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

Parallels Desktop 10.2.0 - Run Windows a...
Parallels Desktop is simply the world's bestselling, top-rated, and most trusted solution for running Windows applications on your Mac. With Parallels Desktop for Mac, you can seamlessly run both... Read more
LaunchBar 6.2 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Firefox 37.0 - Fast, safe Web browser. (...
Firefox offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and casual... Read more
Arq 4.11 - Online backup to Google Drive...
Arq is super-easy online backup for the Mac. Back up to your own Google Drive storage (15GB free storage), your own Amazon Glacier ($.01/GB per month storage) or S3, or any SFTP server. Arq backs up... Read more
MacFamilyTree 7.3.4 - 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
Yummy FTP 1.10.2 - FTP/SFTP/FTPS client...
Yummy FTP is an FTP + SFTP + FTPS file transfer client which focuses on speed, reliability and productivity. Whether you need to transfer a few files or a few thousand, schedule automatic backups, or... Read more
VueScan 9.5.08 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Iridient Developer 3.0.1 - Powerful imag...
Iridient Developer (was RAW Developer) is a powerful image conversion application designed specifically for OS X. Iridient Developer gives advanced photographers total control over every aspect of... Read more
Monodraw 0.8.4.1 - Powerful ASCII art ed...
Monodraw allows you to easily create text-based art (like diagrams, layouts, flow charts) and visually represent algorithms, data structures, binary formats and more. Because it's all just text, it... Read more
Air Video Server HD 2.1.0 - Stream video...
Air Video Server HD streams videos instantly from your computer on your iPhone, iPad, iPod touch or Apple TV. No need to worry about converting or transferring files. We took everything that was... Read more

Marvel Mighty Heroes, the Ultimate Marve...
DeNA and Marvel Entertainment have brought us a new action-packed brawler: Marvel Mighty Heroes. You can play with up to four of your friends as you favorite marvel heroes like Iron Man, Thor, Spider-Man, Captain America, Star-Lord, Hulk, and... | Read more »
Take Note - The Jot Script 2 Evernote Ed...
Adonit's Jot Script 2 sylus has an all-new edition that's meant to be Evernote's BFF. The sylus has been redesigned to work better with iPads and give you faster stroke tracking, smoother line rendering, and better tip-to-line accuracy. | Read more »
INFINIT Lets Mobile Users Send Files of...
Infinit  is a file sharing app that ignores file size limits. It maintains the original quality of your photos and videos so you can be sure they look awesome after sending. You can move entire albums of photos or full HD films from your iPhone to... | Read more »
Serious Sam Double D Developer is Making...
There's nothing like the thrill of watching a horse race, especially when the horses are drunk.  | Read more »
2K Announces WWE 2K, Mobile's First...
It seems like this month has been pretty big for wrestling. First Wrestlemania, then 2K has announces that they're releasing  WWE 2K for iOS. It's a simulation-based WWE game where you'll get to play with several WWE superstars such as John Cena, ... | Read more »
How the Apple Watch Could Change the Fac...
The Apple Watch is still a ways out, but my previous musings on the wearable’s various features got me thinking: what might it be like a year after launch? Two years? Five years? What if it becomes a symbiotic part of the iOS framework to the point... | Read more »
You Can Start Challenging Your Friends t...
Last year we reported that Sebastian Gosztyla's new game, Dual, was theorized to be released sometime during the summer of 2014. Sadly that did not become a reality, but the good news it there is now an official release date. | Read more »
Forgotten Memories : Alternate Realities...
Forgotten Memories : Alternate Realities, from Psychoz Interactive, is planned for release on April 23. The Resident Evil, Silent Hill, and Alone in the Dark inspired horror game puts you in the shoes of Rose Hawkins as she searches for a missing... | Read more »
Pie In The Sky: A Pizza Odyssey (Games)
Pie In The Sky: A Pizza Odyssey 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: A game about delivering pizza. In space. | Read more »
Chosen Gives Hopeful Singers, Songwriter...
If YouTube videos and reality TV shows like The Voice have taught us one thing, it’s that there are a lot of people out there who are anxious to show the world their talents. And if they’ve taught us a second thing, it’s that there’s an almost... | Read more »

Price Scanner via MacPrices.net

Will Microsoft’s Surface 3 Give The 12-inch M...
The more I ruminate over the new 12-inch MacBook, the more it occurs that it’s probably going to be more of a cannibalization threat to high-end iPads (including a new 12-inch ‘Pad when/if that... Read more
13-inch 2.4GHz Retina MacBook Pro available f...
MacMall has the 2013 13″ 2.4GHz/128GB Retina MacBook Pro available for $949.99 for a limited time. Shipping is free. Their price is $350 off original MSRP, and it’s the only sub-$1000 new Retina... Read more
Adobe Brings Powerful Layout-Design Capabilit...
Adobe today announced the availability of Adobe Comp CC, a free iPad app that enables rapid creation of layout concepts for mobile, Web and print projects. With Comp CC, designers can rough out and... Read more
13-inch 2.6GHz/256GB Retina MacBook Pro avail...
Best Buy has clearance 2014 13″ 2.6GHz/256GB Retina MacBook Pros available for $1199.99 including free shipping. Their price is $300 off original MSRP, and it’s the lowest price for this model.... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
21-inch 1.4GHz iMac on sale for $999, save $1...
Best Buy has the 21″ 1.4GHz iMac on sale for $999.99 on their online store. Choose free shipping or free local store pick up. Price is for online orders only, in-store prices may vary. Their price is... Read more
2.6GHz Mac mini on sale for $649, save $50
Amazon has the 2.6GHz Mac mini on sale for $649.99 including free shipping. Their price is $50 off MSRP, and it’s the lowest price available for this model. Read more
Textkraft Professional 3.2 Powerful iPad Text...
Finally it’s springtime, at least theoretically in my neck of the woods, where we’re still navigating canyons between towering snowbanks with temperatures well below freezing in winter weather that... Read more
Apple offering refurbished 27-inch 5K iMacs f...
The Apple Store is offering Apple Certified Refurbished 27″ 3.5GHz 5K iMacs for $2119 including free shipping. Their price is $380 off the price of new models, and it’s the lowest price available for... Read more
16GB iPad mini on sale for $199, save $50
Walmart has 16GB iPad minis (1st generation) available for $199.99 on their online store, including free shipping. Their price is $50 off MSRP. Online orders only. Read more

Jobs Board

DevOps Software Engineer - *Apple* Pay, iOS...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.