feat(p7-devices): finalize device/special-file statuses (devices/copy/write -> implemented, specials -> Impossible/Divergence for sockets) + coverage

README.md

@@ -63,8 +63,12 @@ replacement for every rsync feature or protocol mode.
 - Archive mode does not yet provide all of rsync's `-rlptgoD` behavior.
 - Symlink transfer is incomplete; link targets are not yet recreated in all
   modes.
-- Owner/group, ACL, xattr, hard-link, device, and special-file handling is
-  incomplete or unavailable.
+- Owner/group, ACL, xattr, and hard-link handling is incomplete or
+  unavailable.
+- Device and special-file preservation is implemented with documented
+  divergences: recreated device nodes require `CAP_MKNOD` on the receiver (a
+  non-root receiver skips the entry), and sockets cannot be recreated (FIFOs
+  are).
 - Sparse-file handling does not yet preserve all holes correctly.
 - `--partial`, `--partial-dir`, `-P`, `--append`, and `--append-verify` are not
   yet full rsync-style resumable transfers. Interrupted files are not retained

RSYNC_COMPAT.md

@@ -248,10 +248,10 @@ why plain `--append` works on the normal atomic path, not only with `--inplace`.
 | `-X`, `--xattrs` | Preserve extended attributes | ✅ Implemented | Preserves unprivileged `user.*` extended attributes (Linux `listxattr`/`getxattr` on capture, `fsetxattr` on the written destination fd). Both capture (sender) and application (receiver) are restricted to the `user.*` namespace and the two POSIX ACL xattrs, so a client can **never** force a `security.*`/`trusted.*`/privileged attribute onto the destination; the receiver independently re-validates every incoming name against this whitelist and rejects anything else. Payloads are bounded (per-name ≤255B, per-value ≤1MiB, per-file count ≤256 total bytes ≤4MiB) on both ends, and an oversized/malformed frame is a clean protocol rejection (no OOM). Applied fd-relative to the exact written file. Implies metadata transmission. Incompatible with `-s` (chunk serialization), rejected up front (see the notes); a `--link-dest`/`-H` hard-link copy fallback re-applies the attributes so they are not dropped when a link is refused |
 | `-H`, `--hard-links` | Preserve hard links | ✅ Implemented | Files on the source that share an inode (`st_dev`+`st_ino`, e.g. a `cp -al` tree) are re-created as hard links to one another on the destination, so duplicate links stay deduplicated and only the first member's data is sent (later members are transmitted as payload-less `STATUS_HARDLINK` frames). The receiver links each sibling to the first member's installed file with an atomic link + rename; on `link()` failure it falls back to a byte-identical local copy of the first member, never a partial/corrupt file. Requires the sequential scan for ordering (the first member is always emitted and installed before any sibling is linked). Works single-threaded and under `-j`/`--threads`, `--inplace`, `--delay-updates` (links staged and published by rename) and `--partial`. Crosses the wire (`preserve_hard_links` bool; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0**, peers must match). Incompatible with `-s` (chunk serialization) and `--append`/`--append-verify`, rejected up front with a distinct error. See the Phase-4 hard-links notes below |
 | `-D` | Same as --devices --specials | ✅ Implemented | Implies `--devices --specials`. `-D` was unassigned in FastSync (verified: no collision), so it is free to imply both device-node and special-file preservation. See the `--devices`/`--specials` rows and the Phase-4 devices notes below |
-| `--devices` | Preserve device files | ⚠️ Partial | Recreates char/block device nodes on the destination via `mknod` instead of transferring content. Type + rdev are validated strictly (S_IFMT from the transmitted mode; major/minor range-checked, non-negative), and creation is **privilege-gated**: `mknod` needs `CAP_MKNOD`, so a non-root receiver (CI runs via setpriv as non-root) logs a warning and **skips the device entry safely** — the whole transfer never aborts just because the node could not be made. The node is created fd-relative below the receive root (`mknodat` on the confined secure parent), so it can never be placed outside the authorized root, never follows a symlink, and never replaces an existing directory. Only a char/block mode is honored. Crosses the wire (a new `STATUS_SPECIAL` frame carries the path + metadata mode + rdev; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). Divergence: per-entry skip (not a hard error) when the receiver lacks `CAP_MKNOD`, documented in the Phase-4 devices notes |
-| `--specials` | Preserve special files | ⚠️ Partial | Recreates **FIFOs** on the destination via `mkfifo` (unprivileged, so this is a real, assertable behavior under CI). Sockets cannot be recreated by any standard filesystem call and are skipped with an explicit note (best-effort / unsupported, matching the plan). FIFO creation is privileged-gated only in the sense of graceful skip on any permission failure. Node creation is confined below the receive root (`mkfifoat` on the secure fd-relative parent; no `..`, no symlink follow). Crosses the wire like `--devices` (the `STATUS_SPECIAL` frame; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). See the Phase-4 devices notes |
-| `--copy-devices` | Copy device contents as file | ⚠️ Partial | Copy a device's CONTENT into an ordinary regular file on the destination instead of recreating the node — non-privileged and safe. FastSync scans a device/FIFO as a regular file: its reported size (`st_size`, typically 0 for char devices and FIFOs) is copied, so a FIFO or a non-readable device becomes an empty (or size-bounded) regular file without ever blocking or reading unbounded pseudo-device streams. The run always succeeds and never crashes on such input. **Deliberate, safe divergence from rsync's dd-like unbounded device read.** See the Phase-4 devices notes |
-| `--write-devices` | Write to devices as files | ⚠️ Partial | Write the received data directly into an **existing** device node on the destination instead of creating a regular file. Restricted and best-effort: the destination must already exist and be a char/block device (opened only under the confined receive root, with `O_NOFOLLOW` + `O_NONBLOCK`); a missing, symlinked, FIFO-with-no-reader (`ENXIO`), non-device destination, or any write failure is **skipped with a warning** rather than allowed, so a run can never clobber the system, never blocks on a special-file target, and never aborts on an unusable target. See the Phase-4 devices notes |
+| `--devices` | Preserve device files | ✅ Implemented | Recreates char/block device nodes on the destination via `mknod` instead of transferring content. Type + rdev are validated strictly (S_IFMT from the transmitted mode; major/minor range-checked, non-negative), and creation is **privilege-gated**: `mknod` needs `CAP_MKNOD`, so a non-root receiver (CI runs via setpriv as non-root) logs a warning and **skips the device entry safely** — the whole transfer never aborts just because the node could not be made. The node is created fd-relative below the receive root (`mknodat` on the confined secure parent), so it can never be placed outside the authorized root, never follows a symlink, and never replaces an existing directory. Only a char/block mode is honored. Crosses the wire (a new `STATUS_SPECIAL` frame carries the path + metadata mode + rdev; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). Divergence: per-entry skip (not a hard error) when the receiver lacks `CAP_MKNOD`, documented in the Phase-4 devices notes |
+| `--specials` | Preserve special files | ⛔ Impossible/Divergence | **FIFO recreation works**: FIFOs are recreated on the destination via `mkfifo` (unprivileged, so this is a real, assertable behavior under CI). **Only socket recreation is impossible**: a socket entry can be created only by `bind(2)` on a live socket, not by any filesystem call, so a source socket is skipped with an explicit note. That one unsupported node kind is why the flag is classified Impossible/Divergence even though FIFO recreation itself works; its normal path is otherwise complete. FIFO creation is privileged-gated only in the sense of graceful skip on any permission failure. Node creation is confined below the receive root (`mkfifoat` on the secure fd-relative parent; no `..`, no symlink follow). Crosses the wire like `--devices` (the `STATUS_SPECIAL` frame; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). See the Phase-4 devices notes |
+| `--copy-devices` | Copy device contents as file | ✅ Implemented | Copy a device's CONTENT into an ordinary regular file on the destination instead of recreating the node — non-privileged and safe. FastSync scans a device/FIFO as a regular file: its reported size (`st_size`, typically 0 for char devices and FIFOs) is copied, so a FIFO or a non-readable device becomes an empty (or size-bounded) regular file without ever blocking or reading unbounded pseudo-device streams. The run always succeeds and never crashes on such input. **Deliberate, safe divergence from rsync's dd-like unbounded device read.** See the Phase-4 devices notes |
+| `--write-devices` | Write to devices as files | ✅ Implemented | Write the received data directly into an **existing** device node on the destination instead of creating a regular file. Restricted and best-effort: the destination must already exist and be a char/block device (opened only under the confined receive root, with `O_NOFOLLOW` + `O_NONBLOCK`); a missing, symlinked, FIFO-with-no-reader (`ENXIO`), non-device destination, or any write failure is **skipped with a warning** rather than allowed, so a run can never clobber the system, never blocks on a special-file target, and never aborts on an unusable target. See the Phase-4 devices notes |
 | `-U`, `--atimes` | Preserve access times | ✅ Implemented | Captures the source access time (from the scanner's pre-read stat, so it is not clobbered by reading the file for transfer) and transmits it over the wire; the receiver restores it together with the mtime via `futimens`/`utimensat`. Implies metadata transmission (the times travel inside the `-M` metadata payload), but does not enable ownership application (that stays opt-in via the identity flags). Wire: new `atime` fields on the metadata frame + a `preserve_atimes` config boolean; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0** |
 | `-N`, `--crtimes` | Preserve create times | ⚠️ Partial | Captures the source birth time via `statx(STATX_BTIME)` on Linux and transmits it (recorded as a wire field), but there is **no portable way to set a birth time** (`utimensat` can only set atime/mtime), so the receiver explicitly does NOT apply it: it logs a debug note and continues — never failing the transfer and never pretending it worked. On platforms without `statx` it parses as a documented no-op (flag accepted; nothing is captured). Implies metadata transmission. Wire: new `crtime` fields + a `preserve_crtimes` config boolean; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0** (see the Phase-4 metadata-time notes) |
 | `-O`, `--omit-dir-times` | Omit dirs from --times | 🔄 Compatibility No-op | Accepted and parsed for CLI compatibility, and the config boolean crosses the wire, but it has **no effect**: FastSync never preserves directory mtimes in the first place (directories are created via `mkdir` with no metadata, a documented divergence under `-d`/recursive), so there is nothing for an "omit" to suppress. It never breaks a normal run |
@@ -813,7 +813,7 @@ These are the last compatibility items and the closing phase toward rsync flag p
 
 **Wave B — Output & filesystem completion.** `-S`/`--sparse` (`⚠️→✅`): real hole preservation (skip zero runs / `SEEK_HOLE` read, `ftruncate` sizing) instead of accepted-and-stored. `-P` (`⚠️→✅`): interrupted-file retention enabling true resumable `--partial` transfers (today only `--progress` is honored). `--block-size=SIZE` (`⚠️→✅`): make the delta checksum block-size genuinely configurable/honored rather than merely parsed as `--delta-block`. `--fake-super` replay (`⚠️→✅` or `Impossible/Divergence`): the FastSync-native `user.fastsync.stat` xattr already records uid/gid/mode/mtime → parse and re-apply it on a later privileged run (possible → implement). `--stderr=client` (`⚠️`): FastSync has no client-side rsync message channel → implement a minimal message classification **or** mark **Impossible/Divergence** (decide in-wave). `-N`/`--crtimes` (`⚠️→Impossible/Divergence`): birth-times cannot be set by any portable fs call → promote from "Partial" to explicit **Impossible/Divergence** (capture + transmit stays).
 
-**Wave C — Devices & special files (finalize statuses + tests).** `--devices`, `--specials`, `--copy-devices`, `--write-devices` (`⚠️`) are already functionally implemented with documented, safety-driven divergences (CAP_MKNOD per-entry skip; FIFO-recreate-with-no-socket; size-bounded content copy; confined best-effort device write). During this wave each is promoted to its final status with coverage tests: `--specials` **sockets** cannot be recreated by any standard filesystem call → mark **Impossible/Divergence**; the rest are complete → **✅**.
+**Wave C — Devices & special files (finalize statuses + tests) (✅ implemented).** The four special-file rows are finalized with coverage tests. `--devices`, `--copy-devices`, and `--write-devices` are **✅ Implemented**, each with a documented, safety-driven divergence: device-node creation is privilege-gated, so a receiver without `CAP_MKNOD` skips that entry with a warning (a per-entry skip, never a transfer failure); `--copy-devices` copies a device/FIFO's reported size into an ordinary regular file (a size-bounded safe divergence from rsync's unbounded dd-like read); `--write-devices` writes only into an existing char/block node under the confined receive root and skips every unusable target rather than clobbering or aborting. `--specials` is classified **⛔ Impossible/Divergence** for one reason only: **FIFO recreation works** (unprivileged `mkfifo`, asserted under CI), but **sockets cannot be recreated by any standard filesystem call**, so a source socket is skipped with an explicit note. Tests assert FIFO recreation, the safe socket skip, the regular-file result of `--copy-devices`, the skipped/missing and non-device `--write-devices` targets, and (root-gated) real device-node creation; a root runner additionally drops the receiver to an unprivileged user to assert the `CAP_MKNOD` skip is graceful.
 
 **Wave D — Times superstructure & arg-protection no-ops (`🔄`).** `-O`/`--omit-dir-times`, `-J`/`--omit-link-times` (`🔄`) are no-ops *only because* FastSync never preserves directory/symlink times in the first place. To make them real (honoring "all possible flags"): **add directory-mtime and symlink-mtime/owner preservation**, so `-O`/`-J` become meaningful modifiers — an intentional behavior addition that reverses the old "never preserves dir times" divergence. If instead this is judged out of scope at Wave-D time, mark both **Impossible/Divergence**. `--secluded-args` (`🔄→Impossible/Divergence`): a true arg-send protocol is large and FastSync already builds remote SSH argv securely (single-quote-escaped shell words, injection-safe), so there is no argument-leak to close; document the already-safe behavior.
 

tests/integration/test_features.py

@@ -3,6 +3,7 @@ import filecmp
 import os
 import random
 import shutil
+import socket
 import stat
 import subprocess
 import sys
@@ -14,7 +15,8 @@ from common import (
     PROJECT_ROOT, BUILD_DIR, TEST_DATA_DIR,
     run_client, CountingProxy,
     generate_test_files, verify_transfer, clean_dir, make_result,
-    get_dest_received_dir, CLIENT_CMD, ServerManager,
+    get_dest_received_dir, CLIENT_CMD, SERVER_CMD, ServerManager,
+    _find_free_port, _wait_for_port,
 )
 
 SOURCE_DIR = os.path.join(TEST_DATA_DIR, "feature_source")
@@ -64,14 +66,44 @@ class TestDeviceSpecial:
         received = get_dest_received_dir(DEVICE_DEST, DEVICE_SOURCE)
         assert stat.S_ISFIFO(os.stat(os.path.join(received, "pipe.fifo")).st_mode)
 
-    def test_copy_devices_non_crash(self, shared_server):
-        """--copy-devices treats a special/device source as a regular-file copy;
-        a FIFO (st_size 0) must transfer without hanging or crashing."""
+    def test_specials_socket_source_skipped_safely(self, shared_server):
+        """A socket cannot be recreated by any standard filesystem call, so
+        --specials must skip it with a note and still complete the run (the
+        adjacent regular file transfers normally; no socket node appears)."""
+        self._setup()
+        sock_path = os.path.join(DEVICE_SOURCE, "source.sock")
+        s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        try:
+            s.bind(sock_path)
+            result, _ = run_client(DEVICE_SOURCE, DEVICE_DEST,
+                                   flags=["--specials"], port=shared_server.port)
+        finally:
+            s.close()
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:200]}"
+        received = get_dest_received_dir(DEVICE_DEST, DEVICE_SOURCE)
+        with open(os.path.join(received, "plain.txt")) as f:
+            assert f.read() == "regular content\n"
+        assert not os.path.lexists(os.path.join(received, "source.sock")), (
+            "socket source must be skipped, not materialized"
+        )
+
+    def test_copy_devices_fifo_becomes_regular_file(self, shared_server):
+        """--copy-devices treats a special source as an ordinary regular-file
+        copy: a FIFO (st_size 0) becomes a zero-length REGULAR file on the
+        destination (never a FIFO, never a hang), and the run succeeds."""
         self._setup()
         os.mkfifo(os.path.join(DEVICE_SOURCE, "device_copy.fifo"))
         result, _ = run_client(DEVICE_SOURCE, DEVICE_DEST,
                                flags=["--copy-devices"], port=shared_server.port)
         assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:200]}"
+        received = get_dest_received_dir(DEVICE_DEST, DEVICE_SOURCE)
+        copied = os.path.join(received, "device_copy.fifo")
+        assert os.path.lexists(copied), "copy-devices source was not transferred"
+        st = os.lstat(copied)
+        assert stat.S_ISREG(st.st_mode), (
+            f"copy-devices must produce a regular file, got mode {oct(st.st_mode)}"
+        )
+        assert st.st_size == 0, f"expected a size-bounded 0-byte copy, got {st.st_size}"
 
     def test_write_devices_non_crash(self, shared_server):
         """--write-devices writes into an existing device only; when the
@@ -85,6 +117,57 @@ class TestDeviceSpecial:
                                flags=["--write-devices"], port=shared_server.port)
         assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:200]}"
 
+    def test_write_devices_regular_file_target_skipped(self, shared_server):
+        """--write-devices only ever writes into an existing char/block node: a
+        pre-existing REGULAR file at the destination path is left byte-identical
+        (not clobbered) and the run still succeeds."""
+        self._setup()
+        received = get_dest_received_dir(DEVICE_DEST, DEVICE_SOURCE)
+        os.makedirs(received, exist_ok=True)
+        target = os.path.join(received, "plain.txt")
+        with open(target, "wb") as f:
+            f.write(b"pre-existing local content\n")
+        result, _ = run_client(DEVICE_SOURCE, DEVICE_DEST,
+                               flags=["--write-devices"], port=shared_server.port)
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:200]}"
+        with open(target, "rb") as f:
+            assert f.read() == b"pre-existing local content\n", (
+                "write-devices clobbered a non-device destination"
+            )
+
+    @pytest.mark.setpriv
+    def test_devices_nonroot_receiver_skips_safely(self):
+        """A receiver without CAP_MKNOD must skip a device entry with a warning
+        and never abort.  A root runner drops the receiver (server) to nobody
+        via setpriv; on a non-root runner (or without setpriv) the test skips."""
+        if os.geteuid() != 0 or shutil.which("setpriv") is None:
+            pytest.skip("requires root + setpriv to run the receiver unprivileged")
+        self._setup()
+        os.mknod(os.path.join(DEVICE_SOURCE, "chardev"), stat.S_IFCHR | 0o666,
+                 os.makedev(1, 3))
+        # The unprivileged receiver must be able to create the destination tree.
+        os.makedirs(DEVICE_DEST, exist_ok=True)
+        os.chmod(DEVICE_DEST, 0o777)
+        port = _find_free_port()
+        server = subprocess.Popen(
+            ["setpriv", "--reuid=65534", "--regid=65534", "--clear-groups"] +
+            SERVER_CMD + ["-p", str(port), "--allow-unauthenticated"],
+            stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        try:
+            _wait_for_port(port)
+            result, _ = run_client(DEVICE_SOURCE, DEVICE_DEST,
+                                   flags=["--devices"], port=port)
+        finally:
+            server.terminate()
+            server.wait(timeout=5)
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:300]}"
+        received = get_dest_received_dir(DEVICE_DEST, DEVICE_SOURCE)
+        with open(os.path.join(received, "plain.txt")) as f:
+            assert f.read() == "regular content\n"
+        assert not os.path.lexists(os.path.join(received, "chardev")), (
+            "a receiver without CAP_MKNOD must skip the device node, not create it"
+        )
+
     @pytest.mark.skipif(os.geteuid() != 0, reason="requires root to create device nodes")
     def test_devices_recreates_real_char_device(self, shared_server):
         """Root-only: a source char device node is recreated on the destination

tests/test_file.c

@@ -33,6 +33,7 @@ static void test_file_special_rdev_valid() {
   mode_t fake_char = S_IFCHR | 0600;
   mode_t fake_blk = S_IFBLK | 0600;
   mode_t fake_fifo = S_IFIFO | 0600;
+  mode_t fake_sock = S_IFSOCK | 0600;
   /* char/block devices: accept a legal pair, reject negative / oversized. */
   EXPECT_TRUE(file_special_rdev_valid(1, 3, fake_char));
   EXPECT_TRUE(file_special_rdev_valid(0xffff, 0x00ffffff, fake_blk));
@@ -43,6 +44,8 @@ static void test_file_special_rdev_valid() {
   /* FIFOs/sockets must carry an empty rdev. */
   EXPECT_TRUE(file_special_rdev_valid(0, 0, fake_fifo));
   EXPECT_FALSE(file_special_rdev_valid(1, 0, fake_fifo));
+  EXPECT_TRUE(file_special_rdev_valid(0, 0, fake_sock));
+  EXPECT_FALSE(file_special_rdev_valid(0, 1, fake_sock));
   EXPECT_FALSE(file_special_rdev_valid(0, 0, (mode_t)(S_IFREG | 0600)));
 }