Merge ~cjwatson/charm-clamav-database-mirror:initial into charm-clamav-database-mirror:main

[Colin Watson]

Add new charm

Much of the project skeleton came from `charmcraft init --profile machine`.

`lib/charms/operator_libs_linux/v0/apt.py` is maintained by the `update-lib` script; the convention for operator charms is to vendor these files.

I considered using either the existing `apache2` charm or the existing `nginx` charm. However, `apache2` currently only works up to focal, and the `clamav-cvdupdate` package is only available starting from jammy; while the `nginx` charm doesn't allow deploying a site as a subordinate, which makes it rather cumbersome to use here. Since it's fairly trivial to handle installing `nginx` directly, I just went with that.

The test suite doesn't quite have 100% coverage, but there's enough here that it caught a number of my mistakes during development, and I wanted to get this up for review without too much more delay.

[Andrey Fedoseev (andrey-fedoseev)]

review: Approve

diff --git a/.gitignore b/.gitignore
 new file mode 100644
index 0000000..a26d707
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,9 @@
+venv/
+build/
+*.charm
+.tox/
+.coverage
+__pycache__/
+*.py[cod]
+.idea
+.vscode/
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
 new file mode 100644
index 0000000..5863a00
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,31 @@
+# Contributing
+
+To make contributions to this charm, you'll need a working [development setup](https://juju.is/docs/sdk/dev-setup).
+
+You can use the environments created by `tox` for development:
+
+```shell
+tox --notest -e unit
+source .tox/unit/bin/activate
+```
+
+## Testing
+
+This project uses `tox` for managing test environments. There are some pre-configured environments
+that can be used for linting and formatting code when you're preparing contributions to the charm:
+
+```shell
+tox -e fmt           # update your code according to linting rules
+tox -e lint          # code style
+tox -e unit          # unit tests
+tox -e integration   # integration tests
+tox                  # runs 'lint' and 'unit' environments
+```
+
+## Build the charm
+
+Build the charm in this git repository using:
+
+```shell
+charmcraft pack
+```
diff --git a/LICENSE b/LICENSE
 new file mode 100644
index 0000000..7e9d504
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
+
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+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+   Copyright 2022 Canonical Ltd.
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+   Licensed under the Apache License, Version 2.0 (the "License");
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diff --git a/README.md b/README.md
 new file mode 100644
index 0000000..d78d2a3
--- /dev/null
+++ b/README.md
@@ -0,0 +1,12 @@
+# clamav-database-mirror
+
+Charmhub package name: clamav-database-mirror
+More information: https://charmhub.io/clamav-database-mirror
+
+Maintains a local mirror of the latest ClamAV databases.
+
+## Other resources
+
+- [Contributing](CONTRIBUTING.md) <!-- or link to other contribution documentation -->
+
+- See the [Juju SDK documentation](https://juju.is/docs/sdk) for more information about developing and improving charms.
diff --git a/charmcraft.yaml b/charmcraft.yaml
 new file mode 100644
index 0000000..0cd3b34
--- /dev/null
+++ b/charmcraft.yaml
@@ -0,0 +1,16 @@
+# This file configures Charmcraft.
+# See https://juju.is/docs/sdk/charmcraft-config for guidance.
+
+type: charm
+bases:
+  - build-on:
+    - name: ubuntu
+      channel: "22.04"
+    run-on:
+    - name: ubuntu
+      channel: "22.04"
+parts:
+  charm:
+    prime:
+      - files/*
+      - templates/*
diff --git a/config.yaml b/config.yaml
 new file mode 100644
index 0000000..f100171
--- /dev/null
+++ b/config.yaml
@@ -0,0 +1,13 @@
+options:
+  host:
+    type: string
+    default: "localhost"
+    description: The mirror's host name.
+  port:
+    type: int
+    default: 80
+    description: The mirror's listen port.
+  http-proxy:
+    type: string
+    default: ""
+    description: HTTP proxy to use for requests.
diff --git a/files/cvdupdate.timer b/files/cvdupdate.timer
 new file mode 100644
index 0000000..dda6d5d
--- /dev/null
+++ b/files/cvdupdate.timer
@@ -0,0 +1,12 @@
+[Unit]
+Description=Update ClamAV database mirror
+Documentation=man:cvdupdate(1)
+
+[Timer]
+OnCalendar=*-*-* 0/4:30:00
+RandomizedDelaySec=1h
+FixedRandomDelay=true
+Persistent=true
+
+[Install]
+WantedBy=timers.target
diff --git a/lib/charms/operator_libs_linux/v0/apt.py b/lib/charms/operator_libs_linux/v0/apt.py
 new file mode 100644
index 0000000..2b5c8f2
--- /dev/null
+++ b/lib/charms/operator_libs_linux/v0/apt.py
@@ -0,0 +1,1329 @@
+# Copyright 2021 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Abstractions for the system's Debian/Ubuntu package information and repositories.
+
+This module contains abstractions and wrappers around Debian/Ubuntu-style repositories and
+packages, in order to easily provide an idiomatic and Pythonic mechanism for adding packages and/or
+repositories to systems for use in machine charms.
+
+A sane default configuration is attainable through nothing more than instantiation of the
+appropriate classes. `DebianPackage` objects provide information about the architecture, version,
+name, and status of a package.
+
+`DebianPackage` will try to look up a package either from `dpkg -L` or from `apt-cache` when
+provided with a string indicating the package name. If it cannot be located, `PackageNotFoundError`
+will be returned, as `apt` and `dpkg` otherwise return `100` for all errors, and a meaningful error
+message if the package is not known is desirable.
+
+To install packages with convenience methods:
+
+```python
+try:
+    # Run `apt-get update`
+    apt.update()
+    apt.add_package("zsh")
+    apt.add_package(["vim", "htop", "wget"])
+except PackageNotFoundError:
+    logger.error("a specified package not found in package cache or on system")
+except PackageError as e:
+    logger.error("could not install package. Reason: %s", e.message)
+````
+
+To find details of a specific package:
+
+```python
+try:
+    vim = apt.DebianPackage.from_system("vim")
+
+    # To find from the apt cache only
+    # apt.DebianPackage.from_apt_cache("vim")
+
+    # To find from installed packages only
+    # apt.DebianPackage.from_installed_package("vim")
+
+    vim.ensure(PackageState.Latest)
+    logger.info("updated vim to version: %s", vim.fullversion)
+except PackageNotFoundError:
+    logger.error("a specified package not found in package cache or on system")
+except PackageError as e:
+    logger.error("could not install package. Reason: %s", e.message)
+```
+
+
+`RepositoryMapping` will return a dict-like object containing enabled system repositories
+and their properties (available groups, baseuri. gpg key). This class can add, disable, or
+manipulate repositories. Items can be retrieved as `DebianRepository` objects.
+
+In order add a new repository with explicit details for fields, a new `DebianRepository` can
+be added to `RepositoryMapping`
+
+`RepositoryMapping` provides an abstraction around the existing repositories on the system,
+and can be accessed and iterated over like any `Mapping` object, to retrieve values by key,
+iterate, or perform other operations.
+
+Keys are constructed as `{repo_type}-{}-{release}` in order to uniquely identify a repository.
+
+Repositories can be added with explicit values through a Python constructor.
+
+Example:
+
+```python
+repositories = apt.RepositoryMapping()
+
+if "deb-example.com-focal" not in repositories:
+    repositories.add(DebianRepository(enabled=True, repotype="deb",
+                     uri="https://example.com", release="focal", groups=["universe"]))
+```
+
+Alternatively, any valid `sources.list` line may be used to construct a new
+`DebianRepository`.
+
+Example:
+
+```python
+repositories = apt.RepositoryMapping()
+
+if "deb-us.archive.ubuntu.com-xenial" not in repositories:
+    line = "deb http://us.archive.ubuntu.com/ubuntu xenial main restricted"
+    repo = DebianRepository.from_repo_line(line)
+    repositories.add(repo)
+```
+"""
+
+import fileinput
+import glob
+import logging
+import os
+import re
+import subprocess
+from collections.abc import Mapping
+from enum import Enum
+from subprocess import PIPE, CalledProcessError, check_call, check_output
+from typing import Iterable, List, Optional, Tuple, Union
+from urllib.parse import urlparse
+
+logger = logging.getLogger(__name__)
+
+# The unique Charmhub library identifier, never change it
+LIBID = "7c3dbc9c2ad44a47bd6fcb25caa270e5"
+
+# Increment this major API version when introducing breaking changes
+LIBAPI = 0
+
+# Increment this PATCH version before using `charmcraft publish-lib` or reset
+# to 0 if you are raising the major API version
+LIBPATCH = 7
+
+
+VALID_SOURCE_TYPES = ("deb", "deb-src")
+OPTIONS_MATCHER = re.compile(r"\[.*?\]")
+
+
+class Error(Exception):
+    """Base class of most errors raised by this library."""
+
+    def __repr__(self):
+        """String representation of Error."""
+        return "<{}.{} {}>".format(type(self).__module__, type(self).__name__, self.args)
+
+    @property
+    def name(self):
+        """Return a string representation of the model plus class."""
+        return "<{}.{}>".format(type(self).__module__, type(self).__name__)
+
+    @property
+    def message(self):
+        """Return the message passed as an argument."""
+        return self.args[0]
+
+
+class PackageError(Error):
+    """Raised when there's an error installing or removing a package."""
+
+
+class PackageNotFoundError(Error):
+    """Raised when a requested package is not known to the system."""
+
+
+class PackageState(Enum):
+    """A class to represent possible package states."""
+
+    Present = "present"
+    Absent = "absent"
+    Latest = "latest"
+    Available = "available"
+
+
+class DebianPackage:
+    """Represents a traditional Debian package and its utility functions.
+
+    `DebianPackage` wraps information and functionality around a known package, whether installed
+    or available. The version, epoch, name, and architecture can be easily queried and compared
+    against other `DebianPackage` objects to determine the latest version or to install a specific
+    version.
+
+    The representation of this object as a string mimics the output from `dpkg` for familiarity.
+
+    Installation and removal of packages is handled through the `state` property or `ensure`
+    method, with the following options:
+
+        apt.PackageState.Absent
+        apt.PackageState.Available
+        apt.PackageState.Present
+        apt.PackageState.Latest
+
+    When `DebianPackage` is initialized, the state of a given `DebianPackage` object will be set to
+    `Available`, `Present`, or `Latest`, with `Absent` implemented as a convenience for removal
+    (though it operates essentially the same as `Available`).
+    """
+
+    def __init__(
+        self, name: str, version: str, epoch: str, arch: str, state: PackageState
+    ) -> None:
+        self._name = name
+        self._arch = arch
+        self._state = state
+        self._version = Version(version, epoch)
+
+    def __eq__(self, other) -> bool:
+        """Equality for comparison.
+
+        Args:
+          other: a `DebianPackage` object for comparison
+
+        Returns:
+          A boolean reflecting equality
+        """
+        return isinstance(other, self.__class__) and (
+            self._name,
+            self._version.number,
+        ) == (other._name, other._version.number)
+
+    def __hash__(self):
+        """A basic hash so this class can be used in Mappings and dicts."""
+        return hash((self._name, self._version.number))
+
+    def __repr__(self):
+        """A representation of the package."""
+        return "<{}.{}: {}>".format(self.__module__, self.__class__.__name__, self.__dict__)
+
+    def __str__(self):
+        """A human-readable representation of the package."""
+        return "<{}: {}-{}.{} -- {}>".format(
+            self.__class__.__name__,
+            self._name,
+            self._version,
+            self._arch,
+            str(self._state),
+        )
+
+    @staticmethod
+    def _apt(
+        command: str,
+        package_names: Union[str, List],
+        optargs: Optional[List[str]] = None,
+    ) -> None:
+        """Wrap package management commands for Debian/Ubuntu systems.
+
+        Args:
+          command: the command given to `apt-get`
+          package_names: a package name or list of package names to operate on
+          optargs: an (Optional) list of additioanl arguments
+
+        Raises:
+          PackageError if an error is encountered
+        """
+        optargs = optargs if optargs is not None else []
+        if isinstance(package_names, str):
+            package_names = [package_names]
+        _cmd = ["apt-get", "-y", *optargs, command, *package_names]
+        try:
+            check_call(_cmd, stderr=PIPE, stdout=PIPE)
+        except CalledProcessError as e:
+            raise PackageError(
+                "Could not {} package(s) [{}]: {}".format(command, [*package_names], e.output)
+            ) from None
+
+    def _add(self) -> None:
+        """Add a package to the system."""
+        self._apt(
+            "install",
+            "{}={}".format(self.name, self.version),
+            optargs=["--option=Dpkg::Options::=--force-confold"],
+        )
+
+    def _remove(self) -> None:
+        """Removes a package from the system. Implementation-specific."""
+        return self._apt("remove", "{}={}".format(self.name, self.version))
+
+    @property
+    def name(self) -> str:
+        """Returns the name of the package."""
+        return self._name
+
+    def ensure(self, state: PackageState):
+        """Ensures that a package is in a given state.
+
+        Args:
+          state: a `PackageState` to reconcile the package to
+
+        Raises:
+          PackageError from the underlying call to apt
+        """
+        if self._state is not state:
+            if state not in (PackageState.Present, PackageState.Latest):
+                self._remove()
+            else:
+                self._add()
+        self._state = state
+
+    @property
+    def present(self) -> bool:
+        """Returns whether or not a package is present."""
+        return self._state in (PackageState.Present, PackageState.Latest)
+
+    @property
+    def latest(self) -> bool:
+        """Returns whether the package is the most recent version."""
+        return self._state is PackageState.Latest
+
+    @property
+    def state(self) -> PackageState:
+        """Returns the current package state."""
+        return self._state
+
+    @state.setter
+    def state(self, state: PackageState) -> None:
+        """Sets the package state to a given value.
+
+        Args:
+          state: a `PackageState` to reconcile the package to
+
+        Raises:
+          PackageError from the underlying call to apt
+        """
+        if state in (PackageState.Latest, PackageState.Present):
+            self._add()
+        else:
+            self._remove()
+        self._state = state
+
+    @property
+    def version(self) -> "Version":
+        """Returns the version for a package."""
+        return self._version
+
+    @property
+    def epoch(self) -> str:
+        """Returns the epoch for a package. May be unset."""
+        return self._version.epoch
+
+    @property
+    def arch(self) -> str:
+        """Returns the architecture for a package."""
+        return self._arch
+
+    @property
+    def fullversion(self) -> str:
+        """Returns the name+epoch for a package."""
+        return "{}.{}".format(self._version, self._arch)
+
+    @staticmethod
+    def _get_epoch_from_version(version: str) -> Tuple[str, str]:
+        """Pull the epoch, if any, out of a version string."""
+        epoch_matcher = re.compile(r"^((?P<epoch>\d+):)?(?P<version>.*)")
+        matches = epoch_matcher.search(version).groupdict()
+        return matches.get("epoch", ""), matches.get("version")
+
+    @classmethod
+    def from_system(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Locates a package, either on the system or known to apt, and serializes the information.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`. If an
+                architecture is not specified, this will be used for selection.
+
+        """
+        try:
+            return DebianPackage.from_installed_package(package, version, arch)
+        except PackageNotFoundError:
+            logger.debug(
+                "package '%s' is not currently installed or has the wrong architecture.", package
+            )
+
+        # Ok, try `apt-cache ...`
+        try:
+            return DebianPackage.from_apt_cache(package, version, arch)
+        except (PackageNotFoundError, PackageError):
+            # If we get here, it's not known to the systems.
+            # This seems unnecessary, but virtually all `apt` commands have a return code of `100`,
+            # and providing meaningful error messages without this is ugly.
+            raise PackageNotFoundError(
+                "Package '{}{}' could not be found on the system or in the apt cache!".format(
+                    package, ".{}".format(arch) if arch else ""
+                )
+            ) from None
+
+    @classmethod
+    def from_installed_package(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Check whether the package is already installed and return an instance.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`.
+                If an architecture is not specified, this will be used for selection.
+        """
+        system_arch = check_output(
+            ["dpkg", "--print-architecture"], universal_newlines=True
+        ).strip()
+        arch = arch if arch else system_arch
+
+        # Regexps are a really terrible way to do this. Thanks dpkg
+        output = ""
+        try:
+            output = check_output(["dpkg", "-l", package], stderr=PIPE, universal_newlines=True)
+        except CalledProcessError:
+            raise PackageNotFoundError("Package is not installed: {}".format(package)) from None
+
+        # Pop off the output from `dpkg -l' because there's no flag to
+        # omit it`
+        lines = str(output).splitlines()[5:]
+
+        dpkg_matcher = re.compile(
+            r"""
+        ^(?P<package_status>\w+?)\s+
+        (?P<package_name>.*?)(?P<throwaway_arch>:\w+?)?\s+
+        (?P<version>.*?)\s+
+        (?P<arch>\w+?)\s+
+        (?P<description>.*)
+        """,
+            re.VERBOSE,
+        )
+
+        for line in lines:
+            try:
+                matches = dpkg_matcher.search(line).groupdict()
+                package_status = matches["package_status"]
+
+                if not package_status.endswith("i"):
+                    logger.debug(
+                        "package '%s' in dpkg output but not installed, status: '%s'",
+                        package,
+                        package_status,
+                    )
+                    break
+
+                epoch, split_version = DebianPackage._get_epoch_from_version(matches["version"])
+                pkg = DebianPackage(
+                    matches["package_name"],
+                    split_version,
+                    epoch,
+                    matches["arch"],
+                    PackageState.Present,
+                )
+                if (pkg.arch == "all" or pkg.arch == arch) and (
+                    version == "" or str(pkg.version) == version
+                ):
+                    return pkg
+            except AttributeError:
+                logger.warning("dpkg matcher could not parse line: %s", line)
+
+        # If we didn't find it, fail through
+        raise PackageNotFoundError("Package {}.{} is not installed!".format(package, arch))
+
+    @classmethod
+    def from_apt_cache(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Check whether the package is already installed and return an instance.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`.
+                If an architecture is not specified, this will be used for selection.
+        """
+        system_arch = check_output(
+            ["dpkg", "--print-architecture"], universal_newlines=True
+        ).strip()
+        arch = arch if arch else system_arch
+
+        # Regexps are a really terrible way to do this. Thanks dpkg
+        keys = ("Package", "Architecture", "Version")
+
+        try:
+            output = check_output(
+                ["apt-cache", "show", package], stderr=PIPE, universal_newlines=True
+            )
+        except CalledProcessError as e:
+            raise PackageError(
+                "Could not list packages in apt-cache: {}".format(e.output)
+            ) from None
+
+        pkg_groups = output.strip().split("\n\n")
+        keys = ("Package", "Architecture", "Version")
+
+        for pkg_raw in pkg_groups:
+            lines = str(pkg_raw).splitlines()
+            vals = {}
+            for line in lines:
+                if line.startswith(keys):
+                    items = line.split(":", 1)
+                    vals[items[0]] = items[1].strip()
+                else:
+                    continue
+
+            epoch, split_version = DebianPackage._get_epoch_from_version(vals["Version"])
+            pkg = DebianPackage(
+                vals["Package"],
+                split_version,
+                epoch,
+                vals["Architecture"],
+                PackageState.Available,
+            )
+
+            if (pkg.arch == "all" or pkg.arch == arch) and (
+                version == "" or str(pkg.version) == version
+            ):
+                return pkg
+
+        # If we didn't find it, fail through
+        raise PackageNotFoundError("Package {}.{} is not in the apt cache!".format(package, arch))
+
+
+class Version:
+    """An abstraction around package versions.
+
+    This seems like it should be strictly unnecessary, except that `apt_pkg` is not usable inside a
+    venv, and wedging version comparisions into `DebianPackage` would overcomplicate it.
+
+    This class implements the algorithm found here:
+    https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
+    """
+
+    def __init__(self, version: str, epoch: str):
+        self._version = version
+        self._epoch = epoch or ""
+
+    def __repr__(self):
+        """A representation of the package."""
+        return "<{}.{}: {}>".format(self.__module__, self.__class__.__name__, self.__dict__)
+
+    def __str__(self):
+        """A human-readable representation of the package."""
+        return "{}{}".format("{}:".format(self._epoch) if self._epoch else "", self._version)
+
+    @property
+    def epoch(self):
+        """Returns the epoch for a package. May be empty."""
+        return self._epoch
+
+    @property
+    def number(self) -> str:
+        """Returns the version number for a package."""
+        return self._version
+
+    def _get_parts(self, version: str) -> Tuple[str, str]:
+        """Separate the version into component upstream and Debian pieces."""
+        try:
+            version.rindex("-")
+        except ValueError:
+            # No hyphens means no Debian version
+            return version, "0"
+
+        upstream, debian = version.rsplit("-", 1)
+        return upstream, debian
+
+    def _listify(self, revision: str) -> List[str]:
+        """Split a revision string into a listself.
+
+        This list is comprised of  alternating between strings and numbers,
+        padded on either end to always be "str, int, str, int..." and
+        always be of even length.  This allows us to trivially implement the
+        comparison algorithm described.
+        """
+        result = []
+        while revision:
+            rev_1, remains = self._get_alphas(revision)
+            rev_2, remains = self._get_digits(remains)
+            result.extend([rev_1, rev_2])
+            revision = remains
+        return result
+
+    def _get_alphas(self, revision: str) -> Tuple[str, str]:
+        """Return a tuple of the first non-digit characters of a revision."""
+        # get the index of the first digit
+        for i, char in enumerate(revision):
+            if char.isdigit():
+                if i == 0:
+                    return "", revision
+                return revision[0:i], revision[i:]
+        # string is entirely alphas
+        return revision, ""
+
+    def _get_digits(self, revision: str) -> Tuple[int, str]:
+        """Return a tuple of the first integer characters of a revision."""
+        # If the string is empty, return (0,'')
+        if not revision:
+            return 0, ""
+        # get the index of the first non-digit
+        for i, char in enumerate(revision):
+            if not char.isdigit():
+                if i == 0:
+                    return 0, revision
+                return int(revision[0:i]), revision[i:]
+        # string is entirely digits
+        return int(revision), ""
+
+    def _dstringcmp(self, a, b):  # noqa: C901
+        """Debian package version string section lexical sort algorithm.
+
+        The lexical comparison is a comparison of ASCII values modified so
+        that all the letters sort earlier than all the non-letters and so that
+        a tilde sorts before anything, even the end of a part.
+        """
+        if a == b:
+            return 0
+        try:
+            for i, char in enumerate(a):
+                if char == b[i]:
+                    continue
+                # "a tilde sorts before anything, even the end of a part"
+                # (emptyness)
+                if char == "~":
+                    return -1
+                if b[i] == "~":
+                    return 1
+                # "all the letters sort earlier than all the non-letters"
+                if char.isalpha() and not b[i].isalpha():
+                    return -1
+                if not char.isalpha() and b[i].isalpha():
+                    return 1
+                # otherwise lexical sort
+                if ord(char) > ord(b[i]):
+                    return 1
+                if ord(char) < ord(b[i]):
+                    return -1
+        except IndexError:
+            # a is longer than b but otherwise equal, greater unless there are tildes
+            if char == "~":
+                return -1
+            return 1
+        # if we get here, a is shorter than b but otherwise equal, so check for tildes...
+        if b[len(a)] == "~":
+            return 1
+        return -1
+
+    def _compare_revision_strings(self, first: str, second: str):  # noqa: C901
+        """Compare two debian revision strings."""
+        if first == second:
+            return 0
+
+        # listify pads results so that we will always be comparing ints to ints
+        # and strings to strings (at least until we fall off the end of a list)
+        first_list = self._listify(first)
+        second_list = self._listify(second)
+        if first_list == second_list:
+            return 0
+        try:
+            for i, item in enumerate(first_list):
+                # explicitly raise IndexError if we've fallen off the edge of list2
+                if i >= len(second_list):
+                    raise IndexError
+                # if the items are equal, next
+                if item == second_list[i]:
+                    continue
+                # numeric comparison
+                if isinstance(item, int):
+                    if item > second_list[i]:
+                        return 1
+                    if item < second_list[i]:
+                        return -1
+                else:
+                    # string comparison
+                    return self._dstringcmp(item, second_list[i])
+        except IndexError:
+            # rev1 is longer than rev2 but otherwise equal, hence greater
+            # ...except for goddamn tildes
+            if first_list[len(second_list)][0][0] == "~":
+                return 1
+            return 1
+        # rev1 is shorter than rev2 but otherwise equal, hence lesser
+        # ...except for goddamn tildes
+        if second_list[len(first_list)][0][0] == "~":
+            return -1
+        return -1
+
+    def _compare_version(self, other) -> int:
+        if (self.number, self.epoch) == (other.number, other.epoch):
+            return 0
+
+        if self.epoch < other.epoch:
+            return -1
+        if self.epoch > other.epoch:
+            return 1
+
+        # If none of these are true, follow the algorithm
+        upstream_version, debian_version = self._get_parts(self.number)
+        other_upstream_version, other_debian_version = self._get_parts(other.number)
+
+        upstream_cmp = self._compare_revision_strings(upstream_version, other_upstream_version)
+        if upstream_cmp != 0:
+            return upstream_cmp
+
+        debian_cmp = self._compare_revision_strings(debian_version, other_debian_version)
+        if debian_cmp != 0:
+            return debian_cmp
+
+        return 0
+
+    def __lt__(self, other) -> bool:
+        """Less than magic method impl."""
+        return self._compare_version(other) < 0
+
+    def __eq__(self, other) -> bool:
+        """Equality magic method impl."""
+        return self._compare_version(other) == 0
+
+    def __gt__(self, other) -> bool:
+        """Greater than magic method impl."""
+        return self._compare_version(other) > 0
+
+    def __le__(self, other) -> bool:
+        """Less than or equal to magic method impl."""
+        return self.__eq__(other) or self.__lt__(other)
+
+    def __ge__(self, other) -> bool:
+        """Greater than or equal to magic method impl."""
+        return self.__gt__(other) or self.__eq__(other)
+
+    def __ne__(self, other) -> bool:
+        """Not equal to magic method impl."""
+        return not self.__eq__(other)
+
+
+def add_package(
+    package_names: Union[str, List[str]],
+    version: Optional[str] = "",
+    arch: Optional[str] = "",
+    update_cache: Optional[bool] = False,
+) -> Union[DebianPackage, List[DebianPackage]]:
+    """Add a package or list of packages to the system.
+
+    Args:
+        name: the name(s) of the package(s)
+        version: an (Optional) version as a string. Defaults to the latest known
+        arch: an optional architecture for the package
+        update_cache: whether or not to run `apt-get update` prior to operating
+
+    Raises:
+        PackageNotFoundError if the package is not in the cache.
+    """
+    cache_refreshed = False
+    if update_cache:
+        update()
+        cache_refreshed = True
+
+    packages = {"success": [], "retry": [], "failed": []}
+
+    package_names = [package_names] if type(package_names) is str else package_names
+    if not package_names:
+        raise TypeError("Expected at least one package name to add, received zero!")
+
+    if len(package_names) != 1 and version:
+        raise TypeError(
+            "Explicit version should not be set if more than one package is being added!"
+        )
+
+    for p in package_names:
+        pkg, success = _add(p, version, arch)
+        if success:
+            packages["success"].append(pkg)
+        else:
+            logger.warning("failed to locate and install/update '%s'", pkg)
+            packages["retry"].append(p)
+
+    if packages["retry"] and not cache_refreshed:
+        logger.info("updating the apt-cache and retrying installation of failed packages.")
+        update()
+
+        for p in packages["retry"]:
+            pkg, success = _add(p, version, arch)
+            if success:
+                packages["success"].append(pkg)
+            else:
+                packages["failed"].append(p)
+
+    if packages["failed"]:
+        raise PackageError("Failed to install packages: {}".format(", ".join(packages["failed"])))
+
+    return packages["success"] if len(packages["success"]) > 1 else packages["success"][0]
+
+
+def _add(
+    name: str,
+    version: Optional[str] = "",
+    arch: Optional[str] = "",
+) -> Tuple[Union[DebianPackage, str], bool]:
+    """Adds a package.
+
+    Args:
+        name: the name(s) of the package(s)
+        version: an (Optional) version as a string. Defaults to the latest known
+        arch: an optional architecture for the package
+
+    Returns: a tuple of `DebianPackage` if found, or a :str: if it is not, and
+        a boolean indicating success
+    """
+    try:
+        pkg = DebianPackage.from_system(name, version, arch)
+        pkg.ensure(state=PackageState.Present)
+        return pkg, True
+    except PackageNotFoundError:
+        return name, False
+
+
+def remove_package(
+    package_names: Union[str, List[str]]
+) -> Union[DebianPackage, List[DebianPackage]]:
+    """Removes a package from the system.
+
+    Args:
+        package_names: the name of a package
+
+    Raises:
+        PackageNotFoundError if the package is not found.
+    """
+    packages = []
+
+    package_names = [package_names] if type(package_names) is str else package_names
+    if not package_names:
+        raise TypeError("Expected at least one package name to add, received zero!")
+
+    for p in package_names:
+        try:
+            pkg = DebianPackage.from_installed_package(p)
+            pkg.ensure(state=PackageState.Absent)
+            packages.append(pkg)
+        except PackageNotFoundError:
+            logger.info("package '%s' was requested for removal, but it was not installed.", p)
+
+    # the list of packages will be empty when no package is removed
+    logger.debug("packages: '%s'", packages)
+    return packages[0] if len(packages) == 1 else packages
+
+
+def update() -> None:
+    """Updates the apt cache via `apt-get update`."""
+    check_call(["apt-get", "update"], stderr=PIPE, stdout=PIPE)
+
+
+class InvalidSourceError(Error):
+    """Exceptions for invalid source entries."""
+
+
+class GPGKeyError(Error):
+    """Exceptions for GPG keys."""
+
+
+class DebianRepository:
+    """An abstraction to represent a repository."""
+
+    def __init__(
+        self,
+        enabled: bool,
+        repotype: str,
+        uri: str,
+        release: str,
+        groups: List[str],
+        filename: Optional[str] = "",
+        gpg_key_filename: Optional[str] = "",
+        options: Optional[dict] = None,
+    ):
+        self._enabled = enabled
+        self._repotype = repotype
+        self._uri = uri
+        self._release = release
+        self._groups = groups
+        self._filename = filename
+        self._gpg_key_filename = gpg_key_filename
+        self._options = options
+
+    @property
+    def enabled(self):
+        """Return whether or not the repository is enabled."""
+        return self._enabled
+
+    @property
+    def repotype(self):
+        """Return whether it is binary or source."""
+        return self._repotype
+
+    @property
+    def uri(self):
+        """Return the URI."""
+        return self._uri
+
+    @property
+    def release(self):
+        """Return which Debian/Ubuntu releases it is valid for."""
+        return self._release
+
+    @property
+    def groups(self):
+        """Return the enabled package groups."""
+        return self._groups
+
+    @property
+    def filename(self):
+        """Returns the filename for a repository."""
+        return self._filename
+
+    @filename.setter
+    def filename(self, fname: str) -> None:
+        """Sets the filename used when a repo is written back to diskself.
+
+        Args:
+            fname: a filename to write the repository information to.
+        """
+        if not fname.endswith(".list"):
+            raise InvalidSourceError("apt source filenames should end in .list!")
+
+        self._filename = fname
+
+    @property
+    def gpg_key(self):
+        """Returns the path to the GPG key for this repository."""
+        return self._gpg_key_filename
+
+    @property
+    def options(self):
+        """Returns any additional repo options which are set."""
+        return self._options
+
+    def make_options_string(self) -> str:
+        """Generate the complete options string for a a repository.
+
+        Combining `gpg_key`, if set, and the rest of the options to find
+        a complex repo string.
+        """
+        options = self._options if self._options else {}
+        if self._gpg_key_filename:
+            options["signed-by"] = self._gpg_key_filename
+
+        return (
+            "[{}] ".format(" ".join(["{}={}".format(k, v) for k, v in options.items()]))
+            if options
+            else ""
+        )
+
+    @staticmethod
+    def prefix_from_uri(uri: str) -> str:
+        """Get a repo list prefix from the uri, depending on whether a path is set."""
+        uridetails = urlparse(uri)
+        path = (
+            uridetails.path.lstrip("/").replace("/", "-") if uridetails.path else uridetails.netloc
+        )
+        return "/etc/apt/sources.list.d/{}".format(path)
+
+    @staticmethod
+    def from_repo_line(repo_line: str, write_file: Optional[bool] = True) -> "DebianRepository":
+        """Instantiate a new `DebianRepository` a `sources.list` entry line.
+
+        Args:
+            repo_line: a string representing a repository entry
+            write_file: boolean to enable writing the new repo to disk
+        """
+        repo = RepositoryMapping._parse(repo_line, "UserInput")
+        fname = "{}-{}.list".format(
+            DebianRepository.prefix_from_uri(repo.uri), repo.release.replace("/", "-")
+        )
+        repo.filename = fname
+
+        options = repo.options if repo.options else {}
+        if repo.gpg_key:
+            options["signed-by"] = repo.gpg_key
+
+        # For Python 3.5 it's required to use sorted in the options dict in order to not have
+        # different results in the order of the options between executions.
+        options_str = (
+            "[{}] ".format(" ".join(["{}={}".format(k, v) for k, v in sorted(options.items())]))
+            if options
+            else ""
+        )
+
+        if write_file:
+            with open(fname, "wb") as f:
+                f.write(
+                    (
+                        "{}".format("#" if not repo.enabled else "")
+                        + "{} {}{} ".format(repo.repotype, options_str, repo.uri)
+                        + "{} {}\n".format(repo.release, " ".join(repo.groups))
+                    ).encode("utf-8")
+                )
+
+        return repo
+
+    def disable(self) -> None:
+        """Remove this repository from consideration.
+
+        Disable it instead of removing from the repository file.
+        """
+        searcher = "{} {}{} {}".format(
+            self.repotype, self.make_options_string(), self.uri, self.release
+        )
+        for line in fileinput.input(self._filename, inplace=True):
+            if re.match(r"^{}\s".format(re.escape(searcher)), line):
+                print("# {}".format(line), end="")
+            else:
+                print(line, end="")
+
+    def import_key(self, key: str) -> None:
+        """Import an ASCII Armor key.
+
+        A Radix64 format keyid is also supported for backwards
+        compatibility. In this case Ubuntu keyserver will be
+        queried for a key via HTTPS by its keyid. This method
+        is less preferrable because https proxy servers may
+        require traffic decryption which is equivalent to a
+        man-in-the-middle attack (a proxy server impersonates
+        keyserver TLS certificates and has to be explicitly
+        trusted by the system).
+
+        Args:
+          key: A GPG key in ASCII armor format,
+                      including BEGIN and END markers or a keyid.
+
+        Raises:
+          GPGKeyError if the key could not be imported
+        """
+        key = key.strip()
+        if "-" in key or "\n" in key:
+            # Send everything not obviously a keyid to GPG to import, as
+            # we trust its validation better than our own. eg. handling
+            # comments before the key.
+            logger.debug("PGP key found (looks like ASCII Armor format)")
+            if (
+                "-----BEGIN PGP PUBLIC KEY BLOCK-----" in key
+                and "-----END PGP PUBLIC KEY BLOCK-----" in key
+            ):
+                logger.debug("Writing provided PGP key in the binary format")
+                key_bytes = key.encode("utf-8")
+                key_name = self._get_keyid_by_gpg_key(key_bytes)
+                key_gpg = self._dearmor_gpg_key(key_bytes)
+                self._gpg_key_filename = "/etc/apt/trusted.gpg.d/{}.gpg".format(key_name)
+                self._write_apt_gpg_keyfile(key_name=self._gpg_key_filename, key_material=key_gpg)
+            else:
+                raise GPGKeyError("ASCII armor markers missing from GPG key")
+        else:
+            logger.warning(
+                "PGP key found (looks like Radix64 format). "
+                "SECURELY importing PGP key from keyserver; "
+                "full key not provided."
+            )
+            # as of bionic add-apt-repository uses curl with an HTTPS keyserver URL
+            # to retrieve GPG keys. `apt-key adv` command is deprecated as is
+            # apt-key in general as noted in its manpage. See lp:1433761 for more
+            # history. Instead, /etc/apt/trusted.gpg.d is used directly to drop
+            # gpg
+            key_asc = self._get_key_by_keyid(key)
+            # write the key in GPG format so that apt-key list shows it
+            key_gpg = self._dearmor_gpg_key(key_asc.encode("utf-8"))
+            self._gpg_key_filename = "/etc/apt/trusted.gpg.d/{}.gpg".format(key)
+            self._write_apt_gpg_keyfile(key_name=key, key_material=key_gpg)
+
+    @staticmethod
+    def _get_keyid_by_gpg_key(key_material: bytes) -> str:
+        """Get a GPG key fingerprint by GPG key material.
+
+        Gets a GPG key fingerprint (40-digit, 160-bit) by the ASCII armor-encoded
+        or binary GPG key material. Can be used, for example, to generate file
+        names for keys passed via charm options.
+        """
+        # Use the same gpg command for both Xenial and Bionic
+        cmd = ["gpg", "--with-colons", "--with-fingerprint"]
+        ps = subprocess.run(
+            cmd,
+            stdout=PIPE,
+            stderr=PIPE,
+            input=key_material,
+        )
+        out, err = ps.stdout.decode(), ps.stderr.decode()
+        if "gpg: no valid OpenPGP data found." in err:
+            raise GPGKeyError("Invalid GPG key material provided")
+        # from gnupg2 docs: fpr :: Fingerprint (fingerprint is in field 10)
+        return re.search(r"^fpr:{9}([0-9A-F]{40}):$", out, re.MULTILINE).group(1)
+
+    @staticmethod
+    def _get_key_by_keyid(keyid: str) -> str:
+        """Get a key via HTTPS from the Ubuntu keyserver.
+
+        Different key ID formats are supported by SKS keyservers (the longer ones
+        are more secure, see "dead beef attack" and https://evil32.com/). Since
+        HTTPS is used, if SSLBump-like HTTPS proxies are in place, they will
+        impersonate keyserver.ubuntu.com and generate a certificate with
+        keyserver.ubuntu.com in the CN field or in SubjAltName fields of a
+        certificate. If such proxy behavior is expected it is necessary to add the
+        CA certificate chain containing the intermediate CA of the SSLBump proxy to
+        every machine that this code runs on via ca-certs cloud-init directive (via
+        cloudinit-userdata model-config) or via other means (such as through a
+        custom charm option). Also note that DNS resolution for the hostname in a
+        URL is done at a proxy server - not at the client side.
+        8-digit (32 bit) key ID
+        https://keyserver.ubuntu.com/pks/lookup?search=0x4652B4E6
+        16-digit (64 bit) key ID
+        https://keyserver.ubuntu.com/pks/lookup?search=0x6E85A86E4652B4E6
+        40-digit key ID:
+        https://keyserver.ubuntu.com/pks/lookup?search=0x35F77D63B5CEC106C577ED856E85A86E4652B4E6
+
+        Args:
+          keyid: An 8, 16 or 40 hex digit keyid to find a key for
+
+        Returns:
+          A string contining key material for the specified GPG key id
+
+
+        Raises:
+          subprocess.CalledProcessError
+        """
+        # options=mr - machine-readable output (disables html wrappers)
+        keyserver_url = (
+            "https://keyserver.ubuntu.com" "/pks/lookup?op=get&options=mr&exact=on&search=0x{}"
+        )
+        curl_cmd = ["curl", keyserver_url.format(keyid)]
+        # use proxy server settings in order to retrieve the key
+        return check_output(curl_cmd).decode()
+
+    @staticmethod
+    def _dearmor_gpg_key(key_asc: bytes) -> bytes:
+        """Converts a GPG key in the ASCII armor format to the binary format.
+
+        Args:
+          key_asc: A GPG key in ASCII armor format.
+
+        Returns:
+          A GPG key in binary format as a string
+
+        Raises:
+          GPGKeyError
+        """
+        ps = subprocess.run(["gpg", "--dearmor"], stdout=PIPE, stderr=PIPE, input=key_asc)
+        out, err = ps.stdout, ps.stderr.decode()
+        if "gpg: no valid OpenPGP data found." in err:
+            raise GPGKeyError(
+                "Invalid GPG key material. Check your network setup"
+                " (MTU, routing, DNS) and/or proxy server settings"
+                " as well as destination keyserver status."
+            )
+        else:
+            return out
+
+    @staticmethod
+    def _write_apt_gpg_keyfile(key_name: str, key_material: bytes) -> None:
+        """Writes GPG key material into a file at a provided path.
+
+        Args:
+          key_name: A key name to use for a key file (could be a fingerprint)
+          key_material: A GPG key material (binary)
+        """
+        with open(key_name, "wb") as keyf:
+            keyf.write(key_material)
+
+
+class RepositoryMapping(Mapping):
+    """An representation of known repositories.
+
+    Instantiation of `RepositoryMapping` will iterate through the
+    filesystem, parse out repository files in `/etc/apt/...`, and create
+    `DebianRepository` objects in this list.
+
+    Typical usage:
+
+        repositories = apt.RepositoryMapping()
+        repositories.add(DebianRepository(
+            enabled=True, repotype="deb", uri="https://example.com", release="focal",
+            groups=["universe"]
+        ))
+    """
+
+    def __init__(self):
+        self._repository_map = {}
+        # Repositories that we're adding -- used to implement mode param
+        self.default_file = "/etc/apt/sources.list"
+
+        # read sources.list if it exists
+        if os.path.isfile(self.default_file):
+            self.load(self.default_file)
+
+        # read sources.list.d
+        for file in glob.iglob("/etc/apt/sources.list.d/*.list"):
+            self.load(file)
+
+    def __contains__(self, key: str) -> bool:
+        """Magic method for checking presence of repo in mapping."""
+        return key in self._repository_map
+
+    def __len__(self) -> int:
+        """Return number of repositories in map."""
+        return len(self._repository_map)
+
+    def __iter__(self) -> Iterable[DebianRepository]:
+        """Iterator magic method for RepositoryMapping."""
+        return iter(self._repository_map.values())
+
+    def __getitem__(self, repository_uri: str) -> DebianRepository:
+        """Return a given `DebianRepository`."""
+        return self._repository_map[repository_uri]
+
+    def __setitem__(self, repository_uri: str, repository: DebianRepository) -> None:
+        """Add a `DebianRepository` to the cache."""
+        self._repository_map[repository_uri] = repository
+
+    def load(self, filename: str):
+        """Load a repository source file into the cache.
+
+        Args:
+          filename: the path to the repository file
+        """
+        parsed = []
+        skipped = []
+        with open(filename, "r") as f:
+            for n, line in enumerate(f):
+                try:
+                    repo = self._parse(line, filename)
+                except InvalidSourceError:
+                    skipped.append(n)
+                else:
+                    repo_identifier = "{}-{}-{}".format(repo.repotype, repo.uri, repo.release)
+                    self._repository_map[repo_identifier] = repo
+                    parsed.append(n)
+                    logger.debug("parsed repo: '%s'", repo_identifier)
+
+        if skipped:
+            skip_list = ", ".join(str(s) for s in skipped)
+            logger.debug("skipped the following lines in file '%s': %s", filename, skip_list)
+
+        if parsed:
+            logger.info("parsed %d apt package repositories", len(parsed))
+        else:
+            raise InvalidSourceError("all repository lines in '{}' were invalid!".format(filename))
+
+    @staticmethod
+    def _parse(line: str, filename: str) -> DebianRepository:
+        """Parse a line in a sources.list file.
+
+        Args:
+          line: a single line from `load` to parse
+          filename: the filename being read
+
+        Raises:
+          InvalidSourceError if the source type is unknown
+        """
+        enabled = True
+        repotype = uri = release = gpg_key = ""
+        options = {}
+        groups = []
+
+        line = line.strip()
+        if line.startswith("#"):
+            enabled = False
+            line = line[1:]
+
+        # Check for "#" in the line and treat a part after it as a comment then strip it off.
+        i = line.find("#")
+        if i > 0:
+            line = line[:i]
+
+        # Split a source into substrings to initialize a new repo.
+        source = line.strip()
+        if source:
+            # Match any repo options, and get a dict representation.
+            for v in re.findall(OPTIONS_MATCHER, source):
+                opts = dict(o.split("=") for o in v.strip("[]").split())
+                # Extract the 'signed-by' option for the gpg_key
+                gpg_key = opts.pop("signed-by", "")
+                options = opts
+
+            # Remove any options from the source string and split the string into chunks
+            source = re.sub(OPTIONS_MATCHER, "", source)
+            chunks = source.split()
+
+            # Check we've got a valid list of chunks
+            if len(chunks) < 3 or chunks[0] not in VALID_SOURCE_TYPES:
+                raise InvalidSourceError("An invalid sources line was found in %s!", filename)
+
+            repotype = chunks[0]
+            uri = chunks[1]
+            release = chunks[2]
+            groups = chunks[3:]
+
+            return DebianRepository(
+                enabled, repotype, uri, release, groups, filename, gpg_key, options
+            )
+        else:
+            raise InvalidSourceError("An invalid sources line was found in %s!", filename)
+
+    def add(self, repo: DebianRepository, default_filename: Optional[bool] = False) -> None:
+        """Add a new repository to the system.
+
+        Args:
+          repo: a `DebianRepository` object
+          default_filename: an (Optional) filename if the default is not desirable
+        """
+        new_filename = "{}-{}.list".format(
+            DebianRepository.prefix_from_uri(repo.uri), repo.release.replace("/", "-")
+        )
+
+        fname = repo.filename or new_filename
+
+        options = repo.options if repo.options else {}
+        if repo.gpg_key:
+            options["signed-by"] = repo.gpg_key
+
+        with open(fname, "wb") as f:
+            f.write(
+                (
+                    "{}".format("#" if not repo.enabled else "")
+                    + "{} {}{} ".format(repo.repotype, repo.make_options_string(), repo.uri)
+                    + "{} {}\n".format(repo.release, " ".join(repo.groups))
+                ).encode("utf-8")
+            )
+
+        self._repository_map["{}-{}-{}".format(repo.repotype, repo.uri, repo.release)] = repo
+
+    def disable(self, repo: DebianRepository) -> None:
+        """Remove a repository. Disable by default.
+
+        Args:
+          repo: a `DebianRepository` to disable
+        """
+        searcher = "{} {}{} {}".format(
+            repo.repotype, repo.make_options_string(), repo.uri, repo.release
+        )
+
+        for line in fileinput.input(repo.filename, inplace=True):
+            if re.match(r"^{}\s".format(re.escape(searcher)), line):
+                print("# {}".format(line), end="")
+            else:
+                print(line, end="")
+
+        self._repository_map["{}-{}-{}".format(repo.repotype, repo.uri, repo.release)] = repo
diff --git a/metadata.yaml b/metadata.yaml
 new file mode 100644
index 0000000..3cd1f95
--- /dev/null
+++ b/metadata.yaml
@@ -0,0 +1,14 @@
+name: clamav-database-mirror
+display-name: ClamAV Database Mirror
+summary: A local mirror of the ClamAV database.
+description: |
+  Maintains a local mirror of the latest ClamAV databases.
+
+  Workloads that perform ClamAV scans in ephemeral environments need to
+  fetch fresh copies of virus definitions before doing anything else; but if
+  they do that using the default configuration that points to
+  database.clamav.net, they will likely find themselves rate-limited in
+  short order.  To avoid that, point those workloads at a deployment of this
+  charm instead, which maintains a local mirror more economically.
+series:
+  - jammy
diff --git a/pyproject.toml b/pyproject.toml
 new file mode 100644
index 0000000..2edc519
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,33 @@
+# Testing tools configuration
+[tool.coverage.run]
+branch = true
+
+[tool.coverage.report]
+show_missing = true
+
+[tool.pytest.ini_options]
+minversion = "6.0"
+log_cli_level = "INFO"
+
+# Formatting tools configuration
+[tool.black]
+line-length = 99
+target-version = ["py38"]
+
+[tool.isort]
+line_length = 99
+profile = "black"
+
+# Linting tools configuration
+[tool.flake8]
+max-line-length = 99
+max-doc-length = 99
+max-complexity = 10
+exclude = [".git", "__pycache__", ".tox", "build", "dist", "*.egg_info", "venv"]
+select = ["E", "W", "F", "C", "N", "R", "D", "H"]
+# Ignore W503, E501 because using black creates errors with this
+# Ignore D107 Missing docstring in __init__
+ignore = ["W503", "E501", "D107"]
+# D100, D101, D102, D103: Ignore missing docstrings in tests
+per-file-ignores = ["tests/*:D100,D101,D102,D103,D104"]
+docstring-convention = "google"
diff --git a/requirements.txt b/requirements.txt
 new file mode 100644
index 0000000..4bbf401
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,2 @@
+jinja2
+ops >= 1.5.0
diff --git a/src/charm.py b/src/charm.py
 new file mode 100755
index 0000000..fbbf2c0
--- /dev/null
+++ b/src/charm.py
@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+#
+# Learn more at: https://juju.is/docs/sdk
+
+"""Charm the service.
+
+Refer to the following post for a quick-start guide that will help you
+develop a new k8s charm using the Operator Framework:
+
+    https://discourse.charmhub.io/t/4208
+"""
+
+import logging
+import shutil
+import subprocess
+from pathlib import Path
+
+from charms.operator_libs_linux.v0 import apt
+from jinja2 import Environment, FileSystemLoader
+from ops.charm import CharmBase
+from ops.main import main
+from ops.model import ActiveStatus, MaintenanceStatus
+
+logger = logging.getLogger(__name__)
+
+db_path = "/srv/clamav-database-mirror/database"
+
+
+class ClamAVDatabaseMirrorCharm(CharmBase):
+    """Charm the service."""
+
+    def __init__(self, *args):
+        super().__init__(*args)
+        self.framework.observe(self.on.install, self._on_install)
+        self.framework.observe(self.on.config_changed, self._on_config_changed)
+
+    def _set_maintenance_step(self, description):
+        self.unit.status = MaintenanceStatus(description)
+        logger.info(description)
+
+    def _install(self):
+        """Install our dependencies."""
+        self._set_maintenance_step("Installing dependencies")
+        apt.add_package(package_names=["clamav-cvdupdate", "nginx"], update_cache=True)
+        subprocess.run(["systemctl", "disable", "--now", "nginx.service"], check=True)
+        Path("/etc/nginx/sites-enabled/default").unlink(missing_ok=True)
+
+    def _run_as(self, user, args, **kwargs):
+        subprocess.run(
+            ["setpriv", "--reuid", user, "--regid", user, "--init-groups", "--"] + args, **kwargs
+        )
+
+    def _configure_database(self):
+        """Configure the database."""
+        self._set_maintenance_step("Configuring database")
+        subprocess.run(["mkdir", "-p", db_path])
+        subprocess.run(["chown", "ubuntu:ubuntu", db_path])
+        self._run_as("ubuntu", ["cvdupdate", "config", "set", "--dbdir", db_path])
+
+    def _configure_timer(self):
+        """Create a systemd timer to update the database automatically."""
+        self._set_maintenance_step("Configuring timer")
+        template_env = Environment(loader=FileSystemLoader(str(self.charm_dir / "templates")))
+        template = template_env.get_template("cvdupdate.service.j2")
+        service = template.render(config=self.config)
+        Path("/lib/systemd/system/cvdupdate.service").write_text(service)
+        shutil.copy(
+            self.charm_dir / "files" / "cvdupdate.timer", "/lib/systemd/system/cvdupdate.timer"
+        )
+        subprocess.run(["systemctl", "daemon-reload"])
+        # Start the update service once before enabling the timer, to ensure
+        # that the database is populated immediately.
+        subprocess.run(["systemctl", "start", "cvdupdate.service"], check=True)
+        subprocess.run(["systemctl", "enable", "--now", "cvdupdate.timer"], check=True)
+
+    def _configure_nginx(self):
+        """Configure nginx to serve the database."""
+        self._set_maintenance_step("Configuring nginx")
+        template_env = Environment(loader=FileSystemLoader(str(self.charm_dir / "templates")))
+        template = template_env.get_template("nginx-site.conf.j2")
+        site = template.render(config=self.config, db_path=db_path)
+        available_conf = Path("/etc/nginx/sites-available/clamav-database-mirror.conf")
+        enabled_conf = Path("/etc/nginx/sites-enabled/clamav-database-mirror.conf")
+        available_conf.write_text(site)
+        if not enabled_conf.exists():
+            enabled_conf.symlink_to(available_conf)
+        subprocess.run(["systemctl", "enable", "nginx.service"], check=True)
+        subprocess.run(["systemctl", "reload-or-restart", "nginx.service"], check=True)
+
+    def _on_install(self, event):
+        self._install()
+        self._configure_database()
+        self._configure_timer()
+        self._configure_nginx()
+        self.unit.status = ActiveStatus()
+
+    def _on_config_changed(self, event):
+        self._configure_timer()
+        self._configure_nginx()
+        self.unit.status = ActiveStatus()
+
+
+if __name__ == "__main__":  # pragma: nocover
+    main(ClamAVDatabaseMirrorCharm)
diff --git a/templates/cvdupdate.service.j2 b/templates/cvdupdate.service.j2
 new file mode 100644
index 0000000..3946693
--- /dev/null
+++ b/templates/cvdupdate.service.j2
@@ -0,0 +1,22 @@
+[Unit]
+Description=Update ClamAV database mirror
+Documentation=man:cvdupdate(1)
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/cvdupdate update
+User=ubuntu
+{% if config["http-proxy"] -%}
+Environment=http_proxy={{ config["http-proxy"] }}
+Environment=https_proxy={{ config["http-proxy"] }}
+{% endif -%}
+ProtectSystem=full
+PrivateTmp=true
+PrivateDevices=true
+ProtectHostname=true
+ProtectClock=true
+ProtectKernelTunables=true
+ProtectKernelModules=true
+ProtectKernelLogs=true
+ProtectControlGroups=true
+
diff --git a/templates/nginx-site.conf.j2 b/templates/nginx-site.conf.j2
 new file mode 100644
index 0000000..5fec382
--- /dev/null
+++ b/templates/nginx-site.conf.j2
@@ -0,0 +1,9 @@
+server {
+    server_name {{ config["host"] }};
+    listen {{ config["port"] }};
+    location / {
+        alias {{ db_path }}/;
+        autoindex on;
+    }
+}
+
diff --git a/tests/integration/test_charm.py b/tests/integration/test_charm.py
 new file mode 100644
index 0000000..ffcc9ec
--- /dev/null
+++ b/tests/integration/test_charm.py
@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+import asyncio
+import logging
+from pathlib import Path
+
+import pytest
+import yaml
+from pytest_operator.plugin import OpsTest
+
+logger = logging.getLogger(__name__)
+
+METADATA = yaml.safe_load(Path("./metadata.yaml").read_text())
+APP_NAME = METADATA["name"]
+
+
[e-mail]_on_fail
+async def test_build_and_deploy(ops_test: OpsTest):
+    """Build the charm-under-test and deploy it together with related charms.
+
+    Assert on the unit status before any relations/configurations take place.
+    """
+    # Build and deploy charm from local source folder
+    charm = await ops_test.build_charm(".")
+
+    # Deploy the charm and wait for active/idle status
+    await asyncio.gather(
+        ops_test.model.deploy(charm, application_name=APP_NAME),
+        ops_test.model.wait_for_idle(
+            apps=[APP_NAME], status="active", raise_on_blocked=True, timeout=1000
+        ),
+    )
diff --git a/tests/unit/test_charm.py b/tests/unit/test_charm.py
 new file mode 100644
index 0000000..bae3788
--- /dev/null
+++ b/tests/unit/test_charm.py
@@ -0,0 +1,88 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+#
+# Learn more about testing at: https://juju.is/docs/sdk/testing
+
+from pathlib import Path
+
+import ops.testing
+import pytest
+from ops.model import ActiveStatus
+from ops.testing import Harness
+
+from charm import ClamAVDatabaseMirrorCharm
+
+# The "fs" fixture is a fake filesystem from pyfakefs; the "fp" fixture is
+# from pytest-subprocess.
+
+
[e-mail](autouse=True)
+def simulate_can_connect(monkeypatch):
+    # Enable more accurate simulation of container networking.
+    # For more information, see https://juju.is/docs/sdk/testing#heading--simulate-can-connect
+    monkeypatch.setattr(ops.testing, "SIMULATE_CAN_CONNECT", True)
+
+
[e-mail]
+def harness():
+    harness = Harness(ClamAVDatabaseMirrorCharm)
+    harness.begin()
+    yield harness
+    harness.cleanup()
+
+
+def test_install(harness, fs, fp):
+    fs.add_real_directory(harness.charm.charm_dir / "files")
+    fs.add_real_directory(harness.charm.charm_dir / "templates")
+    Path("/lib/systemd/system").mkdir(parents=True)
+    Path("/etc/nginx/sites-available").mkdir(parents=True)
+    Path("/etc/nginx/sites-enabled").mkdir(parents=True)
+    fp.keep_last_process(True)
+    fp.register(
+        ["apt-cache", "show", "clamav-cvdupdate"],
+        stdout="Package: clamav-cvdupdate\nArchitecture: all\nVersion: 0.1\n",
+    )
+    fp.register(
+        ["apt-cache", "show", "nginx"], stdout="Package: nginx\nArchitecture: all\nVersion: 0.2\n"
+    )
+    fp.register([fp.any()])
+
+    harness.charm.on.install.emit()
+
+    assert harness.model.unit.status == ActiveStatus()
+    run_as_ubuntu = ["setpriv", "--reuid", "ubuntu", "--regid", "ubuntu", "--init-groups", "--"]
+    assert list(fp.calls) == [
+        ["apt-get", "update"],
+        ["dpkg", "--print-architecture"],
+        ["dpkg", "-l", "clamav-cvdupdate"],
+        ["dpkg", "--print-architecture"],
+        ["apt-cache", "show", "clamav-cvdupdate"],
+        [
+            "apt-get",
+            "-y",
+            "--option=Dpkg::Options::=--force-confold",
+            "install",
+            "clamav-cvdupdate=0.1",
+        ],
+        ["dpkg", "--print-architecture"],
+        ["dpkg", "-l", "nginx"],
+        ["dpkg", "--print-architecture"],
+        ["apt-cache", "show", "nginx"],
+        [
+            "apt-get",
+            "-y",
+            "--option=Dpkg::Options::=--force-confold",
+            "install",
+            "nginx=0.2",
+        ],
+        ["systemctl", "disable", "--now", "nginx.service"],
+        ["mkdir", "-p", "/srv/clamav-database-mirror/database"],
+        ["chown", "ubuntu:ubuntu", "/srv/clamav-database-mirror/database"],
+        run_as_ubuntu
+        + ["cvdupdate", "config", "set", "--dbdir", "/srv/clamav-database-mirror/database"],
+        ["systemctl", "daemon-reload"],
+        ["systemctl", "start", "cvdupdate.service"],
+        ["systemctl", "enable", "--now", "cvdupdate.timer"],
+        ["systemctl", "enable", "nginx.service"],
+        ["systemctl", "reload-or-restart", "nginx.service"],
+    ]
diff --git a/tox.ini b/tox.ini
 new file mode 100644
index 0000000..dc12427
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,73 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+[tox]
+skipsdist=True
+skip_missing_interpreters = True
+envlist = lint, unit
+
+[vars]
+src_path = {toxinidir}/src/
+tst_path = {toxinidir}/tests/
+all_path = {[vars]src_path} {[vars]tst_path} 
+
+[testenv]
+setenv =
+  PYTHONPATH = {toxinidir}:{toxinidir}/lib:{[vars]src_path}
+  PYTHONBREAKPOINT=pdb.set_trace
+  PY_COLORS=1
+passenv =
+  PYTHONPATH
+  CHARM_BUILD_DIR
+  MODEL_SETTINGS
+
+[testenv:fmt]
+description = Apply coding style standards to code
+deps =
+    black
+    isort
+commands =
+    isort {[vars]all_path}
+    black {[vars]all_path}
+
+[testenv:lint]
+description = Check code against coding style standards
+deps =
+    black
+    flake8-docstrings
+    flake8-builtins
+    pyproject-flake8
+    pep8-naming
+    isort
+    codespell
+commands =
+    codespell {toxinidir}/. --skip {toxinidir}/.git --skip {toxinidir}/.tox \
+      --skip {toxinidir}/build --skip {toxinidir}/lib --skip {toxinidir}/venv \
+      --skip {toxinidir}/.mypy_cache --skip {toxinidir}/icon.svg
+    # pflake8 wrapper supports config from pyproject.toml
+    pflake8 {[vars]all_path}
+    isort --check-only --diff {[vars]all_path}
+    black --check --diff {[vars]all_path}
+
+[testenv:unit]
+description = Run unit tests
+deps =
+    pyfakefs
+    pytest
+    pytest-subprocess
+    coverage[toml]
+    -r{toxinidir}/requirements.txt
+commands =
+    coverage run --source={[vars]src_path} \
+        -m pytest --ignore={[vars]tst_path}integration -v --tb native -s {posargs}
+    coverage report
+
+[testenv:integration]
+description = Run integration tests
+deps =
+    pytest
+    juju
+    pytest-operator
+    -r{toxinidir}/requirements.txt
+commands =
+    pytest -v --tb native --ignore={[vars]tst_path}unit --log-cli-level=INFO -s {posargs}
diff --git a/update-lib b/update-lib
 new file mode 100755
index 0000000..943e8fe
--- /dev/null
+++ b/update-lib
@@ -0,0 +1,4 @@
+#! /bin/sh
+set -e
+
+charmcraft fetch-lib charms.operator_libs_linux.v0.apt