Fix incorrect fqdn on linux in some edge cases

1 files changed, 28 insertions, 9 deletions

diff --git a/util/system/hostname.cpp b/util/system/hostname.cpp
index 386f646d6b..e377910d5c 100644
--- a/util/system/hostname.cpp
+++ b/util/system/hostname.cpp
@@ -34,8 +34,6 @@ namespace {
 
     struct TFQDNHostNameHolder {
         inline TFQDNHostNameHolder() {
-            struct addrinfo hints;
-            struct addrinfo* ais{nullptr};
             char buf[1024];
 
             memset(buf, 0, sizeof(buf));
@@ -44,20 +42,41 @@ namespace {
                 ythrow TSystemError() << "can not get hostname";
             }
 
+#ifdef _darwin_
+            // On Darwin gethostname returns fqdn, see hostname.c in shell_cmds:
+            // https://github.com/apple-oss-distributions/shell_cmds/blob/main/hostname/hostname.c
+            // There are macs in the wild that don't have fqdn hostnames, but
+            // which have search domains in their resolv.conf, so any attempt to
+            // resolve AI_CANONNAME for the short hostname will result in the
+            // EAI_NONAME error.
+            // It seems using gethostname is enough to emulate the result of
+            // `hostname -f`, which still works on those macs.
+            FQDNHostName = buf;
+#else
+            // On Linux `hostname -f` calls getaddrinfo with AI_CANONNAME flag
+            // to find the fqdn and will fail on any error.
+            // Hosts often have a short hostname and fqdn is resolved over dns.
+            // It is also very common to have a short hostname alias in
+            // /etc/hosts, which works as a fallback (e.g. no fqdn in search
+            // domains, otherwise `hostname -f` fails with an error and it is
+            // obvious the host is not configured correctly).
+            // Note that getaddrinfo may sometimes return EAI_NONAME even when
+            // host actually has fqdn, but dns is temporary unavailable, so we
+            // cannot ignore any errors on Linux.
+            struct addrinfo hints;
+            struct addrinfo* ais{nullptr};
+
             memset(&hints, 0, sizeof(hints));
             hints.ai_family = AF_UNSPEC;
             hints.ai_flags = AI_CANONNAME;
             res = getaddrinfo(buf, nullptr, &hints, &ais);
             if (res) {
-                if (res != EAI_NONAME) {
-                    ythrow TSystemError() << "can not get FQDN (return code is " << res << ", hostname is \"" << buf << "\")";
-                }
-                FQDNHostName = buf;
-            } else {
-                FQDNHostName = ais->ai_canonname;
-                freeaddrinfo(ais);
+                ythrow TSystemError() << "can not get FQDN (return code is " << res << ", hostname is \"" << buf << "\")";
             }
+            FQDNHostName = ais->ai_canonname;
             FQDNHostName.to_lower();
+            freeaddrinfo(ais);
+#endif
         }
 
         TString FQDNHostName;