Implement basic varlink API and rhc-server daemon

[mjcr99]

• Card ID: CCT-1753
• Card ID: CCT-1754

Description

Hi team,

This PR implements a preliminary version of the varlink API we will need to communicate with the rhc-server daemon, which is also implemented as a first approach, providing a very basic functionality to test the communication.

Testing

Created a custom package from the branch, using RHEL 10.1, following dependencies are valid to have a working environment:

sudo dnf update -y
sudo dnf install python3 pip go bash-completion nano rpm-build tree -y
python3 -m pip install meson ninja go-vendor-tools
sudo dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-10.noarch.rpm -y
sudo dnf install mock -y

Locate in the repository folder and run:

make srpm
mock -r fedora-43-x86_64 ~/rpmbuild/SRPMS/rhc-*.src.rpm

Install custom package;

sudo dnf install /var/lib/mock/fedora-43-x86_64/result/rhc-0.3.8-1.fc43.x86_64.rpm

We can now, enable the socket

[vagrant@lv-rhel101-1 rhc]$ sudo systemctl enable --now rhc-server.socket
Created symlink '/etc/systemd/system/sockets.target.wants/rhc-server.socket' → '/usr/lib/systemd/system/rhc-server.socket'.

The socket now shows as active, but the rhc-server daemon is not:

[vagrant@lv-rhel101-1 rhc]$ sudo systemctl status rhc-server.socket 
● rhc-server.socket - rhc server socket
     Loaded: loaded (/usr/lib/systemd/system/rhc-server.socket; enabled; preset: disabled)
     Active: active (listening) since Thu 2026-03-05 17:02:26 UTC; 1min 28s ago
 Invocation: f178d69c82594686b376a67eb73dfaa9
   Triggers: ● rhc-server.service
       Docs: https://github.com/RedHatInsights/rhc
     Listen: /run/rhc/com.redhat.rhc (Stream)
     CGroup: /system.slice/rhc-server.socket

Mar 05 17:02:26 lv-rhel101-1 systemd[1]: Listening on rhc-server.socket - rhc server socket.

[vagrant@lv-rhel101-1 rhc]$ sudo systemctl status rhc-server
○ rhc-server.service - rhc server
     Loaded: loaded (/usr/lib/systemd/system/rhc-server.service; disabled; preset: disabled)
     Active: inactive (dead)
TriggeredBy: ● rhc-server.socket
       Docs: https://github.com/RedHatInsights/rhc

Mar 05 16:20:28 lv-rhel101-1 rhc-server[20233]: 2026/03/05 16:20:28 INFO PID lock acquired pid=20233 pidFile=/run/rhc/rhc-server.pid
Mar 05 16:20:28 lv-rhel101-1 rhc-server[20233]: 2026/03/05 16:20:28 INFO Using systemd socket activation address=/run/rhc/com.redha>
Mar 05 16:20:28 lv-rhel101-1 rhc-server[20233]: 2026/03/05 16:20:28 INFO rhc-server starting version=0.3.8
Mar 05 16:20:28 lv-rhel101-1 rhc-server[20233]: 2026/03/05 16:20:28 INFO Listening on socket address=/run/rhc/com.redhat.rhc
Mar 05 17:01:04 lv-rhel101-1 systemd[1]: Stopping rhc-server.service - rhc server...
Mar 05 17:01:04 lv-rhel101-1 rhc-server[20233]: 2026/03/05 17:01:04 INFO Received signal, shutting down gracefully signal=terminated
Mar 05 17:01:04 lv-rhel101-1 rhc-server[20233]: 2026/03/05 17:01:04 INFO rhc-server stopped
Mar 05 17:01:04 lv-rhel101-1 rhc-server[20233]: 2026/03/05 17:01:04 INFO PID lock released
Mar 05 17:01:04 lv-rhel101-1 systemd[1]: rhc-server.service: Deactivated successfully.
Mar 05 17:01:04 lv-rhel101-1 systemd[1]: Stopped rhc-server.service - rhc server.

Then, we can send a request to the socket, the rhc-server will automatically start, we will get a response and the server will keep now listening for other calls:

[vagrant@lv-rhel101-1 rhc]$ varlinkctl call unix:/run/rhc/com.redhat.rhc com.redhat.rhc.internal.Test '{"input": "Helloo!"}'
{
        "output" : "Echo from rhc-server: Helloo!"
}

[vagrant@lv-rhel101-1 rhc]$ sudo systemctl status rhc-server
● rhc-server.service - rhc server
     Loaded: loaded (/usr/lib/systemd/system/rhc-server.service; disabled; preset: disabled)
     Active: active (running) since Thu 2026-03-05 17:04:35 UTC; 1min 18s ago
 Invocation: 7ea42d18d74b4384be2c632b37d7cd1c
TriggeredBy: ● rhc-server.socket
       Docs: https://github.com/RedHatInsights/rhc
   Main PID: 20611 (rhc-server)
      Tasks: 6 (limit: 16770)
     Memory: 3M (peak: 3.7M)
        CPU: 12ms
     CGroup: /system.slice/rhc-server.service
             └─20611 /usr/libexec/rhc/rhc-server

Mar 05 17:04:35 lv-rhel101-1 systemd[1]: Started rhc-server.service - rhc server.
Mar 05 17:04:35 lv-rhel101-1 rhc-server[20611]: 2026/03/05 17:04:35 INFO PID lock acquired pid=20611 pidFile=/run/rhc/rhc-server.pid
Mar 05 17:04:35 lv-rhel101-1 rhc-server[20611]: 2026/03/05 17:04:35 INFO Using systemd socket activation address=/run/rhc/com.redha>
Mar 05 17:04:35 lv-rhel101-1 rhc-server[20611]: 2026/03/05 17:04:35 INFO rhc-server starting version=0.3.8
Mar 05 17:04:35 lv-rhel101-1 rhc-server[20611]: 2026/03/05 17:04:35 INFO Listening on socket address=/run/rhc/com.redhat.rhc

[vagrant@lv-rhel101-1 rhc]$ varlinkctl call unix:/run/rhc/com.redhat.rhc com.redhat.rhc.internal.Test '{"input": "Hello again!"}'
{
        "output" : "Echo from rhc-server: Hello again!"
}

The service can be safely stopped, and the socket remains:

[vagrant@lv-rhel101-1 rhc]$ sudo systemctl stop rhc-server
Stopping 'rhc-server.service', but its triggering units are still active:
rhc-server.socket
[vagrant@lv-rhel101-1 rhc]$ ls /run/rhc
com.redhat.rhc

The socket can be reconnected, and the service will automatically boot as well.

[vagrant@lv-rhel101-1 rhc]$ sudo varlinkctl call unix:/run/rhc/com.redhat.rhc com.redhat.rhc.internal.Test '{"input": "Hello again after stopping service!"}'
{
        "output" : "Echo from rhc-server: Hello again after stopping service!"
}

[pkoprda]

Thanks for the PR, I have left some comments below.

[jirihnidek]

Hi @mjcr99 ,
Thanks for the PR. Please modify Makefile and please add this line to build target:

go build -ldflags "-X main.Version=${VERSION}" -o rhc-server ./cmd/rhc-server

Then the rhc-server will be build, when make is run.

Thanks in advance

[jirihnidek]

Thanks for the PR. I have few comments and request in comments.

I have another request here: could you please add rhc-server.service file and could you please modify rhc.spec file, because your PR contains some code that is not possible test without these changes.

[pkoprda]

Some comments below.

Please also fix the typo in the commit message d367b32 to feat(varlink api): added preliminary varlink API implementation (preliminar -> preliminary) and remove the dot so it would fit the conventional commit format.

[pkoprda]

Can you also write some unit tests?

[jirihnidek]

Thanks for your update. I can confirm that it works as expected and the service is started automatically, when rhc-server.socket is enabled and call the Varlink method using varlinkctl.

However, when I stop the rhc-server.service using systemctl stop rhc-server.service, then something deletes the /run/rhc directory including socket file and then it is not possible to call varlink method again, because the socket service does not have the socket file and it cannot trigger the rhc-server.service. Maybe, there is something wrong in service configuration or some function in rhc-server has side-effect and it deletes this directory.

[jirihnidek]

👍

[pkoprda]

Looks good from my side, I will let @jirihnidek and @m-horky finalize the review :)