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Taking The Complexity Out Of Automating FTP

When faced with a requirement to automate some file transfers, a common reaction is, “I can roll my own solution with a simple batch / VB / etc. script, right?” At first glance, it seems simple enough. However, the devil (as always) is in the details – and there are a LOT of details. This article will highlight a few of the more common pitfalls of automating FTP sessions and their solutions.

Lack of Standard Directory Listing Format

One of the details that turns what sounds like a one-hour FTP automation project into weeks of headaches is the lack of a standard directory listing format with FTP servers.

Almost all FTP automation workflows eventually include the need to determine what files and folders are on the server, and to retrieve information about those files and folders. The only way to do this is to retrieve and parse a directory listing. That’s where things get tricky – there is no standard way for an FTP server to provide this information.

Here are three examples of directory listings returned from different FTP servers:

AS/400 FTP Server Directory Listing

                 24576 07.12.94 10:55:06 *DIR       subdir/
 TTS               512 99-06-12 09:08:00 *FILE      file1.txt
 TTS            256512 09-12-07 08:30:00 *FILE      file2.txt
 TTS         128256512 10-01-14 22:20:00 *FILE      file3.txt

UNIX FTP Server Directory Listing

 drw-rw----   1 administrator root              0 Nov  5 05:20 subdir
 -rw-rw----   1 administrator domain users    512 Jun 12 1999  file1.txt
 -rw-rw----   1 administrator sys          256512 Dec  7 08:30 file2.txt
 -rw-rw----   1 1161          1232      128256512 Jan 14 22:20 file3.txt

Novell FTP Server Directory Listing

 total 0
 d [R----F--] supervisor          512 May 09 17:00 subdir
 - [RWCE-FM-] stan                512 Jun 12  1999 file1.txt
 - [RWCE-FM-] kyle             256512 Dec 07 08:30 file2.txt
 - [RWCE-FM-] eric          128256512 Jan 14 10:20 file3.txt

If that were not complicated enough, the format returned by the same server can vary depending on the circumstances. For example, many servers return a different date format depending on whether the file’s last modified date/time stamp was for this year or over a year ago.

The number of permutations are nearly limitless, which means writing code to parse that information manually is complex, time-consuming, and prone to error.

RFC 3659 was published in 2007, updating the original FTP protocol to include a type of standardized, machine-readable directory listing (among other improvements). Unfortunately, this new feature has not been universally adopted, so it is not possible to count on using it in production environments.

Lack of Standard FTP Protocol Implementation

Directory listings are not the only area where FTP servers differ from one another. The implementation of the FTP protocol itself can vary in unpredictable ways. The FTP protocol was first described in RFC 959 in 1980 and has gone through numerous changes and additions since that time. FTP vendors made their own interpretations of how that standard should be implemented, and some made choices that directly contradict the standard, often to add a proprietary feature to distinguish their product in the marketplace or to meet some other business need.

Your FTP client automation code may get wildly different results when connecting to different servers, requiring endless patches and conditional code to handle all the exceptions as they arise. This turns a simple, straight-forward VB script into hundreds of lines of hard-to-maintain spaghetti code.

Changing Requirements Create Work

The lack of standardization discussed so far all applies even if you are only dealing with one protocol, FTP. While the variations between one FTP server and another can be significant, the differences between an FTP server and an SFTP server (for example) are huge. What if your requirements change and the FTP workflow you so carefully automated now needs to use SFTP instead due to a new business requirement? You might be starting from scratch!

Don’t Attempt To Reinvent The Wheel

The good news about all of this is that products are readily available that take care of all this complexity for you. For example, Robo-FTP from Serengeti Systems Incorporated provides a simple script interface that lets you concentrate on your business logic. Their engineers have spent over a decade testing and re-testing to make sure Robo-FTP automatically handles all of the variations that remote servers might throw at it (including FTP, FTPS, SFTP, HTTP, and HTTPS) without any extra effort on your part.

For example, this Robo-FTP script logs onto an FTP server and downloads all files that have been modified in the last 10 minutes.

 LOOPCOUNT 3
 :LogonLoop
 FTPLOGON "my_ftp_site.com" /timeout=60
 IFERROR= $ERROR_SUCCESS GOTO Operation1
 ;; Try again for up to 3 attempts
 LOOPTO LogonLoop
 STOP
 :Operation1
 SET temp = %datetime
 DATETIMESUB temp 10 /minute
 SET ten_min_ago = temp
 FTPGETFILE "*.txt"
 IFERROR= $ERROR_NO_FILE_FOUND GOTO Disconnect
 IFDATETIME> %sitefiledatetime ten_min_ago GOTO Operation2
 GOTO Operation1
 :Operation2
 ;; File has been modified within last 10 minutes, so download it
 RCVFILE %sitefile
 GOTO Operation1
 :Disconnect
 FTPLOGOFF
 EXIT

The key here is that in under 20 lines of scripting (not including commments), you have an automated workflow that will work with any server. A roll-your-own solution might be many times as long. Worse, even if you get it working on one test server, it may not work at all when connecting to the production server. Once you put in the extra work to get it working with that server, you may still be right back to the drawing board if a requirement arises to automate the same workflow with yet another server.

Clearly, the cost of purchasing a solution that handles these details for you is easily eclipsed by the cost and frustration of trying to handle all those possible variations on your own.

About the author

Errol Siegel is a Product Manager at Serengeti Systems Incorporated, a leading provider of secure, automated file transfer solutions for small to medium-sized businesses. Since 2001, Siegel has lead the team responsible for the Robo-FTP suite, a secure file transfer server and client built from the ground up for automating FTP, FTPS, SFTP, HTTP, and HTTPS file transfers and related tasks such as PGP encryption, ZIP, email (SMTP), and database access (ODBC).

Siegel holds a Bachelor’s degree in Aerospace Engineering from the University of Michigan.

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