Hi Simon, If I understood your approach correctly, then this will work only if I am the one that implements the client, right ? What about cases when client is browser or curl, not my c++ app ?
Thank you, -Grigor On Tue, Aug 22, 2017 at 1:13 PM, Simon De Uvarow <sdeuva...@gmail.com> wrote: > "No olvides, no traiciones, lo que llevas bien dentro de ti. No olvides, no > traiciones, lo que siempre te ha hecho vivir." > > On Tue, Aug 22, 2017 at 11:36 AM, André Warnier (tomcat) <a...@ice-sa.com> > wrote: > > > On 22.08.2017 10:50, Grigor Aleksanyan wrote: > > > >> Hi, > >> > >> I have a web application (.war file) running under > *apache-tomcat-7.0.52*. > >> It is a proxy application between my c++ client and server apps. Once > HTTP > >> request (from the client) is received by web application, it propagates > >> request to the server and sends response back to the client once it is > >> ready. Server may need long time before it produces some data to send to > >> the client (also it can send data by chunks with really long delays > etc.). > >> > >> My question is. > >> > >> *Is there a way to detect client disconnect before the time server has > >> something ready to be written to the output stream?* In case if server > >> writes something after client's disconnect, obviously I will get an > >> exception and can handle it properly. But my goal is to avoid waiting > for > >> the server to produce some data to write, to detect this. I saw a couple > >> of > >> forums and mailing lists where people say that only way to do this, is > by > >> writing to outputstream. But in case of websockets I know that I can get > >> notifications that connection was closed by the client. > >> > >> I believe this is a very common issue people face and there should be a > >> graceful solution for this for HTTP as well. > >> > >> Can you please advice ? > >> > >> > > Hi. > > You describe the problem well, and even the solution. > > > > The problem is not at the Tomcat level, nor at the HTTP level. The > problem > > is at the lower TCP/IP level, and there is not much that Tomcat or HTTP > can > > do about it. > > When a client establishes a TCP connection to a server, this is a > > "virtual" connection. There is no hardware or physical line that is > > dedicated to this connection. In other words, it exists only as long as > the > > server and the client agree that it exists. > > (And if there are any firewalls or proxies in-between, it is not even one > > connection, it is multiple chained connections). > > > > If the client just decides to "go away", without explicitly telling the > > server so, the server side is totally unaware that the client has gone, > > until the server tries to send a packet on the connection, and (some time > > after that) expects to receive an "ACK" and does not get one. > > In the case of websocket, you have a well-behaved client, that > > (supposedly) tells the server when it is closing the connection. So the > > application could test this, by sending some kind of "probe" from time to > > time, to check that the client is still there. > > And the client would expect such a probe, and know that it is a probe, > and > > that it is not data. So it could just respond with some kind of "ack", > that > > the server also would interpret correctly. > > But even then, if the client host were to just crash (or anything > > in-between, like a firewall or a router e.g.) you would have the same > issue > > : nothing is sent to the server saying that the connection no longer > > exists, so the server thinks it is still there, as long as it does not > send > > anything. > > > > And you are also right to say that it affects a lot of people and their > > applications. > > It is frustrating to e.g. start some long and heavy search in a database, > > and then when the result appears, find out that there is nobody listening > > anymore (*). > > There may be some good universal solutions to this, but so far I don't > > know of any. > > Fame awaits you, if you find one that can be universally applicable. > > > > > > (*) and even if you knew that the client has gone, some tasks which you > > started in the background, may not be so easy to stop in the middle > either. > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org > > For additional commands, e-mail: users-h...@tomcat.apache.org > > > > > For cases that could have the described issue (HTTP request that may take > too long), I decided to create the "Interactive Task Manager". > The HTTP request starts a task to process something at server side, and > gets a quick response with the UUID of the task. Then the client can pool > asking if the task has finished. > When the task finishes, it stores the result as JSON in a temporal file. > When the client gets the result, the Interactive Task Manager deletes the > temporal file. > The Interactive Task Manager has it own thread pool to process the tasks. > > It adds some overhead: HTTP requests asking for news + storing the result > to file + and reading it back. But it doesn't depend on configuration > changes, or hardware speed. It's robust. > > I have the idea that HTTP requests should be resolved quikly (always less > than some seconds). If not, it's a bug, so we need to reimplement the > backend to fix it. > > It's one possible solution. Maybe not the best. > Hope it helps. > -- ------------------------------ *CONFIDENTIALITY NOTE:* THIS E-MAIL MESSAGE AND ANY ATTACHMENTS MAY CONTAIN CONFIDENTIAL AND PRIVILEGED INFORMATION OF ONEMARKETDATA, LLC. 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