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 \todo Do we want to support separate read and write policies. This allows to treat pipes within
27 this framework however, is this worth the effort?
29 \idea Creating a new Socket will create 4 (!) new instances (The handle, the body, the policy
30 and the protocol) of which 3 (argh) (body, policy and protocol) live on the heap. This is
31 expensive. We should convert all the policy classes to singletons and assign the same
32 instance to all socket bodies with the same policy. This would reduce the number of heap
33 allocations per socket handle to two.
36 /** \defgroup policy_group The Policy Framework
39 <map name="socketPolicy">
40 <area shape="rect" alt="SocketPolicy" href="structsenf_1_1SocketPolicy.html" title="SocketPolicy" coords="276,90,558,213" />
41 <area shape="rect" alt="WritePolicyBase" href="structsenf_1_1WritePolicyBase.html" title="WritePolicyBase" coords="39,243,174,268" />
42 <area shape="rect" alt="ReadPolicyBase" href="structsenf_1_1ReadPolicyBase.html" title="ReadPolicyBase" coords="42,204,174,231" />
43 <area shape="rect" alt="CommunicationPolicyBase" href="structsenf_1_1CommunicationPolicyBase.html" title="CommunicationPolicyBase" coords="0,166,215,193" />
44 <area shape="rect" alt="FramingPolicyBase" href="structsenf_1_1FramingPolicyBase.html" title="FramingPolicyBase" coords="30,129,185,155" />
45 <area shape="rect" alt="AddressingPolicyBase" href="structsenf_1_1AddressingPolicyBase.html" title="AddressingPolicyBase" coords="17,90,200,116" />
47 <img src="SocketPolicy.png" border="0" alt="Socket Policy" usemap="#socketPolicy">
50 \section policy_group_introduction Introduction to the Policy Framework
52 The policy framework conceptually implements a list of parallel inheritance hierarchies each
53 covering a specific interface aspect of the socket handle. The socket handle itself only
54 provides minimal functionality. All further functionality is relayed to a policy class, or more
55 precisely, to a group of policy classes, one for each policy axis. The policy axis are
57 <dl><dt><em>addressingPolicy</em></dt><dd>configures, whether a socket is addressable and if
58 so, configures the address type</dd>
60 <dt><em>framingPolicy</em></dt> <dd>configures the type of framing the socket provides: either
61 no framing providing a simple i/o stream or packet framing</dd>
63 <dt><em>communicationPolicy</em></dt><dd>configures,if and how the communication partner is
66 <dt><em>readPolicy</em></dt><dd>configures the readability of the socket</dd>
68 <dt><em>writePolicy</em></dt><dd>configures the writability of the socket</dd>
70 The template senf::SocketPolicy combines these policy axis to form a concrete socket policy. In
71 a concrete policy, each of these policy axis is assigned a value, the policy value. This value
72 is identified by a class type, a policy class. E.g. possible values for <em>framingPolicy</em>
73 are <tt>DatagramFramingPolicy</tt> or <tt>StreamFramingPolicy</tt> which are classes derived
74 from the axis base class <tt>FramingPolicyBase</tt>. This base class also doubles as
75 <tt>UnspecifiedFramingPolicy</tt> (which is just a typedef alias). If a policy axis is assigned
76 this Unspecified type, the axis is left unspecified, the concrete policy will be incomplete.
78 The senf::SocketPolicy template defines the behavior of a socket handle. The socket handle
79 instances do not implement any socket functionality themselves instead deferring the
80 implementation to the policy classes. The SocketHandle interface is therefore \e not implemented
81 using virtual members, all important socket functions can be inlined by the compiler to create
82 highly efficient code.
84 A senf::SocketPolicy instance can be incomplete. In this case it does \e not completely specify
85 the socket interface, it leaves some aspects open by assigning the Unspecified value to one or
86 more of the policy axis. A senf::SocketHandle based on such a policy will have a reduced
87 interface: It will only support those members for which the corresponding policies are defined.
89 To build a senf::SocketPolicy instance the senf::MakeSocketPolicy helper is provided. This
90 helper template takes any number (it is really limited to 6 Arguments but more arguments don't
91 make sense) of policy classes as it's argument. The MakeSocketPolicy helper will take the
92 arguments in the order they are specified and for each argument will check to which axis the
93 policy class belongs (by checking the base classes of that class) and assign it to the correct
94 policy axis in the senf::SocketPolicy template. If any policy axis are not specified, they are
95 defaulted to their corresponding Unspecified value. This helper frees you to specify the policy
96 classes in any order. An additional feature is, that you may specify a complete policy as a
97 first argument. This policy will then be used to provide default values for unspecified axis.
99 Two senf::SocketHandle's with different policies can be \e compatible. If they are, the more
100 specific SocketHandle can be converted (assigned to) the more basic SocketHandle. A SocketHandle
101 is more specific then another SocketHandle if the policy of the former is more specific then
102 that of the latter which means, that for each policy axis separately, the value of that axis of
103 the more specific policy is derived from or the same as the value of that axis in the more basic
104 policy. This is like converting a derived class pointer to a base class pointer, only it happens
105 separately but at the same time for each policy axis:
108 // This defines an incomplete policy where addressingPolicy and writePolicy
110 typedef senf::MakeSocketPolicy<
111 senf::StreamFramingPolicy,
112 senf::ConnectedCommunicationPolicy,
114 >::policy MyReadableSocketPolicy
116 typedef senf::ClientSocketHandle<MyReadableSocketPolicy> MyReadableHandle;
118 // TCPv4ClientSocketHandle is a socket handle with the policy equivalent to
119 // senf::MakeSocketPolicy<
120 // INet4AddressingPolicy,
121 // StreamFramingPolicy,
122 // ConnectedCommunicationPolicy,
124 // WritablePolicy>::policy
125 senf::TCPv4ClientSocketHandle tcpHandle (...);
127 MyReadableHandle myHandle (tcpHandle); // Conversion to more basic socket handle
130 \section policy_group_details The Policy Framework Classes
132 In the following discussion, deeper insight into C++ and especially the concepts of template
133 meta-programming are needed. However, this information is only needed if you want to write new
134 policy classes or want to use the policy framework explicitly for your own involved
135 optimizations ... or if you are just plain curious :-)
137 In the following discussion we will use the following conventions:
138 \li \e Axis is one or \c AddressingPolicy, \c FramingPolicy, \c CommunicationPolicy, \c
139 ReadPolicy or \c WritePolicy
140 \li \e socketPolicy is any socket policy (that is, an instantiation of the SocketPolicy
142 \li \e trait is an any policy class (that is, any class derived from one of the axis base
145 Each axis is comprised of a number of classes and templates (all in namespace senf of course):
147 <dl><dt>\e Axis \c Base (ex: AddressingPolicyBase)</dt><dd>Baseclass of all policies in this
150 <dt>\c Unspecified \e Axis (ex: \ref UnspecifiedAddressingPolicy)</dt> <dd>An alias (typedef)
151 for \e Axis \c Base</dd>
153 <dt>\e Axis \c Is < \e socketPolicy, \e trait > (ex: AddressingPolicyIs)</dt> <dd>A template
154 metafunction returning \c boost::true_type, if \e trait (any class derived from \e Axis \c
155 Base) is a compatible policy value of the given \e socketPolicy</dd>
157 <dt>\c If \e Axis \c Is < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIs)</dt> <dd>This
158 is a combination of \e Axis \c Is and \c boost::enable_if</dd>
160 <dt>\c If \e Axis \c IsNot < \e socketPolicy, \e trait > (ex: IfAddressingPolicyIsNot)</dt>
161 <dd>The inverse of above</dd> </dl>
163 These classes form the basis of the policy framework. To bind the policy axis together, there
164 are some more classes and templates.
166 <dl><dt>\c class \c SocketPolicyBase</dt> <dd>This class is the base class of the SocketPolicy
167 template. It is used to validate, that a class is really a SocketPolicy (by checking, that it
168 derives from SocketPolicyBase. This is simpler than checking the template directly).</dd>
170 <dt>\c template \c SocketPolicy < \e addressingPolicy, \e framingPolicy, \e communicationPolicy,
171 \e readPolicy, \e writePolicy ></dt> <dd>This is the central SocketPolicy
172 template. It combines a complete set of policy classes, one for each axis.</dd>
174 <dt>\c template \c MakeSocketPolicy < \e args ></dt> <dd>\c MakeSocketPolicy is a template
175 metafunction which simplifies building SocketPolicy instantiations. It takes any number (ok, up
176 to a maximum of 6) of policy classes as an argument (in any order). It will sort these arguments
177 into the SocketPolicy template arguments. If for some axis no class is specified, it's slot will
178 be filled with \c Unspecified \e Axis. Additionally, the first Argument may optionally be ab
179 arbitrary SocketPolicy. It will provide default values for unspecified axis</dd>
181 <dt>\c template \c SocketPolicyIsBaseOf < \e base, \e derived ></dt> <dd>This template
182 metafunction will check, whether the socket policy \e derived is convertible to \e base. This
183 means, that for each axis, the corresponding policy class in \e derived must be derived or be
184 the same as the one on \e base.</dd> </dl>
186 \implementation All these classes are created automatically. The \c SENF_SOCKET_POLICIES macro
187 is a Boost.Preprocessor style sequence listing all policy axis. The Boost.Preprocessor library
188 is then used to generate the respective classes.
190 \section policy_implement Implementing Policy Classes
192 To define a new policy class, derive from the corresponding base class for your policy axes. The
193 only policy axis which might possibly need to be extended is the addressing policy
194 (AddressingPolicyBase). See the Documentation of these classes for more information on which
195 members can be implemented.
197 All members you define must be static. For any of the policy classes, you must only define those
198 members which are supported by your implementation. If you leave out a member you automatically
199 disable the corresponding functionality in the ClientSocketHandle/ServerSocketHandle interface.
201 The member prototypes given in the base class documentation only specify the call signature not
202 the way, the member must be defined (FileHandle really is not a FileHandle but an arbitrary
205 If the existence of a member depends on other policies, you should use the
206 <code>If</code><i>SomePolicy</i><code>Is</code> and
207 <code>If</code><i>SomePolicy</i><code>IsNot</code> templates to dynamically enable/disable the
208 member depending on some other policy:
211 struct ExampleAddressingPolicy
213 template <class Policy>
214 void connect(senf::SocketHandle<Policy> handle, Address & addr,
215 typename senf::IfCommmunicationPolicyIs<
216 Policy, senf::ConnectedCommunicationPolicy>::type * = 0);
220 The \c connect member in this example will only be enabled, it the communication policy of the
221 socket handle is ConnectedCommunicationPolicy (or a derived type). See <a
222 href="http://www.boost.org/libs/utility/enable_if.html">Boost.Enable_If</a> for a discussion of
223 the third argument (\c senf::ConnectedCommunicationPolicyIs is based on the \c boost::enable_if
226 \see \ref extend_policy \n
227 <a href="http://www.boost.org/libs/utility/enable_if.html">The Boost enable_if utility</a> \n
228 <a href="http://www.boost.org/libs/mpl/doc/index.html">The Boost.MPL library</a> \n
229 <a href="http://www.boost.org/libs/preprocessor/doc/index.html">The Boost.Preprocessor library</a>
231 \idea We could combine all the \e Axis \c Is templates into a single template. Since the \e
232 trait argument will automatically specify the axis to be used, it is not necessary to specify
233 that axis in the template functor's name. We could even combine this with \c
234 SocketPolicyIsBaseOf.
237 /** \defgroup policy_impl_group Policy Implementation classes
238 \ingroup policy_group
240 Here you will find all policy classes. Also included are some supporting classes which are used
241 as base classes to build other policy classes.
244 #ifndef HH_SocketPolicy_
245 #define HH_SocketPolicy_ 1
249 //#include "SocketPolicy.mpp"
250 ///////////////////////////////hh.p////////////////////////////////////////
254 /// \addtogroup policy_group
257 // This may be adapted to change the supported policies (however, ClientSocketHandle and
258 // ServerSocketHandle will probably have to be adjusted accordingly)
260 /** \brief List all policy axis
264 This define symbol is used to configure the policy axis. The base class for each of these
265 axis must be defined explicitly (e.g. AddressingPolicyBase). The implementation files will
266 then automatically generate all the other classes from this list.
270 # define SENF_SOCKET_POLICIES \
273 (CommunicationPolicy) \
277 // Wer define these classes explicitly (and not with some macro
279 // a) AddressingPolicyBase is different from all the others
280 // b) We want to document each one explicitly
282 /** \brief Policy defining socket addressing
284 AddressingPolicyBase is the baseclass of all addressing policy classes. When defining a new
285 addressing policy, the following members can be defined. All methods must be static.
288 <tr><td>typedef</td> <td><tt>Address</tt></td> <td>Address type</td></tr>
289 <tr><td>method</td> <td><tt>void local(FileHandle, Address &)</tt></td> <td>Get local socket address</td></tr>
290 <tr><td>method</td> <td><tt>void peer(FileHandle, Address &)</tt></td> <td>Get remote socket address</td></tr>
291 <tr><td>method</td> <td><tt>void bind(FileHandle, Address const &)</tt></td> <td>Bind socket to local address</td></tr>
292 <tr><td>method</tr> <td><tt>void connect(FileHandle, Address const &)</tt></td> <td>Connect to remote address</td></tr>
297 struct AddressingPolicyBase
299 virtual ~AddressingPolicyBase() {}
301 class Address { Address(); };
304 /** \brief Policy defining the framing format
306 This policy does not define any operations since it does have no influence on any method
307 signature. It does however affect the semantics of the \c read() and \c write() operations.
309 \note This policy axis probably only has two sensible states: StreamFramingPolicy and
310 DatagramFramingPolicy.
314 struct FramingPolicyBase
316 virtual ~FramingPolicyBase() {}
319 /** \brief Policy defining, how peers are selected
321 The CommunicationPolicy may define two members:
324 <tr><td>method</td> <td><tt>void listen(FileHandle, unsigned backlog)</tt></td> <td>Switch socket into listening state</td></tr>
325 <tr><td>method</td> <td><tt>int accept(FileHandle, Address &)</tt></td> <td>Accept a new connection</td></tr>
326 <tr><td>method</td> <td><tt>int accept(FileHandle)</tt></td> <td>Accept a new connection</td></tr>
329 The \c listen member is straight forward. The \c accept() member must return a new file
330 descriptor (which will be used to create a new SocketHandle of the correct
333 \note This Policy only has two meaningful states: ConnectedCommunicationPolicy and
334 UnconnectedCommunicationPolicy. It is probably not sensible to define a new
335 CommunicationPolicy type.
339 struct CommunicationPolicyBase
341 virtual ~CommunicationPolicyBase() {}
344 /** \brief Policy defining the readability
346 The ReadPolicy defines, whether the socket is readable. It may define two members:
349 <tr><td>method</td> <td><tt>unsigned read(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
350 <tr><td>method</td> <td><tt>unsigned readfrom(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
353 The second member should only be enabled if the communication policy is
354 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
355 is fixed) (see AddressingPolicyBase on how to do this).
357 \note This Policy only has two meaningful states: ReadablePolicy and NotReadablePolicy. It
358 probably does not make sense to define new read policy types.
362 struct ReadPolicyBase
364 virtual ~ReadPolicyBase() {}
367 /** \brief Policy defining the writability
369 The WritePolicy defines, whether the socket is writable. It may define two members:
372 <tr><td>method</td> <td><tt>unsigned write(FileHandle, char * buffer, unsigned size)</tt></td> <td>read data from socket</td></tr>
373 <tr><td>method</td> <td><tt>unsigned writeto(FileHandle, char * buffer, unsigned size, Address &)</tt></td> <td>read data from unconnected socket</td></tr>
376 The second member should only be enabled if the communication policy is
377 UnconnectedCommunicationPolicy (otherwise it does not make sense since the communication partner
378 is fixed) (see AddressingPolicyBase on how to do this).
380 \note This Policy only has two meaningful states: WritablePolicy and NotWritablePolicy. It
381 probably does not make sense to define new write policy types.
385 struct WritePolicyBase
387 virtual ~WritePolicyBase() {}
390 // The implementation file will for each Policy declared above
391 // define the following (SomePolicy is one of the above):
393 // struct SomePolicyBase;
394 // typedef UndefinedSomePolicy;
395 // template SomePolicyIs< SocketPolicy, Axis >
396 // template IfSomePolicyIs< SocketPolicy, Axis >
397 // template IfSomePolicyIsNot< SocketPolicy, Axis >
399 // Additionally the following are defined:
401 // class SocketPolicyBase
402 // template SocketPolicy< ..policies.. >
403 // template MakeSocketPolicy< ..args.. >
404 // template SocketPolicyIsBaseOf< Base, Derived >
408 // The following stub definitions are only visible to doxygen
410 /** \brief Alias of AddressingPolicyBase for better readability
411 \see \ref policy_group
413 typedef AddressingPolicyBase UnspecifiedAddressingPolicy;
415 /** \brief Check single policy axis
417 This template is an example of the \e Axis \c Is family of template metafunctions. It will
418 check, whether \c Trait is a valid compatible Policy class of \c SocketPolicy. \c Trait must
419 be derived from AddressingPolicyBase (respectively \c Policy \c Base).
421 \see \ref policy_group
423 template <class SocketPolicy, class Trait>
424 struct AddressingPolicyIs
427 /** \brief Enable template overload depending on policy value
429 This template is an example of the \c If \e Axis \c Is family of templates. It is used like
430 <a href="http://www.boost.org/libs/utility/enable_if.html">Boost.enable_if</a> to enable a
431 templated overload only, if the AddressingPolicy of \e Axis is compatible with \c Trait
432 (that is the AddressingPolicy of \c Policy is derived from \c Trait).
436 template <class SocketPolicy, class Trait>
437 struct IfAddressingPolicyIs
440 /** \brief Inversion of \c IfAddressingPolicyIs
443 template <class SocketPolicy, class Trait>
444 struct IfAddressingPolicyIsNot
447 /** \brief Baseclass of all SocketPolicies
451 This class provides the baseclass of all socket policies (bundles). It serves two purposes:
452 \li It allows us to easily identify a socket policy bundle by checking a classes baseclass.
453 \li It provides an abstract (virtual) interface to access the policy axes
457 struct SocketPolicyBase
459 /** \brief Polymorphic access to policy axes
461 This is an example of a policy axes accessor. It returns a reference to the policy axes
462 used by the concrete protocol bundle. This reference can then be checked using RTTI
465 AddressingPolicyBase const & theAddressingPolicy() const = 0;
468 /** \brief Collection of policy classes
470 The SocketPolicy template defines the complete Policy used by the socket library. It
471 contains one policy class for each policy axis. This template takes one policy from each
472 axis as it's template arguments (this example implementation only has AddressingPolicy as an
475 A SocketPolicy can be complete or incomplete. An incomplete SocketPolicy will have at least
476 one axis set to \c Undefined \e Axis (or a generic derived class which is used to group some
477 other policies but does not (completely) define the policy behavior). A complete
478 SocketPolicy will have a concrete definition of the desired behavior for each policy axis.
482 template < class AddressingPolicy >
485 /** \brief Check dynamic policy compatibility
487 This check will validate, that a socket with \a other as it's policy is convertible to a
488 socket with the current SocketPolicy as it's policy. This is true, if for each policy
489 axis, the policy class of that axis as defined in the \a other policy is convertible to
490 the policy class of that same axis in the current SocketPolicy instance (as is defined
491 by the template arguments). This again is true, if the \a other policy class is derived
492 from (or is the same as) the policy class taken from the current SocketPolicy instance.
494 In other words, this call checks, that the current SocketPolicy (as defined via the
495 template arguments) is more generic than the \a other socket policy.
497 \param[in] other SocketPolicy to check
498 \throws std::bad_cast if \a other is not a compatible policy
500 static void checkBaseOf(SocketPolicyBase const & other);
503 /** \brief Metafunction to create SocketPolicy
505 This template metafunction simplifies the creation of a SocketPolicy instantiation. It takes
506 any number (that is up to 6) of Policy classes as arguments in any Order. It will create a
507 SocketPolicy from these policy classes. Any axis not specified will be left as \c
512 template <class Arg1, class Arg2, class ArgN>
513 struct MakeSocketPolicy
516 /** \brief Check policy compatibility
518 This template metafunction checks, whether the SocketPolicy \c Derived is more specialized
519 than \c Base (and therefore a SocketHandle with policy \c Derived is convertible to a
520 SocketHandle with policy \c Base).
522 The metafunction will return true (that is inherits from \c boost::true_type, see the <a
523 href="http://www.boost.org/libs/mpl/doc/index.html">Boost.MPL</a> library documentation for
524 more information) if each policy class in \c Base is a baseclass of (or the same as) the
525 corresponding policy class in \c Derived.
529 template <class Base, class Derived>
530 struct SocketPolicyIsBaseOf
538 //////////////////////////////hh.e////////////////////////////////////////
539 #include "SocketPolicy.ih"
540 //#include "SocketPolicy.cci"
541 #include "SocketPolicy.ct"
542 //#include "SocketPolicy.cti"
549 // c-file-style: "senf"
550 // indent-tabs-mode: nil
551 // ispell-local-dictionary: "american"
552 // compile-command: "scons -u test"
553 // comment-column: 40