NaviServer - programmable web server

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# ns_sockselect(n) 4.99.8 naviserver "NaviServer Built-in Commands"

## Name

ns_sockselect - Determine readable file id's

## Table Of Contents

## Synopsis

- ns_sockselect ?timeout? rfds wfds efds

## Description

ns_sockselect uses a select() call to determine which file id's re readable, writeable, or have exceptional conditions. ns_sockselect returns a list of three lists of: readable file id's, writeable file id's, and file id's with exceptions. The -timeout option specifies the length of time to wait in seconds for ns_sockselect to return before timing out. The rfds, wfds, and efds arguments are lists of readable file id's, writeable file id's, and file id's with exceptions, respectively.

## COMMANDS

ns_sockselect ?timeout? rfds wfds efds

## EXAMPLES

    # Start nonblocking connect()'s to www01 through
    #www09.foo.com and remember the read fileid which
    #corresponds to each write fileid.
    for {set n 1} {$n < 10} {incr n} {
      set host [format "www%2d.foo.com" $n]
      set fds [ns_sockopen -nonblock $host 80]
      set r [lindex $fds ]
      set w [lindex $fds 1]
      set w2r($w) $r
      lappend wfds $w
    }
    # All connect()'s are in progress, use select to wait for one or
    # more to become writable in the next two seconds which means #
    # they may have connected.  We're not interested in readable or
    # exception sockets so the corresponding lists are empty
    # (i.e., {}).
    set sel [ns_sockselect -timeout 2 {} $wfds {}]
    # Select returned - get the sockets ready to write to.
    set wfds [lindex $sel 1]
    # Use ns_sockcheck to see if the sockets actually connected and
    # didn't become writable because the connect() failed (e.g., no
    # Web server was running on port 80 on the corresponding machine).
    # Note that the wfds list may be empty, meaning all sockets timed
    # out on connect.
    set ok ""
    foreach w $wfds {
      if [ns_sockcheck $w] {
        # Socket is connected - send a GET HTTP request.
        lappend ok $w
        puts $w "GET /index.htm HTTP/1.0\r\n\r"

        # The flush is important, otherwise the remote
        # server may never see the data.
        flush $w
      }
    }
    # Get the read ids for each socket which we sent the GET request to.
    foreach w $ok {
       lappend rfds $w2r($w)
    }
    # Use select again to wait for the read sockets to have data
    # available in response to the GET request.
    set sel [ns_sockselect -timeout 2 $rfds {} {}]
    set rfds [lindex $sel 0]
    # Read the pages which came back.
    foreach r $rfds {
      if [ns_sockcheck $r] {
        set page($r) [read $r]
      }
    }
    # Close all the sockets
    foreach w [array names w2r] {
       close $w
       close $w2r($w)
    }

## See Also

nsd

## Keywords

NaviServer, socket