Improve the 'network_id' configuration option:

The 'network_id' option allows an administrator to specify to which
network they intend a server to connect. Servers can leverage this
information to optimize routing and prune automatically discovered
cross-network connections.

This commit will, if merged:

- add support for the devnet keyword, which corresponds to network ID #2;
- report the network ID, if one is configured, in server_info

src/ripple/app/misc/NetworkOPs.cpp

@@ -2167,6 +2167,9 @@ Json::Value NetworkOPsImp::getServerInfo (bool human, bool admin, bool counters)
     if (human)
         info [jss::hostid] = getHostId (admin);
 
+    if (auto const netid = app_.overlay().networkID())
+        info [jss::network_id] = static_cast<Json::UInt>(*netid);
+
     info [jss::build_version] = BuildInfo::getVersionString ();
 
     info [jss::server_state] = strOperatingMode (admin);

src/ripple/overlay/Overlay.h

@@ -253,6 +253,18 @@ public:
     virtual
     Json::Value
     crawlShards(bool pubKey, std::uint32_t hops) = 0;
+
+    /** Returns the ID of the network this server is configured for, if any.
+
+        The ID is just a numerical identifier, with the IDs 0, 1 and 2 used to
+        identify the mainnet, the testnet and the devnet respectively.
+
+        @return The numerical identifier configured by the administrator of the
+                server. An unseated optional, otherwise.
+    */
+    virtual
+    boost::optional<std::uint32_t>
+    networkID() const = 0;
 };
 
 struct ScoreHasLedger

src/ripple/overlay/impl/OverlayImpl.cpp

@@ -1328,14 +1328,17 @@ setup_Overlay (BasicConfig const& config)
             if (id == "testnet")
                 id = "1";
 
+            if (id == "devnet")
+                id = "2";
+
             setup.networkID = beast::lexicalCastThrow<std::uint32_t>(id);
         }
     }
     catch (...)
     {
         Throw<std::runtime_error>(
-            "Configured [network_id] section is invalid: "
+            "Configured [network_id] section is invalid: must be a number "
-            "must be a number or one of the strings 'main' or 'testnet'");
+            "or one of the strings 'main', 'testnet' or 'devnet'.");
     }
 
     return setup;

src/ripple/overlay/impl/OverlayImpl.h

@@ -359,10 +359,15 @@ public:
         return peerDisconnectsCharges_;
     }
 
+    boost::optional<std::uint32_t>
+    networkID() const override
+    {
+        return networkID_;
+    }
+
     Json::Value
     crawlShards(bool pubKey, std::uint32_t hops) override;
 
-
     /** Called when the last link from a peer chain is received.
 
         @param id peer id that received the shard info.

src/ripple/protocol/jss.h

@@ -351,6 +351,7 @@ JSS ( missingCommand );             // error
 JSS ( name );                       // out: AmendmentTableImpl, PeerImp
 JSS ( needed_state_hashes );        // out: InboundLedger
 JSS ( needed_transaction_hashes );  // out: InboundLedger
+JSS ( network_id );                 // out: NetworkOPs
 JSS ( network_ledger );             // out: NetworkOPs
 JSS ( next_refresh_time );          // out: ValidatorSite
 JSS ( no_ripple );                  // out: AccountLines