Add support for XML environmental variables parsing [10697]

[mauropasse]

This commit would allow to use OS environmental variables in XML profiles. For example:

# In bash terminal
export ROBOT_IP_ADDRESS=192.168.0.1

# In XML profile
<?xml version="1.0" encoding="UTF-8" ?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <participant profile_name="env_var_parsing_example">
        <rtps>
            <builtin>
                <initialPeersList>
                    <locator>
                        <udpv4>
                            <address>ROBOT_IP_ADDRESS</address>
                        </udpv4>
                    </locator>
                </initialPeersList>
            </builtin>
        </rtps>
    </participant>
</profiles>

[richiware]

Build status:

• Linux
• Linux aarch64
• Mac
• Windows

[irobot-ros]

Hi, sorry for resurrecting this old PR.
Is there anything that is preventing it to be merged?

[MiguelCompany]

@irobot-ros Just that we did not have time to review it. Will do it now.

[MiguelCompany]

Even though this is a nice-to-have feature, it cannot be merged as-is.

First, it is only adding the possibility to use an environmental variable on pure string values. I think we should replace every tinyxml2::XMLElement::GetText method call with a call to an auxiliary method receiving a tinyxml2::XMLElement* and returning a const char*, that will be the one performing the environmental variable access.

Methods XMLParser::getXMLInt, XMLParser::getXMLUint, and XMLParser::getXMLBool should also include environmental variable support.

I also think that using a special character (like $) to clearly indicate the environmental variable should be used is desirable.

Using method std::getenv gives a warning on Windows about that method being unsafe.

Finally, adding this new feature should add tests and documentation for it. I suggest extending the unit tests on this file, and adding the corresponding PR to the documentation repo

[JLBuenoLopez]

Hi @irobot-ros,

The base branch for this PR (2.0.x) is becoming EOL (end of life) this very month (see release support document). This is not going to be merged into this branch because there is still work pending. If you want to keep this PR open, you can change the base branch to one of the branches still alive and rebase it: 2.1.x used in ROS 2 Foxy, 2.3.x used in ROS 2 Galactic, or directly to master.

Sorry for the inconvenience!

[alsora]

Sure, sorry for keeping this PR open for so long but we didn't have time to fully implement it as requested.
Will close this PR.

[JLBuenoLopez]

I am closing this PR, though the feature is something which will be interesting to have in Fast DDS. I have opened #3377 to keep track of this feature. Also, this PR is targeting a branch that is no longer alive. A PR targeting master with this feature can be opened in the future.

[mauropasse]

#3841
This PR should add support for this feature