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<h1>8 External Configuration Data</h1>
<a name="top"></a>
<h3><a name="id77631">8.1
General</a></h3>
<p>To avoid hard coding data values related to the test and/or SUT (System
Under Test) in the test suites, the data may instead be specified by means
of configuration files or strings that Common Test reads before
the start of a test run. External configuration data makes it possible to
change test properties without having to modify the actual test suites
using the data. Examples of configuration data:</p>
<ul>
<li>Addresses to the test plant or other instruments</li>
<li>User login information</li>
<li>Names of files needed by the test</li>
<li>Names of programs that should be executed during the test</li>
<li>Any other variable needed by the test</li>
</ul>
<h3><a name="id77671">8.2
Syntax</a></h3>
<p>A configuration file can contain any number of elements of the type:</p>
<div class="example"><pre>
{CfgVarName,Value}.</pre></div>
<p>where</p>
<div class="example"><pre>
CfgVarName = atom()
Value = term() | [{CfgVarName,Value}]</pre></div>
<h3><a name="id77695">8.3
Requiring and reading configuration data</a></h3>
<a name="require_config_data"></a>
<p>In a test suite, one must <strong>require</strong> that a configuration
variable (<span class="code">CfgVarName</span> in the definition above) exists before
attempting to read the associated value in a test case or config function.</p>
<p><span class="code">require</span> is an assert statement that can be part of the <span class="bold_code"><a href="write_test_chapter.html#suite">test suite info function</a></span> or
<span class="bold_code"><a href="write_test_chapter.html#info_function">test case info
function</a></span>. If the required variable is not available, the
test is skipped (unless a default value has been specified, see the
<span class="bold_code"><a href="write_test_chapter.html#info_function">test case info
function</a></span> chapter for details). There is also a function
<span class="code"><span class="bold_code"><a href="ct.html#require-1">ct:require/1/2</a></span></span> which can be called from a test case
in order to check if a specific variable is available. The return
value from this function must be checked explicitly and appropriate
action be taken depending on the result (e.g. to skip the test case
if the variable in question doesn't exist).</p>
<p>A <span class="code">require</span> statement in the test suite info- or test case
info-list should look like this:
<span class="code">{require,CfgVarName}</span> or <span class="code">{require,AliasName,CfgVarName}</span>.
The arguments <span class="code">AliasName</span> and <span class="code">CfgVarName</span> are the same as the
arguments to <span class="code"><span class="bold_code"><a href="ct.html#require-1">ct:require/1/2</a></span></span> which are described in the
reference manual for <span class="bold_code"><a href="ct.html">ct</a></span>.
<span class="code">AliasName</span> becomes an alias for the configuration variable,
and can be used as reference to the configuration data value.
The configuration variable may be associated with an
arbitrary number of alias names, but each name must be unique within
the same test suite. There are two main uses for alias names:</p>
<ul>
<li>They may be introduced to identify connections (see below).</li>
<li>They may used to help adapt configuration data to a test suite
(or test case) and improve readability.</li>
</ul>
<p>To read the value of a config variable, use the function
<span class="code"><span class="bold_code"><a href="ct.html#get_config-1">get_config/1/2/3</a></span></span>
which is also described in the reference
manual for <span class="bold_code"><a href="ct.html">ct</a></span>.</p>
<p>Example:</p>
<div class="example"><pre>
suite() ->
[{require, domain, 'CONN_SPEC_DNS_SUFFIX'}].
...
testcase(Config) ->
Domain = ct:get_config(domain),
...</pre></div>
<h3><a name="id77839">8.4
Using configuration variables defined in multiple files</a></h3>
<p>If a configuration variable is defined in multiple files and you
want to access all possible values, you may use the <span class="code"><span class="bold_code"><a href="ct.html#get_config-3">ct:get_config/3</a></span></span>
function and specify <span class="code">all</span> in the options list. The values will then
be returned in a list and the order of the elements corresponds to the order
that the config files were specified at startup. Please see
the <span class="bold_code"><a href="ct.html">ct</a></span> reference manual for details.</p>
<h3><a name="id77870">8.5
Encrypted configuration files</a></h3>
<a name="encrypted_config_files"></a>
<p>It is possible to encrypt configuration files containing sensitive data
if these files must be stored in open and shared directories.</p>
<p>Call <span class="code"><span class="bold_code"><a href="ct.html#encrypt_config_file-2">ct:encrypt_config_file/2/3</a></span></span> to have Common Test encrypt a
specified file using the DES3 function in the OTP <span class="code">crypto</span> application.
The encrypted file can then be used as a regular configuration file,
in combination with other encrypted files or normal text files. The key
for decrypting the configuration file must be provided when running the test,
however. This can be done by means of the <span class="code">decrypt_key</span> or
<span class="code">decrypt_file</span> flag/option, or a key file in a predefined location.</p>
<p>Common Test also provides decryption functions,
<span class="code"><span class="bold_code"><a href="ct.html#decrypt_config_file-2">ct:decrypt_config_file/2/3</a></span></span>, for recreating the original text
files.</p>
<p>Please see the <span class="bold_code"><a href="ct.html">ct</a></span> reference manual for
more information.</p>
<h3><a name="id77934">8.6
Opening connections by using configuration data</a></h3>
<p>There are two different methods for opening a connection
by means of the support functions in e.g. <span class="code"><span class="bold_code"><a href="ct_ssh.html">ct_ssh</a></span></span>, <span class="code"><span class="bold_code"><a href="ct_ftp.html">ct_ftp</a></span></span>,
and <span class="code"><span class="bold_code"><a href="ct_telnet.html">ct_telnet</a></span></span>:</p>
<ul>
<li>Using a configuration target name (an alias) as reference.</li>
<li>Using the configuration variable as reference.</li>
</ul>
<p>When a target name is used for referencing the configuration data
(that specifies the connection to be opened), the same name may be used
as connection identity in all subsequent calls related to the connection
(also for closing it). It's only possible to have one open connection
per target name. If attempting to open a new connection using a name
already associated with an open connection, Common Test will
return the already existing handle so that the previously opened connection
will be used. This is a practical feature since it makes it possible to
call the function for opening a particular connection whenever
useful. An action like this will not necessarily open any new
connections unless it's required (which could be the case if e.g. the
previous connection has been closed unexpectedly by the server).
Another benefit of using named connections is that it's not
necessary to pass handle references around in the suite for these
connections.
</p>
<p>When a configuration variable name is used as reference to the data
specifying the connection, the handle returned as a result of opening
the connection must be used in all subsequent calls (also for closing
the connection). Repeated calls to the open function with the same
variable name as reference will result in multiple connections
being opened. This can be useful e.g. if a test case needs to open
multiple connections to the same server on the target node (using the
same configuration data for each connection).
</p>
<h3><a name="id78002">8.7
User specific configuration data formats</a></h3>
<p>It is possible for the user to specify configuration data on a
different format than key-value tuples in a text file, as described
so far. The data can e.g. be read from arbitrary files, fetched from
the web over http, or requested from a user specific process.
To support this, Common Test provides a callback module plugin
mechanism to handle configuration data.</p>
<h4>Default callback modules for handling configuration data</h4>
<p>The Common Test application includes default callback modules
for handling configuration data specified in standard config files
(see above) and in xml files:</p>
<ul>
<li>
<span class="code">ct_config_plain</span> - for reading configuration files with
key-value tuples (standard format). This handler will be used to
parse configuration files if no user callback is specified.
</li>
<li>
<span class="code">ct_config_xml</span> - for reading configuration data from XML
files.
</li>
</ul>
<h4>Using XML configuration files</h4>
<p>This is an example of an XML configuration file:</p>
<div class="example"><pre>
<config>
<ftp_host>
<ftp>"targethost"</ftp>
<username>"tester"</username>
<password>"letmein"</password>
</ftp_host>
<lm_directory>"/test/loadmodules"</lm_directory>
</config></pre></div>
<p>This configuration file, once read, will produce the same configuration
variables as the following text file:</p>
<div class="example"><pre>
{ftp_host, [{ftp,"targethost"},
{username,"tester"},
{password,"letmein"}]}.
{lm_directory, "/test/loadmodules"}.</pre></div>
<h4>How to implement a user specific handler</h4>
<p>The user specific handler can be written to handle special
configuration file formats. The parameter can be either file
name(s) or configuration string(s) (the empty list is valid).</p>
<p>The callback module implementing the handler is responsible for
checking correctness of configuration strings.</p>
<p>To perform validation of the configuration strings, the callback module
should have the following function exported:</p>
<p><span class="code">Callback:check_parameter/1</span></p>
<p>The input argument will be passed from Common Test, as defined in the test
specification or given as an option to <span class="code">ct_run</span> or <span class="code">ct:run_test</span>.</p>
<p>The return value should be any of the following values indicating if given
configuration parameter is valid:</p>
<ul>
<li>
<span class="code">{ok, {file, FileName}}</span> - parameter is a file name and
the file exists,
</li>
<li>
<span class="code">{ok, {config, ConfigString}}</span> - parameter is a config string
and it is correct,
</li>
<li>
<span class="code">{error, {nofile, FileName}}</span> - there is no file with the given
name in the current directory,
</li>
<li>
<span class="code">{error, {wrong_config, ConfigString}}</span> - the configuration string
is wrong.
</li>
</ul>
<p>To perform reading of configuration data - initially before the tests
start, or as a result of data being reloaded during test execution -
the following function should be exported from the callback module:</p>
<p><span class="code">Callback:read_config/1</span></p>
<p>The input argument is the same as for the <span class="code">check_parameter/1</span> function.</p>
<p>The return value should be either:</p>
<ul>
<li>
<span class="code">{ok, Config}</span> - if the configuration variables are read successfully,
</li>
<li>
<span class="code">{error, {Error, ErrorDetails}}</span> - if the callback module fails to
proceed with the given configuration parameters.
</li>
</ul>
<p><span class="code">Config</span> is the proper Erlang key-value list, with possible
key-value sublists as values, like for the configuration file
example above:</p>
<div class="example"><pre>
[{ftp_host, [{ftp, "targethost"}, {username, "tester"}, {password, "letmein"}]},
{lm_directory, "/test/loadmodules"}]</pre></div>
<h3><a name="id78216">8.8
Examples of configuration data handling</a></h3>
<p>A config file for using the FTP client to access files on a remote
host could look like this:</p>
<div class="example"><pre>
{ftp_host, [{ftp,"targethost"},
{username,"tester"},
{password,"letmein"}]}.
{lm_directory, "/test/loadmodules"}.</pre></div>
<p>The XML version shown in the chapter above can also be used, but it should be
explicitly specified that the <span class="code">ct_config_xml</span> callback module is to be
used by Common Test.</p>
<p>Example of how to assert that the configuration data is available and
use it for an FTP session:</p>
<div class="example"><pre>
init_per_testcase(ftptest, Config) ->
{ok,_} = ct_ftp:open(ftp),
Config.
end_per_testcase(ftptest, _Config) ->
ct_ftp:close(ftp).
ftptest() ->
[{require,ftp,ftp_host},
{require,lm_directory}].
ftptest(Config) ->
Remote = filename:join(ct:get_config(lm_directory), "loadmodX"),
Local = filename:join(?config(priv_dir,Config), "loadmodule"),
ok = ct_ftp:recv(ftp, Remote, Local),
...</pre></div>
<p>An example of how the above functions could be rewritten
if necessary to open multiple connections to the FTP server:</p>
<div class="example"><pre>
init_per_testcase(ftptest, Config) ->
{ok,Handle1} = ct_ftp:open(ftp_host),
{ok,Handle2} = ct_ftp:open(ftp_host),
[{ftp_handles,[Handle1,Handle2]} | Config].
end_per_testcase(ftptest, Config) ->
lists:foreach(fun(Handle) -> ct_ftp:close(Handle) end,
?config(ftp_handles,Config)).
ftptest() ->
[{require,ftp_host},
{require,lm_directory}].
ftptest(Config) ->
Remote = filename:join(ct:get_config(lm_directory), "loadmodX"),
Local = filename:join(?config(priv_dir,Config), "loadmodule"),
[Handle | MoreHandles] = ?config(ftp_handles,Config),
ok = ct_ftp:recv(Handle, Remote, Local),
...</pre></div>
<h3><a name="id78268">8.9
Example of user specific configuration handler</a></h3>
<p>A simple configuration handling driver which will ask an external server for
configuration data can be implemented this way:</p>
<div class="example"><pre>
-module(config_driver).
-export([read_config/1, check_parameter/1]).
read_config(ServerName)->
ServerModule = list_to_atom(ServerName),
ServerModule:start(),
ServerModule:get_config().
check_parameter(ServerName)->
ServerModule = list_to_atom(ServerName),
case code:is_loaded(ServerModule) of
{file, _}->
{ok, {config, ServerName}};
false->
case code:load_file(ServerModule) of
{module, ServerModule}->
{ok, {config, ServerName}};
{error, nofile}->
{error, {wrong_config, "File not found: " ++ ServerName ++ ".beam"}}
end
end.</pre></div>
<p>The configuration string for this driver may be "config_server", if the
config_server.erl module below is compiled and exists in the code path
during test execution:</p>
<div class="example"><pre>
-module(config_server).
-export([start/0, stop/0, init/1, get_config/0, loop/0]).
-define(REGISTERED_NAME, ct_test_config_server).
start()->
case whereis(?REGISTERED_NAME) of
undefined->
spawn(?MODULE, init, [?REGISTERED_NAME]),
wait();
_Pid->
ok
end,
?REGISTERED_NAME.
init(Name)->
register(Name, self()),
loop().
get_config()->
call(self(), get_config).
stop()->
call(self(), stop).
call(Client, Request)->
case whereis(?REGISTERED_NAME) of
undefined->
{error, {not_started, Request}};
Pid->
Pid ! {Client, Request},
receive
Reply->
{ok, Reply}
after 4000->
{error, {timeout, Request}}
end
end.
loop()->
receive
{Pid, stop}->
Pid ! ok;
{Pid, get_config}->
{D,T} = erlang:localtime(),
Pid !
[{localtime, [{date, D}, {time, T}]},
{node, erlang:node()},
{now, erlang:now()},
{config_server_pid, self()},
{config_server_vsn, ?vsn}],
?MODULE:loop()
end.
wait()->
case whereis(?REGISTERED_NAME) of
undefined->
wait();
_Pid->
ok
end.</pre></div>
<p>In this example, the handler also provides the ability to dynamically reload
configuration variables. If <span class="code">ct:reload_config(localtime)</span> is called from
the test case function, all variables loaded with <span class="code">config_driver:read_config/1</span>
will be updated with their latest values, and the new value for variable
<span class="code">localtime</span> will be returned.</p>
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