Create health_check rpc

* Gives a summary of the health of the node:
  Healthy, Warning, or Critical

* Last validated ledger age:
  <7s is Healthy,
  7s to 20s is Warning
  > 20s is Critcal

* If amendment blocked, Critical

* Number of peers:
  > 7 is Healthy
  1 to 7 is Warning
  0 is Critical

* server state:
  One of full, validating or proposing is Healthy
  One of syncing, tracking or connected is Warning
  All other states are Critical

* load factor:
  <= 100 is Healthy
  101 to 999 is Warning
  >= 1000 is Critical

* If not Healthy, info field contains data that is considered not
  Healthy.

Fixes: XRPLF#2809

Builds/CMake/RippledCore.cmake

@@ -573,6 +573,7 @@ target_sources (rippled PRIVATE
   src/ripple/rpc/handlers/FetchInfo.cpp
   src/ripple/rpc/handlers/GatewayBalances.cpp
   src/ripple/rpc/handlers/GetCounts.cpp
+  src/ripple/rpc/handlers/HealthCheck.cpp
   src/ripple/rpc/handlers/LedgerAccept.cpp
   src/ripple/rpc/handlers/LedgerCleanerHandler.cpp
   src/ripple/rpc/handlers/LedgerClosed.cpp

src/ripple/app/main/Main.cpp

@@ -147,6 +147,7 @@ void printHelp (const po::options_description& desc)
            "     fetch_info [clear]\n"
            "     gateway_balances [<ledger>] <issuer_account> [ <hotwallet> [ <hotwallet> ]]\n"
            "     get_counts\n"
+           "     health_check\n"
            "     json <method> <json>\n"
            "     ledger [<id>|current|closed|validated] [full]\n"
            "     ledger_accept\n"

src/ripple/net/impl/RPCCall.cpp

@@ -1178,6 +1178,7 @@ class RPCParser
             {   "fetch_info",           &RPCParser::parseFetchInfo,             0,  1   },
             {   "gateway_balances",     &RPCParser::parseGatewayBalances,       1, -1   },
             {   "get_counts",           &RPCParser::parseGetCounts,             0,  1   },
+            {   "health_check",         &RPCParser::parseAsIs,                  0,  0   },
             {   "json",                 &RPCParser::parseJson,                  2,  2   },
             {   "json2",                &RPCParser::parseJson2,                 1,  1   },
             {   "ledger",               &RPCParser::parseLedger,                0,  2   },

src/ripple/rpc/handlers/Handlers.h

@@ -47,6 +47,7 @@ Json::Value doFee                   (RPC::JsonContext&);
 Json::Value doFetchInfo             (RPC::JsonContext&);
 Json::Value doGatewayBalances       (RPC::JsonContext&);
 Json::Value doGetCounts             (RPC::JsonContext&);
+Json::Value doHealthCheck           (RPC::JsonContext&);
 Json::Value doLedgerAccept          (RPC::JsonContext&);
 Json::Value doLedgerCleaner         (RPC::JsonContext&);
 Json::Value doLedgerClosed          (RPC::JsonContext&);

src/ripple/rpc/handlers/HealthCheck.cpp

@@ -0,0 +1,119 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2012-2014 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/app/misc/NetworkOPs.h>
+#include <ripple/json/json_value.h>
+#include <ripple/net/RPCErr.h>
+#include <ripple/protocol/jss.h>
+#include <ripple/rpc/Context.h>
+#include <ripple/rpc/impl/TransactionSign.h>
+#include <ripple/rpc/Role.h>
+
+namespace ripple {
+
+Json::Value
+doHealthCheck(RPC::JsonContext& context)
+{
+    bool constexpr humanReadable = true;
+    bool constexpr noAdmin = false;
+    bool constexpr noCounters = false;
+    auto info = context.netOps.getServerInfo(
+                    humanReadable, noAdmin, noCounters);
+
+    int last_validated_ledger_age = std::numeric_limits<int>::max();
+    if (info.isMember("validated_ledger"))
+        last_validated_ledger_age = info["validated_ledger"]["age"].asInt();
+    bool amendment_blocked = false;
+    if (info.isMember("amendment_blocked"))
+        amendment_blocked = true;
+    int number_peers = info["peers"].asInt();
+    std::string server_state = info["server_state"].asString();
+    auto load_factor = info["load_factor"].asDouble();
+
+    Json::Value ret = Json::objectValue;
+    enum {healthy, warning, critical};
+    int health = healthy;
+    auto set_health = [&health](int state)
+        {
+            if (health < state)
+                health = state;
+        };
+
+    if (last_validated_ledger_age >= 7)
+    {
+        ret[jss::info]["validated_ledger"] = last_validated_ledger_age;
+        if (last_validated_ledger_age < 20)
+            set_health(warning);
+        else
+            set_health(critical);
+    }
+
+    if (amendment_blocked)
+    {
+        ret[jss::info]["amendment_blocked"] = true;
+        set_health(critical);
+    }
+
+    if (number_peers <= 7)
+    {
+        ret[jss::info]["peers"] = number_peers;
+        if (number_peers != 0)
+            set_health(warning);
+        else
+            set_health(critical);
+    }
+
+    if (!(server_state == "full" || server_state == "validating" ||
+          server_state == "proposing"))
+    {
+        ret[jss::info]["server_state"] = server_state;
+        if (server_state == "syncing" || server_state == "tracking" ||
+            server_state == "connected")
+        {
+            set_health(warning);
+        }
+        else
+            set_health(critical);
+    }
+
+    if (load_factor > 100)
+    {
+        ret[jss::info]["load_factor"] = load_factor;
+        if (load_factor < 1000)
+            set_health(warning);
+        else
+            set_health(critical);
+    }
+
+    switch (health)
+    {
+    case healthy:
+        ret["health"] = "Healthy";
+        break;
+    case warning:
+        ret["health"] = "Warning";
+        break;
+    default:
+        ret["health"] = "Critical";
+        break;
+    }
+    return ret;
+}
+
+} // ripple

src/ripple/rpc/impl/Handler.cpp

@@ -80,6 +80,7 @@ Handler const handlerArray[] {
     {   "feature",              byRef (&doFeature),             Role::ADMIN,   NO_CONDITION     },
     {   "fee",                  byRef (&doFee),                 Role::USER,    NEEDS_CURRENT_LEDGER     },
     {   "fetch_info",           byRef (&doFetchInfo),           Role::ADMIN,   NO_CONDITION     },
+    {   "health_check",         byRef (&doHealthCheck),         Role::USER,  NO_CONDITION     },
     {   "ledger_accept",        byRef (&doLedgerAccept),        Role::ADMIN,   NEEDS_CURRENT_LEDGER  },
     {   "ledger_cleaner",       byRef (&doLedgerCleaner),       Role::ADMIN,   NEEDS_NETWORK_CONNECTION  },
     {   "ledger_closed",        byRef (&doLedgerClosed),        Role::USER,  NO_CONDITION   },