Source Services are tools to validate, generate or modify sources in a trustable way. They are designed as smallest possible tools and can be combined following the powerful idea of the classic UNIX design.
Design goals of source services were:
Source Services may be used to validate sources. This can happen per package, which is useful when the packager wants to validate that downloaded sources are really from the original maintainer. Or validation can happen for an entire project to apply general policies. These services can't get skipped in any package
Validation can happen by validating files (for example using the verify_file or source_validator service. These services just fail in the error case which leads to the build state "broken". Or validation can happen by redoing a certain action and store the result as new file as download_files is doing. In this case the newly generated file will be used instead of the committed one during build.
Each service can be used in a special mode defining when it should run and how to use the result. This can be done per package or globally for an entire project.
The default mode of a service is to always run after each commit on the server side and locally before every local build.
The trylocal mode is running the service locally when using current osc versions. The result gets committed as standard files and not named with _service: prefix. Additionally the service runs on the server by default, but usually the service should detect that the result is the same and skip the generated files. In case they differ for any reason (because the webui or api was used for example) they get generated and added on the server.
The localonly mode is running the service locally when using current osc versions. The result gets committed as standard files and not named with _service: prefix. The service is never running on the server side. It is also not possible to trigger it manually.
The disabled mode is neither running the service locally or on the server side. It can be used to temporarily disable the service but keeping the definition as part of the service definition. Or it can be used to define the way how to generate the sources and doing so by manually calling
osc service disabledrun
The result will get committed as standard files again.
The called services are always defined in a _service file. It is either part of the package sources or used project-wide when stored inside the _project package.
The _service file contains a list of services which get called in this order. Each service may define a list of parameters and a mode. The project wide services get called after the per package defined services. The _service file is an xml file like this example:
<services> <service name="download_files" mode="trylocal" /> <service name="verify_file"> <param name="file">krabber-1.0.tar.gz</param> <param name="verifier">sha256</param> <param name="checksum">7f535a96a834b31ba2201a90c4d365990785dead92be02d4cf846713be938b78</param> </service> <service name="update_source" mode="disabled" /> </services>
This example downloads the files via download_files service via the given URLs from the spec file. When using osc this file gets committed as part of the commit. Afterwards the krabber-1.0.tar.gz file will always be compared with the sha256 checksum. And last but not least there is the update_source service mentioned, which is usually not executed. Except when osc service disabledrun is called, which will try to upgrade the package to a newer source version available online.