RPC/blockchain: getmempoolinfo: Enable specifying with_fee_histogram as a boolean to use a sensible default set of fee rate levels

src/rpc/client.cpp

@@ -251,6 +251,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "pruneblockchain", 0, "height" },
     { "keypoolrefill", 0, "newsize" },
     { "getmempoolinfo", 0, "fee_histogram" },
+    { "getmempoolinfo", 0, "with_fee_histogram" },
     { "getrawmempool", 0, "verbose" },
     { "getrawmempool", 1, "mempool_sequence" },
     { "estimatesmartfee", 0, "conf_target" },

src/rpc/mempool.cpp

@@ -745,7 +745,7 @@ static RPCHelpMan getmempoolinfo()
     return RPCHelpMan{"getmempoolinfo",
         "Returns details on the active state of the TX memory pool.\n",
         {
-            {"fee_histogram", RPCArg::Type::ARR, RPCArg::Optional::OMITTED, "Fee statistics grouped by fee rate ranges",
+            {"fee_histogram|with_fee_histogram", {RPCArg::Type::ARR, RPCArg::Type::BOOL}, RPCArg::Optional::OMITTED, "Fee statistics grouped by fee rate ranges",
                 {
                     {"fee_rate", RPCArg::Type::NUM, RPCArg::Optional::NO, "Fee rate (in " + CURRENCY_ATOM + "/vB) to group the fees by"},
                 },
@@ -790,7 +790,11 @@ static RPCHelpMan getmempoolinfo()
     MempoolHistogramFeeRates histogram_floors;
     std::optional<MempoolHistogramFeeRates> histogram_floors_opt = std::nullopt;
 
-    if (!request.params[0].isNull()) {
+    if (request.params[0].isBool()) {
+        if (request.params[0].isTrue()) {
+            histogram_floors_opt = MempoolInfoToJSON_const_histogram_floors;
+        }
+    } else if (!request.params[0].isNull()) {
         const UniValue histogram_floors_univalue = request.params[0].get_array();
 
         if (histogram_floors_univalue.empty()) {

src/rpc/mempool.h

@@ -15,6 +15,15 @@ class UniValue;
 
 typedef std::vector<CAmount> MempoolHistogramFeeRates;
 
+/* TODO: define log scale formular for dynamically creating the
+ * feelimits but with the property of not constantly changing
+ * (and thus screw up client implementations) */
+static const MempoolHistogramFeeRates MempoolInfoToJSON_const_histogram_floors{
+    1, 2, 3, 4, 5, 6, 7, 8, 10,
+    12, 14, 17, 20, 25, 30, 40, 50, 60, 70, 80, 100,
+    120, 140, 170, 200, 250, 300, 400, 500, 600, 700, 800, 1000,
+    1200, 1400, 1700, 2000, 2500, 3000, 4000, 5000, 6000, 7000, 8000, 10000};
+
 /** Mempool information to JSON */
 UniValue MempoolInfoToJSON(const CTxMemPool& pool, const std::optional<MempoolHistogramFeeRates>& histogram_floors);
 

test/functional/mempool_fee_histogram.py

@@ -156,6 +156,28 @@ class MempoolFeeHistogramTest(BitcoinTestFramework):
 
         assert_equal(expected_histogram, info['fee_histogram'])
 
+        self.log.info("Test fee rate histogram with default groups")
+        info = node.getmempoolinfo(with_fee_histogram=True)
+
+        # Verify that the 6 sat/vB fee rate group has one transaction, and the 8-9 sat/vB fee rate group has two
+        for collapse_n in (9, 11, 13, 15):
+            for field in ('count', 'size', 'fees'):
+                expected_frg[str(collapse_n - 1)][field] += expected_frg[str(collapse_n)][field]
+            del expected_frg[str(collapse_n)]
+
+        for new_n in (17, 20, 25) + tuple(range(30, 90, 10)) + (100, 120, 140, 170, 200, 250) + tuple(range(300, 900, 100)) + (1000, 1200, 1400, 1700, 2000, 2500) + tuple(range(3000, 9000, 1000)) + (10000,):
+            assert(info['fee_histogram']['fee_rate_groups'][str(new_n)] == {
+                'from': new_n,
+                'count': 0,
+                'fees': 0,
+                'size': 0,
+            })
+            del info['fee_histogram']['fee_rate_groups'][str(new_n)]
+        assert_equal(expected_histogram, info['fee_histogram'])
+
+        self.log.info("Test getmempoolinfo(with_fee_histogram=False) does not return fee histogram")
+        assert('fee_histogram' not in node.getmempoolinfo(with_fee_histogram=False))
+
     def histogram_stats(self, histogram):
         total_fees = 0
         empty_count = 0