Add a novision build tag so the server can be built and tested off-device

server/common/kvm_vision.go

@@ -1,3 +1,5 @@
+//go:build !novision
+
 package common
 
 /*

server/common/kvm_vision_stub.go

@@ -0,0 +1,56 @@
+//go:build novision
+
+package common
+
+import (
+	"sync"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// This stub replaces the cgo capture bindings when the "novision" build tag is
+// set. The real implementation links against libkvm in dl_lib through cgo, so
+// building it needs CGO_ENABLED=1 and the riscv64 cross-compiler. Without this
+// stub, every package that reaches common is therefore out of reach of go vet
+// and go test on a workstation. It is never used in a device build.
+
+var (
+	kvmVision     *KvmVision
+	kvmVisionOnce sync.Once
+)
+
+type KvmVision struct{}
+
+func GetKvmVision() *KvmVision {
+	kvmVisionOnce.Do(func() {
+		kvmVision = &KvmVision{}
+		log.Debugf("kvm vision stub initialized")
+	})
+
+	return kvmVision
+}
+
+func (k *KvmVision) ReadMjpeg(width uint16, height uint16, quality uint16) (data []byte, result int) {
+	return nil, -1
+}
+
+func (k *KvmVision) ReadH264(width uint16, height uint16, bitRate uint16) (data []byte, result int) {
+	return nil, -1
+}
+
+func (k *KvmVision) SetHDMI(enable bool) int {
+	return 0
+}
+
+// HasHDMISignal reports no signal, which is what the real binding also returns
+// when the library is closed. A caller that polls it therefore sees a valid
+// state rather than a build without an input.
+func (k *KvmVision) HasHDMISignal() bool {
+	return false
+}
+
+func (k *KvmVision) SetGop(gop uint8) {}
+
+func (k *KvmVision) SetFrameDetect(frame uint8) {}
+
+func (k *KvmVision) Close() {}