContentEncoder? That's what i'm looking for.
SomeSerializableObject obj = ...
// This won't work becuase the HttpMessage expects a ChannelBuffer
HttpRequest res = ...
res.setContent(obj);
Channel ch = ...
ch.write(res);
After looking into it a bit more though i'm unsure if this is what HttpContentEncoder is meant to do or rather do stuff like compression?

Most object serialization/deserialization libraries use InputStream and OutputStream. You could create a dynamic buffer (or a wrapped buffer for deserialization), wrap it with ChannelBufferOutputStream (or ChannelBufferInputStream) to feed the serialization library. For example:
// Deserialization
HttpMessage m = ...;
ChannelBuffer content = m.getContent();
InputStream in = new ChannelBufferInputStream(content);
Object contentObject = myDeserializer.decode(in);
// Serialization
HttpMessage m = ...;
Object contentObject = ...;
ChannelBuffer content = ChannelBuffers.dynamicBuffer();
OutputStream out = new ChannelBufferOutputStream(content);
mySerializer.encode(contentObject, out);
m.setContent(content);
If the serialization library allows you to use a byte array instead of streams, this can be much simpler using ChannelBuffer.array() and ChannelBuffer.arrayOffset().

Client-side string encoding java

My team and I have this nasty problem with parsing a string received from our server. The server is pretty simple socket stuff done in qt here is the sendData function:
void sendData(QTcpSocket *client,QString response){
QString text = response.toUtf8();
QByteArray block;
QDataStream out(&block, QIODevice::WriteOnly);
out << (quint32)0;
out << text;
out.device()->seek(0);
out << (quint32)(block.size() - sizeof(quint32));
try{
client->write(block);
}
catch(...){...
The client is in Java and is also pretty standard socket stuff, here is where we are at now after trying many many different ways of decoding the response from the server:
Socket s;
try {
s = new Socket(URL, 1987);
PrintWriter output = new PrintWriter(s.getOutputStream(), true);
InputStreamReader inp = new InputStreamReader(s.getInputStream(), Charset.forName("UTF-8"));
BufferedReader rd = new BufferedReader( inp );
String st;
while ((st = rd.readLine()) != null){
System.out.println(st);
}...
If a connection is made with the server it sends a string "Send Handshake" with the size of the string in bytes sent before it as seen in the first block of code. This notifies the client that it should send authentication to the server. As of now the string we get from the server looks like this:
������ ��������S��e��n��d�� ��H��a��n��d��s��h��a��k��e
We have used tools such as string encode/decode tool to try and assess how the string is encoded but it fails on every configuration.
We are out of ideas as to what encoding this is, if any, or how to fix it.
Any help would be much appreciated.

At a glance, the line where you convert the QString parameter to a Utf8 QByteArray and then back to a QString seems odd:
QString text = response.toUtf8();
When the QByteArray returned by toUtf8() is assigned to text, I think it is assumed that the QByteArray contains an Ascii (char*) buffer.

I'm pretty sure that QDataStream is intended to be used only within Qt. It provides a platform-independent way of serializing data that is then intended to be deserialized with another QDataStream somewhere else. As you noticed, it's including a lot of extra stuff besides your raw data, and that extra stuff is subject to change at the next Qt version. (This is why the documentation suggests including in your stream the version of QDataStream being used ... so it can use the correct deserialization logic.)
In other words, the extra stuff you are seeing is probably meta-data included by Qt and it is not guaranteed to be the same with the next Qt version. From the docs:
QDataStream's binary format has evolved since Qt 1.0, and is likely to
continue evolving to reflect changes done in Qt. When inputting or
outputting complex types, it's very important to make sure that the
same version of the stream (version()) is used for reading and
writing.
If you are going to another language, this isn't practical to use. If it is just text you are passing, use a well-known transport mechanism (JSON, XML, ASCII text, UTF-8, etc.) and bypass the QDataStream altogether.