5 files changed, 91 insertions, 1 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index 6852ef408a..e2727ac522 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -125,6 +125,7 @@ BITCOIN_CORE_H = \
   index/txindex.h \
   indirectmap.h \
   init.h \
+  interfaces/chain.h \
   interfaces/handler.h \
   interfaces/node.h \
   interfaces/wallet.h \
@@ -233,6 +234,7 @@ libbitcoin_server_a_SOURCES = \
   httpserver.cpp \
   index/base.cpp \
   index/txindex.cpp \
+  interfaces/chain.cpp \
   interfaces/handler.cpp \
   interfaces/node.cpp \
   init.cpp \
diff --git a/src/interfaces/README.md b/src/interfaces/README.md
index e93b91d23c..57d41df746 100644
--- a/src/interfaces/README.md
+++ b/src/interfaces/README.md
@@ -4,7 +4,7 @@ The following interfaces are defined here:
 
 * [`Chain`](chain.h) — used by wallet to access blockchain and mempool state. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
 
-* [`Chain::Client`](chain.h) — used by node to start & stop `Chain` clients. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
+* [`ChainClient`](chain.h) — used by node to start & stop `Chain` clients. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
 
 * [`Node`](node.h) — used by GUI to start & stop bitcoin node. Added in [#10244](https://github.com/bitcoin/bitcoin/pull/10244).
 
diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
new file mode 100644
index 0000000000..28b36717d5
--- /dev/null
+++ b/src/interfaces/chain.cpp
@@ -0,0 +1,20 @@
+// Copyright (c) 2018 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 <interfaces/chain.h>
+
+#include <util/system.h>
+
+namespace interfaces {
+namespace {
+
+class ChainImpl : public Chain
+{
+};
+
+} // namespace
+
+std::unique_ptr<Chain> MakeChain() { return MakeUnique<ChainImpl>(); }
+
+} // namespace interfaces
diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
new file mode 100644
index 0000000000..8a40cb4cda
--- /dev/null
+++ b/src/interfaces/chain.h
@@ -0,0 +1,44 @@
+// Copyright (c) 2018 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_INTERFACES_CHAIN_H
+#define BITCOIN_INTERFACES_CHAIN_H
+
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace interfaces {
+
+//! Interface for giving wallet processes access to blockchain state.
+class Chain
+{
+public:
+    virtual ~Chain() {}
+};
+
+//! Interface to let node manage chain clients (wallets, or maybe tools for
+//! monitoring and analysis in the future).
+class ChainClient
+{
+public:
+    virtual ~ChainClient() {}
+};
+
+//! Return implementation of Chain interface.
+std::unique_ptr<Chain> MakeChain();
+
+//! Return implementation of ChainClient interface for a wallet client. This
+//! function will be undefined in builds where ENABLE_WALLET is false.
+//!
+//! Currently, wallets are the only chain clients. But in the future, other
+//! types of chain clients could be added, such as tools for monitoring,
+//! analysis, or fee estimation. These clients need to expose their own
+//! MakeXXXClient functions returning their implementations of the ChainClient
+//! interface.
+std::unique_ptr<ChainClient> MakeWalletClient(Chain& chain, std::vector<std::string> wallet_filenames);
+
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_CHAIN_H
diff --git a/src/interfaces/wallet.cpp b/src/interfaces/wallet.cpp
index 14c6bd0330..e9f4669f4d 100644
--- a/src/interfaces/wallet.cpp
+++ b/src/interfaces/wallet.cpp
@@ -7,6 +7,7 @@
 #include <amount.h>
 #include <chain.h>
 #include <consensus/validation.h>
+#include <interfaces/chain.h>
 #include <interfaces/handler.h>
 #include <net.h>
 #include <policy/feerate.h>
@@ -20,11 +21,17 @@
 #include <timedata.h>
 #include <ui_interface.h>
 #include <uint256.h>
+#include <util/system.h>
 #include <validation.h>
 #include <wallet/feebumper.h>
 #include <wallet/fees.h>
 #include <wallet/wallet.h>
 
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
 namespace interfaces {
 namespace {
 
@@ -456,8 +463,25 @@ public:
     CWallet& m_wallet;
 };
 
+class WalletClientImpl : public ChainClient
+{
+public:
+    WalletClientImpl(Chain& chain, std::vector<std::string> wallet_filenames)
+        : m_chain(chain), m_wallet_filenames(std::move(wallet_filenames))
+    {
+    }
+
+    Chain& m_chain;
+    std::vector<std::string> m_wallet_filenames;
+};
+
 } // namespace
 
 std::unique_ptr<Wallet> MakeWallet(const std::shared_ptr<CWallet>& wallet) { return MakeUnique<WalletImpl>(wallet); }
 
+std::unique_ptr<ChainClient> MakeWalletClient(Chain& chain, std::vector<std::string> wallet_filenames)
+{
+    return MakeUnique<WalletClientImpl>(chain, std::move(wallet_filenames));
+}
+
 } // namespace interfaces