Double-encoded cookies

[elacuesta]

When cookies are passed as UTF8 encoded bytes to the Request constructor, they end up being encoded twice and escaped in the Cookie header.

$ scrapy shell
(...)
In [1]: fetch(scrapy.Request('https://httpbin.org/cookies', cookies={'a': u'á'.encode('utf8')}))

In [2]: request.headers['Cookie']
Out[2]: b"a=b'\\xc3\\xa1'"

In [3]: print(response.text)
{
  "cookies": {
    "a": "b'\\xc3\\xa1'"
  }
}

This seems to happen only in Python 3.

$ scrapy version -v
Scrapy       : 1.5.0
lxml         : 4.2.6.0
libxml2      : 2.9.8
cssselect    : 1.0.3
parsel       : 1.5.1
w3lib        : 1.19.0
Twisted      : 18.9.0
Python       : 3.6.0 (default, Sep  1 2017, 10:59:37) - [GCC 4.8.4]
pyOpenSSL    : 18.0.0 (OpenSSL 1.1.0j  20 Nov 2018)
cryptography : 2.4.2
Platform     : Linux-4.4.0-134-generic-x86_64-with-debian-jessie-sid

[elacuesta]

This is fixed by #2400