v0.3.4: one implementation of apply/revert (patch/mw_patch.py)

The "strip the TRUECLOUD_PATCH block" logic existed twice -- in apply.sh's heredoc
and in an inline heredoc in uninstall.sh -- and the uninstall copy was the untested
one. That is precisely how the two could have drifted apart, with apply.sh
reverting one set of files and uninstall.sh another.

Both now call patch/mw_patch.py. 17 new tests cover it, including that
revert_nested never touches restic.py: that file carries a TRUECLOUD_PATCH block
too, but it belongs to the providers module, and removing it would silently break
B2 backups.

apply.sh imports it fail-safe -- on ImportError the backend patch is skipped and
middlewared starts stock, which is this script's whole design principle. The
import uses sys.path.append, never insert(0): prepending would give patch/
precedence over the stdlib for that interpreter, so a future patch/json.py would
shadow the real json module and break the boot.

Also: the README's create_task.py example still taught `--password <secret>`, which
is how a security fix quietly fails to land. It now shows --password-stdin.

132 tests, ruff and shellcheck clean.

patch/apply.sh

@@ -32,7 +32,7 @@
 # Derive PATCH_DIR from this script's location (parent of the patch/ directory).
 PATCH_DIR="$(cd "$(dirname "$0")/.." && pwd)"
 LOG="$PATCH_DIR/apply.log"
-VERSION="0.3.3"
+VERSION="0.3.4"
 
 # Rotate log at 512 KB to avoid unbounded growth on a system volume.
 # Keep two prior generations (.1 and .2) so the last three boots are always available.
@@ -468,65 +468,24 @@ if _tc_nested is not None:
 """
 
 
-def patch_file(path, block):
-    with open(path, encoding="utf-8") as fh:
-        content = fh.read()
-    marker = "\n# TRUECLOUD_PATCH"
-    idx = content.find(marker)
-    base = content[:idx] if idx != -1 else content
-    with open(path, "w", encoding="utf-8") as fh:
-        fh.write(base.rstrip("\n") + "\n" + block)
+# Single implementation of the block apply/revert logic (patch/mw_patch.py), so
+# uninstall.sh and apply.sh cannot drift apart. Fail-safe: if it cannot be
+# imported, skip the backend patch entirely -- middlewared then starts stock,
+# which is the whole design principle of this script.
+# APPEND, never insert(0): this dir would otherwise take precedence over the
+# stdlib for this interpreter, so a future patch/json.py (say) would shadow the
+# real json module and break the boot. Appending fails safe -- worst case our
+# import misses and the backend patch is skipped.
+sys.path.append(os.path.dirname(nested_src))
+try:
+    from mw_patch import patch_file, revert_nested
+except ImportError as _e:
+    print(f'WARNING: cannot import patch/mw_patch.py ({_e}) — skipping backend patch.')
+    print('WARNING: middlewared will start with stock (unpatched) modules.')
+    sys.exit(1)
 
-
-def unpatch_file(path):
-    """Strip our appended block, restoring the stock file. True if it was patched."""
-    try:
-        with open(path, encoding="utf-8") as fh:
-            content = fh.read()
-    except OSError:
-        return False
-    idx = content.find("\n# TRUECLOUD_PATCH")
-    if idx == -1:
-        return False
-    try:
-        with open(path, "w", encoding="utf-8") as fh:
-            fh.write(content[:idx].rstrip("\n") + "\n")
-    except OSError:
-        return False
-    return True
-
-
-def revert_nested(cloud_dir, sync_path):
-    """Undo the nested patch. Returns the names of what was actually reverted.
-
-    Skipping the patch is NOT enough to disable the feature. The overlay persists
-    for the whole boot, so an earlier run this boot may already have written the
-    patched files -- and middlewared re-imports them on the restart that
-    install.sh performs. Without this, `install.sh --disable-nested-snapshots`
-    would report "disabled" while the feature kept running until the next reboot.
-    """
-    reverted = []
-
-    # Remove the module FIRST. Every injected block is guarded by
-    # `if _tc_nested is not None`, so once it is gone they all no-op even if a
-    # later step here fails -- the guard is restored no matter what.
-    try:
-        os.unlink(os.path.join(cloud_dir, '_truecloud_nested.py'))
-        reverted.append('_truecloud_nested.py')
-    except OSError:
-        pass
-
-    # NB: restic.py also carries a TRUECLOUD_PATCH block, but that belongs to the
-    # providers module. Only these three are ours to revert.
-    for name, path in (
-        ('crud.py', os.path.join(cloud_dir, 'crud.py')),
-        ('sync.py', sync_path),
-        ('snapshot.py', os.path.join(cloud_dir, 'snapshot.py')),
-    ):
-        if unpatch_file(path):
-            reverted.append(name)
-
-    return reverted
+# .../middlewared/plugins/cloud -> .../middlewared
+mw_dir = os.path.dirname(os.path.dirname(cloud_dir))
 
 b2_ok = restic_ok = False
 nested_ok = False
@@ -582,7 +541,7 @@ if not nested_needed:
         nested_detail = 'not needed'
         print('INFO: Nested module skipped.')
 
-    reverted = revert_nested(cloud_dir, sync_path)
+    reverted = revert_nested(mw_dir)
     if reverted:
         print('OK: Reverted a previously-applied nested patch (' + ', '.join(reverted) + ').')
         print('    The stock nesting guard is restored once middlewared restarts.')