Introduce BigEndian wrapper and use it for netaddress ports

Author: sipa

src/netaddress.h

@@ -141,7 +141,7 @@ class CSubNet
 class CService : public CNetAddr
 {
     protected:
-        unsigned short port; // host order
+        uint16_t port; // host order
 
     public:
         CService();
@@ -168,13 +168,7 @@ class CService : public CNetAddr
         template <typename Stream, typename Operation>
         inline void SerializationOp(Stream& s, Operation ser_action) {
             READWRITE(ip);
-
-            // TODO: introduce native support for BE serialization in serialize.h
-            unsigned short portN = htons(port);
-            READWRITE(Span<unsigned char>((unsigned char*)&portN, 2));
-            if (ser_action.ForRead()) {
-                 port = ntohs(portN);
-            }
+            READWRITE(WrapBigEndian(port));
         }
 };
 

src/serialize.h

@@ -79,6 +79,11 @@ template<typename Stream> inline void ser_writedata16(Stream &s, uint16_t obj)
     obj = htole16(obj);
     s.write((char*)&obj, 2);
 }
+template<typename Stream> inline void ser_writedata16be(Stream &s, uint16_t obj)
+{
+    obj = htobe16(obj);
+    s.write((char*)&obj, 2);
+}
 template<typename Stream> inline void ser_writedata32(Stream &s, uint32_t obj)
 {
     obj = htole32(obj);
@@ -101,6 +106,12 @@ template<typename Stream> inline uint16_t ser_readdata16(Stream &s)
     s.read((char*)&obj, 2);
     return le16toh(obj);
 }
+template<typename Stream> inline uint16_t ser_readdata16be(Stream &s)
+{
+    uint16_t obj;
+    s.read((char*)&obj, 2);
+    return be16toh(obj);
+}
 template<typename Stream> inline uint32_t ser_readdata32(Stream &s)
 {
     uint32_t obj;
@@ -411,6 +422,40 @@ class CVarInt
     }
 };
 
+/** Serialization wrapper class for big-endian integers.
+ *
+ * Use this wrapper around integer types that are stored in memory in native
+ * byte order, but serialized in big endian notation. This is only intended
+ * to implement serializers that are compatible with existing formats, and
+ * its use is not recommended for new data structures.
+ *
+ * Only 16-bit types are supported for now.
+ */
+template<typename I>
+class BigEndian
+{
+protected:
+    I& m_val;
+public:
+    explicit BigEndian(I& val) : m_val(val)
+    {
+        static_assert(std::is_unsigned<I>::value, "BigEndian type must be unsigned integer");
+        static_assert(sizeof(I) == 2 && std::numeric_limits<I>::min() == 0 && std::numeric_limits<I>::max() == std::numeric_limits<uint16_t>::max(), "Unsupported BigEndian size");
+    }
+
+    template<typename Stream>
+    void Serialize(Stream& s) const
+    {
+        ser_writedata16be(s, m_val);
+    }
+
+    template<typename Stream>
+    void Unserialize(Stream& s)
+    {
+        m_val = ser_readdata16be(s);
+    }
+};
+
 class CCompactSize
 {
 protected:
@@ -461,6 +506,9 @@ class LimitedString
 template<VarIntMode Mode=VarIntMode::DEFAULT, typename I>
 CVarInt<Mode, I> WrapVarInt(I& n) { return CVarInt<Mode, I>{n}; }
 
+template<typename I>
+BigEndian<I> WrapBigEndian(I& n) { return BigEndian<I>(n); }
+
 /**
  * Forward declarations
  */