Prototype with single host server and no admin panel (#2)

Reviewed-on: wrenn/sandbox#2
Co-authored-by: pptx704 <rafeed@omukk.dev>
Co-committed-by: pptx704 <rafeed@omukk.dev>

internal/network/allocator.go

@@ -0,0 +1,41 @@
+package network
+
+import (
+	"fmt"
+	"sync"
+)
+
+// SlotAllocator manages network slot indices for sandboxes.
+// Each sandbox needs a unique slot index for its network addressing.
+type SlotAllocator struct {
+	mu    sync.Mutex
+	inUse map[int]bool
+}
+
+// NewSlotAllocator creates a new slot allocator.
+func NewSlotAllocator() *SlotAllocator {
+	return &SlotAllocator{
+		inUse: make(map[int]bool),
+	}
+}
+
+// Allocate returns the next available slot index (1-based).
+func (a *SlotAllocator) Allocate() (int, error) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	for i := 1; i <= 65534; i++ {
+		if !a.inUse[i] {
+			a.inUse[i] = true
+			return i, nil
+		}
+	}
+	return 0, fmt.Errorf("no free network slots")
+}
+
+// Release frees a slot index for reuse.
+func (a *SlotAllocator) Release(index int) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	delete(a.inUse, index)
+}