# Router

Guillotina uses `aiohttp` for it's webserver. In order to route requests against
Guillotina's traversal url structure, Guillotina provides it's own router
that does traversal: `guillotina.traversal.router`.


.. automodule:: guillotina.traversal

  .. autofunction:: TraversalRouter


## Providing your own router

Guillotina allows you to provide your own customized router using the `router`
settings.

Here is an example router that provides `/v1` and `/v2` type url structure:

``python
from guillotina import configure
from guillotina.content import Resource
from guillotina.interfaces import IContainer
from guillotina.interfaces import IDefaultLayer
from guillotina.interfaces import IRequest
from guillotina.interfaces import IResource
from guillotina.traversal import TraversalRouter
from guillotina.traversal import traverse
from zope.interface import alsoProvides


class IV1Layer(IDefaultLayer):
    pass


class IV2Layer(IDefaultLayer):
    pass


@configure.service(method='GET', name='@foobar',
                   permission='guillotina.AccessContent',
                   layer=IV1Layer)
async def v1_service(context, request):
    return {
        'version': '1'
    }


@configure.service(method='GET', name='@foobar',
                   permission='guillotina.AccessContent',
                   layer=IV2Layer)
async def v2_service(context, request):
    return {
        'version': '2'
    }


@configure.contenttype(type_name="VersionRouteSegment")
class VersionRouteSegment(Resource):

    type_name = 'VersionRouteSegment'

    def __init__(self, name, parent):
        super().__init__()
        self.__name__ = self.id = name
        self.__parent__ = parent


class MyRouter(TraversalRouter):
    async def traverse(self, request: IRequest) -> IResource:
        resource, tail = await super().traverse(request)
        if len(tail) > 0 and tail[0] in ('v1', 'v2') and IContainer.providedBy(resource):
            segment = VersionRouteSegment(tail[0], resource)
            if tail[0] == 'v1':
                alsoProvides(request, IV1Layer)
            elif tail[0] == 'v2':
                alsoProvides(request, IV2Layer)

            if len(tail) > 1:
                # finish traversal from here
                return await traverse(request, segment, tail[1:])
            else:
                resource = segment
                tail = tail[1:]
        return resource, tail


app_settings = {
    # provide custom application settings here...
    'router': MyRouter
}
```