Fix incorrect IP family when hostnames resolve to IPv6 addresses

common/transport/DcgmIpc.cpp

@@ -770,19 +770,27 @@ void DcgmIpc::ConnectTcpAsyncImpl(DcgmIpcConnectTcp &tcpConnect)
     bufferevent_setcb(bev, DcgmIpc::StaticReadCB, NULL, DcgmIpc::StaticEventCB, this);
     bufferevent_enable(bev, EV_READ | EV_WRITE);
 
-    /* Allow IPv6 IPs to override family */
-    sa_family_t family    = AF_INET;
+    /* Determine address family:
+     * - Bracketed or literal IPv6 address -> AF_INET6
+     * - Literal IPv4 address -> AF_INET
+     * - Hostname -> AF_UNSPEC so libevent resolves it to whichever family DNS returns */
+    sa_family_t family    = AF_UNSPEC;
     std::string &hostname = tcpConnect.m_hostname;
+    char buf[sizeof(struct in6_addr)];
+    memset(buf, 0, sizeof(buf));
     if (hostname.size() >= 3 && hostname[0] == '[' && hostname[hostname.size() - 1] == ']')
     {
         hostname = hostname.substr(1, hostname.size() - 2);
+        family   = AF_INET6;
     }
-    char buf[16];
-    memset(buf, 0, sizeof(buf));
-    if (inet_pton(AF_INET6, hostname.c_str(), buf) > 0)
+    else if (inet_pton(AF_INET6, hostname.c_str(), buf) > 0)
     {
         family = AF_INET6;
     }
+    else if (inet_pton(AF_INET, hostname.c_str(), buf) > 0)
+    {
+        family = AF_INET;
+    }
 
     int ret = bufferevent_socket_connect_hostname(bev, m_dnsBase, family, hostname.c_str(), tcpConnect.m_port);
     if (0 != ret)

testing/python3/DcgmHandle.py

@@ -16,6 +16,7 @@
 import dcgm_structs
 import dcgm_agent
 import threading
+import ipaddress
 
 
 class DcgmHandle:
@@ -98,6 +99,13 @@ def __init__(self,
             connectParams.persistAfterDisconnect = 0
 
         if ipAddress is not None:
+            # Wrap bare IPv6 literals in brackets so ParseEndpoint can distinguish
+            # the address colons from the host:port separator (e.g. "::1" -> "[::1]").
+            try:
+                if ipaddress.ip_address(ipAddress).version == 6:
+                    ipAddress = "[" + ipAddress + "]"
+            except ValueError:
+                pass  # hostname or already-bracketed address — leave as-is
             connectToAddress = "tcp://" + ipAddress
         else:
             connectToAddress = "unix://" + unixSocketPath

testing/python3/tests/test_connection.py

@@ -45,7 +45,7 @@ def test_connection_disconnect_error_after_shutdown():
 @test_utils.run_with_standalone_host_engine(passAppAsArg=True)
 def test_dcgm_standalone_connection_disconnect_error_after_hostengine_terminate(handle, hostengineApp):
     '''
-    Test that DCGM_ST_CONNECTION_NOT_VALID is returned when the dcgm API is used after 
+    Test that DCGM_ST_CONNECTION_NOT_VALID is returned when the dcgm API is used after
     the hostengine process is terminated via `nv-hostengine --term`.
     '''
 
@@ -70,7 +70,7 @@ def test_dcgm_standalone_connection_disconnect_error_after_hostengine_terminate(
 @test_utils.run_with_standalone_host_engine(passAppAsArg=True)
 def test_dcgm_standalone_connection_disconnect_error_after_hostengine_murder(handle, hostengineApp):
     '''
-    Test that DCGM_ST_CONNECTION_NOT_VALID is returned when the dcgm API is used after 
+    Test that DCGM_ST_CONNECTION_NOT_VALID is returned when the dcgm API is used after
     the hostengine process is killed via a `SIGKILL` signal.
     '''
     handle = pydcgm.DcgmHandle(handle)
@@ -129,6 +129,51 @@ def test_dcgm_ipv6_loopback():
     nvHe.validate()
 
 
+@test_utils.run_only_as_root()
+@test_utils.run_with_ipv6_enabled()
+def test_dcgm_ipv6_hostname_resolution():
+    '''
+    Verify that a hostname which resolves exclusively to an IPv6 address can connect to a
+    host engine bound to [::1].  This exercises the AF_UNSPEC path in ConnectTcpAsyncImpl —
+    the fix for the bug where AF_INET was hardcoded, preventing hostname→IPv6 resolution.
+    The test is skipped when no IPv6-only hostname alias is available on the system.
+    '''
+    import socket as _socket
+
+    def _resolves_only_to_ipv6(hostname):
+        try:
+            if _socket.getaddrinfo(hostname, None, _socket.AF_INET):
+                return False
+        except _socket.gaierror:
+            pass
+        try:
+            return bool(_socket.getaddrinfo(hostname, None, _socket.AF_INET6))
+        except _socket.gaierror:
+            return False
+
+    # ip6-loopback / ip6-localhost are standard aliases for ::1 on many Linux distros
+    test_hostname = next(
+        (h for h in ('ip6-loopback', 'ip6-localhost') if _resolves_only_to_ipv6(h)),
+        None,
+    )
+    if test_hostname is None:
+        test_utils.skip_test("No hostname found that resolves exclusively to an IPv6 address")
+
+    nvHe = apps.NvHostEngineApp(['-b', '[::1]'])
+    nvHe.start(timeout=90)
+
+    handle = pydcgm.DcgmHandle(ipAddress=test_hostname, timeoutMs=90)
+    assert handle
+    dcgmSystem = handle.GetSystem()
+    dcgmSystem.discovery.GetAllGpuIds()
+
+    del handle
+    handle = None
+
+    nvHe.terminate()
+    nvHe.validate()
+
+
 @test_utils.run_with_standalone_host_engine(20)
 @test_utils.run_only_with_live_gpus()
 def test_dcgm_connection_client_cleanup(handle, gpuIds):