fblocked − Test whether the last input operation exhausted
all available input

fblocked channelId

     The fblocked command returns 1 if the most recent input
operation on channelId returned less information than
requested because all available input was exhausted.  For
example, if gets is invoked when there are only three
characters available for input and no end‐of‐line sequence,
gets returns an empty string and a subsequent call to
fblocked will return 1.

     ChannelId must be an identifier for an open channel
such as a Tcl standard channel (stdin, stdout, or stderr),
the return value from an invocation of open or socket, or
the result of a channel creation command provided by a Tcl

The fblocked command is particularly useful when writing
network servers, as it allows you to write your code in a
line‐by‐line style without preventing the servicing of other
connections.  This can be seen in this simple echo‐service:

     # This is called whenever a new client connects to the
server proc connect {chan host port} {
    set clientName [format <%s:%d> $host $port]
    puts "connection from $clientName"
    fconfigure $chan ‐blocking 0 ‐buffering line
    fileevent $chan readable [list echoLine $chan
$clientName] }

# This is called whenever either at least one byte of input
# data is available, or the channel was closed by the
client.  proc echoLine {chan clientName} {
    gets $chan line
    if {[eof $chan]} {
        puts "finishing connection from $clientName"
        close $chan
    } elseif {![fblocked $chan]} {
        # Didn’t block waiting for end‐of‐line
        puts "$clientName ‐ $line"
        puts $chan $line
    } }

# Create the server socket and enter the event‐loop to wait
# for incoming connections...  socket ‐server connect 12345
vwait forever


gets(n), open(n), read(n), socket(n),

blocking, nonblocking