Trying TCP sampler for sending text message to server over TCP and expecting response ack for the same.
getting request success.but response data is blank(expecting response acknowledgment).
Given you have connection established already it automatically means that JMeter has received SYN-ACK from the AUT (application under test) and it has received ASK from JMeter.
TCP handshake looks like:
JMeter a TCP SYNchronize packet to AUT
AUT receives JMeter's SYN
AUT sends a SYNchronize-ACKnowledgement
JMeter receives AUT SYN-ACK
JMeter sends ACKnowledge
AUT receives ACK
Java doesn't have raw sockets support, neither does JMeter so if you want to fully control TCP messages flow and be able to see the headers and flags - you will need to go a level deeper using i.e. jNetCap library from JSR223 Test Elements.
You might also be interested in How to Load Test TCP Protocol Services with JMeter article which explains how you can test your TCP server performance with JMeter and HTTP Raw Request sampler easier to use than JMeter's TCP Sampler
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I am working on a high-performance TCP server, and I see the server not processing fast enough on and off when I pump high traffic using a TCP client. Upon close inspection, I see spikes in "delta time" on the TCP server. And, I see the server sending an ACK and 0.8 seconds later sending PSH,ACK for the same seqno. I am seeing this pattern multiple times in the pcap. Can experts comment on why the server is sending an ACK followed by a PSH,ACK with a delay in between?
TCP SERVER PCAP
To simplify what ACK and PSH means
ACK will always be present, it simply informs the client what was the last received byte by the server.
PSH tells the client/server to push the bytes to the application layer (the bytes forms a full message).
The usual scenario you are used to, is more or less the following:
The OS has a buffer where it stores received data from the client.
As soon as a packet is received, it is added to the buffer.
The application calls the socket receive method and takes the data out of the buffer
The application writes back data into the socket (response)
the OS sends a packet with flags PSH,ACK
Now imagine those scenarios:
step 4 does not happen (application does not write back any data, or takes too long to write it)
=> OS acknowledge the reception with just an ACK (the packet will not have any data in it), if the application decides later on to send something, it will be sent with PSH,ACK.
the message/data sent by the server is too big to fit in one packet:
the first packets will not have PSH flag, and will only have the ACK flag
the the last packet will have the flags PSH,ACK, to inform the end of the message.
I have a strange problem here. I am writing a small server application in C++ on a Raspberry, and a commercial program running on Android is meant to connect to it. The data exchanged are very small packages for position control of a technical device. My program works fine, I set up a standard TCP/IP socket, bind it to an address, start listening and when a SYN signal comes from the client, i accept it. Then the client sends request, I send answers, and all potential error messages and socket errors are of course monitored. The communication from client to server looks like this with other programs using the same protocol (and everything works fine):
Client > SYN
SYN ACK < Server
Client > ACK
Client PSH ACK ... some request ...
ACK < Server
PSH ACK ... some reply ... < Server
and so on. This works fine with other programs using the same protocol, but not with the one on an Android 7 tablet. The reason is that the Client on the tablet sends FIN, ACK followed by SYN immediately when receiving the first reply from the server. The client has received the reply and processed it happily without any error - there is no obvious reason for the FIN! That might be a bug, but I do not have access to the client code. Is there a workaround to handle this aside from calling "accept" again after each write from the server???? Many thanks in advance ...
(Original title: "Weird TCP connection close behavior")
I am troubleshooting TCP connection process using Wireshark. Client opens connection to server (I tried two different servers), and starts receiving long stream of data. At some point in time client wants to stop and sends server [FIN, ACK] packet, but server does not stop sending data, it continues till its own full stream end, and then sends its own completion packet [FIN, PSH, ACK]. I figured it out keeping reading data from the client's socket after client sent FIN packet. Also, after client sent this FIN packet, its state is FIN_WAIT, thus waiting for FIN response from server...
Why servers do not stop sending data and respond to FIN packet with acknowledgment with FIN set?
I would expect, after client sends FIN packet, server will still send several packets which were on the fly before it received FIN, but not the whole pack of long data stream!
Edit: reading this I think that web server is stuck in stage "CLOSE-WAIT: The server waits for the application process on its end to signal that it is ready to close" (third row), and its data sending process "is done" when it flushed all contents to the socket at its end, and this process can not be terminated. Weird.
Edit1: it appears my question is a little different one. I need to totally terminate connection at client's side, so that server stops sending data, and it (server) would not go crazy about forceful termination from client's side, and aborted its data sending thread at its side being ready for next connection.
Edit2: environment is HTTP servers.
The client has only shutdown the connection for output, not closed it. So the server is fully entitled to keep sending.
If the client had closed the connection, it would issue an RST in response to any further data received, which would stop the server from sending any more, modulo buffering.
Why servers do not stop sending data and respond to FIN packet with acknowledgment with FIN set?
Why should they? The client has said it won't send another request, but that doesn't mean it isn't interested in the response to any requests it has already sent.
Most protocols, such as HTTP, specify that the server should complete the response to the current request and only then close the connection. This is not an abnormal abort, it's just a promise not to send anything else.
I am new to ZMQ. I find ZMQ socket implementation much simpler than winsock. But my doubt is that "can a client created using ZMQ TCP socket talk to conventional TCP server?" in other words Can my ZMQ client communicate with a TELNET server implemented using winsock?
No it cannot. ZeroMQ is a messaging library and is not just a pure socket. It uses its own protocol called ZMTP and both endpoints are required to understand it.
Yes you can. It's called a ZMQ_STREAM socket. Documentation is here: zmq_socket.txt
A socket of type ZMQ_STREAM is used to send and receive TCP data from a non-ØMQ peer, when using the tcp:// transport. A ZMQ_STREAM socket can act as client and/or server, sending and/or receiving TCP data asynchronously.
When receiving TCP data, a ZMQ_STREAM socket shall prepend a message part containing the identity of the originating peer to the message before passing it to the application. Messages received are fair-queued from among all connected peers.
When sending TCP data, a ZMQ_STREAM socket shall remove the first part of the message and use it to determine the identity of the peer the message shall be routed to, and unroutable messages shall cause an EHOSTUNREACH or EAGAIN error.
I need to performance test an application [BRM remedy, ar user] that is using an TCP protocol. I don’t have much knowledge on TCP Protocol.
I tried with wireshark to analyze the requests, but it is showing TCP request with data checks [Assuming that my data is splitting into small chunks by TCP protocol implementation].
Can you please suggest me some good tool that can monitor TCP requests and responses [like HTTP fiddler for HTTP Protocol]?
I will be using Jmeter for the perf testing.
You might be seeing packets in the TCP format , but you can docode your packet in wire share too.
Open your capture in wireshark go to Analyze -> Decode As -> and all request will will traslated accodingly.
If you want analyse a specific TCP stream or want to to which tcp stream a packet belong to , right click on packet and click "Follow tcp..." , you will be finding allthe packets belong that particular tcp stream.
It mostly work for me with above two functionality , hope same for you.