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Fix dish socket multicast bind issue #4820

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Fix dish socket multicast bind issue #4820

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6f7f3cf
Fix dish socket multicast bind issue
NoAnyLove Oct 13, 2025
5610f47
Try to fix IPv6 multicast
NoAnyLove Oct 13, 2025
5366c37
Try to fix test
NoAnyLove Oct 13, 2025
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10 changes: 6 additions & 4 deletions src/udp_address.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -125,7 +125,6 @@ int zmq::udp_address_t::resolve (const char *name_, bool bind_, bool ipv6_)
if (_is_multicast || !bind_) {
_bind_address = ip_addr_t::any (_target_address.family ());
_bind_address.set_port (port);
_bind_interface = 0;
} else {
// If we were asked for a bind socket and the address
// provided was not multicast then it was really meant as
Expand All @@ -141,9 +140,12 @@ int zmq::udp_address_t::resolve (const char *name_, bool bind_, bool ipv6_)

// For IPv6 multicast we *must* have an interface index since we can't
// bind by address.
if (ipv6_ && _is_multicast && _bind_interface < 0) {
errno = ENODEV;
return -1;
if (ipv6_ && _is_multicast && bind_) {
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interface index is only needed if it's IPv6 multicast and the socket needs to perform bind(), i.e., the DISH socket.

if (_bind_interface < 0) {
errno = ENODEV;
return -1;
}
_target_address.ipv6.sin6_scope_id = _bind_interface;
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To bind on multicast group in IPv6, it requires to set the scope id to the network interface index, otherwise it will fail.

}

return 0;
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8 changes: 3 additions & 5 deletions src/udp_engine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -133,7 +133,6 @@ void zmq::udp_engine_t::plug (io_thread_t *io_thread_, session_base_t *session_)
rc = rc | set_udp_reuse_address (_fd, true);

const ip_addr_t *bind_addr = udp_addr->bind_addr ();
ip_addr_t any = ip_addr_t::any (bind_addr->family ());
const ip_addr_t *real_bind_addr;

const bool multicast = udp_addr->is_mcast ();
Expand All @@ -143,11 +142,10 @@ void zmq::udp_engine_t::plug (io_thread_t *io_thread_, session_base_t *session_)
// one port as all ports should receive the message
rc = rc | set_udp_reuse_port (_fd, true);

// In multicast we should bind ANY and use the mreq struct to
// specify the interface
any.set_port (bind_addr->port ());
// In multicast we should bind the target address and use the
// mreq struct to specify the interface

real_bind_addr = &any;
real_bind_addr = udp_addr->target_addr ();
} else {
real_bind_addr = bind_addr;
}
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2 changes: 1 addition & 1 deletion tests/test_radio_dish.cpp
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Expand Up @@ -261,7 +261,7 @@ MAKE_TEST_V4V6 (test_radio_dish_udp)
static const char *mcast_url (int ipv6_)
{
if (ipv6_) {
return "udp://[" MCAST_IPV6 "]:5555";
return "udp://eth0;[" MCAST_IPV6 "]:5555";
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the DISH socket now must specify the network interface for bind with this change.

I'm concerned about hard-coding the network interface name here, as it might break on other OS or if the host use different names. Not sure if there is any better choice.

Besides, it seems we cannot bind on lo, as it will result Network is unreachable on my box (not sue if it's a common case or just on my box).

}
return "udp://" MCAST_IPV4 ":5555";
}
Expand Down
14 changes: 8 additions & 6 deletions unittests/unittest_udp_address.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,8 @@ static void test_resolve (bool bind_,
const char *target_addr_,
uint16_t expected_port_,
const char *bind_addr_,
bool multicast_)
bool multicast_,
uint16_t expected_zone = 0)
{
if (family_ == AF_INET6 && !is_ipv6_available ()) {
TEST_IGNORE_MESSAGE ("ipv6 is not available");
Expand Down Expand Up @@ -53,7 +54,7 @@ static void test_resolve (bool bind_,
}

validate_address (family_, addr.target_addr (), target_addr_,
expected_port_);
expected_port_, expected_zone);
validate_address (family_, addr.bind_addr (), bind_addr_, expected_port_);
}

Expand All @@ -62,10 +63,11 @@ static void test_resolve_bind (int family_,
const char *dest_addr_,
uint16_t expected_port_ = 0,
const char *bind_addr_ = NULL,
bool multicast_ = false)
bool multicast_ = false,
uint16_t expected_zone = 0)
{
test_resolve (true, family_, name_, dest_addr_, expected_port_, bind_addr_,
multicast_);
multicast_, expected_zone);
}

static void test_resolve_connect (int family_,
Expand Down Expand Up @@ -172,7 +174,7 @@ static void test_resolve_ipv4_bind_mcast ()

static void test_resolve_ipv6_bind_mcast ()
{
test_resolve_bind (AF_INET6, "[ff00::1]:1234", "ff00::1", 1234, "::", true);
test_resolve_bind (AF_INET6, "eth0;[ff00::1]:1234", "ff00::1", 1234, "fe80::", true, 2);
}

static void test_resolve_ipv4_connect_mcast ()
Expand Down Expand Up @@ -232,7 +234,7 @@ static void test_resolve_ipv6_mcast_src_connect ()
}

zmq::udp_address_t addr;
int rc = addr.resolve ("[1:2:3::4];[ff01::1]:5555", false, true);
int rc = addr.resolve ("[1:2:3::4];[ff01::1]:5555", true, true);
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change bind from false to true. It won't trigger the ENODEV error when bind is false, as RADIO socket does not require the interface for bind.


// For the time being this fails because we only support binding multicast
// by interface name, not interface IP
Expand Down
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