2 =======================================
12 =======================================
13 This application provides means to check the availability of remote hosts
14 through pings to them.
18 ---------------------------------------
19 The application uses ICMP echo requests messages to verify if a given host
22 The host's address can be an IP or a DNS.
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27 There are many ways to invoke the application, the simplest is just type:
29 which uses the configuration values from the configuration file (describled in
30 the Configuration File section).
34 ---------------------------------------
35 Further information about the problem domain can be found in the References
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41 All rights reserved to Intra2net AG.
46 =======================================
47 This section describes the code conventions that must be followed when maintain
52 ---------------------------------------
53 This section is a guideline about the type you MUST use when declaring
54 variables and constants. These types were chose to provide portability and
55 improve code reradability.
57 - Use the std::string to represent array of characters.
59 - Use int32_t, int16_t and int8_t (or their unsigned couter parts) - instead of
60 int, short and char, respectively - when the variable or constant MUST have a
61 specific size (e.g. like in the protocol headers). This documents that the
62 variable has the given number of bits. This states clear the intent of the
63 original programmer and avoids improper modifications.
65 - Use only int for regular integer numbers that do not require any specific
66 size. And document that a variable is non-negative using assertions. Do not
67 use unsigned types to say a number will never be negative.
69 - Use std::size_t for integers that represent sizes of vectors, objects or
70 buffers. Thus leaving the size difinition to the platform.
74 ---------------------------------------
75 The coding style used in this program is in accordance with the Intra2net,
76 which can be found in the following source:
78 - http://intranet/support_wiki/doku.php?id=entwicklung:codingstyle
82 ---------------------------------------
83 Version is built as follows:
84 major.minor[-[a|b|rc]]
86 - major represents big changes in application functionality.
87 - minor means small changes of bug fixes.
88 - a, b and rc stand for Alpha, Beta and Release Candidate respectivelly. Though
89 they are optional and not required in public release.
93 ---------------------------------------
94 There are two basic kinds of errors that shall happen in the program, errors
95 that the program can recover (expected) and errors that the progam can not or
96 should not recover from (exceptional errors). Bellow the description and the
97 method adopted to deal with each one:
98 - Expected: these errors can occur and must be handled by boolean return values.
99 (i.e. if a host is down, if the address was not resolved). This errors can
100 happen, but THE PROGRAM MUST CONTINUE TO OPERATE EVEN IF THEY HAPPEN.
101 - Exceptional: these are the kinds of errors that should not occur. They must be
102 handled by exceptions and THE PROGRAM MUST HALT IF THEY HAPPEN.
103 Thus, to keep things as simple as possible, this program adopts just two kinds
104 of error detection and handling:
105 - Return Boolean Value for expected errors and
106 - Handle Exceptions for exceptional errors.
110 ---------------------------------------
111 Also, it is good to use ASSERTS to document assumptions about:
112 - method's argument values. If you expect that a parameter have certain values,
113 assert it (preconditions)
114 - and if you expect the method deliver a certain value, assert in the end of
115 the method (postcondition).
116 This is known by programming by contract.
121 =======================================
122 In this section is presented an overview of the source code and key design
126 3.1. Main directories
127 ---------------------------------------
128 The sources are spread over these distincts directories:
129 - src: contains the main application.
130 - test: where is located the unit tests.
131 - conf: keeps default and example configuration files.
134 3.2. Main concept of application operation
135 ---------------------------------------
136 This application makes extensive use of asynchronous timers-handlers from
137 Boost ASIO. So this section describes briefly how ASIO works. More information
138 can be found in the References section.
140 The basic idea is to have a handler which will be called when a timer expires.
141 After the timer expires, you have to schedule the timer again to call your
142 handler once more. Given the declaration of the timer:
144 boost::asio::deadline_timer my_timer( my_io_service );
146 you must specify when it will expire:
148 my_timer.expires_at( some_time_in_seconds + seconds( interval_in_seconds ) );
150 and which method will handle when the timer expires.
152 my_timer.async_wait( boost::bind( &MyClass::my_handle_method, this ) );
154 Then, the my_io_service service can be called to perform a loop:
160 4. Configuration file
161 =======================================
162 In this section are describled the configuration items, along with they
163 possible values and meanings. This section is organized in each major
168 ---------------------------------------
169 This configurations are shared among and affect all the hosts.
170 - limit-hosts-down: an absolute number, which ranges from 0 to the number of
171 hosts available. This value represents the minimum number of hosts that have
172 to fail (i.e. do not reply to the ping) in order to alert any external system.
173 - limit-ping-fail: percentage of pings to a host that can fail. If the
174 percentage of failed pings to a host exceed this number, then the host is
179 ---------------------------------------
180 - address: the DNS or IP of the host to ping. Take in consideration that, if a
181 DNS is given, the application pings all IPs in the look up table, however, if
182 IP is provide, it is the only which will be pinged.
187 =======================================
188 [1] http://tools.ietf.org/html/rfc792
189 [2] http://en.wikipedia.org/wiki/Ping
190 [3] http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol
191 [4] http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio.html
192 [5] http://www.boost.org/doc/libs/1_45_0/doc/html/program_options.html