[ip6] allow hop limit 0 (#3077)

src/core/net/ip6.cpp

@@ -138,7 +138,7 @@ otError Ip6::AddTunneledMplOption(Message &aMessage, Header &aHeader, MessageInf
     messageInfo.GetPeerAddr().mFields.m16[7] = HostSwap16(0x00fc);
 
     tunnelHeader.Init();
-    tunnelHeader.SetHopLimit(static_cast<uint8_t>(kDefaultHopLimit));
+    tunnelHeader.SetHopLimit(kDefaultHopLimit);
     tunnelHeader.SetPayloadLength(aHeader.GetPayloadLength() + sizeof(tunnelHeader));
     tunnelHeader.SetDestination(messageInfo.GetPeerAddr());
     tunnelHeader.SetNextHeader(kProtoIp6);
@@ -361,7 +361,7 @@ otError Ip6::SendDatagram(Message &aMessage, MessageInfo &aMessageInfo, IpProto
     header.Init();
     header.SetPayloadLength(payloadLength);
     header.SetNextHeader(aIpProto);
-    header.SetHopLimit(aMessageInfo.mHopLimit ? aMessageInfo.mHopLimit : static_cast<uint8_t>(kDefaultHopLimit));
+    header.SetHopLimit(aMessageInfo.mHopLimit);
 
     if (aMessageInfo.GetSockAddr().IsUnspecified() || aMessageInfo.GetSockAddr().IsMulticast())
     {

src/core/net/ip6.hpp

@@ -103,8 +103,8 @@ class Ip6 : public InstanceLocator
 public:
     enum
     {
-        kDefaultHopLimit   = 64,
-        kMaxDatagramLength = 1280,
+        kDefaultHopLimit   = OPENTHREAD_CONFIG_IPV6_DEFAULT_HOP_LIMIT,
+        kMaxDatagramLength = OPENTHREAD_CONFIG_IPV6_DEFAULT_MAX_DATAGRAM,
     };
 
     /**

src/core/net/socket.hpp

@@ -59,7 +59,11 @@ public:
      * This constructor initializes the object.
      *
      */
-    MessageInfo(void) { memset(this, 0, sizeof(*this)); }
+    MessageInfo(void)
+    {
+        memset(this, 0, sizeof(*this));
+        mHopLimit = kDefaultHopLimit;
+    }
 
     /**
      * This method returns a reference to the local socket address.
@@ -180,6 +184,12 @@ public:
      *
      */
     void SetLinkInfo(const void *aLinkInfo) { mLinkInfo = aLinkInfo; }
+
+private:
+    enum
+    {
+        kDefaultHopLimit = OPENTHREAD_CONFIG_IPV6_DEFAULT_HOP_LIMIT,
+    };
 };
 
 /**

src/core/openthread-core-default-config.h

@@ -1830,4 +1830,24 @@
 #ifndef OPENTHREAD_CONFIG_DEFAULT_SED_DATAGRAM_COUNT
 #define OPENTHREAD_CONFIG_DEFAULT_SED_DATAGRAM_COUNT 1
 #endif
+
+/**
+ * @def OPENTHREAD_CONFIG_IPV6_DEFAULT_HOP_LIMIT
+ *
+ * This setting configures the default hop limit of IPv6.
+ *
+ */
+#ifndef OPENTHREAD_CONFIG_IPV6_DEFAULT_HOP_LIMIT
+#define OPENTHREAD_CONFIG_IPV6_DEFAULT_HOP_LIMIT 64
+#endif
+
+/**
+ * @def OPENTHREAD_CONFIG_IPV6_DEFAULT_MAX_DATAGRAM
+ *
+ * This setting configures the max datagram length of IPv6.
+ *
+ */
+#ifndef OPENTHREAD_CONFIG_IPV6_DEFAULT_MAX_DATAGRAM
+#define OPENTHREAD_CONFIG_IPV6_DEFAULT_MAX_DATAGRAM 1280
+#endif
 #endif // OPENTHREAD_CORE_DEFAULT_CONFIG_H_