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

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