11. Request Content Checksums¶
Various pieces of code can consume the request data and preprocess it. For instance JSON data ends up on the request object already read and processed, form data ends up there as well but goes through a different code path. This seems inconvenient when you want to calculate the checksum of the incoming request data. This is necessary sometimes for some APIs.
Fortunately this is however very simple to change by wrapping the input stream.
The following example calculates the SHA1 checksum of the incoming data as it gets read and stores it in the WSGI environment:
import hashlib class ChecksumCalcStream(object): def __init__(self, stream): self._stream = stream self._hash = hashlib.sha1() def read(self, bytes): rv = self._stream.read(bytes) self._hash.update(rv) return rv def readline(self, size_hint): rv = self._stream.readline(size_hint) self._hash.update(rv) return rv def generate_checksum(request): env = request.environ stream = ChecksumCalcStream(env['wsgi.input']) env['wsgi.input'] = stream return stream._hash
To use this, all you need to do is to hook the calculating stream in
before the request starts consuming data. (Eg: be careful accessing
request.form or anything of that nature.
for instance should be careful not to access it).
@app.route('/special-api', methods=['POST']) def special_api(): hash = generate_checksum(request) # Accessing this parses the input stream files = request.files # At this point the hash is fully constructed. checksum = hash.hexdigest() return 'Hash was: %s' % checksum