[coap] make CoAP start and stop reentrant (#5539)

include/openthread/coap.h

@@ -835,7 +835,8 @@ static inline otError otCoapSendRequest(otInstance *          aInstance,
  * @param[in]  aInstance  A pointer to an OpenThread instance.
  * @param[in]  aPort      The local UDP port to bind to.
  *
- * @retval OT_ERROR_NONE  Successfully started the CoAP server.
+ * @retval OT_ERROR_NONE    Successfully started the CoAP server.
+ * @retval OT_ERROR_FAILED  Failed to start the CoAP server.
  *
  */
 otError otCoapStart(otInstance *aInstance, uint16_t aPort);

src/core/backbone_router/backbone_tmf.hpp

@@ -64,10 +64,10 @@ public:
     }
 
     /**
-     * This method starts the TMF agent.
+     * This method starts the Backbone TMF agent.
      *
      * @retval OT_ERROR_NONE    Successfully started the CoAP service.
-     * @retval OT_ERROR_ALREADY Already started.
+     * @retval OT_ERROR_FAILED  Failed to start the Backbone TMF agent.
      *
      */
     otError Start(void);

src/core/coap/coap.cpp

@@ -1017,10 +1017,10 @@ Coap::Coap(Instance &aInstance)
 
 otError Coap::Start(uint16_t aPort, otNetifIdentifier aNetifIdentifier)
 {
-    otError error;
+    otError error        = OT_ERROR_NONE;
     bool    socketOpened = false;
 
-    VerifyOrExit(!mSocket.IsBound(), error = OT_ERROR_ALREADY);
+    VerifyOrExit(!mSocket.IsBound(), OT_NOOP);
 
     SuccessOrExit(error = mSocket.Open(&Coap::HandleUdpReceive, this));
     socketOpened = true;
@@ -1039,7 +1039,9 @@ exit:
 
 otError Coap::Stop(void)
 {
-    otError error;
+    otError error = OT_ERROR_NONE;
+
+    VerifyOrExit(mSocket.IsBound(), OT_NOOP);
 
     SuccessOrExit(error = mSocket.Close());
     ClearRequestsAndResponses();

src/core/coap/coap.hpp

@@ -610,7 +610,7 @@ public:
      * @param[in]  aNetifIdentifier  The network interface identifier to bind.
      *
      * @retval OT_ERROR_NONE    Successfully started the CoAP service.
-     * @retval OT_ERROR_ALREADY Already started.
+     * @retval OT_ERROR_FAILED  Failed to start CoAP agent.
      *
      */
     otError Start(uint16_t aPort, otNetifIdentifier aNetifIdentifier = OT_NETIF_UNSPECIFIED);

src/core/thread/tmf.hpp

@@ -67,7 +67,7 @@ public:
      * This method starts the TMF agent.
      *
      * @retval OT_ERROR_NONE    Successfully started the CoAP service.
-     * @retval OT_ERROR_ALREADY Already started.
+     * @retval OT_ERROR_FAILED  Failed to start the TMF agent.
      *
      */
     otError Start(void);