Since we are using a Windows file system most of the user’s files will have extensions. This is a good starting point for file type validation. Generally, unless there is a lack of computer skills (or malicious intent) a file’s extension matches its content. To get the extension simply use Legato’s GetExtension function.

string = GetExtension ( string name );

This function returns the extension of the file, with the leading period. Just adding this quick check can reduce the chance of bad data causing unexpected data in your script. Consider a script that takes an HTML file and a CSV file of changes to make to the HTML file. The last thing a developer needs is an upset user because they accidentally selected a XLSX document and it caused the script to screw up their HTML file with bogus edits. Checking the file extension can prevent these kinds of mistakes. However, this doesn’t always help. Certain extensions like XML can have drastically different file contents. An XBRL instance document is nothing like a 13F information table but both are XML format and XML extension.

So what can we do about this? Luckily, with Legato you can have the application test the contents of a file and determine its file type. This test includes narrowing down to specific types of XML if the application understands the XML coding. To do this we have two options:

dword = GetFileTypeCode ( string source, [boolean extensiononly] );

string = GetFileTypeString ( string source, [boolean extensiononly] );

These functions are essentially the same except GetFileTypeCode returns a numerical value to represent the resulting file type while the GetFileTypeString returns a string representing the type. Both functions will open the file and read a small amount of data to determine information about the file. For example, when called on an XML file the function will look at the namespaces of the XML file to determine what kind of XML it is. The extensiononly option skips the file content analysis. This can still be useful since it will deal with file formats that have multiple extensions like HTM or HTML. When using the GetFileTypeCode function there are defines for the different file types. These can be found in the legato SDK header file (Appendix A of the Legato documentation) but here are some of the common ones:

It is important to note that you can also switch between the codes and strings with the following two functions:

dword = FileTypeStringToCode ( string code );

string = FileTypeCodeToString ( dword code );

These functions simply take the code in one format and change it to the other. This can be useful if you want to be efficient with memory by using the dword codes but then want to use the more human friendly version in a log file.

The last function I want to discuss is a more powerful version of the GetFileTypeCode and GetFileTypeString functions. This is the GetFileTypeData function.

string[] = GetFileTypeData ( string source );

This function works like the other two but instead of returning a code or string it returns an array of properties about the file. This goes beyond the size and modified time but into the file’s meta data (if the application knows how to read it for the file). For example, running this function on a GoFiler project would give you the following properties:

FileTypeCode: 0x00007905
FileTypeString: FT_GOFILER_PROJECT_3X
ExtensionTypeCode: 0x00007904
ExtensionTypeString: FT_GOFILER_PROJECT
TypeDescription: GoFiler Project
FilePath: C:\Users\david.theis\Desktop\XBRL Testing\
FileName: test.gfp
FileSize: 6173
FileCreateTime: 2018-04-10T16:13:48
FileModifiedTime: 2013-11-15T16:28:46
MetaAuthor: David Theis
MetaKeywords: 09-30-2012
MetaSubject: 0000990681
MetaTitle: 10-Q

The properties included the type of the file as well as the creator of the project, the report period, CIK and form type. This information means you can put meta information on a dialog about a user’s chosen file to help them verify it was the proper choice. Additionally, for image files you can get the dimension of the picture.

Now that you know how to check the contents of files be sure to use this knowledge to improve your next script. With Legato, checking files is easier than ever.

David Theis has been developing software for Windows operating systems for over fifteen years. He has a Bachelor of Sciences in Computer Science from the Rochester Institute of Technology and co-founded Novaworks in 2006. He is the Vice President of Development and is one of the primary developers of GoFiler, a financial reporting software package designed to create and file EDGAR XML, HTML, and XBRL documents to the U.S. Securities and Exchange Commission.

Additional Resources

Novaworks’ Legato Resources

Legato Script Developers LinkedIn Group

Primer: An Introduction to Legato