Add support for reserved peer slots:

This commit allows server operators to reserve slots for specific
peers (identified by the peer's public node identity) and to make
changes to the reservations while the server is operating.

This commit closes #2938

src/ripple/overlay/impl/OverlayImpl.cpp

@@ -278,18 +278,25 @@ OverlayImpl::onHandoff (std::unique_ptr <beast::asio::ssl_bundle>&& ssl_bundle,
         return handoff;
     }
 
-    auto const result = m_peerFinder->activate (slot, *publicKey,
-        static_cast<bool>(app_.cluster().member(*publicKey)));
-    if (result != PeerFinder::Result::success)
     {
-        m_peerFinder->on_closed(slot);
-        JLOG(journal.debug()) <<
-            "Peer " << remote_endpoint << " redirected, slots full";
-        handoff.moved = false;
-        handoff.response = makeRedirectResponse(slot, request,
-            remote_endpoint.address());
-        handoff.keep_alive = beast::rfc2616::is_keep_alive(request);
-        return handoff;
+        // The node gets a reserved slot if it is in our cluster
+        // or if it has a reservation.
+        bool const reserved {
+            static_cast<bool>(app_.cluster().member(*publicKey))
+            || app_.peerReservations().contains(*publicKey)
+        };
+        auto const result = m_peerFinder->activate(slot, *publicKey, reserved);
+        if (result != PeerFinder::Result::success)
+        {
+            m_peerFinder->on_closed(slot);
+            JLOG(journal.debug())
+                << "Peer " << remote_endpoint << " redirected, slots full";
+            handoff.moved = false;
+            handoff.response = makeRedirectResponse(
+                    slot, request, remote_endpoint.address());
+            handoff.keep_alive = beast::rfc2616::is_keep_alive(request);
+            return handoff;
+        }
     }
 
     auto const peer = std::make_shared<PeerImp>(app_, id,

src/ripple/overlay/impl/PeerImp.cpp

@@ -254,6 +254,12 @@ PeerImp::crawl() const
     return boost::beast::detail::iequals(iter->value(), "public");
 }
 
+bool
+PeerImp::cluster() const
+{
+    return static_cast<bool>(app_.cluster().member(publicKey_));
+}
+
 std::string
 PeerImp::getVersion() const
 {
@@ -1614,7 +1620,7 @@ PeerImp::onMessage (std::shared_ptr <protocol::TMProposeSet> const& m)
 {
     protocol::TMProposeSet& set = *m;
 
-    if (set.has_hops() && ! slot_->cluster())
+    if (set.has_hops() && ! cluster())
         set.set_hops(set.hops() + 1);
 
     auto const sig = makeSlice(set.signature());
@@ -1983,7 +1989,7 @@ PeerImp::onMessage (std::shared_ptr <protocol::TMValidation> const& m)
 {
     auto const closeTime = app_.timeKeeper().closeTime();
 
-    if (m->has_hops() && ! slot_->cluster())
+    if (m->has_hops() && ! cluster())
         m->set_hops(m->hops() + 1);
 
     if (m->validation ().size () < 50)

src/ripple/overlay/impl/PeerImp.h

@@ -281,10 +281,7 @@ public:
     crawl() const;
 
     bool
-    cluster() const override
-    {
-        return slot_->cluster();
-    }
+    cluster() const override;
 
     void
     check();

src/ripple/overlay/impl/PeerReservationTable.cpp

@@ -0,0 +1,168 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2019 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <ripple/overlay/PeerReservationTable.h>
+
+#include <ripple/basics/Log.h>
+#include <ripple/core/DatabaseCon.h>
+#include <ripple/json/json_value.h>
+#include <ripple/protocol/PublicKey.h>
+#include <ripple/protocol/jss.h>
+
+#include <boost/optional.hpp>
+
+#include <algorithm>
+#include <iterator>
+#include <mutex>
+#include <string>
+#include <vector>
+
+namespace ripple {
+
+auto
+PeerReservation::toJson() const -> Json::Value
+{
+    Json::Value result{Json::objectValue};
+    result[jss::node] = toBase58(TokenType::NodePublic, nodeId);
+    if (!description.empty())
+    {
+        result[jss::description] = description;
+    }
+    return result;
+}
+
+auto
+PeerReservationTable::list() const -> std::vector<PeerReservation>
+{
+    std::vector<PeerReservation> list;
+    {
+        std::lock_guard<std::mutex> lock(mutex_);
+        list.reserve(table_.size());
+        std::copy(table_.begin(), table_.end(), std::back_inserter(list));
+    }
+    std::sort(list.begin(), list.end());
+    return list;
+}
+
+// See `ripple/app/main/DBInit.cpp` for the `CREATE TABLE` statement.
+// It is unfortunate that we do not get to define a function for it.
+
+// We choose a `bool` return type to fit in with the error handling scheme
+// of other functions called from `ApplicationImp::setup`, but we always
+// return "no error" (`true`) because we can always return an empty table.
+bool
+PeerReservationTable::load(DatabaseCon& connection)
+{
+    std::lock_guard<std::mutex> lock(mutex_);
+
+    connection_ = &connection;
+    auto db = connection_->checkoutDb();
+
+    boost::optional<std::string> valPubKey, valDesc;
+    // We should really abstract the table and column names into constants,
+    // but no one else does. Because it is too tedious? It would be easy if we
+    // had a jOOQ for C++.
+    soci::statement st =
+        (db->prepare << "SELECT PublicKey, Description FROM PeerReservations;",
+         soci::into(valPubKey),
+         soci::into(valDesc));
+    st.execute();
+    while (st.fetch())
+    {
+        if (!valPubKey || !valDesc)
+        {
+            // This represents a `NULL` in a `NOT NULL` column. It should be
+            // unreachable.
+            continue;
+        }
+        auto const optNodeId =
+            parseBase58<PublicKey>(TokenType::NodePublic, *valPubKey);
+        if (!optNodeId)
+        {
+            JLOG(journal_.warn()) << "load: not a public key: " << valPubKey;
+            continue;
+        }
+        table_.insert(PeerReservation{*optNodeId, *valDesc});
+    }
+
+    return true;
+}
+
+auto
+PeerReservationTable::insert_or_assign(
+        PeerReservation const& reservation)
+    -> boost::optional<PeerReservation>
+{
+    boost::optional<PeerReservation> previous;
+
+    std::lock_guard<std::mutex> lock(mutex_);
+
+    auto hint = table_.find(reservation);
+    if (hint != table_.end()) {
+        // The node already has a reservation. Remove it.
+        // `std::unordered_set` does not have an `insert_or_assign` method,
+        // and sadly makes it impossible for us to implement one efficiently:
+        // https://stackoverflow.com/q/49651835/618906
+        // Regardless, we don't expect this function to be called often, or
+        // for the table to be very large, so this less-than-ideal
+        // remove-then-insert is acceptable in order to present a better API.
+        previous = *hint;
+        // We should pick an adjacent location for the insertion hint.
+        // Decrementing may be illegal if the found reservation is at the
+        // beginning. Incrementing is always legal; at worst we'll point to
+        // the end.
+        auto const deleteme = hint;
+        ++hint;
+        table_.erase(deleteme);
+    }
+    table_.insert(hint, reservation);
+
+    auto db = connection_->checkoutDb();
+    *db << "INSERT INTO PeerReservations (PublicKey, Description) "
+           "VALUES (:nodeId, :desc) "
+           "ON CONFLICT (PublicKey) DO UPDATE SET "
+           "Description=excluded.Description",
+        soci::use(toBase58(TokenType::NodePublic, reservation.nodeId)),
+        soci::use(reservation.description);
+
+    return previous;
+}
+
+auto
+PeerReservationTable::erase(PublicKey const& nodeId)
+    -> boost::optional<PeerReservation>
+{
+    boost::optional<PeerReservation> previous;
+
+    std::lock_guard<std::mutex> lock(mutex_);
+
+    auto const it = table_.find({nodeId});
+    if (it != table_.end())
+    {
+        previous = *it;
+        table_.erase(it);
+        auto db = connection_->checkoutDb();
+        *db << "DELETE FROM PeerReservations WHERE PublicKey = :nodeId",
+            soci::use(toBase58(TokenType::NodePublic, nodeId));
+    }
+
+    return previous;
+}
+
+}  // namespace ripple