Bug in the URL regex used to validate AnyUrl fields

[parthjoshi2007]

Bug

Please complete:

• OS: Ubuntu 18.04
• Python version import sys; print(sys.version): 3.7
• Pydantic version import pydantic; print(pydantic.VERSION): 1.1

Please read the docs and search through issues to
confirm your bug hasn't already been reported.

Where possible please include a self contained code snippet describing your bug:

import pydantic

class Item(pydantic.Model):
    url: pydantic.HttpUrl = ''

item = Item(url='http://twitter.com/@handle')

The above snippet throws an error because of a bug in the url_regex used by all AnyUrl subclasses that makes the validator think that twitter.com/ is the username in this URL because of the presence of @ in the path. This can be fixed trivially by adding / to the characters that cannot be in username (or for that matter, password).

So in pydantic/networks.py, the following line would change from:

url_regex = re.compile(
    r'(?:(?P<scheme>[a-z0-9]+?)://)?'  # scheme
    r'(?:(?P<user>[^\s:]+)(?::(?P<password>\S*))?@)?'  # user info
    r'(?:'
    r'(?P<ipv4>(?:\d{1,3}\.){3}\d{1,3})|'  # ipv4
    r'(?P<ipv6>\[[A-F0-9]*:[A-F0-9:]+\])|'  # ipv6
    r'(?P<domain>[^\s/:?#]+)'  # domain, validation occurs later
    r')?'
    r'(?::(?P<port>\d+))?'  # port
    r'(?P<path>/[^\s?]*)?'  # path
    r'(?:\?(?P<query>[^\s#]+))?'  # query
    r'(?:#(?P<fragment>\S+))?',  # fragment
    re.IGNORECASE,
)

to

url_regex = re.compile(
    r'(?:(?P<scheme>[a-z0-9]+?)://)?'  # scheme
    r'(?:(?P<user>[^\s:/]+)(?::(?P<password>[^\s/]*))?@)?'  # user info
    r'(?:'
    r'(?P<ipv4>(?:\d{1,3}\.){3}\d{1,3})|'  # ipv4
    r'(?P<ipv6>\[[A-F0-9]*:[A-F0-9:]+\])|'  # ipv6
    r'(?P<domain>[^\s/:?#]+)'  # domain, validation occurs later
    r')?'
    r'(?::(?P<port>\d+))?'  # port
    r'(?P<path>/[^\s?]*)?'  # path
    r'(?:\?(?P<query>[^\s#]+))?'  # query
    r'(?:#(?P<fragment>\S+))?',  # fragment
    re.IGNORECASE,
)