Add [overlay] configuration section (experimental):

This configuration section uses the new BasicConfig interface that supports
key-value pairs in the section. Some exposition is added to the example cfg
file. The new settings for overlay are related to the Hub and Spoke feature
which is currently in development. Production servers should not set
these configuration options, they are clearly marked experimental in the
example cfg file.

Conflicts:
	src/ripple/overlay/impl/OverlayImpl.cpp
	src/ripple/overlay/impl/OverlayImpl.h
	src/ripple/overlay/impl/PeerImp.cpp
	src/ripple/overlay/impl/PeerImp.h

src/ripple/overlay/impl/OverlayImpl.cpp

@@ -71,6 +71,17 @@ OverlayImpl::OverlayImpl (Stoppable& parent,
     , m_resolver (resolver)
     , m_nextShortId (0)
 {
+    auto const& section = getConfig()["overlay"];
+    set (setup_.use_handshake, "use_handshake", section);
+    set (setup_.auto_connect, "auto_connect", section);
+    std::string promote;
+    set (promote, "become_superpeer", section);
+    if (promote == "never")
+        setup_.promote = Promote::never;
+    else if (promote == "always")
+        setup_.promote = Promote::always;
+    else
+        setup_.promote = Promote::automatic;
 }
 
 OverlayImpl::~OverlayImpl ()
@@ -83,6 +94,12 @@ OverlayImpl::~OverlayImpl ()
         return this->m_child_count == 0; });
 }
 
+OverlayImpl::Setup const&
+OverlayImpl::setup() const
+{
+    return setup_;
+}
+
 void
 OverlayImpl::accept (socket_type&& socket)
 {
@@ -436,10 +453,10 @@ OverlayImpl::getActivePeers ()
 
     ret.reserve (m_publicKeyMap.size ());
 
-    for (auto const& pair : m_publicKeyMap)
+    for (auto const& e : m_publicKeyMap)
     {
-        assert (pair.second);
-        ret.push_back (pair.second);
+        assert (e.second);
+        ret.push_back (e.second);
     }
 
     return ret;

src/ripple/overlay/impl/OverlayImpl.h

@@ -52,13 +52,29 @@ private:
     using error_code = boost::system::error_code;
     using yield_context = boost::asio::yield_context;
 
+    enum class Promote
+    {
+        automatic,
+        never,
+        always
+    };
+
+    struct Setup
+    {
+        bool use_handshake = false;
+        bool auto_connect = true;
+        Promote promote = Promote::automatic;
+    };
+
     typedef hash_map <PeerFinder::Slot::ptr,
-                      std::weak_ptr <PeerImp>> PeersBySlot;
+        std::weak_ptr <PeerImp>> PeersBySlot;
 
     typedef hash_map <RippleAddress, Peer::ptr> PeerByPublicKey;
 
     typedef hash_map <Peer::ShortId, Peer::ptr> PeerByShortId;
 
+    Setup setup_;
+
     // VFALCO TODO Change to regular mutex and eliminate re-entrancy
     std::recursive_mutex m_mutex;
 
@@ -114,6 +130,9 @@ public:
     OverlayImpl (OverlayImpl const&) = delete;
     OverlayImpl& operator= (OverlayImpl const&) = delete;
 
+    Setup const&
+    setup() const;
+
     void
     connect (beast::IP::Endpoint const& remote_endpoint) override;