Validating URIs

While not as difficult as validating an email address, validating URIs is tricky. Different parts of the URI allow different characters. Those sets sometimes overlap and othertimes they don’t and it’s not very convenient. Luckily, rfc3986 makes validating URIs far simpler.

Example Usage

First we need to create an instance of a Validator which takes no parameters. After that we can call methods on the instance to indicate what we want to validate.

Allowing Only Trusted Domains and Schemes

Let’s assume that we’re building something that takes user input for a URL and we want to ensure that URL is only ever using a specific domain with https. In that case, our code would look like this:

>>> from rfc3986 import validators, uri_reference
>>> user_url = 'https://github.com/sigmavirus24/rfc3986'
>>> validator = validators.Validator().allow_schemes(
...     'https',
... ).allow_hosts(
...     'github.com',
... )
>>> validator.validate(uri_reference(
...     'https://github.com/sigmavirus24/rfc3986'
... ))
>>> validator.validate(uri_reference(
...     'https://github.com/'
... ))
>>> validator.validate(uri_reference(
...     'http://example.com'
... ))
Traceback (most recent call last):
...
rfc3986.exceptions.UnpermittedComponentError

First notice that we can easily reuse our validator object for each URL. This allows users to not have to constantly reconstruct Validators for each bit of user input. Next, we have three different URLs that we validate:

  1. https://github.com/sigmavirus24/rfc3986
  2. https://github.com/
  3. http://example.com

As it stands, our validator will allow the first two URLs to pass but will fail the third. This is specifically because we only allow URLs using https as a scheme and github.com as the domain name.

Preventing Leaks of User Credentials

Next, let’s imagine that we want to prevent leaking user credentials. In that case, we want to ensure that there is no password in the user information portion of the authority. In that case, our new validator would look like this:

>>> from rfc3986 import validators, uri_reference
>>> user_url = 'https://github.com/sigmavirus24/rfc3986'
>>> validator = validators.Validator().allow_schemes(
...     'https',
... ).allow_hosts(
...     'github.com',
... ).forbid_use_of_password()
>>> validator.validate(uri_reference(
...     'https://github.com/sigmavirus24/rfc3986'
... ))
>>> validator.validate(uri_reference(
...     'https://github.com/'
... ))
>>> validator.validate(uri_reference(
...     'http://example.com'
... ))
Traceback (most recent call last):
...
rfc3986.exceptions.UnpermittedComponentError
>>> validator.validate(uri_reference(
...     'https://sigmavirus24@github.com'
... ))
>>> validator.validate(uri_reference(
...     'https://sigmavirus24:not-my-real-password@github.com'
... ))
Traceback (most recent call last):
...
rfc3986.exceptions.PasswordForbidden

Requiring the Presence of Components

Up until now, we have assumed that we will get a URL that has the appropriate components for validation. For example, we assume that we will have a URL that has a scheme and hostname. However, our current validation doesn’t require those items exist.

>>> from rfc3986 import validators, uri_reference
>>> user_url = 'https://github.com/sigmavirus24/rfc3986'
>>> validator = validators.Validator().allow_schemes(
...     'https',
... ).allow_hosts(
...     'github.com',
... ).forbid_use_of_password()
>>> validator.validate(uri_reference('//github.com'))
>>> validator.validate(uri_reference('https:/'))

In the first case, we have a host name but no scheme and in the second we have a scheme and a path but no host. If we want to ensure that those components are there and that they are always what we allow, then we must add one last item to our validator:

>>> from rfc3986 import validators, uri_reference
>>> user_url = 'https://github.com/sigmavirus24/rfc3986'
>>> validator = validators.Validator().allow_schemes(
...     'https',
... ).allow_hosts(
...     'github.com',
... ).forbid_use_of_password(
... ).require_presence_of(
...     'scheme', 'host',
... )
>>> validator.validate(uri_reference('//github.com'))
Traceback (most recent call last):
...
rfc3986.exceptions.MissingComponentError
>>> validator.validate(uri_reference('https:/'))
Traceback (most recent call last):
...
rfc3986.exceptions.MissingComponentError
>>> validator.validate(uri_reference('https://github.com'))
>>> validator.validate(uri_reference(
...     'https://github.com/sigmavirus24/rfc3986'
... ))

Checking the Validity of Components

As of version 1.1.0, rfc3986 allows users to check the validity of a URI Reference using a Validator. Along with the above examples we can also check that a URI is valid per RFC 3986. The validation of the components is pre-determined so all we need to do is specify which components we want to validate:

>>> from rfc3986 import validators, uri_reference
>>> valid_uri = uri_reference('https://github.com/')
>>> validator = validators.Validator().allow_schemes(
...     'https',
... ).allow_hosts(
...     'github.com',
... ).forbid_use_of_password(
... ).require_presence_of(
...     'scheme', 'host',
... ).check_validity_of(
...     'scheme', 'host', 'path',
... )
>>> validator.validate(valid_uri)
>>> invalid_uri = valid_uri.copy_with(path='/#invalid/path')
>>> validator.validate(invalid_uri)
Traceback (most recent call last):
...
rfc3986.exceptions.InvalidComponentsError

Paths are not allowed to contain a # character unless it’s percent-encoded. This is why our invalid_uri raises an exception when we attempt to validate it.