saving octet-stream png file

[Larry Martell]

On Fri, Aug 19, 2016 at 4:24 PM, Chris Kaynor <ckaynor at zindagigames.com> wrote:
> On Fri, Aug 19, 2016 at 12:00 PM, Larry Martell <larry.martell at gmail.com>
> wrote:
>
>> On Fri, Aug 19, 2016 at 1:24 PM, Chris Angelico <rosuav at gmail.com> wrote:
>> > On Sat, Aug 20, 2016 at 3:10 AM, Larry Martell <larry.martell at gmail.com>
>> wrote:
>> >> I have some python code (part of a django app) that processes a
>> >> request that contains a png file. The request is send with
>> >> content_type = 'application/octet-stream'
>> >>
>> >> In the python code I want to write this data to a file and still have
>> >> it still be a valid png file.
>> >>
>> >> The data I get looks like this:
>> >>
>> >> u'\ufffdPNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x01\ufffd\
>> x00\x00\x01\ufffd
>> >> ......'
>> >>
>> >> If I try and write that to a file it fails with a UnicodeEncodeError.
>> >> If I write it with encode('utf8') it writes the file, but then it's no
>> >> longer a valid png file.
>> >>
>> >> Anyone know how I can do this?
>> >
>> > At that point, you've already lost information. Each U+FFFD (shown as
>> > "\ufffd" above) is a marker saying "a byte here was not valid UTF-8"
>> > (or whatever was being used). Something somewhere took the .png file's
>> > bytes and tried to interpret them as text, which they're not.
>> >
>> > What sent you that data? How did you receive it?
>>
>> The request is sent by a client app written in C++ with Qt. It's
>> received by a django based server. I am trying to port a falcon server
>> to django. The falcon server code did this:
>>
>> form = cgi.FieldStorage(fp=req.stream, environ=req.env)
>>
>> and then wrote the png like this:
>>
>> fd.write(form[key].file.read())
>>
>> Whereas in the django server I am doing:
>>
>> fd.write(request.POST[key])
>>
>> I've never used the cgi module. I guess I can try that. I've written a
>> lot with django but never had to receive a PNG file.
>>
>>
> I don't know Django, however a quick search makes it seem like you might
> need to use request.FILES[key] (1) rather than request.POST[key]. You may
> also be able to use request.POST if you set request.encoding first (2). If
> both of those fail, you may need to use request.body and parse the HTTP
> form data manually, though I'd imagine there is an easier way.
>
> [1]
> https://docs.djangoproject.com/en/1.10/ref/request-response/#django.http.HttpRequest.FILES
>
> [2]
> https://docs.djangoproject.com/en/1.10/ref/request-response/#django.http.HttpRequest.encoding

Thanks for the reply. When I get the request, request.FILES is empty.
Yet the content type is multipart/form-data and the method is POST:

(Pdb) print request.META['CONTENT_TYPE']
multipart/form-data;
boundary="boundary_.oOo._NzEwNjIzMTM4MTI4NjUxOTM5OQ==MTY2NjE4MDk5Nw=="

(Pdb) print request.META['REQUEST_METHOD']
POST

(Pdb) print request.FILES
<MultiValueDict: {}>

Tried setting request.encoding, but that messes up the request structure:

(Pdb) type(request.POST[key])
<type 'unicode'>
(Pdb) request.encoding = "iso-8859-1"
(Pdb) type(request.POST[key])
*** MultiValueDictKeyError:
"u'right-carotidartery:63B2E474-D690-445F-B92A-31EBADDC9D93.png'"