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From Apache Wiki <wikidi...@apache.org>
Subject [Subversion Wiki] Update of "ServerDictatedConfiguration" by CMichaelPilato
Date Tue, 06 Dec 2011 15:39:18 GMT
Dear Wiki user,

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The "ServerDictatedConfiguration" page has been changed by CMichaelPilato:
http://wiki.apache.org/subversion/ServerDictatedConfiguration?action=diff&rev1=12&rev2=13

Comment:
Still thinking aloud about scopes and intensities.

  The high-level behavior for repository-dictated configuration is relatively simple: the
repository maintains a list of configuration parameters and values, and upon request, provides
these to the client who then applies them appropriately.
  
  There are a number of specific bits of configuration that existing Subversion users and
administrators wish to have propagated from the server to the client.  There are also different
scopes at which administrators might reasonably wish to apply differing defaults for these
things:  server-wide, repository-wide, or local to a particular directory hierarchy within
a specific repository.  The following is a listing of those that we know about, with some
notes about scope and desired degrees of control:
+ 
  ||'''Configuration''' ||'''Scope''' ||'''Enforceability''' ||'''Notes''' ||
  ||auto-props ||per-directory ||Enforceable via hook scripts ||Clients should be allowed
to override this ||
+ ||ignores ||per-directory ||Enforceable via hook scripts ||Client should be allowed to override
this ||
+ ||use-commit-times ||per-directory ||Unenforceable ||Client should be allowed to override
this ||
  ||log message templates ||per-directory ||Enforceable via hook scripts ||Doesn't fit the
name=value configuration motif quite as readily as some of the others.  Would a client need
to override this? ||
- ||myriad authn-related stuff ||per-server, per-repos ||Un-enforceable ||Lack of enforceability
plus relationship to security means that admins do not want the client to be able to trivially
override this setting.  Precise requirements TBD (is this a boolean "allow/disallow plaintext
password caching", or "require X, Y or Z encrypted password stores", or ...? ||
+ ||myriad authn-related stuff ||per-server, per-repos ||Unenforceable ||Lack of enforceability
plus relationship to security means that admins do not want the client to be able to trivially
override this setting.  Precise requirements TBD (is this a boolean "allow/disallow plaintext
password caching", or "require X, Y or Z encrypted password stores", or ...?) ||
  
  {{{#!wiki warning
  The configuration the server dictates can at best be only a suggestion to the client, with
well-behaving clients honoring that suggestion.  As free software, though, most such clients
could be modified by a malicious user to ignore server-side suggestions.  Server-side enforcement
of desired behaviors (where possible, and often via hook scripts) is still recommended.
  }}}
  
  At least one user specifically called out the need for the server to enforce adherence to
the configured behaviors ''without'' requiring hook scripts to do so.  For example, if the
repository has a configured auto-props list, the Subversion C code is perfectly capable of
validating that incoming committed items obey those settings, failing the commit otherwise.
 This seems like a reasonable request so long as we permit admins to specify which of their
configuration settings are "suggested" versus "required" (again, taking into account that
anything unenforceable can't truly be "required").
+ 
+ Subversion should recognize multiple levels of possible hierarchy in the server-side configuration:
+ 
+  1. server - Settings apply for all repositories and paths therein on the server
+  1. repository - Settings apply for all interactions with the repository and the paths within
it
+  1. subtree within repository - Settings apply for paths at or under a given path in the
repository
+ 
+ And at each level, multiple degrees of insistence in the actual configuration items:
+ 
+  1. weak - The configuration value is proposed to the client, but will be overridden by
any client configuration
+  1. strong - The configuration value is strongly suggested by the client, and may not be
overridden by well-behaved client configuration
+  1. enforced - The configuration value is required and adherence to it is verified by the
server logic
  
  === Server-client transmission mechanism ===
  Over ra-neon/ra-serf, the client will send to the server the sha1 hash of the server-dictated
config that it current has cached as part of the OPTIONS request.  If the server has a different
version, it will send that to the client in the OPTIONS response.  For ra-svn, a similar thing
happens as part of the initial connection handshake/feature exchange.  This is an opportunistic
caching approach, keeping the client in sync with the repository configuration any time the
client contacts the repository.  This mechanism requires that there exist a predictable and
consistent manner in which to calculate the checksum of the configuration.

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