RPC: Add new getzmqnotifications method.

This adds a new RPC method "getzmqnotifications", which returns
information about all active ZMQ notification endpoints.  This is useful
for software that layers on top of bitcoind, so it can verify that
ZeroMQ is enabled and also figure out where it should listen.

See https://github.com/bitcoin/bitcoin/issues/13526.

1 files changed, 61 insertions, 0 deletions

diff --git a/src/zmq/zmqrpc.cpp b/src/zmq/zmqrpc.cpp
new file mode 100644
index 0000000000..4f88bf4eb9
--- /dev/null
+++ b/src/zmq/zmqrpc.cpp
@@ -0,0 +1,61 @@
+// 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 <zmq/zmqrpc.h>
+
+#include <rpc/server.h>
+#include <zmq/zmqabstractnotifier.h>
+#include <zmq/zmqnotificationinterface.h>
+
+#include <univalue.h>
+
+namespace {
+
+UniValue getzmqnotifications(const JSONRPCRequest& request)
+{
+    if (request.fHelp || request.params.size() != 0) {
+        throw std::runtime_error(
+            "getzmqnotifications\n"
+            "\nReturns information about the active ZeroMQ notifications.\n"
+            "\nResult:\n"
+            "[\n"
+            "  {                        (json object)\n"
+            "    \"type\": \"pubhashtx\",   (string) Type of notification\n"
+            "    \"address\": \"...\"       (string) Address of the publisher\n"
+            "  },\n"
+            "  ...\n"
+            "]\n"
+            "\nExamples:\n"
+            + HelpExampleCli("getzmqnotifications", "")
+            + HelpExampleRpc("getzmqnotifications", "")
+        );
+    }
+
+    UniValue result(UniValue::VARR);
+    if (g_zmq_notification_interface != nullptr) {
+        for (const auto* n : g_zmq_notification_interface->GetActiveNotifiers()) {
+            UniValue obj(UniValue::VOBJ);
+            obj.pushKV("type", n->GetType());
+            obj.pushKV("address", n->GetAddress());
+            result.push_back(obj);
+        }
+    }
+
+    return result;
+}
+
+const CRPCCommand commands[] =
+{ //  category              name                                actor (function)                argNames
+  //  -----------------     ------------------------            -----------------------         ----------
+    { "zmq",                "getzmqnotifications",              &getzmqnotifications,           {} },
+};
+
+} // anonymous namespace
+
+void RegisterZMQRPCCommands(CRPCTable& t)
+{
+    for (const auto& c : commands) {
+        t.appendCommand(c.name, &c);
+    }
+}