TweetFollow Us on Twitter

FTP Client in TCL-TK

Volume Number: 14 (1998)
Issue Number: 2
Column Tag: Alternate Environments

An FTP Fetch Client in Tcl/Tk

by Bruce O'Neel, Laurel MD

A light introduction to this powerful, multi-platform scripting language

Overview

Tcl/Tk (pronounced "tickle tee-kay") is a scripting language written by Dr. John Ousterhout while he was a professor at the University of California at Berkeley. Tcl can either be a standalone shell where you issue commands (like those of unix or the MPW shell), or it can be a library which you embed into your compiled program and use to issue commands. Tk is an extension to Tcl which provides graphical interface Tcl commands enabling you to write event driven programs with graphical interfaces.

Tcl/Tk has been very popular in the unix world for a long time and has recently been ported to Mac OS and Win95/NT. As of version 8.0 of Tcl/Tk, the Mac OS and Win95/NT ports have a native look and feel on their respective platforms. This article is going to provide a brief overview of Tcl/Tk and then present a demonstration Tcl/Tk program to fetch files using FTP.

Tcl/Tk Overview

Why is Tcl/Tk interesting? First, it is a dynamic scripting language. At run-time your scripts are byte compiled and run. You can get the names of procedures and variables at run-time; you can define new commands and new control statements at run-time; you can load new source code at run-time; and you can extend Tcl with your own shared libraries at run-time. Second, you can produce Mac like interfaces using the native port of Tk and you can do this quickly and interactively. Think of it as rapid prototyping for the Mac in a free language. Third, you can write scripts which can be moved unchanged from Mac OS to Win95/NT and most unix variants. Finally, you can easily write extensions to Tcl in any compiled language on the Mac, and they can either call and be called by C or produce shared libraries. These extensions also can be cross-platform if written to be portable. As an example, a group of people at NASA's Goddard Space Flight Center have written an extension to Tcl which reads and writes a file format called FITS used in astronomy ftp://legacy.gsfc.nasa.gov/software/ftools/release/other/fitstclmac-src.sit.hqx.

There are a few notes on Tcl's syntax that will make reading the code easier. First, remember that Tcl works by string substitution and that, from your point of view, everything is a string. $varname means look up the value that is currently assigned to a variable and put that string in place of $varname. [command arg arg] means execute what ever is between the square brackets and substitute the value in place of [command arg arg]. Finally, curly braces are used around parts of code you want to execute later and defer evaluation until sometime in the future.

An FTP Client

I thought that a good demo of Tcl/Tk for the Mac would be an FTP client. Now, I didn't want to rewrite Fetch or Anarchie, but, I did want a useful example. The example program works but there are many features left for the reader to complete and the sample probably won't work unless you FTP to a unix system. One develops a lot of respect for Anarchie or Fetch when you try to repeat their author's work.

So, even though this is just a simple example, what made it good for Tcl/Tk? First, it was quick and easy to write. I took about 4-6 hours to write most of the code, with a little bit of time to clean things up for publication. Second, the resulting executable is small at around 27 Kbytes and the UI is very Mac like. Third the same source worked on more than one system. I was also able to run this on a unix system pretty much unchanged for additional testing and on the unix system it looked like I was running a Motif application. Finally I wanted a GUI and TCP/IP sockets in my program and Tcl/Tk has all of this easily built in, debugged, and well documented. Plus, you can experiment interactively with your code rather than compile, link, run, crash, debug,and edit as you must normally do.

There are two downsides to Mac Tcl/Tk applications. The first is that you have to install Tcl/Tk. The small application depends on some shared libraries, but, you could avoid the need to already have installed Tcl/Tk by using the non-shared version. The second downside is that the current version requires quite a bit of memory. The default is 4mb but you might have to bump this up if your programs crash. Many crashes are caused by running out of memory.

Displaying aWindow

The first thing the user sees when they start the program is a dialog produced by the new_connection proc, listed below. The dialog looks like

Figure 1. Open Connection Dialog.

Because Tcl/Tk is interactive, you could download it from http://sunscript.sun.com and type in each following command and watch what happens as you go. This is a very quick way to learn how Tcl/Tk works.

new_connection
This is the main dialog the user interacts with and an example of Tcl/Tk
programming. This asks the user for their hostname, username (optional),
password (optional), and directory to connect to. When they click the
connect button, it brings up a directory list of that directory.

# Procedure to open a new connection.
proc new_connection {} {
  
  # so we can access the global variable FTP
  global FTP

  # This sets the variable named t to the result of the 
  # toplevel command
  # toplevel, like all Tk Widget creation commands returns 
  # the name of the widget,
  # .new_connection in this case, as it's result.
  set t [toplevel .new_connection -menu .menubar]
  wm title $t "Open Connection"
  
  # create a text label
  label $t.title -text "Open a new FTP connection"
  # grid is a geometry manager. This puts the title on the 
  # screen.
  grid $t.title -columnspan 2

  label $t.hostl -text "Hostname:"
  # associate the variable FTP(hostname) with a text entry 
  # area on the screen.
  # note that there is not $ before FTP(hostname)
  entry $t.hoste -textvariable FTP(hostname)
  grid $t.hostl $t.hoste

  label $t.userl -text "Username:"
  entry $t.usere -textvariable FTP(username)
  grid $t.userl $t.usere
  
  label $t.passl -text "Password:"
  # -show * echos * rather than the user's keystrokes
  entry $t.passe -textvariable FTP(password) -show *
  grid $t.passl $t.passe
  
  label $t.dirl -text "Directory:"
  entry $t.dire -textvariable FTP(directory)
  
  # create a button which when it runs the command up_dir
  button $t.dirup -text "Up" -command "up_dir" 
  grid $t.dirl $t.dire $t.dirup
  
  # put up two radio buttons to set datamode. Tied together 
  # by the -variable option.
  radiobutton $t.binary -variable FTP(mode) -text Binary \
    -value Binary
  radiobutton $t.ascii -variable FTP(mode) -text Ascii \
    -value Ascii
  label $t.datamode -text "Data Mode: "
  grid $t.datamode $t.binary $t.ascii
  
  # frames hold things
  frame $t.direc
  label $t.direc.title -text "Remote Directory"
  # pack is another geometry manager and puts the title at 
  # the top of this frame
  pack $t.direc.title -side top
  # the following three commands set up a text box and two 
  # scroll bars
  set FTP(listbox) [listbox $t.direc.list \
    -xscrollcommand [list $t.direc.xscroll set] \
    -yscrollcommand [list $t.direc.yscroll set]]
  scrollbar $t.direc.xscroll -orient horizontal \
    -command [list $t.direc.list xview]
  scrollbar $t.direc.yscroll -orient vertical \
    -command [list $t.direc.list yview]
  # these pack commands put the listbox and the scrollbars on 
  # the screen
  pack $t.direc.xscroll -side bottom -fill x
  pack $t.direc.yscroll -side right -fill y
  pack $t.direc.list -side left -fill both -expand true
  
  # put the whole frame with the remote directory listing on 
  # the screen
  grid $t.direc -columnspan 2
  
  # attach the event of double mouse button 1 (on the Mac, 
  # double click) when within
  # the widget $t.direc.list to the event of running the 
  # command get_file_or_dir.
  # In other words, this sets up a routine such that when you 
  # double click 
  # in the list box your routine get_file_or_dir is called
  bind $t.direc.list <Double-1> {get_file_or_dir}

  button $t.connect -text Connect \
    -command "get_dir $t.direc.list"
  
  # destroy deletes a widget and all of it's children
  button $t.cancel -text Cancel -command "destroy $t"
  grid $t.connect $t.cancel
}

This code doesn't produce the nicest looking dialog, but, it's functional. It would be much prettier if I went through and added space around widgets and added colors. Note that the functions of the dialog are quite separate from the layout. This allows me to go through and change the design of the dialog without changing the supporting code.

Connecting to the Server

Once the user has filled out the connection dialog and clicked Connect it's time to get a directory listing. The bit of code which talks to the remote FTP server and gets directory looks like this:

ftp_get_dir
This bit of code reads the global FTP array variable and returns as its
result the directory listing from the remote system. It connects to
FTP(hostname) as user FTP(username), or anonymous if blank, using a
password of FTP(password), or user@host if blank. It then changes directory
to FTP(directory) and gets that directory and returns the result as a big
string.

# The guts of getting an FTP directory. Note that this is 
# the netscape connect, do 
# something, and quit. Really inefficient but much easier to 
# implement.
proc ftp_get_dir {} {
  global FTP
  set FTP(data_sock) 0

  update_status \
    "Getting directory from site $FTP(hostname)"

  update_status "Establishing FTP connection ..."
  
  # connect to the remote system
  set FTP(ftp_sock) [socket $FTP(hostname) ftp]
  fconfigure $FTP(ftp_sock) -blocking 0 -buffering none
  
  # call a routine ftp_read_line when the remote socket is 
  # readable
  fileevent $FTP(ftp_sock) readable ftp_read_line

  if {[ftp_read] > 3} {
    return
  }

  update_status "Logging in ..."

  # send the username and password
  if {[string compare $FTP(username) ""]} {
    puts $FTP(ftp_sock) "USER $FTP(username)"
  } else {
    puts $FTP(ftp_sock) "USER anonymous"
  }
  if {[ftp_read] > 3} {
    return
  }

  if {[string compare $FTP(password) ""]} {
    puts $FTP(ftp_sock) "PASS $FTP(password)"
  } else {
    puts $FTP(ftp_sock) "PASS user@hostname"
  }
  if {[ftp_read] > 3} {
    return
  }

  # change to the user selected directory or /
  if {[string compare $FTP(directory) ""]} {
    puts $FTP(ftp_sock) "CWD $FTP(directory)"
  } else {
    puts $FTP(ftp_sock) "CWD /"
  }
  if {[ftp_read] > 3} {
    return 
  }

  update_status "Setting up for transfer ..."

  # transfer directories in ascii mode
  puts $FTP(ftp_sock) "TYPE A"
  if {[ftp_read] > 3} {
    return
  }

  # get a server socket on our system so that the remote 
  # system can send
  # us the directory listing
  update_status "Opening server port ..."

  set serv_sock [socket -server notify_connect 0]

  update_status "Setting up to retrieve directory ..."
  
  set hostip [lindex [fconfigure $FTP(ftp_sock) -sockname] 0]
  set serv_port [lindex [fconfigure $serv_sock -sockname] 2]

  # expr is how we do math
  set serv_up [expr "int($serv_port/256)"]
  set serv_lw [expr "$serv_port-$serv_up*256"]
  regsub -all {\.} $hostip "," hostip

  # send the port command to the remote system
  puts $FTP(ftp_sock) "PORT $hostip,$serv_up,$serv_lw"
  if {[ftp_read] > 3} {
    close $serv_sock
    fileevent $FTP(ftp_sock) readable ""
    close $FTP(ftp_sock)
    return
  }

  # send the list command
  puts $FTP(ftp_sock) "LIST"

  if {[ftp_read] > 3} {
    close $serv_sock
    fileevent $FTP(ftp_sock) readable ""
    close $FTP(ftp_sock)  
    return
  }

  update_status "Retrieving dir ..."

  fconfigure $FTP(data_sock) -translation auto

  # keep reading on the server socket until end of file.
  while { ! [eof $FTP(data_sock)] } {
    set buf [read $FTP(data_sock) 1024]
    append result $buf
  }

  # clean up and exit
  update_status "Closing connection ..."

  puts $FTP(ftp_sock) "QUIT"
  fileevent $FTP(ftp_sock) readable ""
  close $FTP(ftp_sock)
  close $serv_sock
  close $FTP(data_sock)
  return $result
}

This bit of code talks to a remote system and implements enough of the FTP protocol to get a file listing. Basically it sends a USER command, followed by a PASS command to log in with a user name and a password. Then it sends a CWD command to change to the proper directory. Next it sends a PORT command, probably the only tricky bit. The FTP protocol uses two channels. The first is the command/result channel which is where we send commands such as USER and PASS and get responses. The second is the data channel which is where we transfer files. This is different from the http protocol where we would use the same channel for both transfers.

To request a file or directory listing from the remote system we set up a server port on the local system and tell the remote system what that port number is with the PORT command. The remote system opens a connection to that port and sends the remote file or directory listing over that connection. The PORT command has a slightly odd syntax of the form A,B,C,D,E,F where the local numeric IP address is A.B.C.D and E is the port address high byte and F is the port address low byte. Once we've gotten the port command sent, we send the LIST command. The remote system opens a socket to the port we gave it and sends the result. Once we see and end of file on our server socket we are done and can send the QUIT command. You can experiment with the FTP protocol by using a telnet client to connect to port 21 on most systems. You can also get ftp://nic.merit.edu/documents/rfc/rfc0959.txt and read all of the gory details.

Retrieving a file is just as easy as getting a listing. The routine ftp_get_file is almost identical to ftp_get_dir, but instead of using a LIST command to get a directory listing, we use a RETR command to get a remote file. Also, we write the file out to disk rather than returning it's contents as a string.

Adding a Menubar

Up to now all of the code has been generic Tcl/Tk. While it's nice to produce portable applications, we use Macs because we like them and we'd like our applications to look Mac-like. Tcl/Tk 8.0 has some nice features built in that we can use to make the application look more like a Mac. If we create a menu widget called say .menubar, and then add an entry to that called .menubar.apple, items on this menu will be in the Apple menu. So, we add a menubar as follows:

part of the main program 
This will add the Mac menus such that they work like Mac menus. We
create a menubar named .menubar and then add Apple and File entries
to it. The Apple entrys will appear under the Apple menu as you'd expect
and the File menu will be the first menu after the Apple menu. We'll add
an accelerator to the Quit menu option with Meta-Q which will be
translated to Command-Q on the Mac.

# make a menubar
menu .menubar -tearoff 0

# add the file menu
.menubar add cascade -menu .menubar.file -label "File"
menu .menubar.file -tearoff 0

# add the apple menu
.menubar add cascade -menu .menubar.apple  
menu .menubar.apple -tearoff 0
# add the about entry
.menubar.apple add command -label "About..." \
  -command aboutbox

# add entries to the file menu
.menubar.file add command -label "New Connection..." \
  -command new_connection
.menubar.file add separator
# this will be the normal mac quit keyboard acclerator
.menubar.file add command -label "Quit" \
  -command exit -accelerator "Meta-Q"

# make the menu the menu for the toplevel . window. Whenever
# the . window is the frontmost window then the menubar 
# .menubar will be the menu at the top of the screen.

. configure -menu .menubar

The only other Mac specific command is console hide at the end of the program. This prevents the Tcl console from appearing. The Tcl console is where you would type Tcl commands if you were using Tcl interactively.

The last thing to do to generate a standalone Mac executable is to drag your Tcl source file onto the program Drag & Drop Tclets and answer the questions. This little program will build a Tcl executable which can be double-clicked to run our Tcl script.

Conclusion

After reading this article you should have gained an appreciation for Tcl/Tk and some things you can do with it on the Mac. It's also possible to control other programs with the TclAppleScript extension, which ships with Tcl/Tk 8.0. This allows you to use Tcl to tie together multiple programs as you can with AppleScript. Now that Tcl/Tk has native look-and-feel, the Mac Tcl scripts look like Mac programs and Tcl/Tk gives you a quick way to write Mac programs.

Bibliography and References

  • Ousterhout, John K. Tcl and the Tk Toolkit, Addison-Wesley, 1994.
  • Welch, Brent B. Practical programming in Tcl & Tk, Prentice Hall, 1997.

For more information you should check the main site at http://sunscript.sun.com/ and an excellent overview paper on Tcl/Tk and scripting languages is from http://www.sunlabs.com/~ouster/scripting.html.


Bruce O'Neil beoneel@macconnect.com spends his work time working on astrophysics satellites and his spare time playing with his lovely wife and children. What time is left is devoted to his PowerBook.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

iExplorer 4.1.10 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
iExplorer 4.1.10 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Adobe InCopy CC 2018 13.0.1.207 - Create...
InCopy CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous InCopy customer). Adobe InCopy CC 2018, ideal for large team projects... Read more
Microsoft Office 2016 15.40 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more
Adobe InDesign CC 2018 13.0.1.207 - Prof...
InDesign CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous InDesign customer). Adobe InDesign CC 2018 is part of Creative Cloud.... Read more
Apple iOS 11.1.2 - The latest version of...
iOS 11 sets a new standard for what is already the world’s most advanced mobile operating system. It makes iPhone better than before. It makes iPad more capable than ever. And now it opens up both to... Read more
Slack 2.9.0 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.9.0: Slack now officially, and fully, supports Japanese.... Read more
iExplorer 4.1.9 - View and transfer file...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
PCalc 4.5.3 - Full-featured scientific c...
PCalc is a full-featured, scriptable scientific calculator with support for hexadecimal, octal, and binary calculations, as well as an RPN mode, programmable functions, and an extensive set of unit... Read more
iExplorer 4.1.9 - View and transfer file...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more

Latest Forum Discussions

See All

Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »
A Boy and His Blob (Games)
A Boy and His Blob 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Fight terrible monsters and collect epic...
Released on Western markets early last month, Dragon Project, created by Japanese developer COLOPL, brings epic monster hunting action to mobile for the very first time. Collect a huge array of weapons and armor, and join up with friends to fight... | Read more »
I Am The Hero (Games)
I Am The Hero 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: I Am The Hero is a pixel art, beat 'em up, fighting game that tells the story of a "Hero" with a glorious but mysterious past.... | Read more »
Kauldron (Music)
Kauldron 1.0 Device: iOS Universal Category: Music Price: $3.99, Version: 1.0 (iTunes) Description: Kauldron is our warmest sounding, punchiest synth yet! A completely new modeling technology, combined with carefully designed... | Read more »
Lineage II: Revolution is mobile’s bigge...
NCSoft’s hit fantasy MMORPG series has just made the leap to mobile with the help of Netmarble in Lineage II: Revolution. With over 1.5 million players having already pre-registered ahead of the game’s launch, Revolution hit the app stores... | Read more »
Swing skilfully in new physics-based pla...
Sometimes it’s the most difficult of obstacles that can be the most rewarding. One game hoping to prove this is OCMO, the new tough but fair platformer from developers Team Ocmo. Primed to set every speedrunner’s pulse racing, as an otherworldly... | Read more »

Price Scanner via MacPrices.net

Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more
Best Apple iPad deals this weekend, up to $80...
Apple resellers are offering 9.7″ iPads and 10.5″ iPad Pros for up to $80 off MSRP this weekend as part of their early Holiday and Black Friday sales: Adorama is offering new 2017 9.7″ 32GB WiFi... Read more
Early Black Friday sale: Apple iMacs for up t...
B&H Photo has 27-inch iMacs in stock and on sale for up $130-$150 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2149 $150 off... Read more
Apple restocks refurbished Mac minis starting...
Apple has restocked Certified Refurbished Mac minis starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: – 1.4GHz Mac mini: $419 $80 off MSRP – 2.6GHz Mac... Read more
Save on 12″ MacBooks, Apple refurbished model...
Apple has Certified Refurbished 2017 12″ Retina MacBooks available for $200-$240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free.... Read more
Early Holiday sale: 12″ iPad Pros for up to $...
B&H Photo has 12″ iPad Pros on sale today for up to $130 off MSRP. Shipping is free, and B&H collects no sales tax outside NY & NJ: – 12″ 64GB WiFi iPad Pro: $749, save $50 – 12″ 256GB... Read more
Holiday sale prices on Apple 13″ MacBook Pros...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for $100-$150 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro... Read more
Sale: 13″ MacBook Airs starting at $899, $100...
B&H Photo has 2017 13″ MacBook Airs on sale today for $100 off MSRP including free shipping. B&H charges NY & NJ sales tax only: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $100 off... Read more
Week’s Best Deal on 13″ MacBook Pros: Apple r...
Apple has a full line of Apple Certified Refurbished 2017 13″ MacBook Pros available for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
Deal: 15″ 2.6GHz MacBook Pro for $1799 w/free...
B&H Photo has clearance 2016 15″ 2.6GHz Touch Bar MacBook Pros in stock today and available for $600 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 15″ 2.... Read more

Jobs Board

Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Pro/Consumer Apps Support Engineer -...
…exemplify AppleCare's expert technical support paired with exceptional customer service for Apple 's software apps. This person is a problem solver, who understands Read more
Partner Marketing Manager, *Apple* Pay - Ap...
Job Summary The Apple Pay partner marketing team is looking for a Marketing Manager to develop and drive US programs. The right candidate will be passionate about Read more
*Apple* Solution Consultant - Apple (United...
# Apple Solution Consultant - Rochester, MN Job Number: 113037950 Rochester, MN, Minnesota, United States Posted: 19-Sep-2017 Weekly Hours: 40.00 **Job Summary** Are Read more
Sr. Experience Producer, Today at *Apple* -...
# Sr. Experience Producer, Today at Apple Job Number: 56495251 Santa Clara Valley, California, United States Posted: 23-Jun-2017 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.