Merge bitcoin/bitcoin#22079: zmq: Add support to listen on IPv6 addresses

e6998838e5548991274ad2bf1697d862905b8837 doc: Add IPv6 address to zmq example (nthumann)
8abe5703a9bb76bc92204a6f69775790e96208fa test: Add IPv6 test to zmq (nthumann)
ded449b726e47f35798ef1c4b1e59123a0dc2b61 zmq: Enable IPv6 on listening socket (nthumann)

Pull request description:

  This PR adds support for listening on IPv6 addresses with bitcoinds ZMQ interface, just like the RPC server.
  Currently, it is not possible to specify an IPv6 address, as the `ZMQ_IPV6` [socket option](http://api.zeromq.org/master:zmq-setsockopt#toc27) is not set and therefore the ZMQ initialization fails, if one does so. The absence of this option has also been noted [here](https://github.com/bitcoin/bitcoin/issues/15198#issuecomment-617378512).
  With this PR one can e.g. set `-zmqpubhashblock=tcp://[::1]:28333` to listen on the IPv6 loopback address.

ACKs for top commit:
  laanwj:
    Code review ACK e6998838e5548991274ad2bf1697d862905b8837
  theStack:
    Tested ACK e6998838e5548991274ad2bf1697d862905b8837 🌱

Tree-SHA512: 43c3043d8d5c79794d475926259c1be975b694db4fcc1f7750a9a28e242f0fa1b531735a63ea5777498003aa5834f6243f39742d0f3941f2f37593d0c7890700

3 files changed, 50 insertions, 1 deletions

diff --git a/doc/zmq.md b/doc/zmq.md
index 85f3370130..0521fe08d8 100644
--- a/doc/zmq.md
+++ b/doc/zmq.md
@@ -84,6 +84,7 @@ For instance:
 
     $ bitcoind -zmqpubhashtx=tcp://127.0.0.1:28332 \
                -zmqpubhashtx=tcp://192.168.1.2:28332 \
+               -zmqpubhashblock="tcp://[::1]:28333" \
                -zmqpubrawtx=ipc:///tmp/bitcoind.tx.raw \
                -zmqpubhashtxhwm=10000
 
@@ -125,6 +126,9 @@ Setting the keepalive values appropriately for your operating environment may
 improve connectivity in situations where long-lived connections are silently
 dropped by network middle boxes.
 
+Also, the socket's ZMQ_IPV6 option is enabled to accept connections from IPv6
+hosts as well. If needed, this option has to be set on the client side too.
+
 ## Remarks
 
 From the perspective of bitcoind, the ZeroMQ socket is write-only; PUB
diff --git a/src/zmq/zmqpublishnotifier.cpp b/src/zmq/zmqpublishnotifier.cpp
index 6ae866cc07..56f4c98317 100644
--- a/src/zmq/zmqpublishnotifier.cpp
+++ b/src/zmq/zmqpublishnotifier.cpp
@@ -6,6 +6,7 @@
 
 #include <chain.h>
 #include <chainparams.h>
+#include <netbase.h>
 #include <node/blockstorage.h>
 #include <rpc/server.h>
 #include <streams.h>
@@ -73,6 +74,20 @@ static int zmq_send_multipart(void *sock, const void* data, size_t size, ...)
     return 0;
 }
 
+static bool IsZMQAddressIPV6(const std::string &zmq_address)
+{
+    const std::string tcp_prefix = "tcp://";
+    const size_t tcp_index = zmq_address.rfind(tcp_prefix);
+    const size_t colon_index = zmq_address.rfind(":");
+    if (tcp_index == 0 && colon_index != std::string::npos) {
+        const std::string ip = zmq_address.substr(tcp_prefix.length(), colon_index - tcp_prefix.length());
+        CNetAddr addr;
+        LookupHost(ip, addr, false);
+        if (addr.IsIPv6()) return true;
+    }
+    return false;
+}
+
 bool CZMQAbstractPublishNotifier::Initialize(void *pcontext)
 {
     assert(!psocket);
@@ -107,6 +122,15 @@ bool CZMQAbstractPublishNotifier::Initialize(void *pcontext)
             return false;
         }
 
+        // On some systems (e.g. OpenBSD) the ZMQ_IPV6 must not be enabled, if the address to bind isn't IPv6
+        const int enable_ipv6 { IsZMQAddressIPV6(address) ? 1 : 0};
+        rc = zmq_setsockopt(psocket, ZMQ_IPV6, &enable_ipv6, sizeof(enable_ipv6));
+        if (rc != 0) {
+            zmqError("Failed to set ZMQ_IPV6");
+            zmq_close(psocket);
+            return false;
+        }
+
         rc = zmq_bind(psocket, address.c_str());
         if (rc != 0)
         {
diff --git a/test/functional/interface_zmq.py b/test/functional/interface_zmq.py
index 1b2a7c20d1..4313b05f88 100755
--- a/test/functional/interface_zmq.py
+++ b/test/functional/interface_zmq.py
@@ -24,6 +24,7 @@ from test_framework.util import (
     assert_equal,
     assert_raises_rpc_error,
 )
+from test_framework.netutil import test_ipv6_local
 from io import BytesIO
 from time import sleep
 
@@ -119,6 +120,7 @@ class ZMQTest (BitcoinTestFramework):
             self.test_mempool_sync()
             self.test_reorg()
             self.test_multiple_interfaces()
+            self.test_ipv6()
         finally:
             # Destroy the ZMQ context.
             self.log.debug("Destroying ZMQ context")
@@ -126,10 +128,12 @@ class ZMQTest (BitcoinTestFramework):
 
     # Restart node with the specified zmq notifications enabled, subscribe to
     # all of them and return the corresponding ZMQSubscriber objects.
-    def setup_zmq_test(self, services, *, recv_timeout=60, sync_blocks=True):
+    def setup_zmq_test(self, services, *, recv_timeout=60, sync_blocks=True, ipv6=False):
         subscribers = []
         for topic, address in services:
             socket = self.ctx.socket(zmq.SUB)
+            if ipv6:
+                socket.setsockopt(zmq.IPV6, 1)
             subscribers.append(ZMQSubscriber(socket, topic.encode()))
 
         self.restart_node(0, [f"-zmqpub{topic}={address}" for topic, address in services] +
@@ -568,5 +572,22 @@ class ZMQTest (BitcoinTestFramework):
         assert_equal(self.nodes[0].getbestblockhash(), subscribers[0].receive().hex())
         assert_equal(self.nodes[0].getbestblockhash(), subscribers[1].receive().hex())
 
+    def test_ipv6(self):
+        if not test_ipv6_local():
+            self.log.info("Skipping IPv6 test, because IPv6 is not supported.")
+            return
+        self.log.info("Testing IPv6")
+        # Set up subscriber using IPv6 loopback address
+        subscribers = self.setup_zmq_test([
+            ("hashblock", "tcp://[::1]:28332")
+        ], ipv6=True)
+
+        # Generate 1 block in nodes[0]
+        self.nodes[0].generatetoaddress(1, ADDRESS_BCRT1_UNSPENDABLE)
+
+        # Should receive the same block hash
+        assert_equal(self.nodes[0].getbestblockhash(), subscribers[0].receive().hex())
+
+
 if __name__ == '__main__':
     ZMQTest().main()