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 <div class="diamap" name="SocketPolicy">
36 <span coords="39,229,182,257">\ref WritePolicyBase</span>
37 <span coords="17,76,210,105">\ref AddressingPolicyBase</span>
38 <span coords="29,114,194,143">\ref FramingPolicyBase</span>
39 <span coords="368,0,463,28">\ref PolicyBase</span>
40 <span coords="275,2,691,185">\ref SocketPolicy</span>
41 <span coords="0,152,227,181">\ref CommunicationPolicyBase</span>
42 <span coords="41,191,180,219">\ref ReadPolicyBase</span>
44 \htmlonly <img src="SocketPolicy.png" border="0" alt="SocketPolicy" usemap="#SocketPolicy"> \endhtmlonly
46 \section policy_group_introduction Introduction to the Policy Framework
48 The policy framework conceptually implements a list of parallel inheritance hierarchies each
49 covering a specific interface aspect of the socket handle. The socket handle itself only
50 provides minimal functionality. All further functionality is relayed to a policy class, or more
51 precisely, to a group of policy classes, one for each policy axis. The policy axis are
53 <dl><dt><em>addressingPolicy</em></dt><dd>configures, whether a socket is addressable and if
54 so, configures the address type</dd>
56 <dt><em>framingPolicy</em></dt> <dd>configures the type of framing the socket provides: either
57 no framing providing a simple i/o stream or packet framing</dd>
59 <dt><em>communicationPolicy</em></dt><dd>configures,if and how the communication partner is
62 <dt><em>readPolicy</em></dt><dd>configures the readability of the socket</dd>
64 <dt><em>writePolicy</em></dt><dd>configures the writability of the socket</dd></dl>
66 The template senf::SocketPolicy combines these policy axis to form a concrete socket policy. In
67 a concrete policy, each of these policy axis is assigned a value, the policy value. This value
68 is identified by a class type, a policy class. E.g. possible values for <em>framingPolicy</em>
69 are <tt>DatagramFramingPolicy</tt> or <tt>StreamFramingPolicy</tt> which are classes derived
70 from the axis base class <tt>FramingPolicyBase</tt>. This base class also doubles as
71 <tt>UnspecifiedFramingPolicy</tt> (which is just a typedef alias). If a policy axis is assigned
72 this Unspecified type, the axis is left unspecified, the concrete policy will be incomplete.
74 The senf::SocketPolicy template defines the behavior of a socket handle. The socket handle
75 instances do not implement any socket functionality themselves instead deferring the
76 implementation to the policy classes. The SocketHandle interface is therefore \e not implemented
77 using virtual members, all important socket functions can be inlined by the compiler to create
78 highly efficient code.
80 A senf::SocketPolicy instance can be incomplete. In this case it does \e not completely specify
81 the socket interface, it leaves some aspects open by assigning the Unspecified value to one or
82 more of the policy axis. A senf::SocketHandle based on such a policy will have a reduced
83 interface: It will only support those members for which the corresponding policies are defined.
85 To build a senf::SocketPolicy instance the senf::MakeSocketPolicy helper is provided. This
86 helper template takes any number (it is really limited to 6 Arguments but more arguments don't
87 make sense) of policy classes as it's argument. The MakeSocketPolicy helper will take the
88 arguments in the order they are specified and for each argument will check to which axis the
89 policy class belongs (by checking the base classes of that class) and assign it to the correct
90 policy axis in the senf::SocketPolicy template. If any policy axis are not specified, they are
91 defaulted to their corresponding Unspecified value. This helper frees you to specify the policy
92 classes in any order. An additional feature is, that you may specify a complete policy as a
93 first argument. This policy will then be used to provide default values for unspecified axis.
95 Two senf::SocketHandle's with different policies can be \e compatible. If they are, the more
96 specific SocketHandle can be converted (assigned to) the more basic SocketHandle. A SocketHandle
97 is more specific then another SocketHandle if the policy of the former is more specific then
98 that of the latter which means, that for each policy axis separately, the value of that axis of
99 the more specific policy is derived from or the same as the value of that axis in the more basic
100 policy. This is like converting a derived class pointer to a base class pointer, only it happens
101 separately but at the same time for each policy axis:
104 // This defines an incomplete policy where addressingPolicy and writePolicy
106 typedef senf::MakeSocketPolicy<
107 senf::StreamFramingPolicy,
108 senf::ConnectedCommunicationPolicy,
110 >::policy MyReadableSocketPolicy
112 typedef senf::ClientSocketHandle<MyReadableSocketPolicy> MyReadableHandle;
114 // TCPv4ClientSocketHandle is a socket handle with the policy equivalent to
115 // senf::MakeSocketPolicy<
116 // INet4AddressingPolicy,
117 // StreamFramingPolicy,
118 // ConnectedCommunicationPolicy,
120 // WritablePolicy>::policy
121 senf::TCPv4ClientSocketHandle tcpHandle (...);
123 MyReadableHandle myHandle (tcpHandle); // Conversion to more basic socket handle
126 \section policy_group_details The Policy Framework Classes
128 In the following discussion, deeper insight into C++ and especially the concepts of template
129 meta-programming are needed. However, this information is only needed if you want to write new
130 policy classes or want to use the policy framework explicitly for your own involved
131 optimizations ... or if you are just plain curious :-)
133 In the following discussion we will use the following conventions:
134 \li \e Axis is one or \c AddressingPolicy, \c FramingPolicy, \c CommunicationPolicy, \c
135 ReadPolicy or \c WritePolicy
136 \li \e socketPolicy is any socket policy (that is, an instantiation of the SocketPolicy
138 \li \e trait is an any policy class (that is, any class derived from one of the axis base
141 Each axis is comprised of a number of classes and templates (all in namespace senf of course):
143 <dl><dt>\e Axis \c Base (ex: AddressingPolicyBase)</dt><dd>Baseclass of all policies in this
146 <dt>\c Unspecified \e Axis (ex: \ref UnspecifiedAddressingPolicy)</dt> <dd>An alias (typedef)
147 for \e Axis \c Base</dd>
149 <dt>\e Axis \c Is < \e socketPolicy, \e trait > (ex: AddressingPolicyIs)</dt> <dd>A template
150 metafunction returning \c boost::true_type, if \e trait (any class derived from \e Axis \c
151 Base) is a compatible policy value of the given \e socketPolicy</dd>
153 <dt>\c If \e Axis \c Is < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIs)</dt> <dd>This
154 is a combination of \e Axis \c Is and \c boost::enable_if</dd>
156 <dt>\c If \e Axis \c IsNot < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIsNot)</dt>
157 <dd>The inverse of above</dd> </dl>
159 These classes form the basis of the policy framework. To bind the policy axis together, there
160 are some more classes and templates.
162 <dl><dt>\c class \c SocketPolicyBase</dt> <dd>This class is the base class of the SocketPolicy
163 template. It is used to validate, that a class is really a SocketPolicy (by checking, that it
164 derives from SocketPolicyBase. This is simpler than checking the template directly).</dd>
166 <dt>\c template \c SocketPolicy < \e addressingPolicy, \e framingPolicy, \e communicationPolicy,
167 \e readPolicy, \e writePolicy ></dt> <dd>This is the central SocketPolicy
168 template. It combines a complete set of policy classes, one for each axis.</dd>
170 <dt>\c template \c MakeSocketPolicy < \e args ></dt> <dd>\c MakeSocketPolicy is a template
171 metafunction which simplifies building SocketPolicy instantiations. It takes any number (ok, up
172 to a maximum of 6) of policy classes as an argument (in any order). It will sort these arguments
173 into the SocketPolicy template arguments. If for some axis no class is specified, it's slot will
174 be filled with \c Unspecified \e Axis. Additionally, the first Argument may optionally be ab
175 arbitrary SocketPolicy. It will provide default values for unspecified axis</dd>
177 <dt>\c template \c SocketPolicyIsBaseOf < \e base, \e derived ></dt> <dd>This template
178 metafunction will check, whether the socket policy \e derived is convertible to \e base. This
179 means, that for each axis, the corresponding policy class in \e derived must be derived or be
180 the same as the one on \e base.</dd> </dl>
182 \implementation All these classes are created automatically. The \c SENF_SOCKET_POLICIES macro
183 is a Boost.Preprocessor style sequence listing all policy axis. The Boost.Preprocessor library
184 is then used to generate the respective classes.
186 \section policy_implement Implementing Policy Classes
188 To define a new policy class, derive from the corresponding base class for your policy axes. The
189 only policy axis which might possibly need to be extended is the addressing policy
190 (AddressingPolicyBase). See the Documentation of these classes for more information on which
191 members can be implemented.
193 All members you define must be static. For any of the policy classes, you must only define those
194 members which are supported by your implementation. If you leave out a member you automatically
195 disable the corresponding functionality in the ClientSocketHandle/ServerSocketHandle interface.
197 The member prototypes given in the base class documentation only specify the call signature not
198 the way, the member must be defined (FileHandle really is not a FileHandle but an arbitrary
201 If the existence of a member depends on other policies, you should use the
202 <code>If</code><i>SomePolicy</i><code>Is</code> and
203 <code>If</code><i>SomePolicy</i><code>IsNot</code> templates to dynamically enable/disable the
204 member depending on some other policy:
207 struct ExampleAddressingPolicy
209 template <class SPolicy>
210 void connect(senf::SocketHandle<SPolicy> handle, Address & addr,
211 typename senf::IfCommmunicationPolicyIs<
212 SPolicy, senf::ConnectedCommunicationPolicy>::type * = 0);
216 The \c connect member in this example will only be enabled, it the communication policy of the
217 socket handle is ConnectedCommunicationPolicy (or a derived type). See <a
218 href="http://www.boost.org/libs/utility/enable_if.html">Boost.Enable_If</a> for a discussion of
219 the third argument (\c senf::ConnectedCommunicationPolicyIs is based on the \c boost::enable_if
222 \see \ref extend_policy \n
223 <a href="http://www.boost.org/libs/utility/enable_if.html">The Boost enable_if utility</a> \n
224 <a href="http://www.boost.org/libs/mpl/doc/index.html">The Boost.MPL library</a> \n
225 <a href="http://www.boost.org/libs/preprocessor/doc/index.html">The Boost.Preprocessor library</a>
227 \idea We could combine all the \e Axis \c Is templates into a single template. Since the \e
228 trait argument will automatically specify the axis to be used, it is not necessary to specify
229 that axis in the template functor's name. We could even combine this with \c
230 SocketPolicyIsBaseOf.
233 /** \defgroup policy_impl_group Policy Implementation classes
234 \ingroup policy_group
236 Here you will find all policy classes. Also included are some supporting classes which are used
237 as base classes to build other policy classes.
240 #ifndef HH_SocketPolicy_
241 #define HH_SocketPolicy_ 1
245 //#include "SocketPolicy.mpp"
246 ///////////////////////////////hh.p////////////////////////////////////////
250 /// \addtogroup policy_group
253 // This may be adapted to change the supported policies (however, ClientSocketHandle and
254 // ServerSocketHandle will probably have to be adjusted accordingly)
256 /** \brief List all policy axis
260 This define symbol is used to configure the policy axis. The base class for each of these
261 axis must be defined explicitly (e.g. AddressingPolicyBase). The implementation files will
262 then automatically generate all the other classes from this list.
266 # define SENF_SOCKET_POLICIES \
269 (CommunicationPolicy) \
273 // Wer define these classes explicitly (and not with some macro
275 // a) AddressingPolicyBase is different from all the others
276 // b) We want to document each one explicitly
278 /** \brief Policy defining socket addressing
280 AddressingPolicyBase is the baseclass of all addressing policy classes. When defining a new
281 addressing policy, the following members can be defined. All methods must be static.
284 <tr><td>typedef</td> <td><tt>Address</tt></td> <td>Address type</td></tr>
285 <tr><td>method</td> <td><tt>void local(FileHandle, Address &)</tt></td> <td>Get local socket address</td></tr>
286 <tr><td>method</td> <td><tt>void peer(FileHandle, Address &)</tt></td> <td>Get remote socket address</td></tr>
287 <tr><td>method</td> <td><tt>void bind(FileHandle, Address const &)</tt></td> <td>Bind socket to local address</td></tr>
288 <tr><td>method</tr> <td><tt>void connect(FileHandle, Address const &)</tt></td> <td>Connect to remote address</td></tr>
293 struct AddressingPolicyBase
295 virtual ~AddressingPolicyBase();
297 class Address { Address(); };
300 /** \brief Policy defining the framing format
302 This policy does not define any operations since it does have no influence on any method
303 signature. It does however affect the semantics of the \c read() and \c write() operations.
305 \note This policy axis probably only has two sensible states: StreamFramingPolicy and
306 DatagramFramingPolicy.
310 struct FramingPolicyBase
312 virtual ~FramingPolicyBase();
315 /** \brief Policy defining, how peers are selected
317 The CommunicationPolicy may define two members:
320 <tr><td>method</td> <td><tt>void listen(FileHandle, unsigned backlog)</tt></td> <td>Switch socket into listening state</td></tr>
321 <tr><td>method</td> <td><tt>int accept(FileHandle, Address &)</tt></td> <td>Accept a new connection</td></tr>
322 <tr><td>method</td> <td><tt>int accept(FileHandle)</tt></td> <td>Accept a new connection</td></tr>
325 The \c listen member is straight forward. The \c accept() member must return a new file
326 descriptor (which will be used to create a new SocketHandle of the correct
329 \note This Policy only has two meaningful states: ConnectedCommunicationPolicy and
330 UnconnectedCommunicationPolicy. It is probably not sensible to define a new
331 CommunicationPolicy type.
335 struct CommunicationPolicyBase
337 virtual ~CommunicationPolicyBase();
340 /** \brief Policy defining the readability
342 The ReadPolicy defines, whether the socket is readable. It may define two members:
345 <tr><td>method</td> <td><tt>unsigned read(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
346 <tr><td>method</td> <td><tt>unsigned readfrom(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
349 The second member should only be enabled if the communication policy is
350 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
351 is fixed) (see AddressingPolicyBase on how to do this).
353 \note This Policy only has two meaningful states: ReadablePolicy and NotReadablePolicy. It
354 probably does not make sense to define new read policy types.
358 struct ReadPolicyBase
360 virtual ~ReadPolicyBase();
363 /** \brief Policy defining the writability
365 The WritePolicy defines, whether the socket is writable. It may define two members:
368 <tr><td>method</td> <td><tt>unsigned write(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
369 <tr><td>method</td> <td><tt>unsigned writeto(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
372 The second member should only be enabled if the communication policy is
373 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
374 is fixed) (see AddressingPolicyBase on how to do this).
376 \note This Policy only has two meaningful states: WritablePolicy and NotWritablePolicy. It
377 probably does not make sense to define new write policy types.
381 struct WritePolicyBase
383 virtual ~WritePolicyBase();
386 // The implementation file will for each Policy declared above
387 // define the following (SomePolicy is one of the above):
389 // struct SomePolicyBase;
390 // typedef UndefinedSomePolicy;
391 // template SomePolicyIs< SocketPolicy, Axis >
392 // template IfSomePolicyIs< SocketPolicy, Axis >
393 // template IfSomePolicyIsNot< SocketPolicy, Axis >
395 // Additionally the following are defined:
397 // class SocketPolicyBase
398 // template SocketPolicy< ..policies.. >
399 // template MakeSocketPolicy< ..args.. >
400 // template SocketPolicyIsBaseOf< Base, Derived >
404 // The following stub definitions are only visible to doxygen
406 /** \brief Alias of AddressingPolicyBase for better readability
407 \see \ref policy_group
409 typedef AddressingPolicyBase UnspecifiedAddressingPolicy;
411 /** \brief Check single policy axis
413 This template is an example of the \e Axis \c Is family of template metafunctions. It will
414 check, whether \c Trait is a valid compatible Policy class of \c SocketPolicy. \c Trait must
415 be derived from AddressingPolicyBase (respectively \c Policy \c Base).
417 \see \ref policy_group
419 template <class SocketPolicy, class Trait>
420 struct AddressingPolicyIs
423 /** \brief Enable template overload depending on policy value
425 This template is an example of the \c If \e Axis \c Is family of templates. It is used like
426 <a href="http://www.boost.org/libs/utility/enable_if.html">Boost.enable_if</a> to enable a
427 templated overload only, if the AddressingPolicy of \e Axis is compatible with \c Trait
428 (that is the AddressingPolicy of \c Policy is derived from \c Trait).
432 template <class SocketPolicy, class Trait>
433 struct IfAddressingPolicyIs
436 /** \brief Inversion of \c IfAddressingPolicyIs
439 template <class SocketPolicy, class Trait>
440 struct IfAddressingPolicyIsNot
443 /** \brief Baseclass of all SocketPolicies
447 This class provides the baseclass of all socket policies (bundles). It serves two purposes:
448 \li It allows us to easily identify a socket policy bundle by checking a classes baseclass.
449 \li It provides an abstract (virtual) interface to access the policy axes
453 struct SocketPolicyBase
455 /** \brief Polymorphic access to policy axes
457 This is an example of a policy axes accessor. It returns a reference to the policy axes
458 used by the concrete protocol bundle. This reference can then be checked using RTTI
461 AddressingPolicyBase const & theAddressingPolicy() const = 0;
464 /** \brief Collection of policy classes
466 The SocketPolicy template defines the complete Policy used by the socket library. It
467 contains one policy class for each policy axis. This template takes one policy from each
468 axis as it's template arguments (this example implementation only has AddressingPolicy as an
471 A SocketPolicy can be complete or incomplete. An incomplete SocketPolicy will have at least
472 one axis set to \c Undefined \e Axis (or a generic derived class which is used to group some
473 other policies but does not (completely) define the policy behavior). A complete
474 SocketPolicy will have a concrete definition of the desired behavior for each policy axis.
478 template < class AddressingPolicy >
481 /** \brief Check dynamic policy compatibility
483 This check will validate, that a socket with \a other as it's policy is convertible to a
484 socket with the current SocketPolicy as it's policy. This is true, if for each policy
485 axis, the policy class of that axis as defined in the \a other policy is convertible to
486 the policy class of that same axis in the current SocketPolicy instance (as is defined
487 by the template arguments). This again is true, if the \a other policy class is derived
488 from (or is the same as) the policy class taken from the current SocketPolicy instance.
490 In other words, this call checks, that the current SocketPolicy (as defined via the
491 template arguments) is more generic than the \a other socket policy.
493 \param[in] other SocketPolicy to check
494 \throws std::bad_cast if \a other is not a compatible policy
496 static void checkBaseOf(SocketPolicyBase const & other);
499 /** \brief Metafunction to create SocketPolicy
501 This template metafunction simplifies the creation of a SocketPolicy instantiation. It takes
502 any number (that is up to 6) of Policy classes as arguments in any Order. It will create a
503 SocketPolicy from these policy classes. Any axis not specified will be left as \c
508 template <class Arg1, class Arg2, class ArgN>
509 struct MakeSocketPolicy
512 /** \brief Check policy compatibility
514 This template metafunction checks, whether the SocketPolicy \c Derived is more specialized
515 than \c Base (and therefore a SocketHandle with policy \c Derived is convertible to a
516 SocketHandle with policy \c Base).
518 The metafunction will return true (that is inherits from \c boost::true_type, see the <a
519 href="http://www.boost.org/libs/mpl/doc/index.html">Boost.MPL</a> library documentation for
520 more information) if each policy class in \c Base is a baseclass of (or the same as) the
521 corresponding policy class in \c Derived.
525 template <class Base, class Derived>
526 struct SocketPolicyIsBaseOf
534 //////////////////////////////hh.e////////////////////////////////////////
535 #include "SocketPolicy.ih"
536 //#include "SocketPolicy.cci"
537 #include "SocketPolicy.ct"
538 //#include "SocketPolicy.cti"
545 // c-file-style: "senf"
546 // indent-tabs-mode: nil
547 // ispell-local-dictionary: "american"
548 // compile-command: "scons -u test"
549 // comment-column: 40