1 // $Id:SocketPolicy.hh 218 2007-03-20 14:39:32Z tho $
4 // Fraunhofer Institute for Open Communication Systems (FOKUS)
5 // Competence Center NETwork research (NET), St. Augustin, GERMANY
6 // Stefan Bund <g0dil@berlios.de>
8 // This program is free software; you can redistribute it and/or modify
9 // it under the terms of the GNU General Public License as published by
10 // the Free Software Foundation; either version 2 of the License, or
11 // (at your option) any later version.
13 // This program is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
18 // You should have received a copy of the GNU General Public License
19 // along with this program; if not, write to the
20 // Free Software Foundation, Inc.,
21 // 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
24 \brief Policy Framework public header
26 \idea Creating a new Socket will create 3 new instances (The handle, the body, the policy) of
27 which 2 (argh) (body, policy) live on the heap. This is expensive. We should convert all the
28 policy classes to singletons and assign the same instance to all socket bodies with the same
29 policy. This would reduce the number of heap allocations per socket handle to one (which is
30 already optimized using the pool_alloc_mixin)
33 /** \defgroup policy_group The Policy Framework
35 \diaimage SocketPolicy.dia
37 \section policy_group_introduction Introduction to the Policy Framework
39 The policy framework conceptually implements a list of parallel inheritance hierarchies each
40 covering a specific interface aspect of the socket handle. The socket handle itself only
41 provides minimal functionality. All further functionality is relayed to a policy class, or more
42 precisely, to a group of policy classes, one for each policy axis. The policy axis are
44 <dl><dt><em>addressingPolicy</em></dt><dd>configures, whether a socket is addressable and if
45 so, configures the address type</dd>
47 <dt><em>framingPolicy</em></dt> <dd>configures the type of framing the socket provides: either
48 no framing providing a simple i/o stream or packet framing</dd>
50 <dt><em>communicationPolicy</em></dt><dd>configures,if and how the communication partner is
53 <dt><em>readPolicy</em></dt><dd>configures the readability of the socket</dd>
55 <dt><em>writePolicy</em></dt><dd>configures the writability of the socket</dd></dl>
57 The template senf::SocketPolicy combines these policy axis to form a concrete socket policy. In
58 a concrete policy, each of these policy axis is assigned a value, the policy value. This value
59 is identified by a class type, a policy class. E.g. possible values for <em>framingPolicy</em>
60 are <tt>DatagramFramingPolicy</tt> or <tt>StreamFramingPolicy</tt> which are classes derived
61 from the axis base class <tt>FramingPolicyBase</tt>. This base class also doubles as
62 <tt>UnspecifiedFramingPolicy</tt> (which is just a typedef alias). If a policy axis is assigned
63 this Unspecified type, the axis is left unspecified, the concrete policy will be incomplete.
65 The senf::SocketPolicy template defines the behavior of a socket handle. The socket handle
66 instances do not implement any socket functionality themselves instead deferring the
67 implementation to the policy classes. The SocketHandle interface is therefore \e not implemented
68 using virtual members, all important socket functions can be inlined by the compiler to create
69 highly efficient code.
71 A senf::SocketPolicy instance can be incomplete. In this case it does \e not completely specify
72 the socket interface, it leaves some aspects open by assigning the Unspecified value to one or
73 more of the policy axis. A senf::SocketHandle based on such a policy will have a reduced
74 interface: It will only support those members for which the corresponding policies are defined.
76 To build a senf::SocketPolicy instance the senf::MakeSocketPolicy helper is provided. This
77 helper template takes any number (it is really limited to 6 Arguments but more arguments don't
78 make sense) of policy classes as it's argument. The MakeSocketPolicy helper will take the
79 arguments in the order they are specified and for each argument will check to which axis the
80 policy class belongs (by checking the base classes of that class) and assign it to the correct
81 policy axis in the senf::SocketPolicy template. If any policy axis are not specified, they are
82 defaulted to their corresponding Unspecified value. This helper frees you to specify the policy
83 classes in any order. An additional feature is, that you may specify a complete policy as a
84 first argument. This policy will then be used to provide default values for unspecified axis.
86 Two senf::SocketHandle's with different policies can be \e compatible. If they are, the more
87 specific SocketHandle can be converted (assigned to) the more basic SocketHandle. A SocketHandle
88 is more specific then another SocketHandle if the policy of the former is more specific then
89 that of the latter which means, that for each policy axis separately, the value of that axis of
90 the more specific policy is derived from or the same as the value of that axis in the more basic
91 policy. This is like converting a derived class pointer to a base class pointer, only it happens
92 separately but at the same time for each policy axis:
95 // This defines an incomplete policy where addressingPolicy and writePolicy
97 typedef senf::MakeSocketPolicy<
98 senf::StreamFramingPolicy,
99 senf::ConnectedCommunicationPolicy,
101 >::policy MyReadableSocketPolicy
103 typedef senf::ClientSocketHandle<MyReadableSocketPolicy> MyReadableHandle;
105 // TCPv4ClientSocketHandle is a socket handle with the policy equivalent to
106 // senf::MakeSocketPolicy<
107 // INet4AddressingPolicy,
108 // StreamFramingPolicy,
109 // ConnectedCommunicationPolicy,
111 // WritablePolicy>::policy
112 senf::TCPv4ClientSocketHandle tcpHandle (...);
114 MyReadableHandle myHandle (tcpHandle); // Conversion to more basic socket handle
117 \section policy_group_details The Policy Framework Classes
119 In the following discussion, deeper insight into C++ and especially the concepts of template
120 meta-programming are needed. However, this information is only needed if you want to write new
121 policy classes or want to use the policy framework explicitly for your own involved
122 optimizations ... or if you are just plain curious :-)
124 In the following discussion we will use the following conventions:
125 \li \e Axis is one or \c AddressingPolicy, \c FramingPolicy, \c CommunicationPolicy, \c
126 ReadPolicy or \c WritePolicy
127 \li \e socketPolicy is any socket policy (that is, an instantiation of the SocketPolicy
129 \li \e trait is an any policy class (that is, any class derived from one of the axis base
132 Each axis is comprised of a number of classes and templates (all in namespace senf of course):
134 <dl><dt>\e Axis \c Base (ex: AddressingPolicyBase)</dt><dd>Baseclass of all policies in this
137 <dt>\c Unspecified \e Axis (ex: \ref UnspecifiedAddressingPolicy)</dt> <dd>An alias (typedef)
138 for \e Axis \c Base</dd>
140 <dt>\e Axis \c Is < \e socketPolicy, \e trait > (ex: AddressingPolicyIs)</dt> <dd>A template
141 metafunction returning \c boost::true_type, if \e trait (any class derived from \e Axis \c
142 Base) is a compatible policy value of the given \e socketPolicy</dd>
144 <dt>\c If \e Axis \c Is < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIs)</dt> <dd>This
145 is a combination of \e Axis \c Is and \c boost::enable_if</dd>
147 <dt>\c If \e Axis \c IsNot < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIsNot)</dt>
148 <dd>The inverse of above</dd> </dl>
150 These classes form the basis of the policy framework. To bind the policy axis together, there
151 are some more classes and templates.
153 <dl><dt>\c class \c SocketPolicyBase</dt> <dd>This class is the base class of the SocketPolicy
154 template. It is used to validate, that a class is really a SocketPolicy (by checking, that it
155 derives from SocketPolicyBase. This is simpler than checking the template directly).</dd>
157 <dt>\c template \c SocketPolicy < \e addressingPolicy, \e framingPolicy, \e communicationPolicy,
158 \e readPolicy, \e writePolicy ></dt> <dd>This is the central SocketPolicy
159 template. It combines a complete set of policy classes, one for each axis.</dd>
161 <dt>\c template \c MakeSocketPolicy < \e args ></dt> <dd>\c MakeSocketPolicy is a template
162 metafunction which simplifies building SocketPolicy instantiations. It takes any number (ok, up
163 to a maximum of 6) of policy classes as an argument (in any order). It will sort these arguments
164 into the SocketPolicy template arguments. If for some axis no class is specified, it's slot will
165 be filled with \c Unspecified \e Axis. Additionally, the first Argument may optionally be ab
166 arbitrary SocketPolicy. It will provide default values for unspecified axis</dd>
168 <dt>\c template \c SocketPolicyIsBaseOf < \e base, \e derived ></dt> <dd>This template
169 metafunction will check, whether the socket policy \e derived is convertible to \e base. This
170 means, that for each axis, the corresponding policy class in \e derived must be derived or be
171 the same as the one on \e base.</dd> </dl>
173 \implementation All these classes are created automatically. The \c SENF_SOCKET_POLICIES macro
174 is a Boost.Preprocessor style sequence listing all policy axis. The Boost.Preprocessor library
175 is then used to generate the respective classes.
177 \section policy_implement Implementing Policy Classes
179 To define a new policy class, derive from the corresponding base class for your policy axes. The
180 only policy axis which might possibly need to be extended is the addressing policy
181 (AddressingPolicyBase). See the Documentation of these classes for more information on which
182 members can be implemented.
184 All members you define must be static. For any of the policy classes, you must only define those
185 members which are supported by your implementation. If you leave out a member you automatically
186 disable the corresponding functionality in the ClientSocketHandle/ServerSocketHandle interface.
188 The member prototypes given in the base class documentation only specify the call signature not
189 the way, the member must be defined (FileHandle really is not a FileHandle but an arbitrary
192 If the existence of a member depends on other policies, you should use the
193 <code>If</code><i>SomePolicy</i><code>Is</code> and
194 <code>If</code><i>SomePolicy</i><code>IsNot</code> templates to dynamically enable/disable the
195 member depending on some other policy:
198 struct ExampleAddressingPolicy
200 template <class SPolicy>
201 void connect(senf::SocketHandle<SPolicy> handle, Address & addr,
202 typename senf::IfCommmunicationPolicyIs<
203 SPolicy, senf::ConnectedCommunicationPolicy>::type * = 0);
207 The \c connect member in this example will only be enabled, it the communication policy of the
208 socket handle is ConnectedCommunicationPolicy (or a derived type). See <a
209 href="http://www.boost.org/libs/utility/enable_if.html">Boost.Enable_If</a> for a discussion of
210 the third argument (\c senf::ConnectedCommunicationPolicyIs is based on the \c boost::enable_if
213 \see \ref extend_policy \n
214 <a href="http://www.boost.org/libs/utility/enable_if.html">The Boost enable_if utility</a> \n
215 <a href="http://www.boost.org/libs/mpl/doc/index.html">The Boost.MPL library</a> \n
216 <a href="http://www.boost.org/libs/preprocessor/doc/index.html">The Boost.Preprocessor library</a>
218 \idea We could combine all the \e Axis \c Is templates into a single template. Since the \e
219 trait argument will automatically specify the axis to be used, it is not necessary to specify
220 that axis in the template functor's name. We could even combine this with \c
221 SocketPolicyIsBaseOf.
224 /** \defgroup policy_impl_group Policy Implementation classes
225 \ingroup policy_group
227 Here you will find all policy classes. Also included are some supporting classes which are used
228 as base classes to build other policy classes.
231 #ifndef HH_SENF_Socket_SocketPolicy_
232 #define HH_SENF_Socket_SocketPolicy_ 1
236 //#include "SocketPolicy.mpp"
237 ///////////////////////////////hh.p////////////////////////////////////////
241 /// \addtogroup policy_group
244 // This may be adapted to change the supported policies (however, ClientSocketHandle and
245 // ServerSocketHandle will probably have to be adjusted accordingly)
247 /** \brief List all policy axis
251 This define symbol is used to configure the policy axis. The base class for each of these
252 axis must be defined explicitly (e.g. AddressingPolicyBase). The implementation files will
253 then automatically generate all the other classes from this list.
257 # define SENF_SOCKET_POLICIES \
260 (CommunicationPolicy) \
264 // Wer define these classes explicitly (and not with some macro
266 // a) AddressingPolicyBase is different from all the others
267 // b) We want to document each one explicitly
269 /** \brief Policy defining socket addressing
271 AddressingPolicyBase is the baseclass of all addressing policy classes. When defining a new
272 addressing policy, the following members can be defined. All methods must be static.
275 <tr><td>typedef</td> <td><tt>Address</tt></td> <td>Address type</td></tr>
276 <tr><td>method</td> <td><tt>void local(FileHandle, Address &)</tt></td> <td>Get local socket address</td></tr>
277 <tr><td>method</td> <td><tt>void peer(FileHandle, Address &)</tt></td> <td>Get remote socket address</td></tr>
278 <tr><td>method</td> <td><tt>void bind(FileHandle, Address const &)</tt></td> <td>Bind socket to local address</td></tr>
279 <tr><td>method</tr> <td><tt>void connect(FileHandle, Address const &)</tt></td> <td>Connect to remote address</td></tr>
284 struct AddressingPolicyBase
286 virtual ~AddressingPolicyBase();
288 class Address { Address(); };
291 /** \brief Policy defining the framing format
293 This policy does not define any operations since it does have no influence on any method
294 signature. It does however affect the semantics of the \c read() and \c write() operations.
296 \note This policy axis probably only has two sensible states: StreamFramingPolicy and
297 DatagramFramingPolicy.
301 struct FramingPolicyBase
303 virtual ~FramingPolicyBase();
306 /** \brief Policy defining, how peers are selected
308 The CommunicationPolicy may define two members:
311 <tr><td>method</td> <td><tt>void listen(FileHandle, unsigned backlog)</tt></td> <td>Switch socket into listening state</td></tr>
312 <tr><td>method</td> <td><tt>int accept(FileHandle, Address &)</tt></td> <td>Accept a new connection</td></tr>
313 <tr><td>method</td> <td><tt>int accept(FileHandle)</tt></td> <td>Accept a new connection</td></tr>
316 The \c listen member is straight forward. The \c accept() member must return a new file
317 descriptor (which will be used to create a new SocketHandle of the correct
320 \note This Policy only has two meaningful states: ConnectedCommunicationPolicy and
321 UnconnectedCommunicationPolicy. It is probably not sensible to define a new
322 CommunicationPolicy type.
326 struct CommunicationPolicyBase
328 virtual ~CommunicationPolicyBase();
331 /** \brief Policy defining the readability
333 The ReadPolicy defines, whether the socket is readable. It may define two members:
336 <tr><td>method</td> <td><tt>unsigned read(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
337 <tr><td>method</td> <td><tt>unsigned readfrom(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
340 The second member should only be enabled if the communication policy is
341 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
342 is fixed) (see AddressingPolicyBase on how to do this).
344 \note This Policy only has two meaningful states: ReadablePolicy and NotReadablePolicy. It
345 probably does not make sense to define new read policy types.
349 struct ReadPolicyBase
351 virtual ~ReadPolicyBase();
354 /** \brief Policy defining the writability
356 The WritePolicy defines, whether the socket is writable. It may define two members:
359 <tr><td>method</td> <td><tt>unsigned write(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
360 <tr><td>method</td> <td><tt>unsigned writeto(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
363 The second member should only be enabled if the communication policy is
364 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
365 is fixed) (see AddressingPolicyBase on how to do this).
367 \note This Policy only has two meaningful states: WritablePolicy and NotWritablePolicy. It
368 probably does not make sense to define new write policy types.
372 struct WritePolicyBase
374 virtual ~WritePolicyBase();
377 // The implementation file will for each Policy declared above
378 // define the following (SomePolicy is one of the above):
380 // struct SomePolicyBase;
381 // typedef UndefinedSomePolicy;
382 // template SomePolicyIs< SocketPolicy, Axis >
383 // template IfSomePolicyIs< SocketPolicy, Axis >
384 // template IfSomePolicyIsNot< SocketPolicy, Axis >
386 // Additionally the following are defined:
388 // class SocketPolicyBase
389 // template SocketPolicy< ..policies.. >
390 // template MakeSocketPolicy< ..args.. >
391 // template SocketPolicyIsBaseOf< Base, Derived >
395 // The following stub definitions are only visible to doxygen
397 /** \brief Alias of AddressingPolicyBase for better readability
398 \see \ref policy_group
400 typedef AddressingPolicyBase UnspecifiedAddressingPolicy;
402 /** \brief Check single policy axis
404 This template is an example of the \e Axis \c Is family of template metafunctions. It will
405 check, whether \c Trait is a valid compatible Policy class of \c SocketPolicy. \c Trait must
406 be derived from AddressingPolicyBase (respectively \c Policy \c Base).
408 \see \ref policy_group
410 template <class SocketPolicy, class Trait>
411 struct AddressingPolicyIs
414 /** \brief Enable template overload depending on policy value
416 This template is an example of the \c If \e Axis \c Is family of templates. It is used like
417 <a href="http://www.boost.org/libs/utility/enable_if.html">Boost.enable_if</a> to enable a
418 templated overload only, if the AddressingPolicy of \e Axis is compatible with \c Trait
419 (that is the AddressingPolicy of \c Policy is derived from \c Trait).
423 template <class SocketPolicy, class Trait>
424 struct IfAddressingPolicyIs
427 /** \brief Inversion of \c IfAddressingPolicyIs
430 template <class SocketPolicy, class Trait>
431 struct IfAddressingPolicyIsNot
434 /** \brief Baseclass of all SocketPolicies
438 This class provides the baseclass of all socket policies (bundles). It serves two purposes:
439 \li It allows us to easily identify a socket policy bundle by checking a classes baseclass.
440 \li It provides an abstract (virtual) interface to access the policy axes
444 struct SocketPolicyBase
446 /** \brief Polymorphic access to policy axes
448 This is an example of a policy axes accessor. It returns a reference to the policy axes
449 used by the concrete protocol bundle. This reference can then be checked using RTTI
452 AddressingPolicyBase const & theAddressingPolicy() const = 0;
454 virtual ~SocketPolicyBase();
457 /** \brief Collection of policy classes
459 The SocketPolicy template defines the complete Policy used by the socket library. It
460 contains one policy class for each policy axis. This template takes one policy from each
461 axis as it's template arguments (this example implementation only has AddressingPolicy as an
464 A SocketPolicy can be complete or incomplete. An incomplete SocketPolicy will have at least
465 one axis set to \c Undefined \e Axis (or a generic derived class which is used to group some
466 other policies but does not (completely) define the policy behavior). A complete
467 SocketPolicy will have a concrete definition of the desired behavior for each policy axis.
471 template < class AddressingPolicy >
474 /** \brief Check dynamic policy compatibility
476 This check will validate, that a socket with \a other as it's policy is convertible to a
477 socket with the current SocketPolicy as it's policy. This is true, if for each policy
478 axis, the policy class of that axis as defined in the \a other policy is convertible to
479 the policy class of that same axis in the current SocketPolicy instance (as is defined
480 by the template arguments). This again is true, if the \a other policy class is derived
481 from (or is the same as) the policy class taken from the current SocketPolicy instance.
483 In other words, this call checks, that the current SocketPolicy (as defined via the
484 template arguments) is more generic than the \a other socket policy.
486 \param[in] other SocketPolicy to check
487 \throws std::bad_cast if \a other is not a compatible policy
489 static void checkBaseOf(SocketPolicyBase const & other);
492 /** \brief Metafunction to create SocketPolicy
494 This template metafunction simplifies the creation of a SocketPolicy instantiation. It takes
495 any number (that is up to 6) of Policy classes as arguments in any Order. It will create a
496 SocketPolicy from these policy classes. Any axis not specified will be left as \c
501 template <class Arg1, class Arg2, class ArgN>
502 struct MakeSocketPolicy
505 /** \brief Check policy compatibility
507 This template metafunction checks, whether the SocketPolicy \c Derived is more specialized
508 than \c Base (and therefore a SocketHandle with policy \c Derived is convertible to a
509 SocketHandle with policy \c Base).
511 The metafunction will return true (that is inherits from \c boost::true_type, see the <a
512 href="http://www.boost.org/libs/mpl/doc/index.html">Boost.MPL</a> library documentation for
513 more information) if each policy class in \c Base is a baseclass of (or the same as) the
514 corresponding policy class in \c Derived.
518 template <class Base, class Derived>
519 struct SocketPolicyIsBaseOf
527 //////////////////////////////hh.e////////////////////////////////////////
528 #include "SocketPolicy.ih"
529 //#include "SocketPolicy.cci"
530 #include "SocketPolicy.ct"
531 //#include "SocketPolicy.cti"
538 // c-file-style: "senf"
539 // indent-tabs-mode: nil
540 // ispell-local-dictionary: "american"
541 // compile-command: "scons -u test"
542 // comment-column: 40