gitolite/doc/4-wildcard-repositories.mkd

# repositories named with wildcards

***IMPORTANT NOTE***:

This branch contains features that are likely to be much more brittle than the
"master" branch.  Creating repositories based on wild cards, giving
"ownership" to the specific user who created it, allowing him/her to hand out
R and RW permissions to other users to collaborate, all these are possible.
And any of these could have a bug in it.

"Brittle" also means some features in "master" may not work here.  For
example, you cannot specify gitconfig values for a wildcard repo; it only
works for actual repos.

There may be other such missing features.  Sometimes it's just not possible to
make it work.  Or it may be cumbersome enough that unless there are *no*
workarounds I may not have the time to code it right away.

----

In this document:

  * wildcard repos
      * wildcard repos with creater name in them
      * wildcard repos without creater name in them
  * side-note: line-anchored regexes
      * contrast with refexes
  * handing out rights to wildcard-matached repos
  * reporting
  * other issues and discussion

This document is mostly "by example".

----

### Wildcard repos

Which of these alternatives you choose depends on your needs, and the social
aspects of your environment.  The first one is a little more rigid, making it
harder to make mistakes, and the second is more flexible and trusting.

#### Wildcard repos with creater name in them

Here's an example snippet:

    @prof       =   u1
    @TAs        =   u2 u3
    @students   =   u4 u5 u6

    repo    assignments/CREATER/a[0-9][0-9]
        C   =   @students
        RW+ =   CREATER
        RW  =   WRITERS @TAs
        R   =   READERS @prof

For now, ignore the special usernames READERS and WRITERS, and just create a
new repo, as user "u4" (a student):

    $ git clone git@server:assignments/u4/a12
    Initialized empty Git repository in /home/sitaram/t/a12/.git/
    Initialized empty Git repository in /home/gitolite/repositories/assignments/u4/a12.git/
    warning: You appear to have cloned an empty repository.

Notice the *two* empty repo inits, and the order in which they occur ;-)  Now
make some changes and push, and after that, that specific repo
(`assignments/u4/a12`) behaves as if the access control looked like this:

    # effective config
    repo    assignments/u4/a12
        RW+ =   u4
        RW  =   WRITERS @TAs
        R   =   READERS @prof

#### Wildcard repos without creater name in them

Here's how the same example would look if you did not want the CREATER's name
to be part of the actual repo name.

    repo    assignments/a[0-9][0-9]
        C   =   @students
        RW+ =   CREATER
        RW  =   WRITERS @TAs
        R   =   READERS @prof

We haven't changed anything except the repo name pattern.  This means that the
first student that creates, say, `assignments/a12` becomes the owner.
Mistakes (such as claiming a12 instead of a13) need to be rectified by an
admin logging on to the back end, though it's not too difficult.

You could also repace the C line like this:

        C   =   @TAs

and have a TA create the repos in advance.

In either case, they could then use the `setperms` feature to specify which
users are "READERS" and which are "WRITERS".  See later for details.

### Side-note: Line-anchored regexes

A regex like

    repo assignments/S[0-9]+/A[0-9]+

would match `assignments/S02/A37`.  It will not match `assignments/S02/ABC`,
or `assignments/S02/a37`, obviously.

But you may be surprised to find that it does not match even
`assignments/S02/A37/B99`.  This is because internally, gitolite
*line-anchors* the given regex; so that regex actually becomes
`^assignments/S[0-9]+/A[0-9]+$` -- notice the line beginning and ending
metacharacters.

#### Contrast with refexes

Just for interest, note that this is in contrast to the refexes for the normal
"branch" permissions, as described in `conf/example.conf` and elsewhere.
Those "refexes" are *not* anchored; a pattern like `refs/heads/master`
actually matches `foo/refs/heads/master01/bar` as well, even if no one will
actually push such a branch!  You can anchor it if you really care, by using
`master$` instead of `master`, but anchoring is *not* the default for
refexes.]

### Handing out rights to wildcard-matached repos

In the examples above, we saw two special "user" names: READERS and WRITERS.
The permissions they have are controlled by the config file, but ***who is
part of this list*** is controlled by the person who created the repository.

The use case is that, although our toy example has only 3 students, in reality
there will be a few dozen, but each assignment will be worked on only by a
handful from among those.  This allows the creater to take ad hoc sets of
users from among the actual users in the system, and place them into one of
two categories (whose permissions are, in this example, R and RW
respectively).  In theory you could do the same thing by creating lots of
little "assignment-NN" groups in the config file but that may be a little too
cumbersome for non-secret environments.

Create a small text file that contains the permissions you desire:

    $ cat > myperms
    R u5
    RW u6
    (hit ctrl-d here)

...and use the new "getperms" command to set permissions for your repo:

    $ ssh git@server setperms assignments/u4/a12 < myperms
    New perms are:
    R u5
    RW u6

'setperms' will helpfully print what the new permissions are but you can also
use 'getperms' to check:

    $ ssh git@server getperms assignments/u4/a12
    R u5
    RW u6

The following points are important:

  * note the syntax of the commands; it's not a "git" command,and there's no
    `:` like in a repo URL.  The first space-separated word is R or RW, and
    the rest are simple usernames.

  * whoever you specify as "R" will match the special user READERS.  "RW" will
    match WRITERS.

### Reporting

Remember the cool stuff you see when you just do `ssh git@server` (grep for
"myrights" in `doc/3-faq-tips-etc.mkd` if you forgot, or go [here][mr]).

[mr]: http://github.com/sitaramc/gitolite/blob/pu/doc/3-faq-tips-etc.mkd#myrights

This still works, except the format is a little more compressed to accommodate
a new column (at the start) for "C" permissions, which indicate that you are
allowed to *create* repos matching that pattern.

### Other issues and discussion

  * *what if the repo name being pushed matches more than one pattern*?

    I think it would be very hard to reason about access if we were to do
    something like combine all the access rights in all the matching patterns.
    No matter how you do it, and how carefully you document it, there'll be
    someone who is surprised by the result.

    And in security, that's a ***Bad Thing***.

    So we don't combine permissions.  At runtime, we die if we find more than
    one match.  Let 'em go holler at the admin for creating multiple matching
    repo patterns :-)

    This can make some repos inaccessible if the patterns changed *after* they
    were created.  The administrator should be careful not to do this.  Most
    of the time, it won't be difficult; the fixed prefix will usually be
    different anyway so there won't be overlaps.

----

Enjoy, and please use with care.  This is pretty powerful stuff.  As they say:
if you break it, you get to keep both pieces :)

[jwzq]: http://regex.info/blog/2006-09-15/247

[av]: http://en.wikipedia.org/wiki/Autovivification