Add C ABI

[colemancda]

Summary

Adds a Swift implementation of the non-socket half of BlueZ's libbluetooth C API: the 17 bluetooth.c entry points, the 10 bt_uuid_* functions, and the 75 pure sdp_* symbols — the SDP data model, PDU wire-format codec, and sdp_record_t attribute accessors. The socket/session half of SDP (sdp_connect, sdp_process, the register/update/unregister and async request families) belongs to BluetoothLinux, along with the rest of libbluetooth.

• Sources/CBluetooth vendors bluetooth.h, uuid.h, sdp.h, sdp_lib.h (and hci.h, only because sdp_lib.h includes it) verbatim from BlueZ, under include/bluetooth/ — GPL-2.0-or-later, isolated in its own directory with its own LICENSE and README so the rest of the package's MIT licensing stays unambiguous — plus C implementations of the four functions that can't be exported from Swift (baprintf/bafprintf/basprintf/basnprintf are C variadics) and small sscanf trampolines for the UUID parser.
• Sources/BluetoothABI and Sources/BluetoothSDP implement the rest in Swift, exported via @c so each signature is checked against the vendored header declaration rather than trusted as a string. sdp_data_t, sdp_list_t and sdp_record_t are transparent structs (every field is read directly by real consumers), so their layout is itself the ABI contract — these functions operate on the imported C types directly, the same pattern already used for bdaddr_t and bt_uuid_t.
• Both targets are opt-in via SWIFTPM_BLUETOOTH_CABI=1, off by default — the ordinary build is unaffected.
• CMakeLists.txt builds the installable artifact (libbluetooth-util.so.0), since soname/export-list/install-name aren't expressible in Package.swift. Scripts/check-exports.sh asserts the built library's exports (102 symbols) against cmake/symbols.txt. Closes Add CMake support #163.
• Conformance/ differentially compares output against the real libbluetooth.so.3, byte for byte, across three drivers (address functions, bt_uuid_*, and the SDP family — the last two build a moderately complex service record, encode it, and decode it back). All three are identical to the reference except three documented bt_compidtostr metadata-freshness deltas and one documented sdp_uuid16_cmp memcmp-magnitude delta (the sign — the only part of memcmp's contract that's actually specified — matches).
• bt_compidtostr's name table is generated ahead of time from the existing assigned-numbers metadata (Scripts/generate-company-names.py) into a static blob, rather than read at runtime — this avoids a Foundation/Bundle.module dependency in the ABI layer.

This work also caught and fixed two real bugs along the way, both confirmed via the differential conformance harness rather than by inspection:

• bt_uuid_cmp/sdp_uuid_cmp-family functions computing an explicit byte difference instead of calling memcmp, after finding that -O optimizes small fixed-size memcmp calls to a normalized ±1 result while the reference's own build does not — silently optimization-level-dependent output for a function whose only real contract is its sign.
• A genuine dangling-pointer bug in the SDP ABI layer: taking the address of a specific member of an imported C union through a pointer's .pointee (&d.pointee.val.uint16) is only valid for the duration of the call it's a direct argument to; extracting that address as a value to store in an array for a later, separate call (the dtds/values array-building pattern this ABI needs throughout) produced heap-layout-dependent corruption. Fixed by taking the address of the whole union instead (stable, since every C union member starts at the same offset) via small helpers in Pointers.swift.

Also in this PR

The BluetoothMetadata dependency (assigned-numbers name lookups on CompanyIdentifier, BluetoothUUID and UnitIdentifier) moves behind a new opt-in Metadata package trait, off by default. It was previously always linked, which pulled in Foundation and a resource bundle unconditionally; gating it keeps the base package dependency-free and buildable outside SwiftPM (which the CMake build needs). The generated numeric definitions (CompanyIdentifier.apple, etc.) are unaffected.

Test plan

• swift build / swift test — default configuration (485 tests)
• swift build --traits Metadata / swift test --traits Metadata — metadata enabled (485 tests)
• SWIFTPM_BLUETOOTH_CABI=1 swift build / swift test — C ABI enabled (517 tests)
• cmake -B build -G Ninja && cmake --build build && cmake --build build --target check-exports — 102/102 symbols match
• Conformance/compare.sh against system libbluetooth.so.3 — identical output modulo the four documented deltas, on both the SwiftPM debug build and the CMake release build, repeated across multiple clean runs to confirm no remaining non-determinism

[github-code-quality]

Code Coverage Overview

Languages: Swift

Swift / code-coverage/llvm-cov

The overall coverage in commit 1abc2ec in the feature/c-abi branch remains at 89%, unchanged from commit 9a6119b in the master branch.

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_{Updated August 03, 2026 17:35 UTC}