How to retrieve the size of a file being uploaded using a!fileUploadField() sail

@Abhi: i think you might find Eduardo's suggestion of post-form validation to work rather well - in my case, when validation fails after submission, the gateway loops through a delete document node and the failed document is removed right away, then it loops straight back into the form where I display a SAIL-style validation message. To the user, it seems as if they never left the form and that the "upload" button just failed.

@Abhinavg: If I understood your requirement clearly the below code can help you identify the file size before you save that to appian.
saveInto:{
a!save(local!FileSize,(a!fileUploadField(target:targetfolder,value:ri!fileToUpload,saveInto:ri!fileToUpload).uploadedDocumentSize))
}
use this local!FileSize variable in validation attribute to validate accordingly

Thanks for sharing Srinivas. This would help in lot of validation for us.

@Srinivas: Is there any other property that we can get in this way before submitting the form. Like documentId, documentName .. I tried few things like '.id', '.documentId', '.uploadedId', '.uploadedDocumentId' ..

@kumar: basically the only meaningful properties we can extract using this trick are size (abbreviated), and document name. I believe the property to use for name is "uploadedDocumentName", but you can check all the properties available by placing it in a text field, like this:
a!textField( readOnly: true(), value: a!fileUploadField( value: local!uploadedDocument ) )

@mschmitt: Checked it. You are right about 'uploadedDocumentName' property. Although the properties are limited, it was really helpful to know this. Especially, we need to display the actual file name of uploaded document in a read only grid right after user uploads. Till now we had to take the user out of screen and come back inside to achieve this. This is great .. Thanks for sharing ..

Also to mention, lot of people are looking for a way to validate minimum / max file upload size right after uploading .. This is a good workaround ..

I mainly use this to validate proper extension, as i've had requirements that certain file types not be allowed. I should note that this is not "officially" supported functionality, as in, there is no guarantee that the property names won't change in between appian versions, among other things. As such, I strongly suggest that you create external rules to handle taking the temporary document and extracting the name - that way if something ever changes, you only need to update your hanler rule(s) instead of any forms that used the literal property names.

Also just be cautious about using this for just-uploaded files in a grid; this makes it possible but at the same time, you're still going to be dealing with an array of "temporary" document IDs that don't become permanent ones until submit time. I'd strongly recommend continuing to submit the form between uploads, unless you have strong reasons not to.

That's a good suggestion. Thanks ..

@mschmitt: You are right there's no guarantee that the property names won't change in future versions.