[Proposal] Android support

.github/workflows/ci.yml

@@ -58,3 +58,33 @@ jobs:
               -destination 'generic/platform=iOS Simulator' \
               CODE_SIGNING_ALLOWED=NO
           done
+
+  # Android gate: cross-compile the package with the official Swift SDK for
+  # Android and run PatchSDKTests on an Android emulator. Apple-only bridges and
+  # renderers are #if canImport-gated out there, so this job guards the
+  # platform-neutral core (WasmKit runtime, loader, Brotli/BSDIFF40, SHA-256,
+  # update lifecycle) against regressions that only show up off Apple
+  # platforms. The action copies the test resource bundle (.wasm fixtures) to
+  # the emulator. Locally: `skip android test`.
+  android:
+    name: build + test (android)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build + test on Android emulator
+        uses: skiptools/swift-android-action@v2
+        with:
+          # Pinned to the toolchain the Android port was verified with. Must be
+          # the full release name: "6.4" resolves to a non-existent download.
+          swift-version: "6.4.0"
+          # Ubuntu runners can run out of disk while installing the emulator.
+          free-disk-space: true
+          # Swift 6.4 (swift-build backend) names the test resource bundle
+          # `PatchSDK_PatchSDKTests.bundle`, but the action only copies
+          # `*.resources` to the emulator, so Bundle.module fatal-errors. Copy the
+          # .bundle too. `${BUILD_DIR}` is the action's own build-products
+          # variable: this value is pasted into its shell script verbatim.
+          copy-files: ${BUILD_DIR}/*.bundle

Package.swift

@@ -74,14 +74,43 @@ let package = Package(
         // TODO(remove-cap): once that PR (or an equivalent) ships in a WasmKit
         // release we depend on, DROP this `swift-system` constraint and let it
         // float again. Tracked in CLAUDE.md §5 / memory `wasmkit-swift-system-170-cap`.
-        .package(url: "https://github.com/apple/swift-system", "1.5.0" ..< "1.7.0")
+        .package(url: "https://github.com/apple/swift-system", "1.5.0" ..< "1.7.0"),
+        // Apple's swift-crypto: the CryptoKit API for platforms without CryptoKit
+        // (Android). Only linked on non-Apple platforms (see the `.when` conditions
+        // below); Apple builds keep using the system CryptoKit, so it adds nothing
+        // to an iOS app. Wide range so it rarely conflicts with a consumer's pin;
+        // SwiftPM skips releases whose tools-version is newer than the active
+        // toolchain (swift-crypto 4.4+ needs 6.1, 5.x needs 6.2), so Swift 6.0
+        // consumers still resolve a compatible version.
+        .package(url: "https://github.com/apple/swift-crypto.git", "3.0.0" ..< "6.0.0")
     ],
     targets: [
-        // System-library shim for libbz2 (ships in the macOS + iOS SDKs). Used by
-        // the client-side bsdiff4 (BSDIFF40) diff applier to inflate the bz2
-        // control/diff/extra blocks the backend produces. Pure system linkage —
-        // no third-party code, cross-compiles for iOS device + simulator.
-        .systemLibrary(name: "CBZ2", path: "Sources/CBZ2"),
+        // The reference libbzip2 (sourceware.org, 1.0.8, BSD-style license),
+        // vendored unmodified. Used by the client-side bsdiff4 (BSDIFF40) diff
+        // applier to inflate the bz2 control/diff/extra blocks the backend
+        // produces. Same library Apple ships as the SDK's libbz2, compiled from
+        // source so it also builds where no system libbz2 exists (Android NDK).
+        // See Sources/CBZ2/README.md for provenance and the update procedure.
+        .target(
+            name: "CBZ2",
+            path: "Sources/CBZ2",
+            exclude: ["LICENSE", "README.md"],
+            sources: ["src"],
+            publicHeadersPath: "include"
+        ),
+
+        // Google's reference Brotli decoder (MIT, v1.2.0), vendored unmodified —
+        // decoder only, no encoder. Inflates the `.wasm.br` modules the backend
+        // serves. Replaces Apple's `Compression` framework so the same code path
+        // builds on non-Apple platforms (Android). See Sources/CBrotliDec/README.md
+        // for provenance and the update procedure.
+        .target(
+            name: "CBrotliDec",
+            path: "Sources/CBrotliDec",
+            exclude: ["LICENSE", "README.md"],
+            sources: ["common", "dec"],
+            publicHeadersPath: "include"
+        ),
 
         // The shared ViewNode IR (Breakthrough #3/#5). Pure Foundation `Codable`
         // value types — NO WasmKit, NO SwiftUI — so it compiles unchanged into
@@ -162,7 +191,12 @@ let package = Package(
                 // WasmKit PR #349 ships. iOS-safe (pure Swift).
                 .product(name: "SystemPackage", package: "swift-system"),
                 // libbz2 shim for diff decompression.
-                "CBZ2"
+                "CBZ2",
+                // Vendored Brotli decoder for module decompression.
+                "CBrotliDec",
+                // SHA-256 where CryptoKit is unavailable (SHA256.swift).
+                .product(name: "Crypto", package: "swift-crypto",
+                         condition: .when(platforms: [.android, .linux]))
             ],
             resources: [
                 // Apple requires a privacy manifest from third-party SDKs. It is
@@ -208,7 +242,10 @@ let package = Package(
                 .product(name: "WasmKit", package: "WasmKit"),
                 // WASI host shim — the generic-host-bridge tests instantiate the
                 // real Swift-compiled guest fixture, which imports WASI Preview 1.
-                .product(name: "WasmKitWASI", package: "WasmKit")
+                .product(name: "WasmKitWASI", package: "WasmKit"),
+                // SHA-256 in tests where CryptoKit is unavailable.
+                .product(name: "Crypto", package: "swift-crypto",
+                         condition: .when(platforms: [.android, .linux]))
             ],
             resources: [
                 // Real Swift-compiled .wasm fixtures used by the runtime tests.

Sources/CBZ2/LICENSE

@@ -0,0 +1,42 @@
+
+--------------------------------------------------------------------------
+
+This program, "bzip2", the associated library "libbzip2", and all
+documentation, are copyright (C) 1996-2019 Julian R Seward.  All
+rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+
+2. The origin of this software must not be misrepresented; you must 
+   not claim that you wrote the original software.  If you use this 
+   software in a product, an acknowledgment in the product 
+   documentation would be appreciated but is not required.
+
+3. Altered source versions must be plainly marked as such, and must
+   not be misrepresented as being the original software.
+
+4. The name of the author may not be used to endorse or promote 
+   products derived from this software without specific prior written 
+   permission.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
+OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+Julian Seward, jseward@acm.org
+bzip2/libbzip2 version 1.0.8 of 13 July 2019
+
+--------------------------------------------------------------------------

Sources/CBZ2/README.md

@@ -0,0 +1,38 @@
+# CBZ2 — vendored libbzip2
+
+The reference bzip2 library (libbzip2), vendored unmodified so PatchSDK can
+inflate the bz2 control/diff/extra blocks of BSDIFF40 patches on every platform.
+Apple ships this same library as the SDK's `libbz2`; the Android NDK does not
+ship it at all, so it is compiled from source here instead.
+
+| Field | Value |
+| --- | --- |
+| Upstream | https://sourceware.org/bzip2/ (git: https://sourceware.org/git/bzip2.git) |
+| Version | 1.0.8 (tag `bzip2-1.0.8`) |
+| Commit | 6a8690fc8d26c815e798c588f796eabe9d684cf0 |
+| License | bzip2 license, BSD-style (see `LICENSE`) |
+
+## What was copied
+
+| Upstream path | Here |
+| --- | --- |
+| `blocksort.c`, `huffman.c`, `crctable.c`, `randtable.c`, `compress.c`, `decompress.c`, `bzlib.c` (the Makefile's `libbz2.a` objects) | `src/` |
+| `bzlib_private.h` | `src/` |
+| `bzlib.h` | `include/` |
+| `LICENSE` | `LICENSE` |
+
+Not copied: the `bzip2` / `bzip2recover` command-line tools, tests, and docs.
+The compressor sources are needed because `bzlib.c` references them.
+
+## Updating
+
+```sh
+git clone --depth 1 --branch <tag> https://sourceware.org/git/bzip2.git /tmp/bzip2
+D=Sources/CBZ2
+cp /tmp/bzip2/{blocksort,huffman,crctable,randtable,compress,decompress,bzlib}.c /tmp/bzip2/bzlib_private.h $D/src/
+cp /tmp/bzip2/bzlib.h $D/include/
+cp /tmp/bzip2/LICENSE $D/LICENSE
+```
+
+Then update the version and commit in the table above. Do not edit the
+vendored sources by hand.