[message] add Message::SubType (#4977)

src/core/common/message.hpp

@@ -242,7 +242,11 @@ public:
         kTypeOther       = 3, ///< Other (data) message.
     };
 
-    enum
+    /**
+     * This enumeration represents the message sub-type.
+     *
+     */
+    enum SubType
     {
         kSubTypeNone                   = 0,  ///< None
         kSubTypeMleAnnounce            = 1,  ///< MLE Announce
@@ -351,7 +355,7 @@ public:
      * @returns The sub type of the message.
      *
      */
-    uint8_t GetSubType(void) const { return GetMetadata().mSubType; }
+    SubType GetSubType(void) const { return static_cast<SubType>(GetMetadata().mSubType); }
 
     /**
      * This method sets the message sub type.
@@ -359,7 +363,7 @@ public:
      * @param[in]  aSubType  The message sub type.
      *
      */
-    void SetSubType(uint8_t aSubType) { GetMetadata().mSubType = aSubType; }
+    void SetSubType(SubType aSubType) { GetMetadata().mSubType = aSubType; }
 
     /**
      * This method returns whether or not the message is of MLE subtype.

src/core/meshcop/dtls.cpp

@@ -902,7 +902,7 @@ void Dtls::HandleMbedtlsDebug(void *ctx, int level, const char *, int, const cha
     }
 }
 
-otError Dtls::HandleDtlsSend(const uint8_t *aBuf, uint16_t aLength, uint8_t aMessageSubType)
+otError Dtls::HandleDtlsSend(const uint8_t *aBuf, uint16_t aLength, Message::SubType aMessageSubType)
 {
     otError      error   = OT_ERROR_NONE;
     ot::Message *message = NULL;

src/core/meshcop/dtls.hpp

@@ -367,7 +367,7 @@ public:
      * @param[in]  aMessageSubType  The default message sub-type.
      *
      */
-    void SetDefaultMessageSubType(uint8_t aMessageSubType) { mMessageDefaultSubType = aMessageSubType; }
+    void SetDefaultMessageSubType(Message::SubType aMessageSubType) { mMessageDefaultSubType = aMessageSubType; }
 
     /**
      * This method returns the DTLS session's peer address.
@@ -425,7 +425,7 @@ private:
     static void HandleUdpReceive(void *aContext, otMessage *aMessage, const otMessageInfo *aMessageInfo);
 
     void    HandleDtlsReceive(const uint8_t *aBuf, uint16_t aLength);
-    otError HandleDtlsSend(const uint8_t *aBuf, uint16_t aLength, uint8_t aMessageSubType);
+    otError HandleDtlsSend(const uint8_t *aBuf, uint16_t aLength, Message::SubType aMessageSubType);
 
     static void HandleUdpTransmit(Tasklet &aTasklet);
     void        HandleUdpTransmit(void);
@@ -489,8 +489,8 @@ private:
     TransportCallback mTransportCallback;
     void *            mTransportContext;
 
-    uint8_t mMessageSubType;
-    uint8_t mMessageDefaultSubType;
+    Message::SubType mMessageSubType;
+    Message::SubType mMessageDefaultSubType;
 };
 
 } // namespace MeshCoP

src/core/thread/mesh_forwarder.hpp

@@ -254,7 +254,7 @@ public:
      *                       Use Message::kSubTypeNone remove all messages for @p aChild.
      *
      */
-    void RemoveMessages(Child &aChild, uint8_t aSubType);
+    void RemoveMessages(Child &aChild, Message::SubType aSubType);
 
     /**
      * This method frees unicast/multicast MLE Data Responses from Send Message Queue if any.

src/core/thread/mesh_forwarder_ftd.cpp

@@ -249,7 +249,7 @@ exit:
     return error;
 }
 
-void MeshForwarder::RemoveMessages(Child &aChild, uint8_t aSubType)
+void MeshForwarder::RemoveMessages(Child &aChild, Message::SubType aSubType)
 {
     Mle::MleRouter &mle = Get<Mle::MleRouter>();
     Message *       nextMessage;