Merge #18740: Remove g_rpc_node global

b3f7f375efb9a9ca9a7a4f2caf41fe3df2262520 refactor: Remove g_rpc_node global (Russell Yanofsky)
ccb5059ee89f6e8dc31ba5b82830b384890bb65e scripted-diff: Remove g_rpc_node references (Russell Yanofsky)
6fca33b2edc09ed62dab2323c780b31585de1750 refactor: Pass NodeContext to RPC and REST methods through util::Ref (Russell Yanofsky)
691c817b340d10e806dc3b1834d2a8fcc5e681fd Add util::Ref class as temporary alternative for c++17 std::any (Russell Yanofsky)

Pull request description:

  This PR removes the `g_rpc_node` global, to get same benefits we see removing other globals and make RPC code more testable, modular, and reusable.

  This uses a hybrid of the approaches suggested in #17548. Instead of using `std::any`, which isn't available in c++11, or `void*`, which isn't type safe, it uses a small new `util::Ref` helper class, which acts like a simplified `std::any` that only holds references, not values.

  Motivation for writing this was to provide an simpler alternative to #18647 by Harris Brakmić (brakmic) which avoids some shortcomings of that PR (https://github.com/bitcoin/bitcoin/pull/18647#issuecomment-617878826)

ACKs for top commit:
  MarcoFalke:
    re-ACK b3f7f375ef, only change is adding back const and more tests 🚾
  ajtowns:
    ACK b3f7f375efb9a9ca9a7a4f2caf41fe3df2262520

Tree-SHA512: 56292268a001bdbe34d641db1180c215351503966ff451e55cc96c9137f1d262225d7d7733de9c9da7ce7d7a4b34213a98c2476266b58c89dbbb0f3cb5aa5d70

1 files changed, 5 insertions, 6 deletions

diff --git a/src/rpc/blockchain.h b/src/rpc/blockchain.h
index 54165af707..453d0bc650 100644
--- a/src/rpc/blockchain.h
+++ b/src/rpc/blockchain.h
@@ -18,6 +18,9 @@ class CBlockIndex;
 class CTxMemPool;
 class UniValue;
 struct NodeContext;
+namespace util {
+class Ref;
+} // namespace util
 
 static constexpr int NUM_GETBLOCKSTATS_PERCENTILES = 5;
 
@@ -47,11 +50,7 @@ UniValue blockheaderToJSON(const CBlockIndex* tip, const CBlockIndex* blockindex
 /** Used by getblockstats to get feerates at different percentiles by weight  */
 void CalculatePercentilesByWeight(CAmount result[NUM_GETBLOCKSTATS_PERCENTILES], std::vector<std::pair<CAmount, int64_t>>& scores, int64_t total_weight);
 
-//! Pointer to node state that needs to be declared as a global to be accessible
-//! RPC methods. Due to limitations of the RPC framework, there's currently no
-//! direct way to pass in state to RPC methods without globals.
-extern NodeContext* g_rpc_node;
-
-CTxMemPool& EnsureMemPool();
+NodeContext& EnsureNodeContext(const util::Ref& context);
+CTxMemPool& EnsureMemPool(const util::Ref& context);
 
 #endif