fix: decide uninstall success by exit status, not by keywords

uninstall_package judged success by searching apt/dnf/apk/pacman output
for failure words. That is guesswork in both directions: apt's commonest
failure ("E: Sub-process /usr/bin/dpkg returned an error code (1)") read
as success until the previous change, and a prerm that prints "Failed to
stop ..." while the removal completes still reads as failure. The exit
status is the answer the package manager actually gives, but every
command went through `_sudo(... || true)`, which throws it away.

Add `_sudo_status()`, which runs the command via `_sudo` followed by
`; echo __NETORK_RC=$?` and returns `(output, exit_status)` with the
marker stripped. The `|| true` of other `_sudo` callers is untouched:
they still want output rather than a status. The marker is matched only
on a line of its own with digits, so an echoed command line (literal
`$?`) is never mistaken for it. If the marker never arrives the status
is None -- unknown, not success.

uninstall_package and its dpkg fallback now use it, and
`_uninstall_failed(output, rc)` lets rc decide whenever it is known,
falling back to the keyword check only when it is not.

Behaviour change worth knowing: removing a package that is not installed
exits 0 on apt (and dnf), so it now reports success where the keyword
"is not installed" used to report failure. The package is absent
afterwards, which is what the caller asked for, and netOrk dropping it
from the installed record is then correct.

Refs christianmanivong/netork#267

napalm_linux/linux.py

@@ -50,6 +50,12 @@ logger = logging.getLogger("napalm_linux")
 # Package managers in detection order
 _PKG_MANAGERS = ["apt", "dnf", "yum", "apk", "pacman"]
 
+#: Printed after a command by ``_sudo_status`` so its exit status survives the
+#: trip through an interactive shell. Matched only on a line of its own with a
+#: number after it — an echoed command line carries the literal ``$?`` instead.
+_RC_MARKER = "__NETORK_RC="
+_RC_MARKER_RE = re.compile(rf"^{_RC_MARKER}(\d+)\s*$", re.MULTILINE)
+
 # DMI field values that carry no useful information (OEM defaults, blanks)
 _BAD_DMI: frozenset[str] = frozenset({
     "", "none", "n/a", "not specified", "not applicable",
@@ -267,6 +273,25 @@ class LinuxDriver(OSDriver):
             return self._send(wrapped, read_timeout=read_timeout)
         return self._send(f'sudo {command}', read_timeout=read_timeout)
 
+    def _sudo_status(self, command: str, read_timeout: float = 100) -> tuple[str, int | None]:
+        """Run *command* via sudo and return ``(output, exit_status)``.
+
+        ``_sudo`` callers append ``|| true`` so a failing command yields output
+        instead of an error, which throws the exit status away. This variant
+        echoes ``$?`` straight after the sudo pipeline instead — sudo passes
+        the command's status through, and a failed password is non-zero too.
+
+        The status is ``None`` when the marker never arrived (output cut short),
+        so a caller can tell "unknown" from "succeeded".
+        """
+        raw = self._sudo(f"{command}; echo {_RC_MARKER}$?", read_timeout=read_timeout)
+        matches = list(_RC_MARKER_RE.finditer(raw))
+        if not matches:
+            return raw, None
+        last = matches[-1]
+        output = (raw[: last.start()] + raw[last.end():]).strip()
+        return output, int(last.group(1))
+
     def _detect_pkg_manager(self) -> str | None:
         """Return the first package manager binary found on PATH."""
         for pm in _PKG_MANAGERS:
@@ -1046,6 +1071,7 @@ class LinuxDriver(OSDriver):
         return {"success": success, "output": raw.strip()}
 
     #: Words in a package manager's output that mean it did not do the job.
+    #: Only consulted when the exit status is unknown; see ``_uninstall_failed``.
     _UNINSTALL_FAILED = ("error:", "failed", "not found", "is not installed", "no packages")
 
     def uninstall_package(self, name: str, purge: bool = False) -> dict[str, Any]:
@@ -1077,42 +1103,49 @@ class LinuxDriver(OSDriver):
         pm = self._pkg_manager
         if pm == "apt":
             action = "purge" if purge else "remove"
-            raw = self._sudo(
-                f"DEBIAN_FRONTEND=noninteractive apt-get {action} -y {safe} 2>&1 || true"
-            )
+            cmd = f"DEBIAN_FRONTEND=noninteractive apt-get {action} -y {safe} 2>&1"
         elif pm in ("dnf", "yum"):
-            raw = self._sudo(f"{pm} remove -y {safe} 2>&1 || true")
+            cmd = f"{pm} remove -y {safe} 2>&1"
         elif pm == "apk":
             # apk and pacman have no separate purge; asking for one is not an
             # error, it simply has nothing extra to do.
-            raw = self._sudo(f"apk del {safe} 2>&1 || true")
+            cmd = f"apk del {safe} 2>&1"
         elif pm == "pacman":
-            raw = self._sudo(f"pacman -R --noconfirm {safe} 2>&1 || true")
+            cmd = f"pacman -R --noconfirm {safe} 2>&1"
         else:
             return {"success": False, "output": f"Unsupported package manager: {pm}"}
 
-        if self._uninstall_failed(raw) and pm == "apt":
-            forced = self._sudo(f"dpkg --purge --force-all {safe} 2>&1 || true")
-            if not self._uninstall_failed(forced):
-                return {
-                    "success": True,
-                    "output": f"{raw.strip()}\n--- dpkg --purge --force-all ---\n{forced.strip()}",
-                }
+        raw, rc = self._sudo_status(cmd)
+        failed = self._uninstall_failed(raw, rc)
+
+        if failed and pm == "apt":
+            forced, forced_rc = self._sudo_status(f"dpkg --purge --force-all {safe} 2>&1")
             raw = f"{raw.strip()}\n--- dpkg --purge --force-all ---\n{forced.strip()}"
+            failed = self._uninstall_failed(forced, forced_rc)
 
-        return {"success": not self._uninstall_failed(raw), "output": raw.strip()}
+        return {"success": not failed, "output": raw.strip()}
 
-    def _uninstall_failed(self, output: str) -> bool:
-        """Whether the package manager said it did not do the job.
+    def _uninstall_failed(self, output: str, rc: int | None = None) -> bool:
+        """Whether the package manager did not do the job.
 
-        apt prefixes its own errors with ``E: `` at the start of a line, and
-        the commonest of them — ``E: Sub-process /usr/bin/dpkg returned an
-        error code (1)`` — contains neither "error:" nor "failed". The keyword
-        list alone therefore read a failed removal as a success, which is the
-        worst direction for this particular answer to be wrong in.
+        The exit status decides whenever there is one (netork#267): it is the
+        answer the package manager actually gives, where the output is prose
+        that every tool phrases differently. A prerm printing "Failed to stop
+        …" while the removal completes is a success; a non-zero exit with
+        nothing alarming in the output is not.
+
+        Only when the status is unknown (``rc is None``) is the output read,
+        as the best answer left. apt prefixes its own errors with ``E: `` at
+        the start of a line, and the commonest of them — ``E: Sub-process
+        /usr/bin/dpkg returned an error code (1)`` — contains neither "error:"
+        nor "failed". The keyword list alone therefore read a failed removal
+        as a success, which is the worst direction for this particular answer
+        to be wrong in.
 
         Matched at line start rather than anywhere: "note: " ends in "e: ".
         """
+        if rc is not None:
+            return rc != 0
         low = output.lower()
         if any(line.lstrip().startswith("e: ") for line in low.splitlines()):
             return True