rpc: create an rpc estimatefeewithforecasters

Given a confirmation target, we use fee estimator module that call all
available fee estimator forcasters and return the fee rate with highest
confidence level that if a transaction use will likely confirm in a given
confirmation target.

Co-authored-by: willcl-ark <will@256k1.dev>

src/rpc/client.cpp

@@ -252,6 +252,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "estimatesmartfee", 0, "conf_target" },
     { "estimaterawfee", 0, "conf_target" },
     { "estimaterawfee", 1, "threshold" },
+    { "estimatefeewithforecasters", 0, "conf_target" },
     { "prioritisetransaction", 1, "dummy" },
     { "prioritisetransaction", 2, "fee_delta" },
     { "setban", 2, "bantime" },

src/rpc/fees.cpp

@@ -7,6 +7,7 @@
 #include <node/context.h>
 #include <policy/feerate.h>
 #include <policy/fees.h>
+#include <policy/estimator.h>
 #include <rpc/protocol.h>
 #include <rpc/request.h>
 #include <rpc/server.h>
@@ -15,6 +16,7 @@
 #include <txmempool.h>
 #include <univalue.h>
 #include <util/fees.h>
+#include <validation.h>
 #include <validationinterface.h>
 
 #include <algorithm>
@@ -96,6 +98,43 @@ static RPCHelpMan estimatesmartfee()
     };
 }
 
+static RPCHelpMan estimatefeewithforecasters()
+{
+    return RPCHelpMan{
+        "estimatefeewithforecasters",
+        "\nEstimates the approximate fee per kilobyte needed for a transaction to begin\n"
+        "confirmation within conf_target blocks if possible Uses virtual transaction size as defined\n"
+        "in BIP 141 (witness data is discounted). By default caches values for 30 seconds to avoid\n"
+        "repeatedly running expensive block-building algorithm.\n",
+        {
+            {"conf_target", RPCArg::Type::NUM, RPCArg::Optional::NO, "Confirmation target in blocks"},
+        },
+        RPCResult{
+            RPCResult::Type::OBJ, "", "",
+            {
+                {RPCResult::Type::NUM, "Fee rate estimate", /*optional=*/true, "estimate fee rate in " + CURRENCY_UNIT + "/kvB (only present if no errors were encountered)"},
+                {RPCResult::Type::ARR, "errors", /*optional=*/true, "Errors encountered during processing (if there are any)",
+                    {{RPCResult::Type::STR, "", "error"},}
+                },
+            }},
+        RPCExamples{HelpExampleCli("estimatefeewithforecasters", "2") + HelpExampleRpc("estimatefeewithforecasters", "2")},
+        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue {
+            FeeEstimator& fee_estimator = EnsureAnyFeeForecasters(request.context);
+            const unsigned int conf_target = request.params[0].getInt<unsigned int>();
+            CFeeRate fee_estimate = fee_estimator.getFeeEstimateForecast(conf_target);
+            UniValue result(UniValue::VOBJ);
+            UniValue errors(UniValue::VARR);
+            if (fee_estimate == CFeeRate(0)) {
+                result.pushKV("Fee rate estimate", ValueFromAmount(fee_estimate.GetFeePerK()));
+            } else {
+                errors.push_back("Failed to get estimate from forecasters");
+                result.pushKV("errors", errors);
+            }
+            return result;
+        },
+    };
+}
+
 static RPCHelpMan estimaterawfee()
 {
     return RPCHelpMan{"estimaterawfee",
@@ -220,6 +259,7 @@ void RegisterFeeRPCCommands(CRPCTable& t)
 {
     static const CRPCCommand commands[]{
         {"util", &estimatesmartfee},
+        {"util", &estimatefeewithforecasters},
         {"hidden", &estimaterawfee},
     };
     for (const auto& c : commands) {

src/rpc/server_util.cpp

@@ -94,6 +94,19 @@ CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context)
     return EnsureFeeEstimator(EnsureAnyNodeContext(context));
 }
 
+FeeEstimator& EnsureFeeForecasters(const NodeContext& node)
+{
+    if (!node.fee_estimator) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Fee estimation disabled");
+    }
+    return *node.fee_estimator;
+}
+
+FeeEstimator& EnsureAnyFeeForecasters(const std::any& context)
+{
+    return EnsureFeeForecasters(EnsureAnyNodeContext(context));
+}
+
 CConnman& EnsureConnman(const NodeContext& node)
 {
     if (!node.connman) {

src/rpc/server_util.h

@@ -11,6 +11,7 @@ class AddrMan;
 class ArgsManager;
 class CBlockPolicyEstimator;
 class CConnman;
+class FeeEstimator;
 class CTxMemPool;
 class ChainstateManager;
 class PeerManager;
@@ -30,6 +31,8 @@ ChainstateManager& EnsureChainman(const node::NodeContext& node);
 ChainstateManager& EnsureAnyChainman(const std::any& context);
 CBlockPolicyEstimator& EnsureFeeEstimator(const node::NodeContext& node);
 CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context);
+FeeEstimator& EnsureFeeForecasters(const node::NodeContext& node);
+FeeEstimator& EnsureAnyFeeForecasters(const std::any& context);
 CConnman& EnsureConnman(const node::NodeContext& node);
 PeerManager& EnsurePeerman(const node::NodeContext& node);
 AddrMan& EnsureAddrman(const node::NodeContext& node);