From 3dd6affd6fde2f0af23b35e7014ba59b6233320a Mon Sep 17 00:00:00 2001
From: Jeff Carr <jcarr@wit.com>
Date: Sat, 22 Mar 2025 08:30:15 -0500
Subject: more hostname things

---
 common.go | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 common.go

(limited to 'common.go')

diff --git a/common.go b/common.go
new file mode 100644
index 0000000..ae4b7ff
--- /dev/null
+++ b/common.go
@@ -0,0 +1,47 @@
+package hostname
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+)
+
+var ErrorEmptyDomainName error = errors.New("domain name is empty")
+var ErrorDomainNameMisconfigured error = errors.New("your OS domain name is not configured correctly")
+
+// returns 'hostname', 'domainname'
+func Split(s string) (string, string) {
+	parts := strings.Fields(s)
+	if len(parts) == 0 {
+		return "", ""
+	}
+	if len(parts) == 1 {
+		return parts[0], ""
+	}
+	return parts[0], strings.Join(parts[1:], ".")
+}
+
+// checks to make sure there is a domainname
+func ValidDomainname(s string) error {
+	_, domainname := Split(s)
+	if domainname == "" {
+		return ErrorEmptyDomainName
+	}
+	return nil
+}
+
+func ReverseLookupFQDN(hostname string) (string, error) {
+	addrs, err := net.LookupIP(hostname)
+	if err != nil || len(addrs) == 0 {
+		return hostname, fmt.Errorf("failed to lookup IP for hostname %s: %w", hostname, err)
+	}
+
+	// Try reverse lookup on the first IP address
+	names, err := net.LookupAddr(addrs[0].String())
+	if err != nil || len(names) == 0 {
+		return hostname, fmt.Errorf("reverse DNS lookup failed for IP %s: %w", addrs[0].String(), err)
+	}
+
+	return names[0], nil
+}
-- 
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