func MustFromContext(ctx context.Context) *Instance {
	v := FromContext(ctx)
	if v == nil {
		panic("V is not in context.")
	}
	return v
}
MustFromContext returns an Instance from the given context, or panics if not present.
package core
import (
	"context"
)
type v2rayKeyType int
const v2rayKey v2rayKeyType = 1
func FromContext(ctx context.Context) *Instance {
	if s, ok := ctx.Value(v2rayKey).(*Instance); ok {
		return s
	}
	return nil
}