1 files changed, 33 insertions, 9 deletions
diff --git a/src/serialize.h b/src/serialize.h
index c454ba16b7..91da6b0f80 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -296,9 +296,31 @@ uint64_t ReadCompactSize(Stream& is)
  * 2^32:           [0x8E 0xFE 0xFE 0xFF 0x00]
  */
 
-template<typename I>
+/**
+ * Mode for encoding VarInts.
+ *
+ * Currently there is no support for signed encodings. The default mode will not
+ * compile with signed values, and the legacy "nonnegative signed" mode will
+ * accept signed values, but improperly encode and decode them if they are
+ * negative. In the future, the DEFAULT mode could be extended to support
+ * negative numbers in a backwards compatible way, and additional modes could be
+ * added to support different varint formats (e.g. zigzag encoding).
+ */
+enum class VarIntMode { DEFAULT, NONNEGATIVE_SIGNED };
+
+template <VarIntMode Mode, typename I>
+struct CheckVarIntMode {
+    constexpr CheckVarIntMode()
+    {
+        static_assert(Mode != VarIntMode::DEFAULT || std::is_unsigned<I>::value, "Unsigned type required with mode DEFAULT.");
+        static_assert(Mode != VarIntMode::NONNEGATIVE_SIGNED || std::is_signed<I>::value, "Signed type required with mode NONNEGATIVE_SIGNED.");
+    }
+};
+
+template<VarIntMode Mode, typename I>
 inline unsigned int GetSizeOfVarInt(I n)
 {
+    CheckVarIntMode<Mode, I>();
     int nRet = 0;
     while(true) {
         nRet++;
@@ -312,9 +334,10 @@ inline unsigned int GetSizeOfVarInt(I n)
 template<typename I>
 inline void WriteVarInt(CSizeComputer& os, I n);
 
-template<typename Stream, typename I>
+template<typename Stream, VarIntMode Mode, typename I>
 void WriteVarInt(Stream& os, I n)
 {
+    CheckVarIntMode<Mode, I>();
     unsigned char tmp[(sizeof(n)*8+6)/7];
     int len=0;
     while(true) {
@@ -329,9 +352,10 @@ void WriteVarInt(Stream& os, I n)
     } while(len--);
 }
 
-template<typename Stream, typename I>
+template<typename Stream, VarIntMode Mode, typename I>
 I ReadVarInt(Stream& is)
 {
+    CheckVarIntMode<Mode, I>();
     I n = 0;
     while(true) {
         unsigned char chData = ser_readdata8(is);
@@ -351,7 +375,7 @@ I ReadVarInt(Stream& is)
 }
 
 #define FLATDATA(obj) CFlatData((char*)&(obj), (char*)&(obj) + sizeof(obj))
-#define VARINT(obj) WrapVarInt(REF(obj))
+#define VARINT(obj, ...) WrapVarInt<__VA_ARGS__>(REF(obj))
 #define COMPACTSIZE(obj) CCompactSize(REF(obj))
 #define LIMITED_STRING(obj,n) LimitedString< n >(REF(obj))
 
@@ -395,7 +419,7 @@ public:
     }
 };
 
-template<typename I>
+template<VarIntMode Mode, typename I>
 class CVarInt
 {
 protected:
@@ -405,12 +429,12 @@ public:
 
     template<typename Stream>
     void Serialize(Stream &s) const {
-        WriteVarInt<Stream,I>(s, n);
+        WriteVarInt<Stream,Mode,I>(s, n);
     }
 
     template<typename Stream>
     void Unserialize(Stream& s) {
-        n = ReadVarInt<Stream,I>(s);
+        n = ReadVarInt<Stream,Mode,I>(s);
     }
 };
 
@@ -461,8 +485,8 @@ public:
     }
 };
 
-template<typename I>
-CVarInt<I> WrapVarInt(I& n) { return CVarInt<I>(n); }
+template<VarIntMode Mode=VarIntMode::DEFAULT, typename I>
+CVarInt<Mode, I> WrapVarInt(I& n) { return CVarInt<Mode, I>{n}; }
 
 /**
  * Forward declarations