libxorp_overview.tex

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\begin{document}

\title{XORP Libxorp Library Overview \\
\vspace{1ex}
Version 0.5}
\author{ XORP Project					\\
	 International Computer Science Institute	\\
	 Berkeley, CA 94704, USA			\\
	 {\it [e-mail]}
}
\date{November 6, 2003}

\maketitle

\thispagestyle{empty}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Introduction}

The \emph{libxorp} library contains a set of classes for basic
XORP functionality such as IP addresses and subnets, timers, event
loops, etc. It is used by virtually every other XORP component, and
its main purpose is to simplify the implementation of those components.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Overview}

Currently, the libxorp library contains the following classes and
components (in alphabetical order):

\begin{itemize}

  \item \emph{asnum.hh: class AsNum}: A class for storing an AS number
  used by protocols such as BGP.

  \item \emph{asyncio.hh: class AsyncFileReader, class AsyncFileWriter}:
  Asynchronous file transfer classes.

  \item \emph{buffer.hh: class Buffer}:  A class for storing buffered
  data.

  \item \emph{c\_format.hh: c\_format()}: A macro that creates a C++ string
  from a C-style printf(3)-formatted string.

  \item \emph{callback.hh:} Callback mechanism.

  \item \emph{config\_param.hh: template class ConfigParam}: A class for
  storing a configuration parameter.

  \item \emph{debug.h}: Provides facility for generating debug messages.

  \item \emph{ether\_compat.h}: Ethernet manipulation compatibility functions.

  \item \emph{eventloop.hh: class EventLoop}: Event loop class for
  coordinated operations between timers and I/O operations on file
  descriptors.

  \item \emph{exceptions.hh}: Standard XORP C++ exceptions.

  \item \emph{heap.hh: class Heap}: Provides Heap data structure.

  \item \emph{ipnet.hh, ipv4net.hh, ipv6net.hh, ipvxnet.hh: class
  IPv4Net, class IPv6Net, class IPvXNet}: Implementation of classes for
  basic subnet addresses (for IPv4, IPv6 and dual IPv4/6 address family
  respectively).

  \item \emph{ipv4.hh, ipv6.hh, ipvx.hh: class
  IPv4, class IPv6, class IPvX}: Implementation of classes for
  basic IP addresses (for IPv4, IPv6 and dual IPv4/6 address family
  respectively).

  \item \emph{mac.hh: class Mac, class EtherMac}: Containers for
  MAC types.

  \item \emph{nexthop.hh}: Classes that contain routing next-hop
  information.

  \item \emph{ref\_ptr.hh: template class ref\_ptr}: Reference counted
  pointer class.

  \item \emph{ref\_trie.hh}: Implementation of a trie to support route
  lookups.  Based on trie.hh, but with reference-counted storage
  supporting delayed deletion.

  \item \emph{selector.hh}: I/O multiplexing interface.

  \item \emph{service.hh}: Provides base for asynchronous service classes.

  \item \emph{status\_codes.h}: Process states status codes used by
  processes when reporting their operational status to the router manager.

  \item \emph{time\_slice.hh: class TimeSlice}: A class for computing
  whether some processing is taking too long.

  \item \emph{timer.hh, class XorpTimer}: XORP timer facility.

  \item \emph{timeval.hh: class TimeVal}: A class for storing time values
  (similar to \emph{struct timeval}).

  \item \emph{token.hh}: Token related definitions.

  \item \emph{transactions.hh}: Facility for transaction operations.

  \item \emph{trie.hh}: Implementation of a trie to support route
  lookups.

  \item \emph{utility.h}: Contains various mini-utilities
  (mostly compiler-related helpers).

  \item \emph{utils.hh}: Contains various utilities (\eg to delete a
  list or array of pointers and the objects pointed to).

  \item \emph{vif.hh: class Vif, class VifAddr}: Virtual interface and
  virtual interface address classes.

  \item \emph{xlog.h}: Provides facility for log messages generation.

  \item \emph{xorp.h}: The XORP main include file that should be included
  by all XORP C and C++ files.

\end{itemize}

Each of the components is described in
Section~\ref{sec:components_description}.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Components Description}
\label{sec:components_description}

This section contains a brief description of each of the components of
the \emph{libxorp} library. This description is for informative
purpose only. The source code for each component is the ultimate source
for programming reference, and implementation details.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{asnum.hh}

This file contains \emph{class AsNum}: a class for storing an AS number
used by protocols such as BGP.
This class can be used to store an AS number that can be either
16 or 32 bits.  Originally, the AS numbers were defined as 16-bit
unsigned numbers.  Later the ``extended'' AS numbers were introduced,
which are unsigned 32-bit numbers.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{asyncio.hh}

This file contains
asynchronous file transfer classes.  These utilize XORP EventLoop
and its SelectorList to read or write files asynchronously.  The
user creates an AsyncFile\{Reader,Writer\} and adds a buffer for
reading or writing with add\_buffer().  A callback provided with
each buffer is called every time I/O happens on the buffer.
Reading or writing only begins when start() is called, and normally
continues until there are no buffers left.

From the developer's point of view, the following classes are of
interest: \emph{class AsyncFileReader, class AsyncFileWriter}.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{buffer.hh}

This file contains \emph{class Buffer}: a class for conveniently storing
and accessing buffered data.
Currently it has limited applicability.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{c\_format.hh}

This file contains \emph{c\_format()}: a macro that creates a C++ string
from a C-style printf(3)-formatted string.
It takes the same arguments as printf(3), but \%n is illegal and
will cause abort to be called.

In practice c\_format() is a nasty macro, but by doing this we can check
the compile time arguments are sane and the run time arguments.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{callback.hh}

This file contains an implementation of a callback mechanism.
XORP is an asynchronous programming environment and as a result there
are many places where callbacks are useful.  Callbacks are typically
invoked to signify the completion or advancement of an asynchronous
operation.

XORP provides a generic and flexible callback interface that utilizes
overloaded templatized functions for generating callbacks in
conjunction with many small templatized classes. Whilst this makes the
syntax a little unpleasant, it provides a great deal of flexibility.

XorpCallback objects are objects created by the callback()
function which returns a reference pointer to a newly created
callback object.  The callback is invoked by calling the dispatch()
method on that object.

For more details on the callback mechanism, and for usage examples, see
the beginning of \emph{callback.hh}.
Note that this file is auto-generated by callback-gen.py (a Python script),
therefore it should never be edited.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{config\_param.hh}

This file contains the implementation of \emph{template class
ConfigParam}: a class for storing a configuration parameter.

This class can be used to store the value of a configuration parameter.
Such parameter has a current and a default value.
The \emph{ConfigParam} class has the facility to add a callback that is
invoked whenever the value of the configuration parameter is changed.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{debug.h}

This file provides facility for debug messages generation.
More specifically, it defines the \verb=debug_msg()=, the macro
responsible for generating debug messages.
It takes the same arguments as printf(3). For example:

\begin{verbatim}
debug_msg("The number is %d\n", 5);
\end{verbatim}

For more details see the comments inside that file.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{ether\_compat.h}

This file contains Ethernet-related manipulation compatibility
functions. For example, it includes the appropriate system files,
and declares functions \verb=ether_aton()= and \verb=ether_ntoa()=
(implemented locally in \emph{ether\_compat.c}) if the system is missing
the corresponding \verb=ether_aton(3)= and \verb=ether_ntoa(3)=.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{eventloop.hh}

This file defines \emph{class EventLoop}.
It is used to co-ordinate interactions between a TimerList and a
SelectorList for XORP processes.  All XorpTimer and select operations
should be co-ordinated through this interface.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{exceptions.hh}

This file contains \emph{class XorpException}: a base class for XORP C++
exceptions. It contains also all standard XORP C++ exceptions.
An example of such exception is \emph{class InvalidFamily} which is
thrown if the address family is invalid (for example, by an IPvX
constructor when invoked with an invalid address family).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{heap.hh}

This file contains \emph{class Heap}.  The Heap class is used by the
TimerList class as it's priority queue for timers. This implementation
supports removal of arbitrary objects from the heap, even if they are
not located at the top.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{ipnet.hh, ipv4net.hh, ipv6net.hh, ipvxnet.hh}

These files contain the declaration of the following classes:
\emph{class IPv4Net, class IPv6Net, class IPvXNet}, which are
classes for basic subnet addresses (for IPv4, IPv6 and dual IPv4/6
address family respectively). IPvXNet can be used to store a subnet
address that has either IPv4 or IPv6 address family.

Most of the implementation is contained in file \emph{ipnet.hh}, which
contains a \emph{template class IPNet}. The IPv4Net, IPv6Net, and
IPvXNet classes are derived from that template.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{ipv4.hh, ipv6.hh, ipvx.hh}

These files contain the declaration for the following classes:
\emph{class IPv4, class IPv6, class IPvX}, which are
classes for basic IP addresses (for IPv4, IPv6 and dual IPv4/6
address family respectively). IPvX can be used to store an
address that has either IPv4 or IPv6 address family.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{mac.hh}

This file declares the following classes: \emph{class Mac, class
EtherMac}. The first class is a generic container for any type of MAC.
The second class is a container for Ethernet MAC address.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{nexthop.hh}

This file declares a number of classes that can be used to contain
routing next-hop information. For example, \emph{class NextHop}
is the generic class for holding information about routing
next hops.  NextHops can be of many types, including immediate
neighbors, remote routers (with IBGP), discard interfaces,
encapsulation endpoints, etc.  NextHop itself doesn't really do
anything useful, except to provide a generic handle for the
specialized subclasses. The specialized subclasses are:

\begin{itemize}

  \item IPPeerNextHop is for next hops that are local peers.

  \item IPEncapsNextHop is for ``next hops'' that are non-local, and require
   encapsulation to reach. An example is the PIM Register Encapsulation.

  \item IPExternalNextHop An IP nexthop that is not an intermediate
  neighbor.

  \item DiscardNextHop is a discard interface.

\end{itemize}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{ref\_ptr.hh}

This file declares \emph{template class ref\_ptr}: reference counted
pointer class.

The ref\_ptr class is a strong reference class.  It maintains a count of
how many references to an object exist and releases the memory associated
with the object when the reference count reaches zero.  The reference
pointer can be dereferenced like an ordinary pointer to call methods
on the reference counted object.

At the time of writing the only supported memory management is
through the new and delete operators.  At a future date, this class
should support the STL allocator classes or an equivalent to
provide greater flexibility.