prevent double slash /a//b when blueprint prefix ends with slash

[zcchen]

Simple example file as below:

from __future__ import print_function

from flask import Flask, Blueprint, redirect

bp = Blueprint('bp', __name__)
app = Flask(__name__)

@bp.route('/b/')
def tmp():
    return "URI should be '/a/b/"


@app.route('/')
def index():
    return redirect("/a/b/")

app.register_blueprint(bp, url_prefix='/a/')

if __name__ == "__main__":
    print("app.url_map: ", app.url_map)
    app.run(port=5000, host='127.0.0.1', debug=True)

With the old code, there is one rule like this <Rule '/a//b/' (HEAD, OPTIONS, GET) ->.
With the new code, that rule would be change to <Rule '/a/b/' (HEAD, OPTIONS, GET) ->.

[ThiefMaster]

I think people should rather not add trailing slashes to their url_prefix ;)

Maybe showing a warning would be better instead of removing consecutive slashes so people can actually fix their code?

PS: The commit message is a bit too long (even GitHub truncates it), first line should be 51 chars max.

[zcchen]

Maybe someone would use url_prefix = '/'?
At that time, bp.route would also have a rule like '/' .

[ThiefMaster]

url_prefix='/' seems to be quite pointless, isn't it?

[zcchen]

Yes.
But should we clear the extra and useless slashes in the URL?

[davidism]

Related to pallets/werkzeug#1132.

url_prefix='' (or just not specifying it at all) already works for registering a blueprint at the root path.

[davidism]

This should probably just strip exactly one trailing slash off the prefix. I don't want to mess with route definitions in general, just the prefixing. If pallets/werkzeug#1132 is implemented, it will handle normalizing routes in general.

[sersorrel]

I agree that some kind of feature to either strip a trailing slash or to warn that it's not necessary should be added – I recently was trying to work out why some things were not working properly when using url_prefix="/", since that seemed like the obvious thing to do to explicitly register a blueprint at the root of the app.