Adds run_once_command rock build option

rockcraft/models/project.py

@@ -257,6 +257,7 @@ class Project(BuildPlanner, BaseProject):  # type: ignore[misc]
     services: dict[str, Service] | None = None
     checks: dict[str, Check] | None = None
     entrypoint_service: str | None = None
+    run_once_command: str | None = None
     platforms: dict[str, Platform | None]  # type: ignore[assignment]
 
     model_config = pydantic.ConfigDict(
@@ -388,6 +389,29 @@ def _validate_entrypoint_service(
 
         return entrypoint_service
 
+    @pydantic.field_validator("run_once_command")
+    @classmethod
+    def _validate_run_once_command(
+        cls, run_once_command: str | None, info: pydantic.ValidationInfo
+    ) -> str | None:
+        """Verify that the entrypoint-service or the services dict are not set."""
+        if not run_once_command:
+            return run_once_command
+
+        craft_cli.emit.message(
+            "Warning: defining a run-once-command will result in a rock with an "
+            "atypical OCI Entrypoint. While that might be acceptable for testing and "
+            "personal use, it shall require prior approval before submitting to a "
+            "Canonical registry namespace."
+        )
+
+        if info.data.get("entrypoint-service") or info.data.get("services"):
+            raise ValueError(
+                "Cannot have run-once-command and entrypoint-service / services at the same time."
+            )
+
+        return run_once_command
+
     @pydantic.field_validator("environment")
     @classmethod
     def _forbid_env_var_bash_interpolation(

rockcraft/oci.py

@@ -354,6 +354,17 @@ def set_default_user(self, user: str) -> None:
         _config_image(image_path, params)
         emit.progress(f"Default user set to {user}")
 
+    def set_run_once_entrypoint(self, command: str) -> None:
+        """Set the OCI image entrypoint to the given command."""
+        emit.progress("Configuring entrypoint...")
+        image_path = self.path / self.image_name
+        params = ["--clear=config.entrypoint"]
+        for entry in shlex.split(command):
+            params.extend(["--config.entrypoint", entry])
+        params.extend(["--clear=config.cmd"])
+        _config_image(image_path, params)
+        emit.progress(f"Entrypoint set to {command}")
+
     def set_entrypoint(self, entrypoint_service: str | None, build_base: str) -> None:
         """Set the OCI image entrypoint. It is always Pebble."""
         emit.progress("Configuring entrypoint...")

rockcraft/services/package.py

@@ -149,13 +149,16 @@ def _pack(
         emit.progress(f"Setting the default OCI user to be {project.run_user}")
         new_image.set_default_user(project.run_user)
 
-    emit.progress("Adding Pebble entrypoint")
-
-    new_image.set_entrypoint(
-        project.entrypoint_service, project.build_base or project.base
-    )
-    if project.services and project.entrypoint_service in project.services:
-        new_image.set_cmd(project.services[project.entrypoint_service].command)
+    if project.run_once_command:
+        emit.progress("Adding run-once-command entrypoint")
+        new_image.set_run_once_entrypoint(project.run_once_command)
+    else:
+        emit.progress("Adding Pebble entrypoint")
+        new_image.set_entrypoint(
+            project.entrypoint_service, project.build_base or project.base
+        )
+        if project.services and project.entrypoint_service in project.services:
+            new_image.set_cmd(project.services[project.entrypoint_service].command)
 
     new_image.set_default_path(project.base)