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[libt2n] / doc / index.doc
1/*! \mainpage libt2n - (talk to neighbor)
2 \section intro_sec Introduction
3 \par
4 libt2n (talk to neighbor) is a C++ library for inter-process communication (IPC \ref notes1 "[1]") with an additional code generator (libt2n-codegen) to make C++ remote procedure calls (RPC \ref notes2 "[2]") simple.
a762a476 5 \htmlonly
3e11fd2c 6 <p><img src="" alt="rpc"/></p>
a762a476 7 \endhtmlonly
8 \par
9 Figure: Remote procedure call overview \ref notes3 "[3]"
10 \par
11 The figure shows an general overview of the steps involved in a remote procedure call. Using libt2n and its code generator only the server procedure implementations have to be written manually. The stubs are generated by the code generator and the inter-process communication routines are provided by libt2n. libt2n provides an abstract interface for
12 \ref libt2n::connection "connections"
c5ca613b 13 hiding the details of the concrete communication mechanism used. At the moment it is implemented for local sockets (a.k.a "Unix domain sockets") and TCP/IP sockets. (\ref libt2n::socket_client_connection, \ref libt2n::socket_server_connection)
14 \par
15 The client procedure stubs provide an interface to the server procedure implementations. To call the server procedure the client stub procedure is called (step 1). The client stub procedure transforms the procedure arguments and signature including the procedure "name" into a sequence of bytes using boost serialization \ref notes6 "[6]". This byte sequence represents a request to call a procedure with those arguments (step 2). Using the communication routines of libt2n the request is sent to the server. (step 3,4). The server procedure stubs de-serialize the request and call the corresponding server procedure using the reconstructed arguments (step 5). The result of the server procedure is serialized and sent back to the client (steps 6,7,8). Finally the result is de-serialized on client side again and returned to the caller. (steps 9,10).
16 \par
17 The input for the code generator is standard C++ code
18 \ref notes4 "[4]"
19 and you mark the procedures you want to expose to other processes. Because the interface is described in C++ directly there is no need for a interface description language (IDL, \ref notes5 "[5]").
b35406fe 20 The code generator is used to create the client and server stubs for the marked procedures. The procedures can be grouped and each group maps to two classes (cmd_group_... and cmd_group_..._client). The cmd_group_..._client class provides the interface to call remote procedures. Each remote procedure maps to a method of this class and the constructor takes a connection object establishing the binding to the remote side. For each group the code generator is called and generates 6 output files: group_common.hxx, group_common.cpp, group_client.hxx, group_client.cpp, group_server.hxx, group_server.cpp. The _common files are used by client and server whereas the _client files contain the client stub code (the cmd_group_..._client class) and the _server files the server stub code.
21 \par
22 To simplify the build process a Makefile snippet is provided that allows to create a server program and a client library (including a corresponding .pc file) using the autotools easily.
23 \section License
24 The libt2n libaray is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License version 2.1 as published by the Free Software Foundation. The code generator (libt2n-codegen) is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
26 \section install_sec Installation
28 \subsection requirements Requirements
3e11fd2c 29 \par libt2n
d321225e 30 - boost <> (serialization <>)
3e11fd2c 31 \par libt2n-codegen
32 - gccxml <>
33 - libxmlpp <>
35 \subsection recommended Recommended
36 - pkg-config <>
3e11fd2c 37 - autotools (autoconf <>, automake, libtool)
39 \subsection Compilation
40 \verbatim
3e11fd2c 41 ./configure && make check && make install
42 \endverbatim
44 \subsection Usage
de51cfa8 45 Take a look at the \ref example.
d321225e 46
47 \subsection References
48 - \anchor notes1
49 [1] inter-process communication (IPC),
50 - \anchor notes2
51 [2] remote procedure call (RPC), and "THE RPC MODEL"
52 - \anchor notes3
53 [3] Figure: Remote procedure call overview,, Jan Newmarch "Web services"
54 - \anchor notes4
55 [4] in fact gccxml is used to parse the C++ code and the XML output of gccxml is used as input for the code generator
56 - \anchor notes5
57 [5] interface description language (IDL),
58 - \anchor notes6
59 [6] boost serialization,
d321225e 60*/
62/*! \page example Usage example
64 In this example we create two packages using the autotools:
65 - server program and client library to connect to the server. The server exports a simple procedure using one group: "t2nexample"
66 - client program using the library
68 \section server Example server program and client library
70 \par The procedure to export (input for the code generator - libt2n-codegen): t2nexample.cpp:
71 First the procedure to export is defined. In this example the procedure throws an exception if the input string is "throw". The exception is passed back to the client transparently. Otherwise some text is appended and returned.
72 \include example1/t2nexample.cpp
74 \par Required includes go into the group header file: t2nexample.hxx:
75 All includes required to get the declarations of the types used by the procedures to export go into the group header file. libt2n uses boost for serialization. This means all types involved in a remote procedure call must be boost serializable. In this example we only use std::string provided by <string> and boost already provides serialization for std::string in the boost/serialization/string.hpp header file.
76 \include example1/t2nexample.hxx
78 \par The server program: server.cpp:
79 We have to provide the main entry point for the server program. In this example we use a local socket and the server program simply waits until a received which then is handled by the generated code directly.
80 \include example1/server.cpp
82 \par Using autoconf and automake to build a example server program and a client library.
83 In the we check for libt2n using the LIBT2N_CHECK m4 macro provided by libt2n.
84 \verbinclude example1/
85 Writing the isn't difficult either. We have to list the command groups used. For each command group we have to list the C++ source files with the procedures to export. For each group we build a client library by listing the generated client code (group_client.cpp) in a corresponding libtool library target. The .pc file for the library is generated automatically. The sources of the server program must include the generated server code (group_server.cpp), the file with the main entry point and of course the procedure definition.
86 \verbinclude example1/
88 \par Build and install the package
89 To build and install the package we first have to create the configure script and the other help scripts of the autotools by running autoreconf.
90 \verbatim
91 autoreconf -f -i && ./configure && make install
92 \endverbatim
94 \section client Client using the library
95 Using the library is as simple as using any other library using pkg-config (the pkg-config .pc file is created automatically by the included Makefile snippet)
96 \par We only have to check that the library is installed
97 \verbinclude example1-client/
98 \par The needs nothing special
99 \verbinclude example1-client/
100 \par The client program: client.cpp:
101 The example client first connects to the local socket. The connection is passed to the constructor of the generated class. To call the remote procedure the "testfunc" method is called. The example first passes "throw" to the remote procedure which will result in a exception to be thrown which is passed back to the client and thrown on the client side again. In the example the exception is caught and it is checked whether the string returned by what() is correct. If so a second remote procedure call is made and its return value is checked. Only if both tests succeed the program will exit with a status value indicating success.
102 \include example1-client/client.cpp
104 \par Build and install the package
105 \verbatim
106 autoreconf -f -i && ./configure && make install
107 \endverbatim
109 \par Test
110 To test whether it works we first start the server that creates a socket 'socket' in the current working directory. Then we run the client and print "ok" if it exited with a status value indicating success.
111 \verbatim
112$ cd /tmp
113$ file socket
114socket: cannot open `socket' (No such file or directory)
115$ libt2n-example1-server &
116[1] 7711
117$ file socket
118socket: socket
119$ libt2n-example1-client && echo ok
121$ kill %1
122$ rm socket
123 \endverbatim