[Ur] returnBlob behavior?

Mon Feb 20 03:27:09 EST 2017

Ah, I figured it out. Yes, Adam is right, everything works as expected.

Regards,
Sergey

2017-02-20 11:22 GMT+03:00 Sergey Mironov <grrwlf at gmail.com>:
> Hi. I could confirm that the application posted by Marko returns file
> content in both branches of [if]. I agree that it is strange.
>
> Below is the code UrWeb generated on my machine. At the first glance,
> it is expected to return blob only on the size check failure. Somehow,
> returnBlob is executed in the both cases.
>
> Regards,
> Sergey
>
>
>   static uw_unit
>    __uwn_wrap_echoLength_4277(uw_context ctx, struct __uws_1 __uwr_x0_0,
>                                uw_unit __uwr___1)
>    {
>    return(({
>            uw_unit __uwr___2 =
>            (uw_begin_region(ctx), uw_Basis_debug(ctx,
>                                    uw_Basis_intToString(ctx,
>                                     uw_Basis_blobSize(ctx,
>                                      uw_Basis_fileData(ctx,
>                                       __uwr_x0_0.__uwf_File)))));
>            uw_end_region(ctx);
>             uw_Basis_htmlifyInt_w(ctx,
>              uw_Basis_strlen(ctx,
>               ({
>                uw_Basis_bool disc =
>                !
>                 (uw_Basis_blobSize(ctx,
>                   uw_Basis_fileData(ctx, __uwr_x0_0.__uwf_File)) <= 100000LL);
>
>                disc == uw_Basis_True ? "Whoa!  That one's too big."
>                  :
>                 disc == uw_Basis_False ?
>                  ({
>                   uw_Basis_blob blob =
>                   uw_Basis_fileData(ctx, __uwr_x0_0.__uwf_File);
>                   uw_Basis_string mimeType =
>                   uw_Basis_blessMime(ctx,
>                    uw_Basis_fileMimeType(ctx, __uwr_x0_0.__uwf_File));
>                   uw_Basis_string
>                   tmp;
>                   uw_return_blob(ctx, blob, mimeType);
>                   tmp;
>                   })
>                   :
>                  ({
>                   uw_Basis_string
>                   tmp;
>                   uw_error(ctx, FATAL,
> "/nix/store/fby0l6fdwqrq0rsr25jbc9hhg2srix08-urweb-urp-Urpf/Urpf.ur:11:32-11:33:
> pattern match failure");
>                   tmp;
>                   });
>                })));
>            }));
>    }
>
> 2017-02-19 18:15 GMT+03:00 Adam Chlipala <adamc at csail.mit.edu>:
>> 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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