Adding upstream version 2.52.6.

Signed-off-by: Daniel Baumann <daniel@debian.org>

middleware/idempotency/locker.go

@@ -0,0 +1,53 @@
+package idempotency
+
+import (
+	"sync"
+)
+
+// Locker implements a spinlock for a string key.
+type Locker interface {
+	Lock(key string) error
+	Unlock(key string) error
+}
+
+type MemoryLock struct {
+	mu sync.Mutex
+
+	keys map[string]*sync.Mutex
+}
+
+func (l *MemoryLock) Lock(key string) error {
+	l.mu.Lock()
+	mu, ok := l.keys[key]
+	if !ok {
+		mu = new(sync.Mutex)
+		l.keys[key] = mu
+	}
+	l.mu.Unlock()
+
+	mu.Lock()
+
+	return nil
+}
+
+func (l *MemoryLock) Unlock(key string) error {
+	l.mu.Lock()
+	mu, ok := l.keys[key]
+	l.mu.Unlock()
+	if !ok {
+		// This happens if we try to unlock an unknown key
+		return nil
+	}
+
+	mu.Unlock()
+
+	return nil
+}
+
+func NewMemoryLock() *MemoryLock {
+	return &MemoryLock{
+		keys: make(map[string]*sync.Mutex),
+	}
+}
+
+var _ Locker = (*MemoryLock)(nil)