How do I properly determine if my client is still connected to the server with C sockets? -


i have client connected server via c berkeley sockets. (try to) periodically check see if connection still valid calling recv() on socket msg_dontwait , msg_peek. however, i'm finding call returns eagain both when connection down in cases (e.g., after connection's interface shut down) , when there no data read. hence, there no way me distinguish whether connection still valid or not using method.

here's function:

/* return 1 if still connected, 0 otherwise */  int still_connected() {     int nbytes_recvd = 0;     char buf[2];     int err;      nbytes_recvd = recv(fd,buf,sizeof(buf),msg_peek|msg_dontwait);     err = errno;      if ( nbytes_recvd == 0 )     {         return 0;     }     else if ( nbytes_recvd < 0 )     {        if ( (err == enotsock) ||             (err == enotconn) ||             (err == einval) ||             (err == econnrefused) ||             (err == ebadf) ||             (err == eopnotsupp) )        {           return -1;        }     }      /* nbytes_recvd > 0 or eagain or ewouldblock */     /* eagain if connection down because shut down    interface */      return 1; }

how can accurately check whether connection still valid?

from point of view of 1 of 2 endpoints of tcp connection, there no difference between peer had disappeared , peer still present isn't sending data. can't distinguish these situations recv() or other method.

the way detect if peer down, has reset, has disappeared, or has become unreachable, send data , see happens. there 2 options:

  • enable tcp keepalives (so_keepalive). cause tcp send keepalive packet once in while , expect ack peer. if peer fails ack, can learn connection has been broken.
  • send actual application data (or application-level keepalive message) on schedule of choice. similarily, if peer fails respond data (or socket error after sending it), can learn connection has been broken.

Comments

Post a Comment

Popular posts from this blog

c# - Send Image in Json : 400 Bad request -

from android trying send image class of data, iis webservice. (c#) the problem 400 bad request . the image being encoded base64 . , placed json rest of class elements. my guess base64 not valid inside json. server not understand it. if set string "" , post accepted fine. so question is, how make base64 valid within json array? ( tried url.encode no success). or how should send image android webservice? gson gson = new gson(); string json = gson.tojson(record); // record has param { string base64photo } how big image? i'm pretty sure surpassing iis json size limit (default 4 mb). check http://geekswithblogs.net/frankw/archive/2008/08/05/how-to-configure-maxjsonlength-in-asp.net-ajax-applications.aspx or http://www.webtrenches.com/post.cfm/iis7-file-upload-size-limits good luck!
Read more

javascript - addthis share facebook and google+ url -

i attempting use addthis create simple url shares whichever current page user on when click share button. of right now, have twitter working. when user clicks, able see url populated in tweet box. when user clicks facebook or google+, url doesn't seem show in share box. <ul class="addthis_toolbox addthis_default_style "> <li><a class="addthis_button_facebook"><img src="/img/facebook-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_twitter"><img src="/img/twitter-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_google_plusone_share"><img src="/img/google-social.png" width="20" height="20" border="0" alt="s...
Read more

ios - Show keyboard with UITextField in the input accessory view -

i have buttona , when buttona clicked, want keyboard show uitextfield in inputaccessoryview. there way have keyboard show manually , set inputaccessoryview without having uitextfield initially? thanks. you cannot summon keyboard without object can become first responder. there 2 ways work around: subclass uiview , implement uikeyinput protocol in it. example: in .h file: @interface inputobject : uiview<uikeyinput> @property (nonatomic, copy) nsstring *text; @property (nonatomic, strong) uiview *inputaccessoryview; // must override inputaccessoryview , since it's readonly default @end in .m file, implement protocol: - (bool)canbecomefirstresponder { return yes; } - (bool)hastext { return [self.text length]; } - (void)inserttext:(nsstring *)text { nsstring *selftext = self.text ? self.text : @""; self.text = [selftext stringbyappendingstring:text]; [[nsnotificationcenter defaultcenter] postnotificationname:kinputobjec...
Read more