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7929 :: How to make HttpServer more robust against too many connection opened?

• alexeypetrushin (orginal) [2021-05-05T13:00:38+02:00] view original

  Is there a way to make HttpServer more robust?

  Like if too many connections opened it should fail but maybe somehow find oldest unused connection and close it, or refuse the new connection or something like that? Currently it would fail.

  import os, asyncdispatch, asynchttpserver, httpclient, httpcore
  
  proc run_server =
    proc handler(req: Request): Future[void] {.gcsafe.} =
      return req.respond(Http200, "ok")
    var server = new_async_http_server()
    async_check server.serve(Port(4000), handler, "localhost")
    run_forever()
  
  proc run_client =
    for _ in 1..1000:
      let client = new_http_client()
      echo client.post_content("http://localhost:4000/db/test", "ask")
  
  case param_str(1)
  of "server": run_server()
  of "client": run_client()
  else:
    echo "wrong command"
    quit(1)
  Run

  Run client and server nim c -r script.nim server and nim c -r script.nim client and the server would fail with the error:

  
  Error: unhandled exception: Too many open files
  Async traceback:
    /alex/projects/nim/play.nim(18)                                play
    /alex/projects/nim/play.nim(10)                                run_server
    /balex/applications/nim-1.4.2/lib/pure/asyncdispatch.nim(1930) runForever
    /balex/applications/nim-1.4.2/lib/pure/asyncdispatch.nim(1627) poll
    /balex/applications/nim-1.4.2/lib/pure/asyncdispatch.nim(1368) runOnce
    /balex/applications/nim-1.4.2/lib/pure/asyncdispatch.nim(208)  processPendingCallbacks
    /balex/applications/nim-1.4.2/lib/pure/asyncmacro.nim(29)      serveNimAsyncContinue
    /balex/applications/nim-1.4.2/lib/pure/asyncmacro.nim(145)     serveIter
    /balex/applications/nim-1.4.2/lib/pure/asyncfutures.nim(372)   read
  Exception message: Too many open files
  Exception type: [OSError]
  Run

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• giaco (orginal) [2021-05-05T13:13:40+02:00] view original

  you're probably hitting user limit for your operating system

  if linux base, what's the output of

  $ ulimit -n
  Run

  ?

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• alexeypetrushin (orginal) [2021-05-05T13:27:05+02:00] view original

  But shouldn't the server be robust and don't fail?

  Like it could refuse to take new connection, or maybe drop old, but not crash.

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• DomoSokrat (orginal) [2021-05-05T14:00:14+02:00] view original

  serve has an optional argument assumedDescriptorsPerRequest which defaults to -1. From the docs:

  If assumedDescriptorsPerRequest is 0 or greater the server cares about the process's maximum file descriptor limit. It then ensures that the process still has the resources for assumedDescriptorsPerRequest file descriptors before accepting a connection.

  That is, use

  async_check server.serve(Port(4000), handler, "localhost", 5)
  Run

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