Do not permit copying FastRandomContexts

Author: sipa

src/random.cpp

@@ -464,6 +464,20 @@ FastRandomContext::FastRandomContext(bool fDeterministic) : requires_seed(!fDete
     rng.SetKey(seed.begin(), 32);
 }
 
+FastRandomContext& FastRandomContext::operator=(FastRandomContext&& from) noexcept
+{
+    requires_seed = from.requires_seed;
+    rng = from.rng;
+    std::copy(std::begin(from.bytebuf), std::end(from.bytebuf), std::begin(bytebuf));
+    bytebuf_size = from.bytebuf_size;
+    bitbuf = from.bitbuf;
+    bitbuf_size = from.bitbuf_size;
+    from.requires_seed = true;
+    from.bytebuf_size = 0;
+    from.bitbuf_size = 0;
+    return *this;
+}
+
 void RandomInit()
 {
     RDRandInit();

src/random.h

@@ -76,6 +76,14 @@ class FastRandomContext {
     /** Initialize with explicit seed (only for testing) */
     explicit FastRandomContext(const uint256& seed);
 
+    // Do not permit copying a FastRandomContext (move it, or create a new one to get reseeded).
+    FastRandomContext(const FastRandomContext&) = delete;
+    FastRandomContext(FastRandomContext&&) = delete;
+    FastRandomContext& operator=(const FastRandomContext&) = delete;
+
+    /** Move a FastRandomContext. If the original one is used again, it will be reseeded. */
+    FastRandomContext& operator=(FastRandomContext&& from) noexcept;
+
     /** Generate a random 64-bit integer. */
     uint64_t rand64()
     {