feat: add OnClose hooks in Client instance (#1054)

Author: pior

client.go

@@ -95,6 +95,9 @@ type (
 	// SuccessHook type is for reacting to request success
 	SuccessHook func(*Client, *Response)
 
+	// CloseHook type is for reacting to client closing
+	CloseHook func()
+
 	// RequestFunc type is for extended manipulation of the Request instance
 	RequestFunc func(*Request) *Request
 
@@ -215,6 +218,7 @@ type Client struct {
 	invalidHooks             []ErrorHook
 	panicHooks               []ErrorHook
 	successHooks             []SuccessHook
+	closeHooks               []CloseHook
 	contentTypeEncoders      map[string]ContentTypeEncoder
 	contentTypeDecoders      map[string]ContentTypeDecoder
 	contentDecompresserKeys  []string
@@ -838,6 +842,15 @@ func (c *Client) OnPanic(h ErrorHook) *Client {
 	return c
 }
 
+// OnClose method adds a callback that will be run whenever the client is closed.
+// The hooks are executed in the order they were registered.
+func (c *Client) OnClose(h CloseHook) *Client {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	c.closeHooks = append(c.closeHooks, h)
+	return c
+}
+
 // ContentTypeEncoders method returns all the registered content type encoders.
 func (c *Client) ContentTypeEncoders() map[string]ContentTypeEncoder {
 	c.lock.RLock()
@@ -2221,10 +2234,14 @@ func (c *Client) Clone(ctx context.Context) *Client {
 
 // Close method performs cleanup and closure activities on the client instance
 func (c *Client) Close() error {
+	// Execute close hooks first
+	c.onCloseHooks()
+
 	if c.LoadBalancer() != nil {
 		silently(c.LoadBalancer().Close())
 	}
 	close(c.certWatcherStopChan)
+
 	return nil
 }
 
@@ -2381,6 +2398,15 @@ func (c *Client) onInvalidHooks(req *Request, err error) {
 	}
 }
 
+// Helper to run closeHooks hooks.
+func (c *Client) onCloseHooks() {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	for _, h := range c.closeHooks {
+		h()
+	}
+}
+
 func (c *Client) debugf(format string, v ...any) {
 	if c.IsDebug() {
 		c.Logger().Debugf(format, v...)

client_test.go

@@ -1524,3 +1524,35 @@ func TestClientCircuitBreaker(t *testing.T) {
 	assertError(t, err)
 	assertEqual(t, uint32(1), c.circuitBreaker.failureCount.Load())
 }
+
+func TestClientOnClose(t *testing.T) {
+	var hookExecuted bool
+
+	c := dcnl()
+	c.OnClose(func() {
+		hookExecuted = true
+	})
+
+	err := c.Close()
+	assertNil(t, err)
+	assertEqual(t, true, hookExecuted)
+}
+
+func TestClientOnCloseMultipleHooks(t *testing.T) {
+	var executionOrder []string
+
+	c := dcnl()
+	c.OnClose(func() {
+		executionOrder = append(executionOrder, "first")
+	})
+	c.OnClose(func() {
+		executionOrder = append(executionOrder, "second")
+	})
+	c.OnClose(func() {
+		executionOrder = append(executionOrder, "third")
+	})
+
+	err := c.Close()
+	assertNil(t, err)
+	assertEqual(t, []string{"first", "second", "third"}, executionOrder)
+}