I think you've gotten the wrong idea about [returnBlob]. It operates in
the style of exceptions, ending the transaction with the given result.
It's not a normal function return, so you can't use it pass a blob from
one part of your program to another. Also, it definitely doesn't
generate strings.
Somewhat intentionally, Ur/Web currently does not provide a way to
introspect into a blob, without using the FFI. It would take some
thought on what the right API would be. In my applications that involve
CSV import, I have their content pasted into textboxes.
On 02/19/2017 10:11 AM, Marko Schütz Schmuck wrote:
I'm confused about the use of returnBlob.
I was looking through the existing urweb demos to see how I could
access the data in a blob of mime type "text/plain" as a string.
Eventually, I want to import into a table from a CSV file the user
uploads.
I hoped that returnBlob used in a transaction string could achieve
this. So I modified demo/upload.ur to
fun echo (r : {File : file}) : transaction string =
if blobSize (fileData r.File) > 100000 then
return "Whoa! That one's too big."
else
returnBlob (fileData r.File) (blessMime (fileMimeType r.File))
fun echoLength (r : {File : file}) : transaction page =
s <- echo r ;
return <xml>{[String.length s]}</xml>
fun main () : transaction page
= return <xml><body>
<h1>The Amazing File Echoer!</h1>
<form>Upload a file: <upload{#File}/> <submit action={echoLength}/></form>
</body></xml>
This compiles and runs, and when I supply a file longer than 100000 I
get the expected page with the result 26, but to my surprise a shorter
file results in a page with the content of the file not it's length.
I'd really appreciate some help.
Thanks in advance and best regards,
Marko
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