[mle] add field-specific length methods to Challenge/Response TLVs (#3937)

src/core/thread/mle.cpp

@@ -2384,7 +2384,7 @@ otError Mle::SendChildUpdateResponse(const uint8_t *aTlvs, uint8_t aNumTlvs, con
             break;
 
         case Tlv::kResponse:
-            SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetLength()));
+            SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetChallengeLength()));
             break;
 
         case Tlv::kLinkFrameCounter:
@@ -3212,7 +3212,7 @@ otError Mle::HandleParentResponse(const Message &aMessage, const Ip6::MessageInf
     // Response
     SuccessOrExit(error = Tlv::GetTlv(aMessage, Tlv::kResponse, sizeof(response), response));
     VerifyOrExit(response.IsValid() &&
-                     memcmp(response.GetResponse(), mParentRequest.mChallenge, response.GetLength()) == 0,
+                     memcmp(response.GetResponse(), mParentRequest.mChallenge, response.GetResponseLength()) == 0,
                  error = OT_ERROR_PARSE);
 
     aMessageInfo.GetPeerAddr().ToExtAddress(extAddress);

src/core/thread/mle_router.cpp

@@ -691,7 +691,7 @@ otError MleRouter::SendLinkAccept(const Ip6::MessageInfo &aMessageInfo,
     SuccessOrExit(error = AppendHeader(*message, command));
     SuccessOrExit(error = AppendVersion(*message));
     SuccessOrExit(error = AppendSourceAddress(*message));
-    SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetLength()));
+    SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetChallengeLength()));
     SuccessOrExit(error = AppendLinkFrameCounter(*message));
     SuccessOrExit(error = AppendMleFrameCounter(*message));
 
@@ -1898,7 +1898,7 @@ void MleRouter::SendParentResponse(Child *aChild, const ChallengeTlv &aChallenge
     SuccessOrExit(error = AppendLeaderData(*message));
     SuccessOrExit(error = AppendLinkFrameCounter(*message));
     SuccessOrExit(error = AppendMleFrameCounter(*message));
-    SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetLength()));
+    SuccessOrExit(error = AppendResponse(*message, aChallenge.GetChallenge(), aChallenge.GetChallengeLength()));
 #if OPENTHREAD_CONFIG_ENABLE_TIME_SYNC
     if (aChild->IsTimeSyncEnabled())
     {

src/core/thread/mle_tlvs.hpp

@@ -411,7 +411,7 @@ public:
     /**
      * This method indicates whether or not the TLV appears to be well-formed.
      *
-     * OpenThread only generates Challenge values with 8-byte length. As a result, a Response value lengths must also
+     * OpenThread only generates Challenge values with 8-byte length. As a result, Response value lengths must also
      * have 8-byte length.
      *
      * @retval TRUE   If the TLV appears to be well-formed.
@@ -420,6 +420,14 @@ public:
      */
     bool IsValid(void) const { return GetLength() >= sizeof(*this) - sizeof(Tlv); }
 
+    /**
+     * This method returns the Response length.
+     *
+     * @returns The Response length.
+     *
+     */
+    uint8_t GetResponseLength(void) const { return GetLength() <= sizeof(mResponse) ? GetLength() : sizeof(mResponse); }
+
     /**
      * This method returns a pointer to the Response value.
      *
@@ -434,7 +442,7 @@ public:
      * @param[in]  aResponse  A pointer to the Response value.
      *
      */
-    void SetResponse(const uint8_t *aResponse) { memcpy(mResponse, aResponse, GetLength()); }
+    void SetResponse(const uint8_t *aResponse) { memcpy(mResponse, aResponse, GetResponseLength()); }
 
 private:
     uint8_t mResponse[kMaxSize];