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What happens when client closes connection before server is done reading bytes from BufferedInputStream?

I am reading a file being uploaded over the web and it is being sent through http and we are receiving through a BufferedInputStream. Sometimes we get a timeout exception in the middle of reading from the stream. My working theory is that the connection is being closed from the client before we can process the whole file. The file is in the order of mb.
Does this theory make sense? Does the client need to keep the connection open in order for the server to completely read bytes from the input stream?

No good news in that case, data lost will occur.

Does this theory make sense? Does the client need to keep the connection open in order for the server to completely read bytes from the input stream?
No.
As long as the BufferedInputStream has bytes in the buffer, any calls to read() / read(byte[]) / read(byte[], int, int) will simply give you data from the buffer and will never even touch the underlying inputstream.
As long as you don't touch said inputstream, it cannot just start throwing exceptions out of the clear blue sky. You need to call something on the actual socket inputstream (be it read, close, flush, write - something), in order to get an exception thrown.
What could happen is a mixed mode operation: You call e.g:
var raw = socket.getInputStream();
var buffered = new BufferedInputStream(raw);
byte[] b = new byte[1000];
buffered.read(b); // actually reads 4000 bytes into buffer, giving 1000 of them.
// 3000 left in the buffer!
byte[] c = new byte[2000];
buffered.read(c); // works fine and never touches raw. Can't throw.
byte[] d = new byte[2000];
buffered.read(d); // 'mixed mode'
Here, in the 'mixed mode' situation, the first 1000 bytes are filled by the buffer, but then raw.available() is invoked (source: The actual source code of BufferedInputStream.java); if it returns a non-zero number, then more data is fetched from raw directly; if it is 0, read() just returns (read() is under no obligation to read ALL the requested bytes; it merely needs to [A] read at least 1, and [B] return how much it did read; usually you want readNBytes instead).
However, in.available() is allowed to throw. If it does, voila.
However, a normal TCP close would not cause TimeoutExceptions.
A much more likely scenario is the following: Your code is simply not processing the data fast enough. The sending entity at some point is just fed up with it all and refuses to continue to let you hog a file handle and just hangs up on you. If you're already using a buffer, perhaps there's some network equipment in between that is dog slow, or the server is configured with unrealistic expectations of how fast your network connections are.

How to deal with a slow consumer in traditional Java NIO?

So, I've been brushing up my understanding of traditional Java non-blocking API. I'm a bit confused with a few aspects of the API that seem to force me to handle backpressure manually.
For example, the documentation on WritableByteChannel.write(ByteBuffer) says the following:
Unless otherwise specified, a write operation will return only after
writing all of the requested bytes. Some types of channels,
depending upon their state, may write only some of the bytes or
possibly none at all. A socket channel in non-blocking mode, for
example, cannot write any more bytes than are free in the socket's
output buffer.
Now, consider this example taken from Ron Hitchens book: Java NIO.
In the piece of code below, Ron is trying to demonstrate how we could implement an echo response in a non-blocking socket application (for context here's a gist with the full example).
//Use the same byte buffer for all channels. A single thread is
//servicing all the channels, so no danger of concurrent access.
private ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
protected void readDataFromSocket(SelectionKey key) throws Exception {
var channel = (SocketChannel) key.channel();
buffer.clear(); //empty buffer
int count;
while((count = channel.read(buffer)) > 0) {
buffer.flip(); //make buffer readable
//Send data; don't assume it goes all at once
while(buffer.hasRemaining()) {
channel.write(buffer);
}
//WARNING: the above loop is evil. Because
//it's writing back to the same nonblocking
//channel it read the data from, this code
//can potentially spin in a busy loop. In real life
//you'd do something more useful than this.
buffer.clear(); //Empty buffer
}
if(count < 0) {
//Close channel on EOF, invalidates the key
channel.close();
}
}
My confusion is on the while loop writing into output channel stream:
//Send data; don't assume it goes all at once
while(buffer.hasRemaining()) {
channel.write(buffer);
}
It really confuses me how NIO is helping me here. Certainly the code may not be blocking as per the description of the WriteableByteChannel.write(ByteBuffer), because if the output channel cannot accept any more bytes because its buffer is full, this write operation does not block, it just writes nothing, returns, and the buffer remains unchanged. But --at least in this example-- there is no easy way to use the current thread in something more useful while we wait for the client to process those bytes. For all that matter, if I only had one thread, the other requests would be piling up in the selector while this while loop wastes precious cpu cycles “waiting” for the client buffer to open some space. There is no obvious way to register for readiness in the output channel. Or is there?
So, assuming that instead of an echo server I was trying to implement a response that needed to send a big number of bytes back to the client (e.g. a file download), and assuming that the client has a very low bandwidth or the output buffer is really small compared to the server buffer, the sending of this file could take a long time. It seems as if we need to use our precious cpu cycles attending other clients while our slow client is chewing our file download bytes.
If we have readiness in the input channel, but not on the output channel, it seems this thread could be using precious CPU cycles for nothing. It is not blocked, but it is as if it were since the thread is useless for undetermined periods of time doing insignificant CPU-bound work.
To deal with this, Hitchens' solution is to move this code to a new thread --which just moves the problem to another place--. Then I wonder, if we had to open a thread every time we need to process a long running request, how is Java NIO better than regular IO when it comes to processing this sort of requests?
It is not yet clear to me how I could use traditional Java NIO to deal with these scenarios. It is as if the promise of doing more with less resources would be broken in a case like this. What if I were implementing an HTTP server and I cannot know how long it would take to service a response to the client?
It appears as if this example is deeply flawed and a good design of the solution should consider listening for readiness on the output channel as well, e.g.:
registerChannel(selector, channel, SelectionKey.OP_WRITE);
But how would that solution look like? I’ve been trying to come up with that solution, but I don’t know how to achieve it appropriately.
I'm not looking for other frameworks like Netty, my intention is to understand the core Java APIs. I appreciate any insights anyone could share, any ideas on what is the proper way to deal with this back pressure scenario just using traditional Java NIO.

NIO's non-blocking mode enables a thread to request reading data from a channel, and only get what is currently available, or nothing at all, if no data is currently available. Rather than remain blocked until data becomes available for reading, the thread can go on with something else.
The same is true for non-blocking writing. A thread can request that some data be written to a channel, but not wait for it to be fully written. The thread can then go on and do something else in the meantime.
What threads spend their idle time on when not blocked in IO calls, is usually performing IO on other channels in the meantime. That is, a single thread can now manage multiple channels of input and output.
So I think you need to rely on the design of the solution by using a design pattern for handling this issue, maybe **Task or Strategy design pattern ** are good candidates and according to the framework or the application you are using you can decide the solution.
But in most cases you don't need to implement it your self as it's already implemented in Tomcat, Jetty etc.
Reference : Non blocking IO

Non-blocking socket writes in Java versus blocking socket writes

Why would someone prefer blocking writes over non-blocking writes? My understanding is that you would only want blocking write if you want to make sure the other side got the TCP packet once the write method returned, but I am not even sure that's possible. You would have to flush and flush would have to flush the underlying operating system write socket buffer. So is there any disadvantage of non-blocking socket writes? Does having a large underlying write socket buffer a bad idea in terms of performance? My understanding is that the smaller the underlying socket write buffer the more likely you will hit slow/buggy client and have to drop/queue packets in the application level while the underlying socket buffer is full and isWritable() is returning false.

My understanding is that you would only want blocking write if you want to make sure the other side got the TCP packet once the write method returned
Your understanding is incorrect. It doesn't ensure that.
Blocking writes block until all the data has been transferred to the socket send buffer, from where it is transferred asynchronously to the network. If the reader is slow, his socket receive buffer will fill up, which will eventually cause your socket send buffer to fill up, which will cause a blocking write to block, blocking the whole thread. Non-blocking I/O gives you a way to detect and handle that situation.

The problem with non blocking writes is that you may not have anything useful to do if the write is incomplete. You can end up with loops like
// non-blocking write
while(bb.remaining() > 0) sc.write(bb);
OR
// blocking write
sc.write(bb);
The first can burn CPU and the second might be more desirable.
The big problem is reads. Once you decide whether you want blocking or non-blocking reads, your writes have to be the same. Unfortunately there is no way to make them different. If you want non-blocking reads, you have to have non-blocking writes.

Sending buffered data through a socket from Android

I develop the first part of an Android application that allows to broadcast video stream through the network. Currently, I'm sending the video in a very direct way, like this:
Socket socket = new Socket(InetAddress.getByName(hostname), port);
ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(socket);
recorder.setOutputFile(pfd.getFileDescriptor());
But unfortunately, it is not very fluid. I want to buffered the data stream before sending it through the socket. One of the way I tried is to write the stream in a file using the Android API for recording media, and to use another thread to stream the file to the server on a conputer.
So my problem is: how can I send by a socket a file which is still under writing?
As BufferedInputStream has not a blocking method for reading, I tried to do things like this one, but without any success
while (inputStream.available() >= BUFFER_SIZE) {
inputStream.read(buffer);
outputStream.write(buffer);
}
outputStream.flush();
But when i'm doing that, if the network is faster than the datastream, I get quickly out of the loop.
Is there a 'good' way to do that? I though about doing active waiting but it is not a good solution, especially for mobiles. Another way is to do something like this :
while (true) {
while (inputStream.available() < BUFFER_SIZE) {
wait(TIME);
}
inputStream.read(buffer);
outputStream.write(buffer);
}
outputStream.flush();
But it sound quite dirty for me... Is there sleeker solution?

What I do in these situations if simply fill up a byte array (my buffer) until either I've hit the end of the data I'm about to transmit, or the buffer is full. In which case the buffer is ready to be passed to my Socket transmission logic. Admittedly, I do not do this on video or audio though … only on “regular” data.
Something worth noting is this will give a "janky" user experience to the recipient of that data (it might look like the network is stopping for short periods then running normally again ... the time the buffer is using to fill up). So if you have to use a buffered approach on either video or audio be careful on what buffer size you decide to work with.
For things like video it's been my experence to use streaming based logic versus buffered, but you apparently have some different and interesting requirements.

I can't think of a pretty way of doing this, but one option might be to create a local socket pair, use the 'client' end of the pair as the MediaRecorder output fd, and buffer between the local-server socket and the remote-server. This way, you can block on the local-server until there is data.
Another possibility is to use a file-based pipe/fifo (so the disk doesn't fill up), but I can't remember if the Java layer exposes mkfifo functionality.
In any event, you probably want to look at FileReader, since reads on that should block.
Hope this helps,
Phil Lello

Java: ignoring an input stream - will buffers overflow and bad things happen?

I have a client connecting to my server. The client sends some messages to the server which I do not care about and do not want to waste time parsing its messages if I'm not going to be using them. All the i/o I'm using is simple java i/o, not nio.
If I create the input stream and just never read from it, can that buffer fill up and cause problems? If so, is there something I can do or a property I can set to have it just throw away data that it sees?
Now what if the server doesn't create the input stream at all? Will that cause any problems on the client/sending side?
Please let me know.
Thanks,
jbu

When you accept a connection from a client, you get an InputStream. If you don't read from that stream, the client's data will buffer up. Eventually, the buffer will fill up and the client will block when it tries to write more data. If the client writes all of its data before reading a response from the server, you will end up with a pretty classic deadlock situation. If you really don't care about the data from the client, just read (or call skip) until EOF and drop the data. Alternatively, if it's not a standard request/response (like HTTP) protocol, fire up a new thread that continually reads the stream to keep it from getting backed up.

If you get no useful data from the client, what's the point of allowing it to connect?

I'm not sure of the implications of never reading from a buffer in Java -- I'd guess that eventually the OS would stop accepting data on that socket, but I'm not sure there.
Why don't you just call the skip method of your InputStream occasionally with a large number, to ensure that you discard the data?

InputStream in = ....
byte[] buffer = new byte[4096] // or whatever
while(true)
in.read(buffer);
if you accept the connection, you should read the data. to tell you the truth i have never seen (or could forsee) a situation where this (a server that ignores all data) could be useful.

I think you get the InputStream once you accept the request, so if you don't acknowledge that request the underlying framework (i.e. tomcat) will drop that request (after some lapsed time).
Regards.