I have a C# server that accepts multiple clients, and multiple messages from each client.
1- In order to start reading from each client i need to pass a buffer (bytes), but the problem is I don't know how much data is the client is going to send. So is there a way to know how much data a client is going to send so that i can start reading for the correct amount of data?
2- Is it oK if i use only 1 byte array to read from all clients? or do i need to create a byte array for reading from each client?
Unless your protocol dictates how much data will be sent, no. Typically you read one buffer's-worth and then potentially read more. It will really depend on the protocol though. If the client can only send one message on each connection, you'll typically keep reading until the next call returns 0 bytes. Otherwise either the messages have delimiters or a length-prefix.
Absolutely not - assuming you're going to be reading from multiple clients concurrently (why else would you use asynchronous communications?) you'd end up with the different clients' data all being written over each other. Create a new byte array for each client. Depending on exactly what you do with the data you may be able to reuse the same byte array for the next read for the same client - and you could reuse the byte array for later clients, if you really wanted... but don't read from multiple clients at the same time into the same buffer.
So is there a way to know how much data a client is going to send so that i can start reading for the correct amount of data?
Any protocol ought to have some mechanism for a client to indicate when it is done sending data, either as a "length" value that is sent before the actual data, or as a special terminating sequence that is sent after the data.
Is it oK if i use only 1 byte array to read from all clients? or do i need to create a byte array for reading from each client?
Depends on how your program works. If you'll have multiple simultaneous clients, obviously you can't have just a single buffer because they'll end up overwriting each other. If it's one client after the other, but only one at a time, there's no problem in having just one buffer.
Related
I have a server that sends telemetry data of varying size to receivers, or as I'll call them, clients, via NetworkStream. I aim for maximum speed, so I want minimal delays. The frequency is uncontrolled, so I'd like to use an infinite loop in my clients, that uses NetworkStream.Read to read the data, process it, then repeat.
My problem is that sometimes, if two packets are sent very quickly, and a client has a slow internet connection, the two packets will be received as a continous stream, resulting unprocessable data. A half-solution I found (mostly to confirm that this is indeed the error) is to have a small delay after/before each transmission, using System.Threading.Thread.Sleep(100), but not only I find Sleep a botchy solution, it's inconsistent, as it also slows down clients with a good connection, and the problem may persist with an even worse connection.
What I'd like to do is to have the server send a gap between each transmission, providing a separation regardless of internet speed, as NetworkStream.Read should finish after the current continous stream ends. I don't understand deeply the working of a NetworkStream, and have no idea what a few bytes of empty stream look like or how it could be implemented. Any ideas?
I would strong advise changing the protocol instead if you possibly can. TCP is a stream-based protocol, and any attempt to effectively ignore that is likely to be unreliable.
Instead, I'd suggest changing to make it a stream of messages where each message has a prefix indicating the length of the body of the message. That way it doesn't matter if a particular message is split across multiple packets or received in the same packet as other messages. It also makes reading easier for clients: they know exactly how much data to read, so can just do that in a simple loop.
If you're concerned that the length prefix will introduce too much overhead (if the data is often small) you could potentially make the protocol slightly more complicated with a single message containing a whole batch of information (multiple telemetry items).
But fundamentally, it's worth assuming that the data will be split into multiple packets, combined again etc. Don't assume that one write operation corresponds to one read operation.
You don't specifically mention the ProtocolType you're using on your NetworkStream but TCP is bound to fail your requirements. Intermediate routers/switches have no way to know your intent is to separate packets by time and will not respect that desire. Furthermore, TCP, being stream oriented, delivers packets in order, and it has error correction against dropped packets and corrupt packets. On any occurrence of one or the other it will hold all further packets until the error packet is retransmitted - and then you'll probably get them all in a bunch.
Use UDP and implement throttling on the receiving (i.e., client) side - throwing out data if you're falling behind.
I want to send huge buffers (from 100MB to 1GB) of data by TCP. I solved it by dividing buffer to smaller (approximately 1MB buffers) and sending by socket.send(). Each call of socket.send() method, send part of data (smaller buffer) packed in specific structure: [start byte(1B), Timestamp(4B), Command(4B), Length of data(4B), Data to send(?B), CRC(1B), End byte(1B)]. Everything works fine, when only one huge buffer is sent by specific port. But when I try to send in the same time buffer with another data (very small, e.g. 20 bytes) using the same TCP port, then TCP mixed data in buffers and it's not possible to decode buffer any more. 'Start byte' and 'end byte' in the buffer are not useful to find start and end of the buffer, because it's probable that these bytes appear in data.
EDIT: Issue does not affect the order or IDs between packages but bytes in the packages. At the beginning everything works fine and each buffer is decoded properly. After a while it is not possible to decode buffer, because it contains incorrect data. It looks like bytes in the buffer were moved or changed. Fields at the beginning of the buffer (timestamp, command, length) contain impossible values. So when I want to get length of sent data, I get e.g. value like -1534501133 instead of 1048556 (1048556 is a correct maximum size of the sent data in one package). It happens randomly but it is always connected with the moment when smaller independent buffer is sent. The additional information is, that the smaller buffers are sent repetitively using timers and the problem happens in random moments. Sometimes it is even possible to send whole data (e.g. 300 MB) without problem but it happens very rarely.
I hope, I described it clearly enough.
Do you have any suggestions how to avoid this problem?
Tag your data with a unique id so you know what data relates to what message. Also, separate the packet header from the packet payload.
So, your first request would be [ID][PACKETTYPE][TIME][COMMAND][LENGTH][CRC]
Second would be [ID][PACKETTYPE][DATA]
You can then match up the IDs with the types of packet. So packet type would be 'HEADER' or 'PAYLOAD', the header would contain the meta data for the payload allowing you to make sure that it doesnt get mixed up with other data.
I am trying to bind Sound and Image Sequence Data through ArrayList in order to get it synchronized and serializing it through Binary formatter to be send over Network stream.
The Server end threw an exception:
THE STREAM CAN NOT SUPPORT SEEK OPERATION.
What should I have to do in order to sync Objects to be sent over a single Network stream Instance
TCP is stream based and not message based (as UDP is). That means that there is no telling when a message starts or ends. TCP only guarantees that all bytes are received and in the correct order. It does not guarantee that everything sent with one Send() will be received with one Receive().
Hence you need to specify some kind of message identification mechanism. In this case, a header is the way to go as Jon suggested.
However, you need to understand that the entire header might not be received at once. And that two messages might arrive at once. So you need to parse the received buffer before sending anything to the BinaryFormatter for deserialization.
I would split each object you want to send out into a separate "message" where a message consists of (say) 4 bytes indicating the body length, and then the body itself.
When you want to send a serialized object, you serialize to a byte array, write out the length, then write out the data.
At the server side, you read the length, read that much data into a byte array, then deserialize from that message. The incoming stream is only used to read messages, not objects.
I have a TCP connection , which client is PHP and server is C#
this socket connection transfers a image to the socket server , but
randomly some times the transfer get corrupted [image hash is different]
PHP Client
$file = file_get_contents('img.bmp');
socket_write($socket,$file.$cordinates); it sends //image + sme other data
$recv = socket_read ($socket, 500, PHP_BINARY_READ) // read the server response
This stream always transfer a Bitmap image + some data .
C#
this.DataSocket = this.Listner.Accept();
int filelength = this.DataSocket.Receive(this.buffer, this.buffer.Length, SocketFlags.None)
i investigated that in a fresh-browser [newly opened ] this never failed. but when i using this created service several times frequently in the same browser this intended to fail.
when i check with a different browser or new instance of the browser it never failed in first few attempts.
i thought it was some problem with caching but i disable caching using headers but same problem exists
You can't simply expect to write an entire file to the socket at once, nor can you expect to read the file from the socket in one operation. The socket read and write APIs for just about any network programming API from BSD sockets to WinSock to .NET network classes are all going to transmit or receive data up to the desired byte count.
If you look at the documentation for PHP socket_write for example:
Returns the number of bytes successfully written to the socket or FALSE on failure. The error code can be retrieved with socket_last_error(). This code may be passed to socket_strerror() to get a textual explanation of the error.
Note:
It is perfectly valid for socket_write() to return zero which means no bytes have been written. Be sure to use the == operator to check for FALSE in case of an error.
You will typically want to choose a block size like 4096 or 16384 and loop transmitting or receiving that block size until you get the desired number of bytes transmitted or received. Your code will have to check the return value of the send or receive function you're calling and adjust your file pointer accordingly. If transmit returns 0, that could just mean the send buffer is full (not fatal) so continue sending (might want a Sleep(0) delay). If receive returns 0, this usually means the other side has cleanly closed the connection.
One of the most critical flaws in your simple network code usage is that you're not sending the size of the file before you send the file data, so there's no way for the receiver to know how much to read before sending their response. For a simple operation like this, I'd suggest just sending a binary 32bit integer (4 bytes). This would be part of the schema for your operation. So the receiver would first read 4 bytes and from that know how many more bytes need to be read (one buffer size at a time). The receiver keeps reading until they have that many bytes.
I hope this helps. It would be great if socket code were as simple as the usage you attempted, but unfortunately it isn't. You have to select a buffer size, and then keep reading or writing buffers of that size until you get what you want, and you have to convey to the other side how much data you plan on sending.
That you think caching has anything to do with the problem implies that either there is a lot of functionality outside of the code you've published which is affecting the result or that you are a very long way from understanding the problem.
Without knowing the structure of bmp files, my first concern would be how you separate the file from the additional info sent. A few things you could try...
If '$cordinates' (sic) is a fixed size, then put this at the front of the message, not the back
Log the size sent from PHP and the size received.
base64 encode the binary file before sending it (and decode at the receiving end)
Non of above solutions didn't work for me , but i found out that create a new instance every time after a one request will solve the problem. but i don't think its a reliable way.
i tried the client using ASP.NET but same results. i think its not a problem with client PHP its surely a problem of the socket server
I am using the NetworkStream of a TcpClient to send bytes from a .NET server to a Silverlight Client that receives them via a Socket. Sending from the client is done via Socket.SendAsync.
My question is, what is the minimum amount of bytes I can expect to be received "in one go" on both sides, without the need to send the message length too and put several byte messages together by myself.
Thanks,
Andrej
You absolutely should send the message length. Network streams are precisely that - streams of information. Basically there are three ways of recognising the end of a message:
Prefix the data with the length (don't forget that it's at least theoretically possible that you won't even get all of the length data in one packet)
Use a message delimiter/terminator
Only send one message each way per connection, and close the connection afterwards
It depends on your network settings, but the default length for network nodes is 1500 bytes and most modems take something off that. So most homes have 1460 bytes packet size.
The optimum size for your situation can be calculated
But people can always have their own settings, so there's no guarantee that you get the optimal packet size for all clients.