DRY private range selection; add missing ranges

DRY a chunk of repeated code for finding a free private range.

Also fix it so that it will consider 10.255.0.1/16 and 192.168.255.1/24
(previously it would only check up to octet 254).

llarp/net/ip_range.cpp

@@ -101,4 +101,25 @@ namespace llarp
     return netmask_bits.ToString();
   }
 
+  std::optional<IPRange>
+  IPRange::FindPrivateRange(const std::list<IPRange>& excluding)
+  {
+    auto good = [&excluding](const IPRange& range) -> bool {
+      for (const auto& ex : excluding)
+        if (ex * range)
+          return false;
+      return true;
+    };
+    for (int oct = 16; oct <= 31; ++oct)
+      if (auto range = IPRange::FromIPv4(172, oct, 0, 1, 16); good(range))
+        return range;
+    for (int oct = 0; oct <= 255; ++oct)
+      if (auto range = IPRange::FromIPv4(10, oct, 0, 1, 16); good(range))
+        return range;
+    for (int oct = 0; oct <= 255; ++oct)
+      if (auto range = IPRange::FromIPv4(192, 168, oct, 1, 24); good(range))
+        return range;
+    return std::nullopt;
+  }
+
 }  // namespace llarp

llarp/net/ip_range.hpp

@@ -1,10 +1,13 @@
 #pragma once
-#include <ostream>
+
 #include "ip.hpp"
 #include "net_bits.hpp"
 #include <llarp/util/bits.hpp>
 #include <llarp/util/buffer.hpp>
 #include <llarp/util/types.hpp>
+
+#include <list>
+#include <optional>
 #include <string>
 
 namespace llarp
@@ -144,6 +147,10 @@ namespace llarp
 
     bool
     BDecode(llarp_buffer_t* buf);
+
+    /// Finds a free private use range not overlapping the given ranges.
+    static std::optional<IPRange>
+    FindPrivateRange(const std::list<IPRange>& excluding);
   };
 
   template <>

llarp/net/posix.cpp

@@ -90,35 +90,7 @@ namespace llarp::net
         }
       });
 
-      auto ownsRange = [&currentRanges](const IPRange& range) -> bool {
-        for (const auto& ownRange : currentRanges)
-        {
-          if (ownRange * range)
-            return true;
-        }
-        return false;
-      };
-      // generate possible ranges to in order of attempts
-      std::list<IPRange> possibleRanges;
-      for (byte_t oct = 16; oct < 32; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(172, oct, 0, 1, 16));
-      }
-      for (byte_t oct = 0; oct < 255; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(10, oct, 0, 1, 16));
-      }
-      for (byte_t oct = 0; oct < 255; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(192, 168, oct, 1, 24));
-      }
-      // for each possible range pick the first one we don't own
-      for (const auto& range : possibleRanges)
-      {
-        if (not ownsRange(range))
-          return range;
-      }
-      return std::nullopt;
+      return IPRange::FindPrivateRange(currentRanges);
     }
 
     std::optional<int> GetInterfaceIndex(ipaddr_t) const override

llarp/net/win32.cpp

@@ -151,35 +151,7 @@ namespace llarp::net
         }
       });
 
-      auto ownsRange = [&currentRanges](const IPRange& range) -> bool {
-        for (const auto& ownRange : currentRanges)
-        {
-          if (ownRange * range)
-            return true;
-        }
-        return false;
-      };
-      // generate possible ranges to in order of attempts
-      std::list<IPRange> possibleRanges;
-      for (byte_t oct = 16; oct < 32; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(172, oct, 0, 1, 16));
-      }
-      for (byte_t oct = 0; oct < 255; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(10, oct, 0, 1, 16));
-      }
-      for (byte_t oct = 0; oct < 255; ++oct)
-      {
-        possibleRanges.emplace_back(IPRange::FromIPv4(192, 168, oct, 1, 24));
-      }
-      // for each possible range pick the first one we don't own
-      for (const auto& range : possibleRanges)
-      {
-        if (not ownsRange(range))
-          return range;
-      }
-      return std::nullopt;
+      return IPRange::FindPrivateRange(currentRanges);
     }
 
     std::string