How to stream a requests response as a file-like object.

stream_response.py

# -*- coding: utf-8 -*-

import requests
from io import BytesIO, SEEK_SET, SEEK_END

class ResponseStream(object):
    def __init__(self, request_iterator):
        self._bytes = BytesIO()
        self._iterator = request_iterator

    def _load_all(self):
        self._bytes.seek(0, SEEK_END)
        for chunk in self._iterator:
            self._bytes.write(chunk)

    def _load_until(self, goal_position):
        current_position = self._bytes.seek(0, SEEK_END)
        while current_position < goal_position:
            try:
                current_position += self._bytes.write(next(self._iterator))
            except StopIteration:
                break

    def tell(self):
        return self._bytes.tell()

    def read(self, size=None):
        left_off_at = self._bytes.tell()
        if size is None:
            self._load_all()
        else:
            goal_position = left_off_at + size
            self._load_until(goal_position)

        self._bytes.seek(left_off_at)
        return self._bytes.read(size)
    
    def seek(self, position, whence=SEEK_SET):
        if whence == SEEK_END:
            self._load_all()
        else:
            self._bytes.seek(position, whence)

def main():
    # Use the class by providing a requests stream iterator.
    response = requests.get('http://example.com/', stream=True)
    # Chunk size of 64 bytes, in this case. Adapt to your use case.
    stream = ResponseStream(response.iter_content(64))

    # Now we can read the first 100 bytes (for example) of the file
    # without loading the rest of it. Of course, it's more useful when
    # loading large files, like music images, or video. 😉
    # Seek and tell will also work as expected; important for some applications.
    stream.read(100)

if __name__ == '__main__':
    main()

z_readme.md

Streaming a requests response as a file

In many applications, you'd like to access a requests response as a file-like object, simply having .read(), .seek(), and .tell() as normal. Especially when you only want to partially download a file, it'd be extra convenient if you could use a normal file interface for it, loading as needed.

This is a wrapper class for doing that. Only bytes you request will be loaded - see the example in the gist itself.

License

This piece of code is licensed under the Unlicense, which means it is in the public domain; free to use without attribution. Go ahead and use it for anything without worries!

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Thanks for this class, @obskyr!

I can confirm the following bug, though:

@obskyr I think you are missing "+" on line 20.

current_position += self._bytes.write(next(self._iterator))

@matbra Fixed it! Thank you.

Do you have a similar script for uploading a huge file. My use case is to upload a large file in chunks (10MB). However, that 10 MB also should be read all together in the memory but read only 8192/4096 bytes at a time and send to requests.

Another bug fix: negative seek doesn’t work as the else block should also run after the if condition (either way, i.e. remove the else and dedent the line that was in that block). Obviously it kind of defeats the purpose to use but may as well work correctly!

Also worth noting that the server must support the “Transfer-Encoding”: “chunked” header (if you get a Content-Length header in the response, it’s not supported)

Edit I built on this to combine it with server-side range requests in a library range-streams. Thanks for giving it a permissive license, you are credited in the design notes in the docs even though you don't demand it 😃

very useful thank you.

I added the following so I could use it in with:

def __enter__(self):
        return self

def __exit__(self, type, value, tb):
    self._bytes.close()