// $Id$
//
-// Copyright (C) 2006
+// Copyright (C) 2006
// Fraunhofer Institut fuer offene Kommunikationssysteme (FOKUS)
// Kompetenzzentrum fuer Satelitenkommunikation (SatCom)
// Stefan Bund <stefan.bund@fokus.fraunhofer.de>
// Free Software Foundation, Inc.,
// 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+/** \file
+ \brief Policy Framework public header
+
+ \todo We should probably remove BufferingPolicy from the interface, it does not make much sense
+ (how did I come to include it ??)
+
+ \todo Do we want to support separate read and write policies. This allows to treat pipes within
+ this framework however, is this worth the effort?
+
+ \idea Creating a new Socket will create 4 (!) new instances (The handle, the body, the policy
+ and the protocol) of which 3 (argh) (body, policy and protocol) live on the heap. This is
+ expensive. We should convert all the policy classes to singletons and assign the same
+ instance to all socket bodies with the same policy. This would reduce the number of heap
+ allocations per socket handle to two.
+ */
+
+/** \defgroup policy_group The Policy Framework
+
+ \image html SocketPolicy.png
+
+ \section policy_group_introduction Introduction to the Policy Framework
+
+ The policy framework conceptually implements a list of parallel inheritance hierarchies each
+ covering a specific interface aspect of the socket handle. The socket handle itself only
+ provides minimal functionality. All further functionality is relayed to a policy class, or more
+ precisely, to a group of policy classes, one for each policy axis. The policy axis are
+
+ <dl><dt><em>addressingPolicy</em></dt><dd>configures, whether a socket is addressable and if
+ so, configures the address type</dd>
+
+ <dt><em>framingPolicy</em></dt> <dd>configures the type of framing the socket provides: either
+ no framing providing a simple i/o stream or packet framing</dd>
+
+ <dt><em>communicationPolicy</em></dt><dd>configures,if and how the communication partner is
+ selected</dd>
+
+ <dt><em>readPolicy</em></dt><dd>configures the readability of the socket</dd>
+
+ <dt><em>writePolicy</em></dt><dd>configures the writability of the socket</dd>
+
+ <dt><em>bufferingPolicy</em></dt><dd>configures, if and how buffering is configured for a
+ socket</dd> </dl>
+
+ The template senf::SocketPolicy combines these policy axis to form a concrete socket policy. In
+ a concrete policy, each of these policy axis is assigned a value, the policy value. This value
+ is identified by a class type, a policy class. E.g. possible values for <em>framingPolicy</em>
+ are <tt>DatagramFramingPolicy</tt> or <tt>StreamFramingPolicy</tt> which are classes derived
+ from the axis base class <tt>FramingPolicyBase</tt>. This base class also doubles as
+ <tt>UnspecifiedFramingPolicy</tt> (which is just a typedef alias). If a policy axis is assigned
+ this Unspecified type, the axis is left unspecified, the concrete policy will be incomplete.
+
+ The senf::SocketPolicy template defines the behavior of a socket handle. The socket handle
+ instances do not implement any socket functionality themselves instead defering the
+ implementation to the policy classes. The SocketHandle interface is therefore \e not implemented
+ using virtual members, all important socket functions can be inlined by the compiler to create
+ highly efficient code.
+
+ A senf::SocketPolicy instance can be incomplete. In this case it does \e not completely specify
+ the socket interface, it leaves some aspects open by assigning the Unspecified value to one or
+ more of the policy axis. A senf::SocketHandle based on such a policy will have a reduced
+ interface: It will only support those members for wich the corresponding policies are defined.
+
+ To build a senf::SocketPolicy instance the senf::MakeSocketPolicy helper is provided. This
+ helper template takes any number (it is really limited to 6 Arguments but more arguments don't
+ make sense) of policy classes as it's argument. The MakeSocketPolicy helper will take the
+ arguments in the order they are specified and for each argument will check to which axis the
+ policy class belongs (by checking the base classes of that class) and assign it to the correct
+ policy axis in the senf::SocketPolicy template. If any policy axis are not specified, they are
+ defaulted to their corresponding Unspecified value. This helper frees you to specify the policy
+ classes in any order. An additional feature is, that you may specify a complete policy as a
+ first argument. This policy will then be used to provide default values for unspecified axis.
+
+ Two senf::SocketHandle's with different policies can be \e compatible. If they are, the more
+ specific SocketHandle can be converted (assigned to) the more basic SocketHandle. A SocketHandle
+ is more specific then another SocketHandle if the policy of the former is more specific then
+ that of the latter which means, that for each policy axis separately, the value of that axis of
+ the more specific policy is derived from or the same as the value of that axis in the more basic
+ policy. This is like converting a derived class pointer to a base class pointer, only it happens
+ separately but at the same time for each policy axis:
+
+ \code
+ // This defines an incomplete policy where addressingPolicy, writePolicy and bufferingPolicy
+ // are unspecified
+ typedef senf::MakeSocketPolicy<
+ senf::StreamFramingPolicy,
+ senf::ConnectedCommunicationPolicy,
+ senf::ReadablePolicy
+ >::policy MyReadableSocketPolicy
+
+ typedef senf::ClientSocketHandle<MyReadableSocketPolicy> MyReadableHandle;
+
+ // TCPv4ClientSocketHandle is a socket handle with the policy equivalent to
+ // senf::MakeSocketPolicy<
+ // INet4AddressingPolicy,
+ // StreamFramingPolicy,
+ // ConnectedCommunicationPolicy,
+ // ReadablePolicy,
+ // WritablePolicy,
+ // SocketBufferingPolicy>::policy
+ senf::TCPv4ClientSocketHandle tcpHandle (...);
+
+ MyReadableHandle myHandle (tcpHandle); // Conversion to more basic socket handle
+ \endcode
+
+ \section policy_group_details The Policy Framework Classes
+
+ In the following discussion, deeper insight into C++ and especially the concepts of template
+ meta-programming are needed. Hoewever, this information is only needed if you want to write new
+ policy classes or want to use the policy framework explicitly for your own involved
+ optimizations ... or if you are just plain curious :-)
+
+ In the following discussion we will use the following conventions:
+ \li \e Axis is one or \c AddressingPolicy, \c FramingPolicy, \c CommunicationPolicy, \c
+ ReadPolicy, \c WritePolicy or \c BufferingPolicy
+ \li \e socketPolicy is any socket policy (that is, an instantiation of the SocketPolicy
+ template)
+ \li \e trait is an any policy class (that is, any class derived from one of the axis base
+ classes)
+
+ Each axis is comprised of a number of classes and templates (all in namespace senf of course):
+
+ <dl><dt>\e Axis \c Base (ex: AddressingPolicyBase)</dt><dd>Baseclass of all policies in this
+ axis</dd>
+
+ <dt>\c Unspecified \e Axis (ex: \ref UnspecifiedAddressingPolicy)</dt> <dd>An alias (typedef)
+ for \e Axis \c Base</dd>
+
+ <dt>\e Axis \c Is < \e socketPolicy, \e trait > (ex: AddressingPolicyIs)</dt> <dd>A template
+ metafunction returning \c boost::true_type, if \e trait (any class derived from \e Axis \c
+ Base) is a compatible policy value of the given \e socketPolicy</dd>
+
+ <dt>\c If \e Axis \c Is < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIs)</dt> <dd>This
+ is a combination of \e Axis \c Is and \c boost::enable_if</dd>
+
+ <dt>\c If \e Axis \c IsNot < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIsNot)</dt>
+ <dd>The inverse of above</dd> </dl>
+
+ These classes form the basis of the policy framework. To bind the policy axis together, there
+ are some more classes and templates.
+
+ <dl><dt>\c class \c SocketPolicyBase</dt> <dd>This class is the base class of the SocketPolicy
+ template. It is used to validate, that a class is really a SocketPolicy (by checking, that it
+ derives from SocketPolicyBase. This is simpler than chacking the template directly).</dd>
+
+ <dt>\c template \c SocketPolicy < \e addressingPolicy, \e framingPolicy, \e communicationPolicy,
+ \e readPolicy, \e writePolicy, \e bufferingPolicy ></dt> <dd>This is the central SocketPolicy
+ template. It combines a complete set of policy classes, one for each axis.</dd>
+
+ <dt>\c template \c MakeSocketPolicy < \e args ></dt> <dd>\c MakeSocketPolicy is a template
+ metafunction which simplifies building SocketPolicy instantiations. It takes any number (ok, up
+ to a maximum of 6) of policy classes as an argument (in any order). It will sort these arguments
+ into the SocketPolicy template arguments. If for some axis no class is specified, it's slot will
+ be filled with \c Unspecified \e Axis. Additionally, the first Argument may optionally be ab
+ arbitrary SocketPolicy. It will provide default values for unspecified axis</dd>
+
+ <dt>\c template \c SocketPolicyIsBaseOf < \e base, \e derived ></dt> <dd>This template
+ metafunction will check, wether the socket policy \e derived is convertible to \e base. This
+ means, that for each axis, the corresponding policy class in \e derived must be derived or be
+ the same as the one on \e base.</dd> </dl>
+
+ \implementation All these classes are created automatically. The \c SENF_SOCKET_POLICIES makro
+ is a Boost.Preprocessor style sequence listing all policy axis. The Boost.Preprocessor library
+ is then used to generate the respective classes.
+
+ \section policy_implement Implementing Policy Classes
+
+ To define a new policy class, derive from the corresponding base class for your policy
+ axies. The only policy axis which might possibly need to be extended are the addressing policy
+ (AddressingPolicyBase) and the buffering policy (BufferingPolicyBase). See the Documentation of
+ these classes for more information on which members can be implemented.
+
+ All members you define must be static. For any of the policy classes, you must only define those
+ members which are supported by your implementation. If you leave out a member you automatically
+ disable the corresponding functionality in the ClientSocketHandle/ServerSocketHandle interface.
+
+ The member prototypes given in the base class documentation only specify the call signature not
+ the way, the member must be defined (FileHandle really is not a FileHandle but an arbitrary
+ SocketHandle).
+
+ If the existence of a member depends on other policies, you should use the
+ <code>If</code><i>SomePolicy</i><code>Is</code> and
+ <code>If</code><i>SomePolicy</i><code>IsNot</code> templates to dynamically enable/disable the
+ member depending on some other policy:
+
+ \code
+ struct ExampleAddressingPolicy
+ {
+ template <class Policy>
+ void connect(senf::SocketHandle<Policy> handle, Address & addr,
+ typename senf::IfCommmunicationPolicyIs<
+ Policy, senf::ConnectedCommunicationPolicy>::type * = 0);
+ };
+ \endcode
+
+ The \c connect member in this example will only be enabled, it the communication policy of the
+ socket handle is ConnectedCommunicationPolicy (or a derived type). See <a
+ href="http://www.boost.org/libs/utility/enable_if.html">Boost.Enable_If</a> for a discussion of
+ the third argument (\c senf::ConnectedCommunicationPolicyIs is based on the \c boost::enable_if
+ template).
+
+ \see \ref extend_policy \n
+ <a class="ext" href="http://www.boost.org/libs/utility/enable_if.html">The Boost enable_if utility</a> \n
+ <a class="ext" href="http://www.boost.org/libs/mpl/doc/index.html">The Boost.MPL library</a> \n
+ <a class="ext" href="http://www.boost.org/libs/preprocessor/doc/index.html">The Boost.Preprocessor library</a>
+
+ \idea We could combine all the \e Axis \c Is templates into a single template. Since the \e
+ trait argument will automatically specify the axis to be used, it is not necessary to specify
+ that axis in the tempalte functor's name. We could even combine this with \c
+ SocketPolicyIsBaseOf.
+ */
+
+/** \defgroup policy_impl_group Policy Implementation classes
+ \ingroup policy_group
+
+ Here you will find all policy classes. Also included are some
+ supporting classes which are used as base classes to build other
+ policy classes.
+ */
+
#ifndef HH_SocketPolicy_
#define HH_SocketPolicy_ 1
// Custom includes
+#include "GenericSockAddr.hh"
+
//#include "SocketPolicy.mpp"
///////////////////////////////hh.p////////////////////////////////////////
namespace senf {
+ /// \addtogroup policy_group
+ /// @{
+
+ // This may be adapted to change the supported policies (however, ClientSocketHandle and
+ // ServerSocketHandle will probably have to be adjusted accordingly)
- // This may be adapted to change the supported policies (however,
- // ClientSocketHandle and ServerSocketHandle will probably have to
- // be adjusted accordingly). However, AddressingPolicy MUST always
- // be the first Policy member ...
+ /** \brief List all policy axis
-# define SENF_SOCKET_POLICIES \
- (AddressingPolicy) \
+ \internal
+
+ This define symbol is used to configure the policy axis. The
+ base class for each of these axis must be defined explicitly
+ (e.g. AddressingPolicyBase). The implementation files will
+ then automatically generate all the other classes from this
+ list.
+
+ \see policy_group
+ */
+# define SENF_SOCKET_POLICIES \
+ (AddressingPolicy) \
(FramingPolicy) \
- (CommunicationPolicy) \
- (ReadPolicy) \
- (WritePolicy) \
- (BufferingPolicy)
-
+ (CommunicationPolicy) \
+ (ReadPolicy) \
+ (WritePolicy) \
+ (BufferingPolicy)
+
+ // Wer define these classes explicitly (and not with some macro
+ // magic) because
+ // a) AddressingPolicyBase is different from all the others
+ // b) We want to document each one explicitly
+
+ /** \brief Policy defining socket addressing
+
+ AddressingPolicyBase is the baseclass of all addressing policy
+ classes. When defining a new addressing policy, the following
+ members can be defined. All methods must be static.
+
+ <table class="senf">
+ <tr><td>typedef</td> <td><tt>Address</tt></td> <td>Address type</td></tr>
+ <tr><td>method</td> <td><tt>void local(FileHandle, Address &)</tt></td> <td>Get local socket address</td></tr>
+ <tr><td>method</td> <td><tt>void peer(FileHandle, Address &)</tt></td> <td>Get remote socket address</td></tr>
+ <tr><td>method</td> <td><tt>void bind(FileHandle, Address const &)</tt></td> <td>Bind socket to local address</td></tr>
+ <tr><td>method</tr> <td><tt>void connect(FileHandle, Address const &)</tt></td> <td>Connect to remote address</td></tr>
+ </table>
+
+ \see policy_group
+ */
+ struct AddressingPolicyBase
+ {
+ virtual ~AddressingPolicyBase() {}
+
+ typedef GenericSockAddr Address;
+ };
+
+ /** \brief Policy defining the framing format
+
+ This policy does not define any operations since it does have
+ no influence on any method signature. It does however affect
+ the semantics of the \c read() and \c write() operations.
+
+ \note This policy axis probably only has two sensible statess:
+ StreamFramingPolicy and DatagramFramingPolicy.
+
+ \see policy_group
+ */
+ struct FramingPolicyBase
+ {
+ virtual ~FramingPolicyBase() {}
+ };
+
+ /** \brief Policy defining, how peers are selected
+
+ The CommunicationPolicy may define two members:
+
+ <table class="senf">
+ <tr><td>method</td> <td><tt>void listen(FileHandle, unsigned backlog)</tt></td> <td>Switch socket into listening state</td></tr>
+ <tr><td>method</td> <td><tt>int accept(FileHandle, Address &)</tt></td> <td>Accept a new connection</td></tr>
+ </table>
+
+ The \c listen member is straight forward. The \c accept() member
+ must return a new file descriptor (which will be used to
+ create a new SocketHandle of the correct type). Additionally,
+ accept() should only be defined, if the Addressing policy is
+ not \c NoAddressingPolicy (which together with
+ ConnectedCommunicationPolicy would identify a point-to-point
+ link with fixed communication partners).
+
+ \note This Policy only has two meaningful states:
+ ConnectedCommunicationPolicy and
+ UnconnectedCommunicationPolicy. It is probably not sensible to
+ define a new CommunicationPolicy type.
+
+ \see policy_group
+ */
+ struct CommunicationPolicyBase
+ {
+ virtual ~CommunicationPolicyBase() {}
+ };
+
+ /** \brief Policy defining the readability
+
+ The ReadPolicy defines, wether the socket is readable. It
+ may define two members:
+
+ <table class="senf">
+ <tr><td>method</td> <td><tt>unsigned read(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
+ <tr><td>method</td> <td><tt>unsigned readfrom(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
+ </table>
+
+ The second member should only be enabled if the communication
+ policy is UnconnectedCommunication (otherwise it does not make
+ sense since the communication partner is fixed) (see
+ AddressingPolicyBase on how to do this).
+
+ \note This Policy only has two meaningful states:
+ ReadablePolicy and NotReadablePolicy. It probably does not
+ make sense to define new read policy types.
+
+ \see policy_group
+ */
+ struct ReadPolicyBase
+ {
+ virtual ~ReadPolicyBase() {}
+ };
+
+ /** \brief Policy defining the writability
+
+ The WritePolicy defines, wether the socket is writable. It may
+ define two members:
+
+ <table class="senf">
+ <tr><td>method</td> <td><tt>unsigned write(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
+ <tr><td>method</td> <td><tt>unsigned writeto(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
+ </table>
+
+ The second member should only be enabled if the communication
+ policy is UnconnectedCommunication (otherwise it does not make
+ sense since the communication partner is fixed) (see
+ AddressingPolicyBase on how to do this).
+
+ \note This Policy only has two meaningful states:
+ WritablePolicy and NotWritablePolicy. It probably does not
+ make sense to define new write policy types.
+
+ \see policy_group
+ */
+ struct WritePolicyBase
+ {
+ virtual ~WritePolicyBase() {}
+ };
+
+ /** \brief Policy defining the buffering interface
+
+ The BufferingPolicy defines the buffer handling of the
+ socket. It may provide the follogin members:
+
+ \see policy_group
+ */
+ struct BufferingPolicyBase
+ {
+ virtual ~BufferingPolicyBase() {}
+ };
+
// The implementation file will for each Policy declared above
// define the following (SomePolicy is one of the above):
//
// template SocketPolicy< ..policies.. >
// template MakeSocketPolicy< ..args.. >
// template SocketPolicyIsBaseOf< Base, Derived >
+
+# ifdef DOXYGEN
+
+ // The following stub definitions are only visible to doxygen
+
+ /** \brief Alias of AddressingPolicyBase for better readability
+ \see \ref policy_group
+ */
+ typedef AddressingPolicyBase UnspecifiedAddressingPolicy;
+
+ /** \brief Check single policy axis
+
+ This template is an example of the \e Axis \c Is family of
+ tempalte metafunctions. It will check, wether \c Trait is a
+ valid compatible Policy class of \c SocketPolicy. \c Trait
+ must be derived from AddressingPolicyBase (respectively \i
+ Policy \c Base).
+
+ \see \ref policy_group
+ */
+ template <class SocketPolicy, class Trait>
+ struct AddressingPolicyIs
+ {};
+
+ /** \brief Enable template overload depending on policy value
+
+ This template is an exmaple of the \c If \e Axis \c Is
+ family of templates. It is used like <a class="ext"
+ href="http://www.boost.org/libs/utility/enable_if.html">Boost.enable_if</a>
+ to enable a templated overload only, if the AddressingPolicy
+ of \e Axis is compatible with \c Trait (that is the
+ AddressingPolicy of \c Policy is derived from \c Trait).
+
+ \see policy_group
+ */
+ template <class SocketPolicy, class Trait>
+ struct IfAddressingPolicyIs
+ {};
+
+ /** \brief Inversion of \c IfAddressingPolicyIs
+ \see policy_group
+ */
+ template <class SocketPolicy, class Trait>
+ struct IfAddressingPolicyIsNot
+ {};
+
+ /** \brief Baseclass of all SocketPolicies
+
+ \internal
+
+ This class provides the baseclass of all socket policies
+ (bundles). It serves two purposes:
+ \li It allows us to easily identify a socket policy bundle by
+ checking a classes baseclass.
+ \li It provides an abstract (virtual) interface to access the
+ policy axes
+
+ \see policy_group
+ */
+ struct SocketPolicyBase
+ {
+ /** \brief Polymorphic access to policy axes
+
+ This is an example of a policy axes accessor. It returns a
+ reference to the policy axes used by the conrecte protocol
+ bundle. This reference can then be checked using RTTI
+ information.
+ */
+ AddressingPolicyBase const & theAddressingPolicy() const = 0;
+ };
+
+ /** \brief Collection of policy classes
+
+ The SocketPolicy template defines the complete Policy used by
+ the socket library. It contains one policy class for each
+ policy axis. This template takes one policy from each axis as
+ it's template arguments (this example implementation only has
+ AddressingPolicy as an argument).
+
+ A SocketPolicy can be complete or incomplete. An incomplete
+ SocketPolicy will have at least one axis set to \c Undefined
+ \e Axis (or a generic derived class which is used to group
+ some other policies but does not (completely) define the
+ policy behavior). A complete SocketPolicy will have a
+ concrete definition of the desired behavior for each policy
+ axis.
+
+ \see policy_group
+ */
+ template < class AddressingPolicy >
+ struct SocketPolicy
+ {
+ /** \brief Check dynamic policy compatibility
+
+ This method will check the socket policy \a other against
+ this policy. It will check, wether \a other is a base
+ policy (or the same) of this policy. This check is done
+ against the \e dynamic type of \a other using RTTI. It
+ will throw \c std::bad_cast, if the policy is not
+ compatible.
+
+ \param[in] other SocketPolicy to check
+ \throws std::bad_cast if \a other is not a compatible
+ policy
+ */
+ static void checkBaseOf(SocketPolicyBase const & other);
+ };
+
+ /** \brief Metafunction to create SocketPolicy
+
+ This template metafunction simplifies the creation of a
+ SocketPolicy instantiation. It takes any number (that is up to
+ 6) of Policy classes as arguments in any Order. It will create
+ a SocketPolicy from these policy classes. Any axis not
+ specified will be left as \c Unspecified \e Axis.
+
+ \see policy_group
+ */
+ template <class Arg1, class Arg2, class ArgN>
+ struct MakeSocketPolicy
+ {};
+
+ /** \brief Check policy compatibility
+
+ This tempalte metafunction checks, wether the SocketPolicy \c
+ Derived is more specialized than \c Base (and therefore a
+ SocketHandle with policy \c Derived is convertible to a
+ SocketHandle with policy \c Base).
+
+ The metafunction will return true (that is inherits from \c
+ boost::true_type, see the <a class="ext"
+ href="http://www.boost.org/libs/mpl/doc/index.html">Boost.MPL</a>
+ library documentation for more information) if each policy
+ class in \c Base is a baseclass of (or the same as) the
+ corresponding policy class in \c Derived.
+
+ \see policy_group
+ */
+ template <class Base, class Derived>
+ struct SocketPolicyIsBaseOf
+ {};
+
+# endif
+
+ /// @}
}
//////////////////////////////hh.e////////////////////////////////////////
\f
// Local Variables:
// mode: c++
+// fill-column: 100
// c-file-style: "senf"
+// indent-tabs-mode: nil
+// ispell-local-dictionary: "american"
// End:
projects / senf.git / blobdiff