Merge #21677: fuzz: Avoid use of low file descriptor ids (which may be in use) in FuzzedSock

6262182b3f Avoid use of low file descriptor ids (which may be in use) in FuzzedSock and StaticContentsSock (practicalswift)

Pull request description:

  Avoid use of low file descriptor ids (which may be in use) in `FuzzedSock`.

  Context: https://github.com/bitcoin/bitcoin/pull/21630/files#r610694541

ACKs for top commit:
  vasild:
    ACK 6262182b3f

Tree-SHA512: e622acb4d01446c3db01adbbbb779038be7247e13f3f4e72c614bc2880c3efd710fd3b189f87abb00f236fa5ddf91f4c215f420ca4eb08a97aaba31593254c3d

src/test/fuzz/util.h

@@ -577,15 +577,15 @@ class FuzzedSock : public Sock
 public:
     explicit FuzzedSock(FuzzedDataProvider& fuzzed_data_provider) : m_fuzzed_data_provider{fuzzed_data_provider}
     {
-          m_socket = fuzzed_data_provider.ConsumeIntegral<SOCKET>();
+          m_socket = fuzzed_data_provider.ConsumeIntegralInRange<SOCKET>(INVALID_SOCKET - 1, INVALID_SOCKET);
     }
 
     ~FuzzedSock() override
     {
         // Sock::~Sock() will be called after FuzzedSock::~FuzzedSock() and it will call
         // Sock::Reset() (not FuzzedSock::Reset()!) which will call CloseSocket(m_socket).
-        // Avoid closing an arbitrary file descriptor (m_socket is just a random number which
-        // may concide with a real opened file descriptor).
+        // Avoid closing an arbitrary file descriptor (m_socket is just a random very high number which
+        // theoretically may concide with a real opened file descriptor).
         Reset();
     }
 

src/test/util/net.h

@@ -78,8 +78,7 @@ public:
     explicit StaticContentsSock(const std::string& contents) : m_contents{contents}, m_consumed{0}
     {
         // Just a dummy number that is not INVALID_SOCKET.
-        static_assert(INVALID_SOCKET != 1000);
-        m_socket = 1000;
+        m_socket = INVALID_SOCKET - 1;
     }
 
     ~StaticContentsSock() override { Reset(); }