fix(backends): make the opus backend build and package on macOS/Darwin (#10523)

The opus Go backend (WebRTC audio codec) never built on macOS, so the
published master-metal-darwin-arm64-opus image shipped source only — no
opus binary and no libopusshim — because every step assumed Linux.

- Makefile: hardcoded libopusshim.so with no OS handling. Mirror
  sherpa-onnx: SHIM_EXT=so / dylib on Darwin and build
  libopusshim.$(SHIM_EXT). On Darwin link the shim with
  -undefined dynamic_lookup so it resolves opus_encoder_ctl from the
  already globally-loaded libopus (codec.go dlopens it RTLD_GLOBAL
  first) instead of baking an absolute Homebrew path into the dylib,
  keeping the packaged shim relocatable.
- run.sh: hardcoded LD_LIBRARY_PATH + libopusshim.so even on macOS. Add
  a Darwin branch exporting DYLD_LIBRARY_PATH and the .dylib shim, like
  sherpa-onnx/run.sh.
- package.sh: bundle libopusshim.$(SHIM_EXT) and libopus*.dylib (not
  just .so) into package/lib so the OCI image (which ships package/.)
  is self-contained on a runtime with no Homebrew; add a Darwin arch
  branch so it doesn't warn/skip.
- backend_build_darwin.yml: install + link opus and pkg-config via brew
  so the Makefile's `pkg-config opus` resolves on the macOS runner, and
  cache opus' Cellar dir.

Go code is unchanged; darwin build is validated in CI.

Assisted-by: Claude:claude-opus-4-8

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

.github/workflows/backend_build_darwin.yml

@@ -99,6 +99,7 @@ jobs:
             /opt/homebrew/Cellar/xxhash
             /opt/homebrew/Cellar/zstd
             /opt/homebrew/Cellar/nlohmann-json
+            /opt/homebrew/Cellar/opus
           key: brew-${{ runner.os }}-${{ runner.arch }}-v1-${{ hashFiles('.github/workflows/backend_build_darwin.yml') }}
 
       - name: Dependencies
@@ -113,7 +114,12 @@ jobs:
           # nlohmann-json is header-only and required by the ds4 backend
           # (dsml_renderer.cpp includes <nlohmann/json.hpp>); on Linux it comes
           # from the apt-installed nlohmann-json3-dev in the build image.
-          brew install protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 fmt hiredis xxhash zstd nlohmann-json
+          # opus + pkg-config are required by the opus go backend: its
+          # Makefile/package.sh call `pkg-config --cflags/--libs opus` to build
+          # libopusshim.dylib and to locate libopus.dylib for bundling. brew's
+          # pkg-config defaults its search path to the Homebrew prefix so the
+          # opus.pc is found.
+          brew install protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 fmt hiredis xxhash zstd nlohmann-json opus pkg-config
           # Force-reinstall ccache so brew re-validates its full runtime-dep
           # closure on every run. This is the durable fix: when the upstream
           # ccache formula gains a new transitive dep (as it has multiple times
@@ -132,7 +138,7 @@ jobs:
           # and decides "already installed" without re-linking, so on a cache-
           # hit run the formulas aren't on PATH. Force-link them; --overwrite
           # tolerates pre-existing symlinks from earlier installs.
-          brew link --overwrite protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 fmt hiredis xxhash zstd nlohmann-json 2>/dev/null || true
+          brew link --overwrite protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 fmt hiredis xxhash zstd nlohmann-json opus pkg-config 2>/dev/null || true
 
       - name: Save Homebrew cache
         if: github.event_name != 'pull_request' && steps.brew-cache.outputs.cache-hit != 'true'
@@ -153,6 +159,7 @@ jobs:
             /opt/homebrew/Cellar/xxhash
             /opt/homebrew/Cellar/zstd
             /opt/homebrew/Cellar/nlohmann-json
+            /opt/homebrew/Cellar/opus
           key: brew-${{ runner.os }}-${{ runner.arch }}-v1-${{ hashFiles('.github/workflows/backend_build_darwin.yml') }}
 
       # ---- ccache for llama.cpp CMake builds ----

backend/go/opus/Makefile

@@ -1,13 +1,30 @@
 GOCMD?=go
 GO_TAGS?=
 
+# The opus shim is a small C wrapper around libopus' variadic
+# opus_encoder_ctl (see csrc/opus_shim.c). It is built as a shared library
+# and dlopen'd at runtime by the Go backend (codec.go). The extension is
+# OS-specific: Linux uses .so, macOS uses .dylib. OS is exported by the root
+# Makefile (`export OS := $(shell uname -s)`).
+SHIM_EXT=so
+
 OPUS_CFLAGS := $(shell pkg-config --cflags opus)
 OPUS_LIBS := $(shell pkg-config --libs opus)
+SHIM_LDFLAGS := $(OPUS_LIBS)
 
-libopusshim.so: csrc/opus_shim.c
-	$(CC) -shared -fPIC -o $@ $< $(OPUS_CFLAGS) $(OPUS_LIBS)
+ifeq ($(OS),Darwin)
+	SHIM_EXT=dylib
+	# Resolve libopus symbols lazily from the already globally-loaded
+	# libopus (codec.go dlopens it RTLD_GLOBAL before the shim) rather than
+	# recording an absolute Homebrew path in the dylib. This keeps the
+	# packaged shim relocatable on machines that have no Homebrew.
+	SHIM_LDFLAGS := -undefined dynamic_lookup
+endif
 
-opus: libopusshim.so
+libopusshim.$(SHIM_EXT): csrc/opus_shim.c
+	$(CC) -shared -fPIC -o $@ $< $(OPUS_CFLAGS) $(SHIM_LDFLAGS)
+
+opus: libopusshim.$(SHIM_EXT)
 	$(GOCMD) build -tags "$(GO_TAGS)" -o opus ./
 
 package: opus
@@ -16,4 +33,7 @@ package: opus
 build: package
 
 clean:
-	rm -f opus libopusshim.so
+	rm -f opus libopusshim.$(SHIM_EXT)
+	rm -rf package
+
+.PHONY: build package clean

backend/go/opus/package.sh

@@ -8,13 +8,23 @@ mkdir -p $CURDIR/package/lib
 cp -avf $CURDIR/opus $CURDIR/package/
 cp -avf $CURDIR/run.sh $CURDIR/package/
 
-# Copy the opus shim library
-cp -avf $CURDIR/libopusshim.so $CURDIR/package/lib/
+# The shim extension is OS-specific (.so on Linux, .dylib on macOS).
+SHIM_EXT=so
+if [ "$(uname)" = "Darwin" ]; then
+    SHIM_EXT=dylib
+fi
 
-# Copy system libopus
+# Copy the opus shim library
+cp -avf $CURDIR/libopusshim.$SHIM_EXT $CURDIR/package/lib/
+
+# Copy system libopus so the backend is self-contained: the runtime base
+# image has neither libopus-dev (Linux) nor Homebrew (macOS), so codec.go's
+# dlopen would otherwise fail. Both name patterns are attempted; only the
+# host's matching one exists.
 if command -v pkg-config >/dev/null 2>&1 && pkg-config --exists opus; then
     LIBOPUS_DIR=$(pkg-config --variable=libdir opus)
-    cp -avfL $LIBOPUS_DIR/libopus.so* $CURDIR/package/lib/ 2>/dev/null || true
+    cp -avf $LIBOPUS_DIR/libopus.so* $CURDIR/package/lib/ 2>/dev/null || true
+    cp -avf $LIBOPUS_DIR/libopus*.dylib $CURDIR/package/lib/ 2>/dev/null || true
 fi
 
 # Detect architecture and copy appropriate libraries
@@ -38,6 +48,8 @@ elif [ -f "/lib/ld-linux-aarch64.so.1" ]; then
     cp -arfLv /lib/aarch64-linux-gnu/libdl.so.2 $CURDIR/package/lib/libdl.so.2
     cp -arfLv /lib/aarch64-linux-gnu/librt.so.1 $CURDIR/package/lib/librt.so.1
     cp -arfLv /lib/aarch64-linux-gnu/libpthread.so.0 $CURDIR/package/lib/libpthread.so.0
+elif [ "$(uname -s)" = "Darwin" ]; then
+    echo "Detected Darwin — system libraries linked dynamically, no bundled loader needed"
 else
     echo "Warning: Could not detect architecture for system library bundling"
 fi

backend/go/opus/run.sh

@@ -3,8 +3,13 @@ set -ex
 
 CURDIR=$(dirname "$(realpath "$0")")
 
-export LD_LIBRARY_PATH="$CURDIR"/lib:$LD_LIBRARY_PATH
-export OPUS_SHIM_LIBRARY="$CURDIR"/lib/libopusshim.so
+if [ "$(uname)" = "Darwin" ]; then
+	export DYLD_LIBRARY_PATH="$CURDIR"/lib:$DYLD_LIBRARY_PATH
+	export OPUS_SHIM_LIBRARY="$CURDIR"/lib/libopusshim.dylib
+else
+	export LD_LIBRARY_PATH="$CURDIR"/lib:$LD_LIBRARY_PATH
+	export OPUS_SHIM_LIBRARY="$CURDIR"/lib/libopusshim.so
+fi
 
 # If there is a lib/ld.so, use it
 if [ -f "$CURDIR"/lib/ld.so ]; then