strip domain suffix of host

coder · johnstcn · Dec 7, 2023 · Dec 7, 2023 · Dec 7, 2023 · Dec 7, 2023
commit 80e49ffc3c612878494fefc70af4b7b4b920607d
diff --git a/cli/cliutil/hostname.go b/cli/cliutil/hostname.go
@@ -2,6 +2,7 @@ package cliutil
 
 import (
 	"os"
+	"strings"
 	"sync"
 
 	"golang.org/x/xerrors"
@@ -12,14 +13,28 @@ var (
 	hostnameOnce sync.Once
 )
 
+// Hostname returns the hostname of the machine, lowercased,
+// with any trailing domain suffix stripped.
+// It is cached after the first call.
+// If the hostname cannot be determined, this will panic.
 func Hostname() string {
-	hostnameOnce.Do(func() {
-		h, err := os.Hostname()
-		if err != nil {
-			// Something must be very wrong if this fails.
-			panic(xerrors.Errorf("lookup hostname: %w", err))
-		}
-		hostname = h
-	})
+	hostnameOnce.Do(func() { hostname = getHostname() })
 	return hostname
 }
+
+func getHostname() string {
+	h, err := os.Hostname()
+	if err != nil {
+		// Something must be very wrong if this fails.
+		panic(xerrors.Errorf("lookup hostname: %w", err))
 	}
+
+	// On some platforms, the hostname can be an FQDN. We only want the hostname.
+	if idx := strings.Index(h, "."); idx != -1 {
+		h = h[:idx]
+	}
+
+	// For the sake of consistency, we also want to lowercase the hostname.
+	// Per RFC 4343, DNS lookups must be case-insensitive.
+	return strings.ToLower(h)
+}