X-Git-Url: http://g0dil.de/git?a=blobdiff_plain;f=Socket%2FMainpage.dox;h=4802f4af5294eb641f8417db998c4bec13322158;hb=9a988902090d28007578e93bffd809f6bd913155;hp=8f8f736b4de7eb88122e3ebba4cec9147ef44ab1;hpb=983ae64545d03ca24e7c5cb2c9ed2749435844eb;p=senf.git diff --git a/Socket/Mainpage.dox b/Socket/Mainpage.dox index 8f8f736..4802f4a 100644 --- a/Socket/Mainpage.dox +++ b/Socket/Mainpage.dox @@ -2,26 +2,22 @@ namespace senf { /** \mainpage The SENF Socket Library - The Socket library provides a high level and object oriented - abstraction of the BSD socket API. The abstraction is based on - several concepts: - - \li The basic visible interface is a \link handle_group handle - object \endlink - \li The socket interface relies on a \link policy_group policy - framework \endlink to configure it's functionality - \li The rest of the socket API is accessible using a classic - inheritance hierarchy of \link protocol_group protocol classes - \endlink - - The handle/body architecture provides automatic reference counted - management of socket instances, the policy framework provides - highly efficient access to the most important socket functions - (like reading and writing) and the inheritance hierarchy provides - convenient access to the multitude of special and protocol - dependent options. - - \see \ref usage \n + The Socket library provides a high level and object oriented abstraction of the BSD socket + API. The abstraction is based on several concepts: + + \li The basic visible interface is a \link handle_group handle object \endlink + \li The socket interface relies on a \link policy_group policy framework \endlink to configure + it's functionality + \li The rest of the socket API is accessible using a classic inheritance hierarchy of \link + protocol_group protocol classes \endlink + + The handle/body architecture provides automatic reference counted management of socket + instances, the policy framework provides highly efficient access to the most important socket + functions (like reading and writing) and the inheritance hierarchy provides convenient access to + the multitude of special and protocol dependent options. + + \see \ref structure \n + \ref usage \n \ref handle_group \n \ref policy_group \n \ref protocol_group \n @@ -29,41 +25,121 @@ namespace senf { \ref implementation */ +/** \page structure Overview of the Socket Library Structure + + \image html Handle.png + + This diagram tries to give a structural overview of the Socket Library, it does \e not directly + show, how the library is implemented. This will be explained later. + + The outside interface to the library is a Handle object. This is the only object, the library + user directly interacts with. Every handle references some socket. This is like the ordinary + POSIX API: the file descriptor (also called file handle, an integer number) references a socket + structure which lives in kernel space. In this library, the Handle object (which is not a simple + integer any more but an object) references the Socket (which is part of the + implementation). Several handles may reference the same Socket. In contrast to the kernel API, + the library employs reference counting to release a socket when the last Handle to it goes out + of scope. + + The behavior of a Socket is defined by it's Protocol. It is divided into two parts: the + policy interface and the protocol interface. Together they provide the + complete API for a specific type of Socket as defined by the Protocol. The policy + interface provides highly efficient access to the most frequently used operations whereas + the protocol interface completes the interface by providing a complete set of all + protocol specific operations not found in the policy interface. This structure allows us to + combine the benefits of two design methodologies: The policy interface utilizes a policy based + design technique and is highly efficient albeit more complex to implement, whereas the protocol + interface is based on a more common inheritance architecture which is not as optimized for + performance but much simpler to implement. We reduce the complexity of the implementation by + reducing the policy interface to a minimal sensible subset of the complete API. + + \section over_policy The Policy Interface + + The policy of a Socket consists of several parts, called policy axis. Each axis + corresponds to one specific interface aspect of the Socket. The exact meaning of the policy axis + are defined elsewhere (see \ref policy_group). The Protocol will always provide a complete set + of policy classes, one for each axis. + + This complete socket policy defines the policy interface of the protocol. This + interface is carried over into the Handle. The socket policy as defined in the Handle however + may be incomplete. This mans, that the \e accessible interface of the Socket depends on + the type of Handle used. The inherent interface does not change but the view of this interface + does if the Handle does not provide the \e complete policy interface. This feature is very + important. It allows to define generic Handle types. A generic Handle with an incompletely + defined policy can point to an arbitrary Socket as long as all those policy axis which \e are + defined match those defined in that Socket's protocol. Using such a generic handle decouples the + implementation parts using this handle from the other socket aspects (e.g. you may define a + generic socket handle for TCP based communication leaving the addressingPolicy undefined which + makes your code independent of the type of addressing, IPv4 or IPv6). + + This can be described as generalized compile-time polymorphism: A base class reference to some + derived class will only give access to a reduced interface (the base class interface) of a + class. The class still is of it's derived type (and inherently has the complete interface) but + only part of it is accessible via the base class reference. Likewise a generic handle (aka base + class reference) will only provide a reduced interface (aka base class interface) to the derived + class instance (aka socket). + + \section over_protocol The Protocol Interface + + The protocol interface is provided by a set of protocol facets. Each facet provides a + part of the interface. Whereas the policy interface is strictly defined (the number and type of + policy axis is fixed and also the possible members provided by the policy interface are fixed), + the protocol interface is much more flexible. Any member needed to provide a complete API for + the specific protocol may be defined, the number and type of facets combined to provide the + complete interface is up to the Protocol implementor. This flexibility is necessary to provide a + complete API for every possible protocol. + + However this flexibility comes at a cost: To access the protocol interface the user must know + the exact protocol of the socket. With other words, the protocol is only accessible if the + handle you use is a protocol specific handle. A protocol specific Handle differs from a + generic Handle in two ways: It always has a complete policy and it knows the exact protocol type + of the socket (which generic handles don't). This allows to access to the complete protocol + interface. + + \section over_impl Implementation of the Socket Libarary Structure + + In the Implementation, the socket policy is identified by an instance of the senf::SocketPolicy + template. The Socket representation is internally represented in a senf::SocketBody which is not + outside visible. The Handle is provided by a hierarchy of handle templates. Each Handle template + uses template arguments for the policy and/or protocol as needed (see \ref handle_group). + + The Handle hierarchy divides the interface into two separate strains: the client interface + (senf::ClientSocketHandle and senf::ProtocolClientSocketHandle) provides the interface of a + client socket whereas the server interface (senf::ServerSocketHandle and + senf::ProtocolServerSocketHandle) provides the interface as used by server sockets. + + The protocol interface is implemented using inheritance: The Protocol class inherits from each + protocol facet using multiple (virtual public) inheritance. The Protocol class therefore + provides the complete protocol API in a unified (see \ref protocol_group). + */ + /** \page usage Using the Socket Library - Whenever you use the socket library, what you will be dealing with - are FileHandle derived instances. The socket library relies - on reference counting to automatically manage the underlying - socket representation. This frees you of having to manage the - socket lifetime explicitly. + Whenever you use the socket library, what you will be dealing with are FileHandle derived + instances. The socket library relies on reference counting to automatically manage the + underlying socket representation. This frees you of having to manage the socket lifetime + explicitly. \section usage_create Creating a Socket Handle - To create a new socket handle (opening a socket), you will need to - use ProtocolClientSocketHandle or - ProtocolServerSocketHandle. You will probably not use these - templates as is but use proper typedefs (for example - TCPv4ClientSocketHandle or PacketSocketHandle). The - documentation for these socket handles are found in the protocol - class (for example TCPv4SocketProtocol or - PacketProtocol). + To create a new socket handle (opening a socket), you will need to use + ProtocolClientSocketHandle or ProtocolServerSocketHandle. You will probably not use these + templates as is but use proper typedefs (for example TCPv4ClientSocketHandle or + PacketSocketHandle). The documentation for these socket handles are found in the protocol class + (for example TCPv4SocketProtocol or PacketProtocol). \section usage_reusable Writing Reusable Components - To make your code more flexible, you should not pass around your - socket in this form. Most of your code will be using only a small - subset of the ProtocolClientSocketHandle or - ProtocolServerSocketHandle API. + To make your code more flexible, you should not pass around your socket in this form. Most of + your code will be using only a small subset of the ProtocolClientSocketHandle or + ProtocolServerSocketHandle API. - If instead of using the - fully specified handle type you use a more incomplete type, you - allow your code to be used with all sockets which fulfill the - minimal requirements of your code. These types are based on the - ClientSocketHandle and ServerSocketHandle templates which implement - the policy interface without providing the concrete protocol interface. - To use those templates you may define a special reduced policy or handle for - your code. By giving only an incomplete policy you thereby reduce the - interface to that required by your module: + If instead of using the fully specified handle type you use a more incomplete type, you allow + your code to be used with all sockets which fulfill the minimal requirements of your code. These + types are based on the ClientSocketHandle and ServerSocketHandle templates which implement the + policy interface without providing the concrete protocol interface. To use those templates you + may define a special reduced policy or handle for your code. By giving only an incomplete policy + you thereby reduce the interface to that required by your module: \code typedef ClientSocketHandle< @@ -74,49 +150,41 @@ namespace senf { \endcode - This defines \c MyReadableHandle as a ClientSocketHandle - which will have only read functionality. Your code expects a - stream interface (in contrast to a packet or datagram based - interface). You will not have \c write or \c readfrom members. \c - write will be disabled since the WritePolicy is unknown, \c - readfrom will be disabled since a socket with the - ConnectedCommunicationPolicy does not have a \c readfrom - member. - */ - + This defines \c MyReadableHandle as a ClientSocketHandle which will have only read + functionality. Your code expects a stream interface (in contrast to a packet or datagram based + interface). You will not have \c write or \c readfrom members. \c write will be disabled since + the WritePolicy is unknown, \c readfrom will be disabled since a socket with the + ConnectedCommunicationPolicy does not have a \c readfrom member. + \see + \ref policy_group \n + \ref handle_group \n + \ref protocol_group + */ /** \page extend Extending the Library - There are two layers, on which the socket library can be - extended: On the protocol layer and on the policy layer. Extending - the protocol layer is quite simple and works as long as the - desired protocol does use the same BSD API used by the standard - internet protocols as implemented in the standard policies - (i.e. it uses ordinary read() and write() or rcvfrom() or sendto() - calls and so on). + There are two layers, on which the socket library can be extended: On the protocol layer and on + the policy layer. Extending the protocol layer is quite simple and works as long as the desired + protocol does use the same BSD API used by the standard internet protocols as implemented in the + standard policies (i.e. it uses ordinary read() and write() or rcvfrom() or sendto() calls and + so on). - If however the implementation of a policy feature needs to be - changed, a new policy class has to be written. This also is not - very complicated however the integration is more complex. + If however the implementation of a policy feature needs to be changed, a new policy class has to + be written. This also is not very complicated however the integration is more complex. \section extend_protocol Writing a new protocol class - Most protocols can be implemented by just implementing a new - protocol class. The protocol class must be derived from - ConcreteSocketProtocol and takes the socket policy (as - created by MakeSocketPolicy) as a template argument. See the - documentation of this class for the interface. - - \attention You may want to use multiple inheritance as it is used - in the implementation of the standard protocols (See \ref - protocol_group). You must however be extra careful to ensure, that - every class ultimately has SocketPolicy as a public \e - virtual base. - - After the protocol class has been defined, you will probably want to - provide typedefs for the new protocol sockets. If the new protocol - is connection oriented, this will be like + Most protocols can be implemented by just implementing a new protocol class. The protocol class + must be derived from ConcreteSocketProtocol and takes the socket policy (as created by + MakeSocketPolicy) as a template argument. See the documentation of this class for the interface. + + \attention You may want to use multiple inheritance as it is used in the implementation of the + standard protocols (See \ref protocol_group). You must however be extra careful to ensure, that + every class ultimately has SocketPolicy as a public \e virtual base. + + After the protocol class has been defined, you will probably want to provide typedefs for the + new protocol sockets. If the new protocol is connection oriented, this will be like \code typedef ProtocolClientSocketHandle MyProtocolClientSocketHandle; typedef ProtocolServerSocketHandle MyProtocolServerSocketHandle; @@ -124,35 +192,28 @@ namespace senf { \section extend_policy Extending the policy framework - If you have to extend the policy framework, you will need to be - aware of some important limitations of the socket library: - - \li When you define a new policy for some axis, this new policy - must not be derived from one of the existing concrete - policy classes (except of course the respective policy axis - base class). This is important since the policy type is \e not - polymorphic. The policy to be used is selected by the compiler - using the \e static type, which is exactly what is desired, - since this allows calls to be efficiently inlined. - - \li Therefore, extending the policy framework will make the new - socket probably \e incompatible with generic code which relies - on the policy axis which is extended. Example: If you write a - new write policy because your protocol does not use ordinary - write() system calls but some protocol specific API, Then any - generic function relying on WritablePolicy will \e not - work with the new socket, since the socket does \e not have - this policy, it has some other kind of write policy. - - Therefore you need to be careful of what you are doing. The first - step is to find out, which policy you will have to implement. For - this, find the ClientSocketHandle and/or - ServerSocketHandle members you want to change (see \ref - ClientSocketHandle and \ref ServerSocketHandle). Not - all policy axis directly contribute to the SocketHandle - interface. However, some policy members additionally depend on - other policy axis (example: AddressingPolicy::connect is only - defined if the communication policy is + If you have to extend the policy framework, you will need to be aware of some important + limitations of the socket library: + + \li When you define a new policy for some axis, this new policy must not be derived + from one of the existing concrete policy classes (except of course the respective policy + axis base class). This is important since the policy type is \e not polymorphic. The policy + to be used is selected by the compiler using the \e static type, which is exactly what is + desired, since this allows calls to be efficiently inlined. + + \li Therefore, extending the policy framework will make the new socket probably \e incompatible + with generic code which relies on the policy axis which is extended. Example: If you write a + new write policy because your protocol does not use ordinary write() system calls but some + protocol specific API, Then any generic function relying on WritablePolicy will \e not work + with the new socket, since the socket does \e not have this policy, it has some other kind + of write policy. + + Therefore you need to be careful of what you are doing. The first step is to find out, which + policy you will have to implement. For this, find the ClientSocketHandle and/or + ServerSocketHandle members you want to change (see \ref ClientSocketHandle and \ref + ServerSocketHandle). Not all policy axis directly contribute to the SocketHandle + interface. However, some policy members additionally depend on other policy axis (example: + AddressingPolicy::connect is only defined if the communication policy is ConnectedCommunication). \see policy_group @@ -162,35 +223,31 @@ namespace senf { - + - + - + - + - + - + - + + ClientSocketHandle/ServerSocketHandle and defined through the policy -
policy collection of policy classes, one for each - policy axis, instantiation of the SocketPolicy template
policy collection of policy classes, one for each policy axis, instantiation of + the SocketPolicy template
policy axis one aspect defined in the socket - policy, typedef and member of the SocketPolicy template
policy axis one aspect defined in the socket policy, typedef and member of the + SocketPolicy template
policy class implementation of a single policy - axis, class derived from the axis base class
policy class implementation of a single policy axis, class derived from the + axis base class
complete policy socket policy where each - axis is specified completely
complete policy socket policy where each axis is specified completely
incomplete policy socket policy, where at - least one axis is not fully specified
incomplete policy socket policy, where at least one axis is not fully + specified
protocol class definition of a protocol as a - class, class inheriting from ConcreteSocketProtocol.
protocol class definition of a protocol as a class, class inheriting from + ConcreteSocketProtocol.
protocol facet a class providing some subset of - the protocol interface, class derived from SocketProtocol but not - from ConcreteSocketProtocol
protocol facet a class providing some subset of the protocol interface, class + derived from SocketProtocol but not from ConcreteSocketProtocol
policy interface interface directly provided by - ClientSocketHandle/ServerSocketHandle and defined through the - policy
protocol interface interface provided by the - protocol class and accessible via the - ProtocolClientSocketHandle::protocol()/ProtocolServerSocketHandle::protocol() +
protocol interface interface provided by the protocol class and accessible via + the ProtocolClientSocketHandle::protocol()/ProtocolServerSocketHandle::protocol() member
@@ -204,19 +261,15 @@ namespace senf { \section impl_notes Arbitrary Implementation Notes - \li The implementation tries to isolate the library user as much - as possible from the system header files since those headers - define a lot of define symbols and introduce a host of symbols - into the global namespace. This is, why some classes define - their own \c enum types to replace system defined define - constants. This also precludes inlining some functionality. - - \li To reduce overhead, template functions/members which are - more than one-liners are often implemented in terms of a - non-template function/member. This is also used to further the - isolation from system headers as defined above (template code - must always be included into every compilation unit together - with all headers need for the implementation). + \li The implementation tries to isolate the library user as much as possible from the system + header files since those headers define a lot of define symbols and introduce a host of + symbols into the global namespace. This is, why some classes define their own \c enum types + to replace system defined define constants. This also precludes inlining some functionality. + + \li To reduce overhead, template functions/members which are more than one-liners are often + implemented in terms of a non-template function/member. This is also used to further the + isolation from system headers as defined above (template code must always be included into + every compilation unit together with all headers need for the implementation). */ }