Snipped from gunicorn

message.py

def set_body_reader(self):
    chunked = False
    content_length = None
    for (name, value) in self.headers:
        if name == "CONTENT-LENGTH":
            content_length = value
        elif name == "TRANSFER-ENCODING":
            chunked = value.lower() == "chunked"
        elif name == "SEC-WEBSOCKET-KEY1":
            content_length = 8

    if chunked:
        self.body = Body(ChunkedReader(self, self.unreader))
    elif content_length is not None:
        try:
            content_length = int(content_length)
        except ValueError:
            raise InvalidHeader("CONTENT-LENGTH", req=self)

        if content_length < 0:
            raise InvalidHeader("CONTENT-LENGTH", req=self)

        self.body = Body(LengthReader(self.unreader, content_length))
    else:
        self.body = Body(EOFReader(self.unreader))