fix(commands): classify command failures for retries

Allow command invocations to define which child exit codes are
considered successful, including checkupdates exit status 2 when no
updates are available.

Classify unexpected child command failures as exporter exit status 1 so
systemd treats them as runtime failures eligible for retry. Keep exit
status 2 for CLI usage errors, which are configuration problems and
should not be retried.

Update the systemd service with RestartPreventExitStatus=2 so only
retryable runtime failures trigger the configured restart policy.

1 files changed, 28 insertions, 12 deletions

diff --git a/prometheus_pacman_exporter/__init__.py b/prometheus_pacman_exporter/__init__.py
index 23ce5a2..ac76dc6 100644
--- a/prometheus_pacman_exporter/__init__.py
+++ b/prometheus_pacman_exporter/__init__.py
@@ -80,7 +80,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.""")
 
 @click.pass_context
 def run_command(
-    ctx: click.Context, command: list[str]
+    ctx: click.Context, command: list[str], success_codes: tuple[int, ...] = (0,)
 ) -> subprocess.CompletedProcess[str]:
     """Run a shell command and return the result.
 
@@ -89,18 +89,21 @@ def run_command(
 
     :param ctx: Click context injected by :func:`click.pass_context`.
     :param command: Command and its arguments.
+    :param success_codes: Exit codes considered successful.
     :return: Completed process with stdout and stderr captured.
     """
     debug("Running command", " ".join(command), err=True)
-    try:
-        return subprocess.run(
-            command, capture_output=True, encoding="utf-8", check=True
+    result = subprocess.run(command, capture_output=True, encoding="utf-8", check=False)
+
+    if result.returncode not in success_codes:
+        error(
+            f"Command ({' '.join(command)}) failed with exit code {result.returncode}"
         )
-    except subprocess.CalledProcessError as e:
-        error(f"Command ({' '.join(command)}) failed with exit code {e.returncode}")
-        if e.stderr:
-            error("stderr:", e.stderr.strip())
-        ctx.exit(e.returncode)
+        if result.stderr:
+            error("stderr:", result.stderr.strip())
+        ctx.exit(1)
+
+    return result
 
 
 @click.command(
@@ -193,36 +196,47 @@ def prometheus_pacman_exporter(
 
     pacman_base_command = ["pacman", "--query"]
     queries = [
-        ([*pacman_base_command], "installed packages", metrics.INSTALLED_PACKAGES),
+        (
+            [*pacman_base_command],
+            "installed packages",
+            metrics.INSTALLED_PACKAGES,
+            (0,),
+        ),
         (
             [*pacman_base_command, "--explicit"],
             "explicitly installed packages",
             metrics.EXPLICIT_PACKAGES,
+            (0,),
         ),
         (
             [*pacman_base_command, "--deps"],
             "packages installed as dependencies",
             metrics.DEPENDS_PACKAGES,
+            (0,),
         ),
         (
             [*pacman_base_command, "--unrequired"],
             "unrequired packages",
             metrics.UNREQUIRED_PACKAGES,
+            (0,),
         ),
         (
             [*pacman_base_command, "--foreign"],
             "foreign packages",
             metrics.FOREIGN_PACKAGES,
+            (0,),
         ),
         (
             [*pacman_base_command, "--native"],
             "native packages",
             metrics.NATIVE_PACKAGES,
+            (0,),
         ),
         (
             [*pacman_base_command, "--deps", "--unrequired"],
             "orphan packages",
             metrics.ORPHAN_PACKAGES,
+            (0,),
         ),
         (
             ["checkupdates"]
@@ -230,6 +244,7 @@ def prometheus_pacman_exporter(
             else [*pacman_base_command, "--upgrades"],
             "updateable packages",
             metrics.UPDATEABLE_PACKAGES,
+            (0, 2) if use_checkupdates_flag else (0, 1),
         ),
     ]
 
@@ -239,11 +254,12 @@ def prometheus_pacman_exporter(
                 shlex.split(cast(str, aur_command)),
                 "AUR updateable packages",
                 metrics.AUR_UPDATEABLE_PACKAGES,
+                (0,),
             )
         )
 
-    for command, description, metric in queries:
-        output = run_command(command)
+    for command, description, metric, success_codes in queries:
+        output = run_command(command, success_codes)
         value = len(output.stdout.splitlines())
         verbose(f"Setting {description}:", str(value), err=True)
         metric.set(value)