java: Adjust how we handle manual cross-compilation

Follow-up to 0453438d. Previously, setting CARGO_BUILD_TARGET before
manually calling build_jni.sh merely did a Cargo build with the same
settings as the host build. However, adding support for cross-compiles
for the server build broke this "ad hoc" cross-compilation.
Fortunately, it was used only in one place: providing both flavors of
Mac library in a built libsignal-client and libsignal-server. We can
use the *new* cross-compilation support for this instead, reducing
special cases.

This also limits the conditions where build_jni.sh will automatically
set CC and other environment variables, and allows that behavior to be
overridden by manually setting them.

.github/workflows/jni_artifacts.yml

@@ -24,9 +24,7 @@ jobs:
         os: [windows-latest, macos-12]
         include:
           - os: windows-latest
-            library: signal_jni.dll
           - os: macos-12
-            library: libsignal_jni.dylib
             additional-rust-target: aarch64-apple-darwin
         # Ubuntu binaries are built using Docker, below
 
@@ -68,27 +66,41 @@ jobs:
     - run: brew install protobuf
       if: matrix.os == 'macos-12'
 
-    - name: Build for host (should be x86_64)
+    - name: Build client for host
       run: java/build_jni.sh desktop
       shell: bash
 
-    - name: Build for alternate target (arm64)
+    - name: Build server for host
+      run: java/build_jni.sh server
+      shell: bash
+
+    - name: Build client for alternate target
       run: java/build_jni.sh desktop
       if: matrix.os == 'macos-12'
       env:
         CARGO_BUILD_TARGET: ${{ matrix.additional-rust-target }}
 
-    - name: Merge library slices (for macOS)
-      # Using target/release/ for both the input and output wouldn't normally be ideal
-      # from a build system perspective, but we're going to immediately upload the merged library.
-      run: lipo -create target/release/${{ matrix.library }} target/${{ matrix.additional-rust-target }}/release/${{ matrix.library }} -output target/release/${{ matrix.library }}
+    - name: Build server for alternate target
+      run: java/build_jni.sh server
       if: matrix.os == 'macos-12'
+      env:
+        CARGO_BUILD_TARGET: ${{ matrix.additional-rust-target }}
 
-    - name: Upload library
+    - name: Upload client libraries
       uses: actions/upload-artifact@5d5d22a31266ced268874388b861e4b58bb5c2f3 # v4.3.1
       with:
-        name: libsignal_jni (${{matrix.os}})
-        path: target/release/${{ matrix.library }}
+        name: libsignal-client libraries (${{matrix.os}})
+        path: |
+          java/client/src/main/resources/*.dll
+          java/client/src/main/resources/*.dylib
+
+    - name: Upload server libraries
+      uses: actions/upload-artifact@5d5d22a31266ced268874388b861e4b58bb5c2f3 # v4.3.1
+      with:
+        name: libsignal-server libraries (${{matrix.os}})
+        path: |
+          java/server/src/main/resources/*.dll
+          java/server/src/main/resources/*.dylib
 
   verify-rust:
     name: Verify JNI bindings
@@ -122,14 +134,19 @@ jobs:
       with:
         submodules: recursive
 
-    - name: Download built libraries
-      id: download
+    - name: Download built client libraries
       uses: actions/download-artifact@c850b930e6ba138125429b7e5c93fc707a7f8427 # v4.1.4
       with:
-        path: artifacts
+        path: java/client/src/main/resources
+        pattern: libsignal-client*
+        merge-multiple: true
 
-    - name: Copy libraries
-      run: mv ${{ steps.download.outputs.download-path }}/*/* java/shared/resources && find java/shared/resources
+    - name: Download built server libraries
+      uses: actions/download-artifact@c850b930e6ba138125429b7e5c93fc707a7f8427 # v4.1.4
+      with:
+        path: java/server/src/main/resources
+        pattern: libsignal-server*
+        merge-multiple: true
 
     - run: make
       if: ${{ inputs.dry_run }}

java/build_jni.sh

@@ -46,9 +46,8 @@ fi
 
 android_abis=()
 
-# usage: build_desktop_for_arch target_triple host_triple
+# usage: build_desktop_for_arch target_triple host_triple output_dir
 build_desktop_for_arch () {
-    local RUSTFLAGS
     local CC
     local CXX
     local CPATH
@@ -68,23 +67,19 @@ build_desktop_for_arch () {
     esac
     if [[ "$1" != "$2" ]]; then
         # Set up cross-compiling flags
-        if [[ "$1" != *-linux-* ]]; then
-            echo "cross-compiling only supported for Linux targets; update build_jni.sh"
-            exit 2
+        if [[ "$1" == *-linux-* && "$2" == *-linux-* && -z "${CC:-}" ]]; then
+            # When cross-compiling *from* Linux *to* Linux,
+            # set up standard cross-compiling environment if not already set
+            echo 'setting Linux cross-compilation options...'
+            export "CARGO_TARGET_$(echo "$cpuarch" | tr "[:lower:]" "[:upper:]")_UNKNOWN_LINUX_GNU_LINKER"="${cpuarch}-linux-gnu-gcc"
+            export CC="${cpuarch}-linux-gnu-gcc"
+            export CXX="${cpuarch}-linux-gnu-g++"
+            export CPATH="/usr/${cpuarch}-linux-gnu/include"
         fi
-        if [[ "$cpuarch" == aarch64 ]]; then
-            RUSTFLAGS="-C target-feature=+v8.2a ${RUSTFLAGS:-}"
-        fi
-        export "CARGO_TARGET_$(echo "$cpuarch" | tr "[:lower:]" "[:upper:]")_UNKNOWN_LINUX_GNU_LINKER"="${cpuarch}-linux-gnu-gcc"
-        export CC="${cpuarch}-linux-gnu-gcc"
-        export CXX="${cpuarch}-linux-gnu-g++"
-        export CPATH="/usr/${cpuarch}-linux-gnu/include"
     fi
     echo_then_run cargo build -p libsignal-jni -p libsignal-jni-testing --release ${FEATURES:+--features "${FEATURES[*]}"} --target "$1"
-    if [[ -z "${CARGO_BUILD_TARGET:-}" ]]; then
-        copy_built_library "target/${1}/release" signal_jni "$lib_dir" "signal_jni_${suffix}"
-        copy_built_library "target/${1}/release" signal_jni_testing "$lib_dir" "signal_jni_testing_${suffix}"
-    fi
+    copy_built_library "target/${1}/release" signal_jni "$lib_dir" "signal_jni_${suffix}"
+    copy_built_library "target/${1}/release" signal_jni_testing "$lib_dir" "signal_jni_testing_${suffix}"
 }
 
 while [ "${1:-}" != "" ]; do
@@ -104,9 +99,11 @@ while [ "${1:-}" != "" ]; do
             host_triple=$(rustc -vV | sed -n 's|host: ||p')
             if [[ "$1" == "server-all" ]]; then
                 build_desktop_for_arch x86_64-unknown-linux-gnu "$host_triple" $lib_dir
-                build_desktop_for_arch aarch64-unknown-linux-gnu "$host_triple" $lib_dir
+                # Enable ARMv8.2 extensions for a production aarch64 server build
+                RUSTFLAGS="-C target-feature=+v8.2a ${RUSTFLAGS:-}" \
+                    build_desktop_for_arch aarch64-unknown-linux-gnu "$host_triple" $lib_dir
             else
-                build_desktop_for_arch "$host_triple" "$host_triple" $lib_dir
+                build_desktop_for_arch "${CARGO_BUILD_TARGET:-$host_triple}" "$host_triple" $lib_dir
             fi
             exit
             ;;