Writing byte stream as jpeg format to disk

Navkirat Singh navkirats at gmail.com
Thu Aug 26 23:28:08 CEST 2010

On 27-Aug-2010, at 2:48 AM, MRAB wrote:

> On 26/08/2010 21:47, Navkirat Singh wrote:
>> On 27-Aug-2010, at 1:57 AM, MRAB wrote:
>>> On 26/08/2010 21:14, Navkirat Singh wrote:
>>>> On 27-Aug-2010, at 1:32 AM, Dave Angel wrote:
>>>>> Navkirat Singh wrote:
>>>>>> Hey guys,
>>>>>> I am programming a webserver, I receive a jpeg file with the POST
>>>>>> method.The file (.jpeg) is encoded in bytes, I parse the bytes by
>>>>>> decoding them to a string. I wanted to know how i could write the
>>>>>> file (now a string) as a jpeg image on disk. When I try to encode the
>>>>>> same string to a bytes and write them in binary format to disk, the
>>>>>> file is not recognized as jpeg. I would be grateful if someone could
>>>>>> help me with this.
>>>>>> Regards,
>>>>>> Nav
>>>>> If by "decoding them to a string" you mean converting to Unicode, then
>>>>> you've already trashed the data. That's only valid if the bytes had
>>>>> been encoded from valid Unicode characters, and then only if you use
>>>>> the corresponding decoding technique.
>>>>> If you mean some other decoding, then the question is meaningless
>>>>> without telling us just what the decoding is, preferably with some code.
>>>>> It also might be useful to know what version of Python you're using,
>>>>> when you post the code.
>>>>> DaveA
>>>> Dave,
>>>> I am using Python3 and I receive a byte stream with a jpeg attached sent
>>>> by the web browser over a socket, which looks like this:
>>>> b': image/jpeg\r\nAccept: text/*\r\nReferer:
>>>>\r\nAccept-Language: en-us\r\nAccept-Encoding:
>>>> gzip, deflate\r\nContent-Length: 91783\r\nConnection:
>>>> keep-alive\r\n\r\n\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xdb\x00\x84\x00\x03\x02\x02\x03\x02\x02\x03\x03\x03\x03\x04\x03\x03\x04\x05\x08\x05\x05\x04\x04\x05\n\x07\x07\x06\x08\x0c\n\x0c\x0c\x0b\n\x0b\x0b\r\x0e\x12\x10\r\x0e\x11\x0e\x0b\x0b\x10\x16\x10\x11\x13\x14\x15\x15\x15\x0c\x0f
>>>> From the above, I need to:
>>>> a) Split the header content from the image content, which comes after
>>>> the keep-alive\r\n\r\n part
>>>> b) Then write the image content to file for further use as a jpeg.
>>> Try:
>>>    image = header.split(b'keep-alive\r\n\r\n', 1)[-1]
>>>    open(image_path, 'wb').write(image)
>>> --
>>> http://mail.python.org/mailman/listinfo/python-list
>> I think I forgot to mention that the original is a stream of bytes decoded using ISO-8859-1 as utf-8 trhrew errors (lack of knowlegdge again).
>> @MRAB - the split() method in python 3 works only on strings and throws an error if I try to use bytes
> All i can say is that it works for me:
> >>> header = b': image/jpeg\r\nAccept: text/*\r\nReferer:\r\nAccept-Language:  en-us\r\nAccept-Encoding: gzip, deflate\r\nContent-Length: 91783\r\nConnection: keep-alive\r\n\r\n\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xdb\x00\x84\x00\x03\x02\x02\x03\x02\x02\x03\x03\x03\x03\x04\x03\x03\x04\x05\x08\x05\x05\x04\x04\x05\n\x07\x07\x06\x08\x0c\n\x0c\x0c\x0b\n\x0b\x0b\r\x0e\x12\x10\r\x0e\x11\x0e\x0b\x0b\x10\x16\x10\x11\x13\x14\x15\x15\x15\x0c\x0f'
> >>> image = header.split(b'keep-alive\r\n\r\n', 1)[-1]
> >>> image
> b'\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xdb\x00\x84\x00\x03\x02\x02\x03\x02\x02\x03\x03\x03\x03\x04\x03\x03\x04\x05\x08\x05\x05\x04\x04\x05\n\x07\x07\x06\x08\x0c\n\x0c\x0c\x0b\n\x0b\x0b\r\x0e\x12\x10\r\x0e\x11\x0e\x0b\x0b\x10\x16\x10\x11\x13\x14\x15\x15\x15\x0c\x0f'
> What error did you get?
> -- 
> http://mail.python.org/mailman/listinfo/python-list


Here is the error:

>>> b = b'asdf'
>>> type(b)
<class 'bytes'>
>>> s = b.split(':')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Type str doesn't support the buffer API

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