Protect pre/post request hooks with RWMutex to mitigate race conditio…

…ns (#597)

Co-authored-by: Jeevanandam M <jeeva@myjeeva.com>

client.go

@@ -139,9 +139,11 @@ type Client struct {
 	proxyURL           *url.URL
 	beforeRequest      []RequestMiddleware
 	udBeforeRequest    []RequestMiddleware
+  udBeforeRequestLock sync.RWMutex
 	preReqHook         PreRequestHook
 	successHooks       []SuccessHook
 	afterResponse      []ResponseMiddleware
+  afterResponseLock   sync.RWMutex
 	requestLog         RequestLogCallback
 	responseLog        ResponseLogCallback
 	errorHooks         []ErrorHook
@@ -432,7 +434,11 @@ func (c *Client) NewRequest() *Request {
 //			return nil 	// if its success otherwise return error
 //		})
 func (c *Client) OnBeforeRequest(m RequestMiddleware) *Client {
+	c.udBeforeRequestLock.Lock()
+	defer c.udBeforeRequestLock.Unlock()
+
 	c.udBeforeRequest = append(c.udBeforeRequest, m)
+
 	return c
 }
 
@@ -447,7 +453,11 @@ func (c *Client) OnBeforeRequest(m RequestMiddleware) *Client {
 //			return nil 	// if its success otherwise return error
 //		})
 func (c *Client) OnAfterResponse(m ResponseMiddleware) *Client {
+	c.afterResponseLock.Lock()
+	defer c.afterResponseLock.Unlock()
+
 	c.afterResponse = append(c.afterResponse, m)
+
 	return c
 }
 
@@ -978,6 +988,14 @@ func (c *Client) GetClient() *http.Client {
 // Executes method executes the given `Request` object and returns response
 // error.
 func (c *Client) execute(req *Request) (*Response, error) {
+	// Lock the user-defined pre-request hooks.
+	c.udBeforeRequestLock.RLock()
+	defer c.udBeforeRequestLock.RUnlock()
+
+	// Lock the post-request hooks.
+	c.afterResponseLock.RLock()
+	defer c.afterResponseLock.RUnlock()
+
 	// Apply Request middleware
 	var err error