feat: rework client to only allow a single provider

.github/workflows/ci.yaml

@@ -19,6 +19,10 @@ on:
     branches:
       - main
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   inclusive-naming-check:
     name: Inclusive naming check

charmcraft.yaml

@@ -25,8 +25,6 @@ parts:
     build-snaps:
       - astral-uv
     charm-requirements: ["requirements.txt"]
-    charm-binary-python-packages:
-      - rpds_py ~= 0.22.3
     override-build: |
       just requirements
       craftctl default
@@ -42,32 +40,33 @@ subordinate: true
 requires:
   filesystem:
     interface: filesystem_info
+    limit: 1
   juju-info:
     interface: juju-info
     scope: container
 
 config:
   options:
-    mounts:
-      default: "{}"
+    mountpoint:
+      description: Location to mount the filesystem on the machine.
       type: string
+    noexec:
+      default: false
       description: |
-        Information to mount filesystems on the machine. This is specified as a JSON object string.
-        Example usage:
-          ```bash
-          $ juju config filesystem-client \
-              mounts=<<EOF
-                {
-                  "cephfs": {
-                    "mountpoint": "/scratch",
-                    "noexec": true
-                  },
-                  "nfs": {
-                    "mountpoint": "/data",
-                    "nosuid": true,
-                    "nodev": true,
-                    "read-only": true,
-                  }
-                }
-              EOF
-          ```
+        Block execution of binaries on the filesystem.
+      type: boolean
+    nosuid:
+      default: false
+      description: |
+        Do not honor suid and sgid bits on the filesystem.
+      type: boolean
+    nodev:
+      default: false
+      description: |
+        Blocking interpretation of character and/or block
+        devices on the filesystem.
+      type: boolean
+    read-only:
+      default: false
+      description: Mount filesystem as read-only.
+      type: boolean

lib/charms/filesystem_client/v0/filesystem_info.py

@@ -582,16 +582,14 @@ class FilesystemRequires(_BaseInterface):
     def __init__(self, charm: CharmBase, relation_name: str) -> None:
         super().__init__(charm, relation_name)
         self.framework.observe(charm.on[relation_name].relation_changed, self._on_relation_changed)
-        self.framework.observe(
-            charm.on[relation_name].relation_departed, self._on_relation_departed
-        )
+        self.framework.observe(charm.on[relation_name].relation_broken, self._on_relation_broken)
 
     def _on_relation_changed(self, event: RelationChangedEvent) -> None:
         """Handle when the databag between client and server has been updated."""
         _logger.debug("emitting `MountFilesystem` event from `RelationChanged` hook")
         self.on.mount_filesystem.emit(event.relation, app=event.app, unit=event.unit)
 
-    def _on_relation_departed(self, event: RelationDepartedEvent) -> None:
+    def _on_relation_broken(self, event: RelationDepartedEvent) -> None:
         """Handle when server departs integration."""
         _logger.debug("emitting `UmountFilesystem` event from `RelationDeparted` hook")
         self.on.umount_filesystem.emit(event.relation, app=event.app, unit=event.unit)

pyproject.toml

@@ -3,9 +3,7 @@ name = "filesystem-client"
 version = "0.0"
 requires-python = "==3.12.*"
 dependencies = [
-    "ops ~= 2.8",
-    "jsonschema ~= 4.23.0",
-    "rpds_py ~= 0.22.3"
+    "ops ~= 2.8"
 ]
 
 [project.optional-dependencies]

src/charm.py

@@ -4,42 +4,40 @@
 
 """Charm for the filesystem client."""
 
-import json
 import logging
-from collections import Counter
+from dataclasses import dataclass
 
 import ops
 from charms.filesystem_client.v0.filesystem_info import FilesystemRequires
-from jsonschema import ValidationError, validate
 
 from utils.manager import MountsManager
 
-logger = logging.getLogger(__name__)
-
-CONFIG_SCHEMA = {
-    "$schema": "http://json-schema.org/draft-04/schema#",
-    "type": "object",
-    "additionalProperties": {
-        "type": "object",
-        "required": ["mountpoint"],
-        "properties": {
-            "mountpoint": {"type": "string"},
-            "noexec": {"type": "boolean"},
-            "nosuid": {"type": "boolean"},
-            "nodev": {"type": "boolean"},
-            "read-only": {"type": "boolean"},
-        },
-    },
-}
+_logger = logging.getLogger(__name__)
 
 
 class StopCharmError(Exception):
     """Exception raised when a method needs to finish the execution of the charm code."""
 
-    def __init__(self, status: ops.StatusBase):
+    def __init__(self, status: ops.StatusBase) -> None:
         self.status = status
 
 
+@dataclass(frozen=True)
+class CharmConfig:
+    """Configuration for the charm."""
+
+    mountpoint: str
+    """Location to mount the filesystem on the machine."""
+    noexec: bool
+    """Block execution of binaries on the filesystem."""
+    nosuid: bool
+    """Do not honour suid and sgid bits on the filesystem."""
+    nodev: bool
+    """Blocking interpretation of character and/or block."""
+    read_only: bool
+    """Mount filesystem as read-only."""
+
+
 # Trying to use a delta charm (one method per event) proved to be a bit unwieldy, since
 # we would have to handle multiple updates at once:
 # - mount requests
@@ -51,11 +49,11 @@ def __init__(self, status: ops.StatusBase):
 # mount requests.
 #
 # A holistic charm (one method for all events) was a lot easier to deal with,
-# simplifying the code to handle all the multiple relations.
+# simplifying the code to handle all the events.
 class FilesystemClientCharm(ops.CharmBase):
     """Charm the application."""
 
-    def __init__(self, framework: ops.Framework):
+    def __init__(self, framework: ops.Framework) -> None:
         super().__init__(framework)
 
         self._filesystems = FilesystemRequires(self, "filesystem")
@@ -66,71 +64,66 @@ def __init__(self, framework: ops.Framework):
         framework.observe(self._filesystems.on.mount_filesystem, self._handle_event)
         framework.observe(self._filesystems.on.umount_filesystem, self._handle_event)
 
-    def _handle_event(self, event: ops.EventBase) -> None:  # noqa: C901
+    def _handle_event(self, event: ops.EventBase) -> None:
+        """Handle a Juju event."""
         try:
             self.unit.status = ops.MaintenanceStatus("Updating status.")
 
+            # CephFS is not supported on LXD containers.
+            if not self._mounts_manager.supported():
+                self.unit.status = ops.BlockedStatus("Cannot mount filesystems on LXD containers.")
+                return
+
             self._ensure_installed()
             config = self._get_config()
             self._mount_filesystems(config)
         except StopCharmError as e:
             # This was the cleanest way to ensure the inner methods can still return prematurely
             # when an error occurs.
-            self.app.status = e.status
+            self.unit.status = e.status
             return
 
-        self.unit.status = ops.ActiveStatus("Mounted filesystems.")
+        self.unit.status = ops.ActiveStatus(f"Mounted filesystem at `{config.mountpoint}`.")
 
-    def _ensure_installed(self):
+    def _ensure_installed(self) -> None:
         """Ensure the required packages are installed into the unit."""
         if not self._mounts_manager.installed:
             self.unit.status = ops.MaintenanceStatus("Installing required packages.")
             self._mounts_manager.install()
 
-    def _get_config(self) -> dict[str, dict[str, str | bool]]:
+    def _get_config(self) -> CharmConfig:
         """Get and validate the configuration of the charm."""
-        try:
-            config = json.loads(str(self.config.get("mounts", "")))
-            validate(config, CONFIG_SCHEMA)
-            config: dict[str, dict[str, str | bool]] = config
-            for fs, opts in config.items():
-                for opt in ["noexec", "nosuid", "nodev", "read-only"]:
-                    opts[opt] = opts.get(opt, False)
-            return config
-        except (json.JSONDecodeError, ValidationError) as e:
+        if not (mountpoint := self.config.get("mountpoint")):
+            raise StopCharmError(ops.BlockedStatus("Missing `mountpoint` in config."))
+
+        return CharmConfig(
+            mountpoint=str(mountpoint),
+            noexec=bool(self.config.get("noexec")),
+            nosuid=bool(self.config.get("nosuid")),
+            nodev=bool(self.config.get("nodev")),
+            read_only=bool(self.config.get("read-only")),
+        )
+
+    def _mount_filesystems(self, config: CharmConfig) -> None:
+        """Mount the filesystem for the charm."""
+        endpoints = self._filesystems.endpoints
+        if not endpoints:
             raise StopCharmError(
-                ops.BlockedStatus(f"invalid configuration for option `mounts`. reason:\n{e}")
+                ops.BlockedStatus("Waiting for an integration with a filesystem provider.")
             )
 
-    def _mount_filesystems(self, config: dict[str, dict[str, str | bool]]):
-        """Mount all available filesystems for the charm."""
-        endpoints = self._filesystems.endpoints
-        for fs_type, count in Counter(
-            [endpoint.info.filesystem_type() for endpoint in endpoints]
-        ).items():
-            if count > 1:
-                raise StopCharmError(
-                    ops.BlockedStatus(f"Too many relations for mount type `{fs_type}`.")
-                )
+        # This is limited to 1 relation.
+        endpoint = endpoints[0]
 
-        self.unit.status = ops.MaintenanceStatus("Ensuring filesystems are mounted.")
+        self.unit.status = ops.MaintenanceStatus("Mounting filesystem.")
 
         with self._mounts_manager.mounts() as mounts:
-            for endpoint in endpoints:
-                fs_type = endpoint.info.filesystem_type()
-                if not (options := config.get(fs_type)):
-                    raise StopCharmError(
-                        ops.BlockedStatus(f"Missing configuration for mount type `{fs_type}`.")
-                    )
-
-                mountpoint = str(options["mountpoint"])
-
-                opts = []
-                opts.append("noexec" if options.get("noexec") else "exec")
-                opts.append("nosuid" if options.get("nosuid") else "suid")
-                opts.append("nodev" if options.get("nodev") else "dev")
-                opts.append("ro" if options.get("read-only") else "rw")
-                mounts.add(info=endpoint.info, mountpoint=mountpoint, options=opts)
+            opts = []
+            opts.append("noexec" if config.noexec else "exec")
+            opts.append("nosuid" if config.nosuid else "suid")
+            opts.append("nodev" if config.nodev else "dev")
+            opts.append("ro" if config.read_only else "rw")
+            mounts.add(info=endpoint.info, mountpoint=config.mountpoint, options=opts)
 
 
 if __name__ == "__main__":  # pragma: nocover