cloudfox-coreshift-core 2.29.0

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/

//! Host-runnable byte model of the NDK parcel wire format used by the handoff
//! `sendBinder` bundle.
//!
//! Compiled on **all** targets so the byte math is exercised by `cargo test`
//! on every host commit, not only on Android where `AParcel` exists. The
//! length the write path emits is *derived* here by running the same write
//! sequence against a byte counter, so the constant can never drift from what
//! is actually written (finding 28).
//!
//! Wire facts (verified against AOSP android-14.0.0_r1):
//! - `AParcel_writeString` (`system/libbinder_ndk/parcel.cpp:318`) writes
//!   `writeInt32(len16)` (UTF-16 code units) then
//!   `writeInplace((len16 + 1) * sizeof(char16_t))` — chars plus the NUL
//!   terminator, padded to 4 by `Parcel::writeInplace` (`pad_size`). So
//!   `String16 "binder"` (6 units) = 4 + pad(14) = 4 + 16 = 20, and
//!   `String16 "exec"` (4 units) = 4 + pad(10) = 4 + 12 = 16. A null string
//!   is a single `writeInt32(-1)`.
//! - `writeStrongBinder` = `flattenBinder` = 24-byte `flat_binder_object`
//!   (`writeObject`) + 4-byte stability int32 (`finishFlattenBinder`) = 28.
//! - `BaseBundle.writeToParcelInner` (`writeInt(length)` + `BUNDLE_MAGIC` +
//!   body): `startPos` is captured after the magic, so `length = endPos -
//!   startPos` counts the map body only (N + key/value entries) — not the
//!   length int itself nor the magic.

use crate::CoreError;
use std::os::raw::c_void;

/// `BaseBundle.BUNDLE_MAGIC` — the int `Parcel.writeBundle` writes before the
/// array-map payload. The handoff walk validates it while skipping a bundle.
pub(crate) const BUNDLE_MAGIC: i32 = 0x4C444E42;
/// Java exception code for "no exception". The leading i32 of every binder
/// reply: `EX_NONE` (0) means the transaction succeeded, any other value is
/// the framework's exception code. `sys::EX_NONE` re-exports this constant so
/// the on-device reply check and the host synthetic-parcel test share it.
pub(crate) const EX_NONE: i32 = 0;
/// `Parcel.writeValue` tag for an `IBinder` (`VAL_IBINDER`). 15, not 22.
pub(crate) const VAL_IBINDER: i32 = 15;
/// Bundle key under which the app reads the handed service binder.
pub(crate) const BUNDLE_KEY: &str = "binder";
/// Bundle key under which the app reads the handed exec binder (A1 delivery:
/// `{"binder": watch, "exec": exec}`). Optional — its absence must never
/// invalidate `"binder"`, so an old manager that only knows `"binder"` still
/// receives the watch service.
pub(crate) const EXEC_KEY: &str = "exec";
/// Bundle key under which the app reads the daemon's per-boot epoch (A1
/// delivery with the exec binder: `{"binder": watch, "exec": exec,
/// "epoch": byte[16]}`). The epoch is the consistency boundary for exec
/// frames (server plan §4.1): the manager echoes it in every request, and a
/// stale request after a daemon restart is rejected by identity, never by
/// numeric collision. Optional like `"exec"` — its absence must never
/// invalidate `"binder"`.
pub(crate) const EPOCH_KEY: &str = "epoch";
/// `Parcel.writeValue` tag for a `byte[]` (`VAL_BYTEARRAY`). 13 — pinned to
/// the AOSP value (`Parcel.java`: `VAL_BYTEARRAY=13`). The epoch bundle entry
/// is a 16-byte array (`writeInt(16)` + 16 raw bytes padded to 4).
pub(crate) const VAL_BYTEARRAY: i32 = 13;
/// `Parcel.writeValue` tag for an `Integer` (`VAL_INTEGER`). 1 — pinned to
/// the AOSP value (`Parcel.java`: `VAL_NULL=-1, VAL_STRING=0, VAL_INTEGER=1`).
/// The handoff-status reply bundle's value is written by the manager's
/// `Bundle.putInt`, whose tag the daemon must match byte-for-byte.
pub(crate) const VAL_INTEGER: i32 = 1;
/// Bundle key under which the manager's `call()` reply reports the handoff
/// outcome (`{"status": int}`). The daemon reads it so a rejected handoff is
/// surfaced instead of silently pinned (finding 4 mirror at the mint boundary).
pub(crate) const HANDOFF_STATUS_KEY: &str = "status";
/// The handoff-accepted status. A manager reply bundle whose `status` is any
/// other value means the handoff was rejected; the daemon must not pin the
/// uid for a capability the app never received.
pub(crate) const HANDOFF_STATUS_OK: i32 = 0;
/// Rejected: the calling uid is not a privileged daemon uid
/// (`CoreShiftProvider`'s uid gate). Distinct codes let the daemon log the
/// reason; Core only tests `!= HANDOFF_STATUS_OK`.
#[cfg(test)]
pub(crate) const HANDOFF_STATUS_REJECTED_UID: i32 = 1;
/// Rejected: the handed binder failed the descriptor shape check
/// (`CoreShiftProvider`'s `isWatchService`/`isExecService` gate).
#[cfg(test)]
pub(crate) const HANDOFF_STATUS_REJECTED_DESCRIPTOR: i32 = 2;

/// The parcel-read surface a reply bundle is read through. Implemented by the
/// real `ParcelReader` on Android and by the host `ByteCursor` in tests, so
/// the exact same read sequence runs against both.
pub(crate) trait BundleSource {
    fn read_i32(&self) -> Result<i32, CoreError>;
    fn read_string(&self) -> Result<Option<String>, CoreError>;
}

/// Read the handoff `call()` reply's status.
///
/// Reply shape (`ContentProviderNative.onTransact`, `CALL_TRANSACTION`):
/// `writeNoException()` writes the leading `EX_NONE` i32 (checked by the
/// caller), then `writeBundle(reply)` writes `writeInt(length)` +
/// `BUNDLE_MAGIC` + body. A `null` reply bundle is a single `writeInt(-1)` —
/// the legacy manager shape, which carried no status (finding 4: a rejection
/// was indistinguishable from success). A present bundle must be exactly
/// `{"status": int}`: `N=1`, key `HANDOFF_STATUS_KEY`, tag `VAL_INTEGER`.
/// Anything else fails closed (`Err`), never silently accepted.
pub(crate) fn read_handoff_status(r: &impl BundleSource) -> Result<i32, CoreError> {
    let length = r.read_i32()?;
    if length == -1 {
        // Legacy manager: null reply, no status observable. Preserve the
        // pre-status behavior (accept) so an old manager keeps working.
        return Ok(HANDOFF_STATUS_OK);
    }
    let magic = r.read_i32()?;
    if magic != BUNDLE_MAGIC {
        return Err(CoreError::binder(magic, "call:reply_bad_bundle_magic"));
    }
    let n = r.read_i32()?;
    if n != 1 {
        return Err(CoreError::binder(n, "call:reply_unexpected_entry_count"));
    }
    let key = r.read_string()?;
    if key.as_deref() != Some(HANDOFF_STATUS_KEY) {
        return Err(CoreError::binder(-1, "call:reply_missing_status_key"));
    }
    let tag = r.read_i32()?;
    if tag != VAL_INTEGER {
        return Err(CoreError::binder(tag, "call:reply_status_not_integer"));
    }
    r.read_i32()
}

/// The parcel-write surface the bundle body is written through. Implemented
/// by the real `ParcelWriter` on Android and by the host `ByteCounter` in
/// tests, so the exact same write sequence runs against both.
pub(crate) trait BundleSink {
    fn write_i32(&self, v: i32) -> Result<(), CoreError>;
    fn write_string(&self, s: Option<&str>) -> Result<(), CoreError>;
    fn write_strong_binder(&self, b: *mut c_void) -> Result<(), CoreError>;
    /// `Parcel.writeByteArray`: `writeInt(len)` + len raw bytes padded to 4.
    /// The epoch bundle entry is a fixed 16-byte array (`VAL_BYTEARRAY`).
    fn write_byte_array(&self, b: &[u8]) -> Result<(), CoreError>;
}

/// Write surface for the uid-observer registration body
/// ([`write_uid_observer_body`]). Inherits the bundle write surface and adds
/// the int-array write. Implemented by `ParcelWriter` on Android and by the
/// host `ByteCounter` in tests, so the exact write sequence — including the
/// conditional `uids` array (finding 24) — runs against both.
pub(crate) trait RegisterBodySink: BundleSink {
    fn write_int32_array(&self, v: &[i32]) -> Result<(), CoreError>;
}

/// Write the `extras` map body of the `sendBinder` bundle (the bytes
/// `BaseBundle.writeToParcelInner` counts after the magic): `N` entries of
/// `writeString(key)` + `writeValue(binder)`.
///
/// This is the single source of truth for the bundle's wire shape — both the
/// on-device transaction and the host byte test run it, so the emitted length
/// (from [`bundle_length`]) and the emitted bytes cannot disagree.
///
/// `epoch` (16 bytes) rides with the exec binder: `{"binder", "exec",
/// "epoch"}`. It is optional like `"exec"` — an old manager that only reads
/// `"binder"` still receives the watch service byte-identically, and a watch
/// -only handoff (no exec) never writes it.
pub(crate) fn write_bundle_body(
    w: &impl BundleSink,
    has_exec: bool,
    epoch: Option<&[u8; 16]>,
    service_binder: *mut c_void,
    exec_binder: *mut c_void,
) -> Result<(), CoreError> {
    let n = if has_exec { 2 } else { 1 } + if epoch.is_some() { 1 } else { 0 };
    w.write_i32(n)?;
    w.write_string(Some(BUNDLE_KEY))?;
    w.write_i32(VAL_IBINDER)?;
    w.write_strong_binder(service_binder)?;
    if has_exec {
        w.write_string(Some(EXEC_KEY))?;
        w.write_i32(VAL_IBINDER)?;
        w.write_strong_binder(exec_binder)?;
    }
    if let Some(epoch) = epoch {
        w.write_string(Some(EPOCH_KEY))?;
        w.write_i32(VAL_BYTEARRAY)?;
        w.write_byte_array(epoch)?;
    }
    Ok(())
}

/// Byte length of the `sendBinder` extras bundle body — derived by running
/// [`write_bundle_body`] through the AOSP-verified byte counter, so it can
/// never disagree with what the write path actually emits. `56` for the
/// single-entry `{"binder": IBinder}` bundle, `104` for the two-entry
/// `{"binder": …, "exec": …}` bundle, `144` with the `"epoch"` entry.
pub(crate) fn bundle_length(has_exec: bool, epoch: Option<&[u8; 16]>) -> i32 {
    let c = ByteCounter::default();
    // ByteCounter writes never fail; the pointers are ignored.
    write_bundle_body(
        &c,
        has_exec,
        epoch,
        std::ptr::null_mut(),
        std::ptr::null_mut(),
    )
    .unwrap();
    c.bytes.get() as i32
}

/// The AIDL reply convention: the reply's leading i32 is the Java exception
/// code (`EX_NONE` = 0). A registration that the framework rejects returns a
/// non-`EX_NONE` code as that first field — the caller that reads it can
/// surface the failure instead of running with a dead observer (finding 25).
/// This pure decision is shared by the on-device `transact_write_checked` and
/// the host synthetic-parcel tests.
pub(crate) fn check_reply_exception(ex: i32) -> Result<(), CoreError> {
    if ex == EX_NONE {
        Ok(())
    } else {
        Err(CoreError::binder(ex, "register:reply_exception"))
    }
}

/// The `registerUidObserverForUids`/`registerUidObserver` argument body.
///
/// AIDL shape: `(IUidObserver observer, int which, int cutpoint, String
/// callingPackage[, int[] uids])`. The trailing `uids` array exists **only** on
/// the `ForUids` variant; the 4-arg `registerUidObserver` fallback must not
/// write it — the server ignores the trailing array and registers **unfiltered**
/// across every uid (finding 24). The write is branched here so the on-device
/// path and the host byte test share the exact sequence.
pub(crate) fn write_uid_observer_body(
    w: &impl RegisterBodySink,
    which: i32,
    cutpoint: i32,
    calling_package: Option<&str>,
    has_for_uids: bool,
    watched_uid: i32,
) -> Result<(), CoreError> {
    w.write_i32(which)?;
    w.write_i32(cutpoint)?;
    w.write_string(calling_package)?;
    if has_for_uids {
        w.write_int32_array(&[watched_uid])?;
    }
    Ok(())
}

/// Byte-accounting `BundleSink` that reproduces the AOSP parcel wire format
/// exactly (see the module docs for the derivation).
#[derive(Default)]
struct ByteCounter {
    bytes: std::cell::Cell<usize>,
}

fn pad4(n: usize) -> usize {
    (n + 3) & !3
}

/// `AParcel_writeString` byte size for an ASCII key: 4-byte UTF-16 length int
/// + `(len16 + 1) * 2` bytes (chars + NUL) padded to 4.
///
/// The bundle keys are ASCII, so UTF-8 byte length == UTF-16 code-unit count.
fn string16_size(s: &str) -> usize {
    4 + pad4((s.len() + 1) * 2)
}

impl BundleSink for ByteCounter {
    fn write_i32(&self, _v: i32) -> Result<(), CoreError> {
        self.bytes.set(self.bytes.get() + 4);
        Ok(())
    }
    fn write_string(&self, s: Option<&str>) -> Result<(), CoreError> {
        let n = match s {
            None => 4, // writeInt32(-1)
            Some(s) => string16_size(s),
        };
        self.bytes.set(self.bytes.get() + n);
        Ok(())
    }
    fn write_strong_binder(&self, _b: *mut c_void) -> Result<(), CoreError> {
        // 24-byte flat_binder_object + 4-byte stability int32.
        self.bytes.set(self.bytes.get() + 28);
        Ok(())
    }
    fn write_byte_array(&self, b: &[u8]) -> Result<(), CoreError> {
        // `AParcel_writeByteArray`: writeInt(len) + len raw bytes padded to 4.
        self.bytes.set(self.bytes.get() + 4 + pad4(b.len()));
        Ok(())
    }
}

impl RegisterBodySink for ByteCounter {
    fn write_int32_array(&self, v: &[i32]) -> Result<(), CoreError> {
        // `AParcel_writeInt32Array`: writeInt32(length) then length ints.
        self.bytes.set(self.bytes.get() + 4 + 4 * v.len());
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn string16_sizes_match_aosp_write_path() {
        // "binder": 6 UTF-16 units → 4 + pad((6+1)*2)=pad(14)=16 → 20.
        assert_eq!(string16_size("binder"), 20);
        // "exec": 4 UTF-16 units → 4 + pad((4+1)*2)=pad(10)=12 → 16.
        // (The pre-test constant undercounted this as 12 — it dropped the NUL
        // terminator and the padding. Finding: BUNDLE_LENGTH_TWO was 100, and
        // the write path requires 104.)
        assert_eq!(string16_size("exec"), 16);
    }

    #[test]
    fn null_string_is_four_bytes() {
        let c = ByteCounter::default();
        c.write_string(None).unwrap();
        assert_eq!(c.bytes.get(), 4);
    }

    /// The `Parcel.writeValue` tags are pinned to their AOSP literals
    /// (`Parcel.java`): a wrong constant here used to round-trip through the
    /// byte tests (they build replies with the same constant) and only failed
    /// on device, where the manager's `Bundle.putInt` wrote the real AOSP tag
    /// `1` and the daemon rejected the handoff reply (`reply_status_not_integer`,
    /// uid never pinned, exec CREATE always denied). `VAL_IBINDER` is 15 (not
    /// 22); `VAL_INTEGER` is 1 (not 2).
    #[test]
    fn write_value_tags_pin_aosp_literals() {
        assert_eq!(VAL_IBINDER, 15);
        assert_eq!(VAL_INTEGER, 1);
        assert_eq!(EX_NONE, 0);
    }

    #[test]
    fn single_bundle_body_is_56() {
        assert_eq!(bundle_length(false, None), 56);
    }

    #[test]
    fn two_bundle_body_is_104() {
        // N=2 (4) + "binder" entry (20 + 4 + 28 = 52) + "exec" entry
        // (16 + 4 + 28 = 48) = 104.
        assert_eq!(bundle_length(true, None), 104);
    }

    #[test]
    fn three_bundle_body_with_epoch_is_144() {
        // N=3 (4) + "binder" entry (52) + "exec" entry (48) + "epoch" entry:
        // "epoch" string16 (4 + pad4(6*2)=12 = 16) + VAL_BYTEARRAY (4) +
        // byte[16] (4 + pad4(16)=16 = 20) = 40. Total 4 + 52 + 48 + 40 = 144.
        let epoch = [0xAB; 16];
        assert_eq!(bundle_length(true, Some(&epoch)), 144);
        // The epoch entry is optional: watch-only handoffs stay byte-identical.
        assert_eq!(bundle_length(false, Some(&epoch)), 96);
    }

    #[test]
    fn write_path_emits_exactly_the_advertised_length() {
        // Construct the full bundle as the transaction writes it (length int,
        // magic, body) and assert the length field equals the body bytes.
        let c = ByteCounter::default();
        c.write_i32(bundle_length(true, None)).unwrap();
        c.write_i32(BUNDLE_MAGIC).unwrap();
        write_bundle_body(&c, true, None, std::ptr::null_mut(), std::ptr::null_mut()).unwrap();
        let total = c.bytes.get();
        // 4 (length int) + 4 (magic) + 104 (body).
        assert_eq!(total, 4 + 4 + 104);
        // And the body alone is exactly what the length field advertised.
        assert_eq!(c.bytes.get() - 8, bundle_length(true, None) as usize);
    }

    #[test]
    fn epoch_write_path_emits_exactly_the_advertised_length() {
        // The epoch-carrying bundle's length field matches its real bytes.
        let epoch = [0x11; 16];
        let c = ByteCounter::default();
        c.write_i32(bundle_length(true, Some(&epoch))).unwrap();
        c.write_i32(BUNDLE_MAGIC).unwrap();
        write_bundle_body(
            &c,
            true,
            Some(&epoch),
            std::ptr::null_mut(),
            std::ptr::null_mut(),
        )
        .unwrap();
        assert_eq!(c.bytes.get(), 4 + 4 + 144);
        assert_eq!(
            c.bytes.get() - 8,
            bundle_length(true, Some(&epoch)) as usize
        );
    }

    #[test]
    fn single_bundle_write_path_is_byte_identical_shape() {
        let c = ByteCounter::default();
        c.write_i32(bundle_length(false, None)).unwrap();
        c.write_i32(BUNDLE_MAGIC).unwrap();
        write_bundle_body(&c, false, None, std::ptr::null_mut(), std::ptr::null_mut()).unwrap();
        assert_eq!(c.bytes.get(), 4 + 4 + 56);
    }

    // ── reply exception check (finding 25) ────────────────────────────────

    #[test]
    fn reply_ex_none_is_ok() {
        assert!(check_reply_exception(EX_NONE).is_ok());
    }

    #[test]
    fn reply_non_ex_none_is_err() {
        // A rejected registration returns the framework exception code as the
        // reply's leading i32; the caller must surface it, not run with a
        // dead observer.
        assert!(check_reply_exception(1).is_err());
        assert!(check_reply_exception(-1).is_err());
        assert!(check_reply_exception(32).is_err());
    }

    #[test]
    fn synthetic_parcel_leading_i32_is_exception_code() {
        // Host model of the reply's first field: little-endian i32. The
        // on-device reader does the same `read_i32` → `check_reply_exception`
        // sequence; this pins the data shape without a device.
        fn parse_leading_i32(buf: &[u8]) -> Result<(), CoreError> {
            let ex = i32::from_le_bytes([buf[0], buf[1], buf[2], buf[3]]);
            check_reply_exception(ex)
        }
        assert!(parse_leading_i32(&0i32.to_le_bytes()).is_ok());
        assert!(parse_leading_i32(&1i32.to_le_bytes()).is_err());
        assert!(parse_leading_i32(&(-2i32).to_le_bytes()).is_err());
    }

    // ── handoff status reply (finding 4 mint-boundary mirror) ─────────────

    /// Host cursor over a synthetic reply parcel (little-endian i32; String16
    /// as `writeString` emits: len16 then `(len16+1)*2` bytes). Implements the
    /// same `BundleSource` surface `ParcelReader` implements on-device, so the
    /// exact read sequence runs against both. Position advances through
    /// interior mutability because the read surface borrows `&self`.
    struct ByteCursor<'a> {
        buf: &'a [u8],
        pos: std::cell::Cell<usize>,
    }

    impl<'a> ByteCursor<'a> {
        fn take(&self, n: usize) -> Result<&'a [u8], CoreError> {
            let pos = self.pos.get();
            if pos + n > self.buf.len() {
                return Err(CoreError::binder(-1, "cursor:past_end"));
            }
            self.pos.set(pos + n);
            Ok(&self.buf[pos..pos + n])
        }
    }

    impl<'a> BundleSource for ByteCursor<'a> {
        fn read_i32(&self) -> Result<i32, CoreError> {
            let b: &[u8] = self.take(4)?;
            Ok(i32::from_le_bytes(b.try_into().unwrap()))
        }
        fn read_string(&self) -> Result<Option<String>, CoreError> {
            let len16 = i32::from_le_bytes(self.take(4)?.try_into().unwrap());
            if len16 == -1 {
                return Ok(None);
            }
            if len16 < 0 {
                return Err(CoreError::binder(len16, "cursor:bad_string_len"));
            }
            // `writeString` writes `(len16+1)*2` bytes (chars + NUL), padded
            // to 4 by `Parcel::writeInplace` — consume the padded extent.
            let padded = ((len16 as usize + 1) * 2).next_multiple_of(4);
            let bytes = self.take(padded)?;
            let mut u16s = Vec::with_capacity(len16 as usize);
            for pair in bytes[..len16 as usize * 2].chunks_exact(2) {
                u16s.push(u16::from_le_bytes([pair[0], pair[1]]));
            }
            Ok(Some(String::from_utf16_lossy(&u16s)))
        }
    }

    /// `writeString` wire bytes for an ASCII key: len16 + `(len+1)*2` chars
    /// (NUL-terminated), padded to 4 — the exact shape `AParcel_writeString`
    /// emits.
    fn string16(buf: &mut Vec<u8>, s: &str) {
        buf.extend((s.len() as i32).to_le_bytes());
        let payload = (s.len() + 1) * 2;
        for c in s.chars() {
            buf.extend((c as u16).to_le_bytes());
        }
        buf.extend(0u16.to_le_bytes()); // NUL terminator
        buf.extend(std::iter::repeat_n(
            0u8,
            payload.next_multiple_of(4) - payload,
        ));
    }

    /// Build the exact reply bytes a manager's `call()` produces for a status
    /// bundle: `writeNoException()` → `[EX_NONE]`, then `writeBundle` →
    /// `[length][BUNDLE_MAGIC][N][key][VAL_INTEGER][status]`.
    fn status_reply(status: i32) -> Vec<u8> {
        let mut b: Vec<u8> = Vec::new();
        b.extend(EX_NONE.to_le_bytes());
        // Bundle body: N=1 + "status" key + VAL_INTEGER tag + status.
        let body = {
            let mut m: Vec<u8> = Vec::new();
            m.extend(1i32.to_le_bytes());
            string16(&mut m, HANDOFF_STATUS_KEY);
            m.extend(VAL_INTEGER.to_le_bytes());
            m.extend(status.to_le_bytes());
            m
        };
        b.extend((body.len() as i32).to_le_bytes());
        b.extend(BUNDLE_MAGIC.to_le_bytes());
        b.extend(body);
        b
    }

    /// A legacy manager returned `null`: `writeBundle(null)` → `writeInt(-1)`.
    fn null_reply() -> Vec<u8> {
        let mut b: Vec<u8> = Vec::new();
        b.extend(EX_NONE.to_le_bytes());
        b.extend((-1i32).to_le_bytes());
        b
    }

    #[test]
    fn status_reply_shape_is_pinned() {
        // EX_NONE(4) + length(4) + magic(4) + [N(4) + "status" String16
        // (4 + pad((6+1)*2)=16 → 20) + VAL_INTEGER(4) + status(4)] = 44.
        assert_eq!(
            status_reply(HANDOFF_STATUS_OK).len(),
            4 + 4 + 4 + 4 + 20 + 4 + 4
        );
    }

    #[test]
    fn read_handoff_status_ok() {
        let c = ByteCursor {
            buf: &status_reply(HANDOFF_STATUS_OK),
            pos: std::cell::Cell::new(4),
        };
        assert_eq!(read_handoff_status(&c).unwrap(), HANDOFF_STATUS_OK);
    }

    #[test]
    fn read_handoff_status_rejected_uid() {
        let c = ByteCursor {
            buf: &status_reply(HANDOFF_STATUS_REJECTED_UID),
            pos: std::cell::Cell::new(4),
        };
        assert_eq!(
            read_handoff_status(&c).unwrap(),
            HANDOFF_STATUS_REJECTED_UID
        );
    }

    #[test]
    fn read_handoff_status_rejected_descriptor() {
        let c = ByteCursor {
            buf: &status_reply(HANDOFF_STATUS_REJECTED_DESCRIPTOR),
            pos: std::cell::Cell::new(4),
        };
        assert_eq!(
            read_handoff_status(&c).unwrap(),
            HANDOFF_STATUS_REJECTED_DESCRIPTOR
        );
    }

    #[test]
    fn read_handoff_status_legacy_null_reply_is_ok() {
        // An old manager that never carried a status returns null on success;
        // the reader must accept it, not reject the handoff.
        let c = ByteCursor {
            buf: &null_reply(),
            pos: std::cell::Cell::new(4),
        };
        assert_eq!(read_handoff_status(&c).unwrap(), HANDOFF_STATUS_OK);
    }

    #[test]
    fn read_handoff_status_bad_magic_fails_closed() {
        let mut r = status_reply(HANDOFF_STATUS_OK);
        r[8..12].copy_from_slice(&0xBAD0u32.to_le_bytes());
        let c = ByteCursor {
            buf: &r,
            pos: std::cell::Cell::new(4),
        };
        assert!(read_handoff_status(&c).is_err());
    }

    #[test]
    fn read_handoff_status_unknown_key_fails_closed() {
        // A manager reply bundle with a different/extra shape must not be
        // silently accepted as OK.
        let mut b: Vec<u8> = Vec::new();
        b.extend(EX_NONE.to_le_bytes());
        let body = {
            let mut m: Vec<u8> = Vec::new();
            m.extend(1i32.to_le_bytes());
            string16(&mut m, "other");
            m.extend(VAL_INTEGER.to_le_bytes());
            m.extend(0i32.to_le_bytes());
            m
        };
        b.extend((body.len() as i32).to_le_bytes());
        b.extend(BUNDLE_MAGIC.to_le_bytes());
        b.extend(body);
        let c = ByteCursor {
            buf: &b,
            pos: std::cell::Cell::new(4),
        };
        assert!(read_handoff_status(&c).is_err());
    }

    // ── uid-observer register body (finding 24) ───────────────────────────

    fn uid_observer_body_len(has_for_uids: bool) -> usize {
        let c = ByteCounter::default();
        write_uid_observer_body(&c, 0x1E, -1, None, has_for_uids, 10123).unwrap();
        c.bytes.get()
    }

    #[test]
    fn uid_observer_for_uids_writes_trailing_uids_array() {
        // 5-arg form: which(4) + cutpoint(4) + null package(4) +
        // int32 array len(4) + one uid(4) = 20.
        assert_eq!(uid_observer_body_len(true), 20);
    }

    #[test]
    fn uid_observer_fallback_omits_trailing_uids_array() {
        // 4-arg fallback: which(4) + cutpoint(4) + null package(4) = 12 —
        // the trailing `int[] uids` must NOT be written, or the server
        // registers unfiltered (finding 24).
        assert_eq!(uid_observer_body_len(false), 12);
    }

    #[test]
    fn uid_observer_register_bodies_differ_exactly_by_uids_array() {
        // The two variants differ by exactly the array: length int + uid.
        assert_eq!(
            uid_observer_body_len(true) - uid_observer_body_len(false),
            8
        );
    }
}