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

OS X Server 4.1.3 - For OS X 10.10 Yosem...
Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, develop software, host your own website, publish wikis, configure Mac, iPhone,... Read more
pwSafe 4.1 - Secure password management...
pwSafe provides simple and secure password management across devices and computers. pwSafe uses iCloud to keep your password databases backed-up and synced between Macs and iOS devices. It is... Read more
Kodi 15.0.rc1 - Powerful media center to...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
Coda 2.5.11 - One-window Web development...
Coda is a powerful Web editor that puts everything in one place. An editor. Terminal. CSS. Files. With Coda 2, we went beyond expectations. With loads of new, much-requested features, a few surprises... Read more
Bookends 12.5.7 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Access the power of Bookends directly from Mellel, Nisus Writer Pro, or MS Word (... Read more
Maya 2016 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
RapidWeaver 6.2.3 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
MacFamilyTree 7.5.2 - Create and explore...
MacFamilyTree gives genealogy a facelift: it's modern, interactive, incredibly fast, and easy to use. We're convinced that generations of chroniclers would have loved to trade in their genealogy... Read more
Paragraphs 1.0.1 - Writing tool just for...
Paragraphs is an app just for writers. It was built for one thing and one thing only: writing. It gives you everything you need to create brilliant prose and does away with the rest. Everything in... Read more
BlueStacks App Player 0.9.21 - Run Andro...
BlueStacks App Player lets you run your Android apps fast and fullscreen on your Mac. Version 0.9.21: Note: Now requires OS X 10.8 or later running on a 64-bit Intel processor. Initial stable... Read more

Rage of Bahamut is Giving Almost All of...
The App Store isn't what it used to be back in 2012, so it's not unexpected to see some games changing their structures with the times. Now we can add Rage of Bahamut to that list with the recent announcement that the game is severely cutting back... | Read more »
Adventures of Pip (Games)
Adventures of Pip 1.0 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** ONE WEEK ONLY — 66% OFF! *** “Adventures of Pip is a delightful little platformer full of charm, challenge and impeccable... | Read more »
Divide By Sheep - Tips, Tricks, and Stre...
Who would have thought splitting up sheep could be so involved? Anyone who’s played Divide by Sheep, that’s who! While we’re not about to give you complete solutions to everything (because that’s just cheating), we will happily give you some... | Read more »
NaturalMotion and Zynga Have Started Tea...
An official sequel to 2012's CSR Racing is officially on the way, with Zynga and NaturalMotion releasing a short teaser trailer to get everyone excited. Well, as excited as one can get from a trailer with no gameplay footage, anyway. [Read more] | Read more »
Grab a Friend and Pick up Overkill 3, Be...
Overkill 3 is a pretty enjoyable third-person shooter that was sort of begging for some online multiplayer. Fortunately the begging can stop, because its newest update has added an online co-op mode. [Read more] | Read more »
Scanner Pro's Newest Update Adds Au...
Scanner Pro is one of the most popular document scanning apps on iOS, thanks in no small part to its near-constant updates, I'm sure. Now we're up to update number six, and it adds some pretty handy new features. [Read more] | Read more »
Heroki (Games)
Heroki 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: CLEAR THE SKIES FOR A NEW HERO!The peaceful sky village of Levantia is in danger! The dastardly Dr. N. Forchin and his accomplice,... | Read more »
Wars of the Roses (Games)
Wars of the Roses 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
TapMon Battle (Games)
TapMon Battle 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: It's time to battle!Tap! Tap! Tap! Try tap a egg to hatch a Tapmon!Do a battle with another tapmons using your hatched tapmons! *... | Read more »
Alchemic Dungeons (Games)
Alchemic Dungeons 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: ### Release Event! ### 2.99$->0.99$ for limited time! ### Roguelike Role Playing Game! ### Alchemic Dungeons is roguelike... | Read more »

Price Scanner via MacPrices.net

Seagate Backup Plus Drives Feature 200GB of C...
Seagate Technology plc has announced that its Backup Plus family of external storage offerings will now include 200GB of OneDrive cloud storage, a major added value, and the addition of Lyve’s photo... Read more
Canon PIXMA MG3620 Wireless Inkjet All-in-One...
Canon U.S.A., Inc. has announced the PIXMA MG3620 Wireless (1) Inkjet All-in-One (AIO) printer for high-quality photo and document printing. Built with convenience in mind for the everyday home user... Read more
July 4th Holiday Weekend 13-inch MacBook Pro...
Save up to $150 on the purchase of a new 2015 13″ Retina MacBook Pro at the following resellers this weekend. Shipping is free with each model: 2.7GHz/128GB MSRP $1299 2.7GHz/... Read more
27-inch 3.5GHz 5K iMac on sale for $2149, sav...
Best Buy has the 27″ 3.5GHz 5K iMac on sale for $2149.99. Choose free shipping or free local store pickup (if available). Sale price for online orders only, in-store prices may vary. Their price is $... Read more
Apple now offering refurbished 2015 11-inch...
The Apple Store is now offering Apple Certified Refurbished 2015 11″ MacBook Airs as well as 13″ MacBook Airs (the latest models), available for up to $180 off the cost of new models. An Apple one-... Read more
15-inch 2.5GHz Retina MacBook Pro on sale for...
Amazon.com has the 15″ 2.5GHz Retina MacBook Pro on sale for $2274 including free shipping. Their price is $225 off MSRP, and it’s the lowest price available for this model. Read more
Finally Safe To Upgrade To Yosemite’?
The reason I’ve held back from upgrading my MacBook Air from OS X 10.9 Mavericks to 10.10 Yosemite for nearly a year isn’t just procrastination. Among other bugs reported, there have been persistent... Read more
Logo Pop Free Vector Logo Design App For OS X...
128bit Technologies has released of Logo Pop Free 1.2 for Mac OS X, a vector based, full-fledged, logo design app available exclusively on the Mac App Store for the agreeable price of absolutely free... Read more
21-inch 1.4GHz iMac on sale for $999, save $1...
B&H Photo has new 21″ 1.4GHz iMac on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Best Buy has the 21″ 1.4GHz iMac on sale for $999.99 on their... Read more
16GB iPad mini 3 on sale for $339, save $60
B&H Photo has the 16GB iPad mini 3 WiFi on sale for $339 including free shipping plus NY tax only. Their price is $60 off MSRP. Read more

Jobs Board

Mobile Payments Counsel, *Apple* Pay (digit...
**Job Summary** Apple is looking for an atto ey to join Apple 's Legal Department to support Apple Pay. **Key Qualifications** 4+ years of relevant experience Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** The ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store which delivers Read more
Partner Marketing Manager, Merchant- *Apple*...
**Job Summary** The Apple Pay partner marketing team is looking for a marketing manager to develop and drive US marketing programs with our merchant partners. The right Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Program Manger, WW *Apple* Direct Fulfillme...
**Job Summary** We are seeking a business analyst to work within our Worldwide Apple Direct Fulfillment Operations team. This role will work closely with related program Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.