BIND 10 #3186: Implement shared library of hooks for the Comcast Demo

[BIND 10 Development]

#3186: Implement shared library of hooks for the Comcast Demo
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            Reporter:  tmark         |                        Owner:  tmark
                Type:  task          |                       Status:
            Priority:  low           |  assigned
           Component:  dhcp          |                    Milestone:
            Keywords:                |  Sprint-DHCP-20131016
           Sensitive:  0             |                   Resolution:
         Sub-Project:  DHCP          |                 CVSS Scoring:
Estimated Difficulty:  0             |              Defect Severity:  N/A
         Total Hours:  0             |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by tmark):

 3186 implements "user_check" hooks shared library which supports subnet
 selection
 based upon the contents of a list of known DHCP lease requesters (i.e.
 clients),
 herein referred to as users.  The initial intent it assign "new" or
 "unregistered"
 users to a restricted subnet, while "known" or "registered" users are
 assigned
 to unrestricted subnets.

 As important as the specific library implementation, this issue always
 lays the ground work for placing hooks libraries developed by ISC under
 version control within the BIND10 repository.  Toward that that end the
 following sub-directories have been added to the BIND10 repo:

 bind10/src/hooks  - base directory for all ISC developed hooks libs

 bind10/src/hooks/dhcp - base directory for all hooks libs pertaining to
 DHCP(Kea)

 bind10/src/hooks/dhcp/user_check - directory containing the hooks library
 developed for Comcast under this issue.

 This directory structure has been added to relevant build files, such that
 it will
 build as part of the normal BIND10 build invocation.  We may wish to
 consider a
 configuration flag to either enable or disable building the hooks tree.

 As to the user_check lib itself, the heart of the solution lies in a new
 class
 hierarchy, centered around the class !UserRegistry.  This class represents
 a
 a maintainable, searchable list of known "users" and their attributes.

 Each entry in the registry is an instance of User.  Users are uniquely
 identified
 by their !UserId.  !UserIds are comprised of data taken from the DHCP
 request.  The
 registry supports both IPv4 and IPv6 users.

 The registry may be manually populated, or loaded from a source of data
 which implements
 the !UserDataSource interface.  Currently, a single implementation has
 been provided,
 !UserFile, which supports reading from a text file in which each line is a
 user entry
 in JSON format.  (See user_file.h for details on file content).

 This user_check library provides callouts for subnet4_select and
 subnet6_select, in
 subnet_select_co.cc.  These two functions implement a straight forward bit
 of logic
 for each inbound DHCP request:

     Refresh the registry.
     Extract user id information from the inbound DHCP packet.
     If the user is in the registry
        generate output to a text file indicating the user was registered
     otherwise
        replace the selected subnet with the last subnet in the list
        subnets available.
        generate output to a text file indicating the user was not
 registered

 By convention, the last subnet in the collection of subnets available is
 assumed to
 be the "restricted access" subnet.  A more sophisticated mechanism if
 likely to be needed.

 Each invocation of the callout generates output to the "user_check
 outcome" file.
 The output contains the  user id, the subnet selected for the user, and
 whether or
 not the user was registered.  This information is written in ini-like
 form,
 "name=value" with one entry per value per line. See subnet_callout.cc for
 details.

 The following class diagram illustrates the new classes:

 [[Image(user_check_classes.svg)]]

-- 
Ticket URL: <http://bind10.isc.org/ticket/3186#comment:4>
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