Remove g_rpc_chain global

Replace with RPC request reference to new WalletContext struct similar to the
existing NodeContext struct and reference.

This PR is a followup to 25ad2c623af30056ffb36dcd203a52edda2b170f
https://github.com/bitcoin/bitcoin/pull/18740 removing the g_rpc_node global.

Some later PRs will follow this up and move more wallet globals to the
WalletContext struct.

Co-authored-by: João Barbosa <joao.paulo.barbosa@gmail.com>

4 files changed, 57 insertions, 14 deletions

diff --git a/src/wallet/context.cpp b/src/wallet/context.cpp
new file mode 100644
index 0000000000..09b2f30467
--- /dev/null
+++ b/src/wallet/context.cpp
@@ -0,0 +1,8 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <wallet/context.h>
+
+WalletContext::WalletContext() {}
+WalletContext::~WalletContext() {}
diff --git a/src/wallet/context.h b/src/wallet/context.h
new file mode 100644
index 0000000000..3c8fdd1c59
--- /dev/null
+++ b/src/wallet/context.h
@@ -0,0 +1,32 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_WALLET_CONTEXT_H
+#define BITCOIN_WALLET_CONTEXT_H
+
+namespace interfaces {
+class Chain;
+} // namespace interfaces
+
+//! WalletContext struct containing references to state shared between CWallet
+//! instances, like the reference to the chain interface, and the list of opened
+//! wallets.
+//!
+//! Future shared state can be added here as an alternative to adding global
+//! variables.
+//!
+//! The struct isn't intended to have any member functions. It should just be a
+//! collection of state pointers that doesn't pull in dependencies or implement
+//! behavior.
+struct WalletContext {
+    interfaces::Chain* chain{nullptr};
+
+    //! Declare default constructor and destructor that are not inline, so code
+    //! instantiating the WalletContext struct doesn't need to #include class
+    //! definitions for smart pointer and container members.
+    WalletContext();
+    ~WalletContext();
+};
+
+#endif // BITCOIN_WALLET_CONTEXT_H
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index c4052d67b0..ae2b19e923 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -21,12 +21,14 @@
 #include <util/fees.h>
 #include <util/message.h> // For MessageSign()
 #include <util/moneystr.h>
+#include <util/ref.h>
 #include <util/string.h>
 #include <util/system.h>
 #include <util/translation.h>
 #include <util/url.h>
 #include <util/vector.h>
 #include <wallet/coincontrol.h>
+#include <wallet/context.h>
 #include <wallet/feebumper.h>
 #include <wallet/rpcwallet.h>
 #include <wallet/wallet.h>
@@ -121,6 +123,14 @@ void EnsureWalletIsUnlocked(const CWallet* pwallet)
     }
 }
 
+WalletContext& EnsureWalletContext(const util::Ref& context)
+{
+    if (!context.Has<WalletContext>()) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Wallet context not found");
+    }
+    return context.Get<WalletContext>();
+}
+
 // also_create should only be set to true only when the RPC is expected to add things to a blank wallet and make it no longer blank
 LegacyScriptPubKeyMan& EnsureLegacyScriptPubKeyMan(CWallet& wallet, bool also_create)
 {
@@ -2584,6 +2594,7 @@ static UniValue loadwallet(const JSONRPCRequest& request)
                 },
             }.Check(request);
 
+    WalletContext& context = EnsureWalletContext(request.context);
     WalletLocation location(request.params[0].get_str());
 
     if (!location.Exists()) {
@@ -2598,7 +2609,7 @@ static UniValue loadwallet(const JSONRPCRequest& request)
 
     bilingual_str error;
     std::vector<bilingual_str> warnings;
-    std::shared_ptr<CWallet> const wallet = LoadWallet(*g_rpc_chain, location, error, warnings);
+    std::shared_ptr<CWallet> const wallet = LoadWallet(*context.chain, location, error, warnings);
     if (!wallet) throw JSONRPCError(RPC_WALLET_ERROR, error.original);
 
     UniValue obj(UniValue::VOBJ);
@@ -2702,6 +2713,7 @@ static UniValue createwallet(const JSONRPCRequest& request)
         },
     }.Check(request);
 
+    WalletContext& context = EnsureWalletContext(request.context);
     uint64_t flags = 0;
     if (!request.params[1].isNull() && request.params[1].get_bool()) {
         flags |= WALLET_FLAG_DISABLE_PRIVATE_KEYS;
@@ -2731,7 +2743,7 @@ static UniValue createwallet(const JSONRPCRequest& request)
 
     bilingual_str error;
     std::shared_ptr<CWallet> wallet;
-    WalletCreationStatus status = CreateWallet(*g_rpc_chain, passphrase, flags, request.params[0].get_str(), error, warnings, wallet);
+    WalletCreationStatus status = CreateWallet(*context.chain, passphrase, flags, request.params[0].get_str(), error, warnings, wallet);
     switch (status) {
         case WalletCreationStatus::CREATION_FAILED:
             throw JSONRPCError(RPC_WALLET_ERROR, error.original);
@@ -4331,5 +4343,3 @@ static const CRPCCommand commands[] =
 // clang-format on
     return MakeSpan(commands);
 }
-
-interfaces::Chain* g_rpc_chain = nullptr;
diff --git a/src/wallet/rpcwallet.h b/src/wallet/rpcwallet.h
index fd8a41ed14..d00221a04c 100644
--- a/src/wallet/rpcwallet.h
+++ b/src/wallet/rpcwallet.h
@@ -16,18 +16,10 @@ class CWallet;
 class JSONRPCRequest;
 class LegacyScriptPubKeyMan;
 class UniValue;
-struct PartiallySignedTransaction;
 class CTransaction;
+struct PartiallySignedTransaction;
+struct WalletContext;
 
-namespace interfaces {
-class Chain;
-}
-
-//! Pointer to chain interface that needs to be declared as a global to be
-//! accessible loadwallet and createwallet methods. Due to limitations of the
-//! RPC framework, there's currently no direct way to pass in state to RPC
-//! methods without globals.
-extern interfaces::Chain* g_rpc_chain;
 Span<const CRPCCommand> GetWalletRPCCommands();
 
 /**
@@ -40,6 +32,7 @@ std::shared_ptr<CWallet> GetWalletForJSONRPCRequest(const JSONRPCRequest& reques
 
 void EnsureWalletIsUnlocked(const CWallet*);
 bool EnsureWalletIsAvailable(const CWallet*, bool avoidException);
+WalletContext& EnsureWalletContext(const util::Ref& context);
 LegacyScriptPubKeyMan& EnsureLegacyScriptPubKeyMan(CWallet& wallet, bool also_create = false);
 
 UniValue getaddressinfo(const JSONRPCRequest& request);