more hostname things

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
+}

get.go

@@ -1,8 +1,8 @@
 package hostname
 
-// functions to import and export the protobuf
-// data to and from config files
-
+// returns the hostname
+// hostname is always set to the best effort
+// error is set if hostname isn't real
 func Get() (string, error) {
 	hostname, err := osGetHostname()
 	return hostname, err

get_darwin.go

@@ -1,10 +1,9 @@
 package hostname
 
-// functions to import and export the protobuf
-// data to and from config files
-
 import (
-	"os"
+	"bytes"
+	"fmt"
+	"os/exec"
 )
 
 // scutil --get HostName
@@ -13,6 +12,17 @@ import (
 // scutil --set HostName my-mac.example.com
 
 func osGetHostname() (string, error) {
-	hostname, err := os.Hostname()
-	return hostname, err
+	return scutil([]string{"-get", "HostName"})
+}
+
+// getDomainName executes the 'domainname' command and returns its output.
+func scutil(args []string) (string, error) {
+	cmd := exec.Command("scutil", args)
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	if err := cmd.Run(); err != nil {
+		return "", fmt.Errorf("failed to execute 'scutil': %w", err)
+	}
+	domain := out.String()
+	return domain, nil
 }

get_linux.go

@@ -4,10 +4,39 @@ package hostname
 // data to and from config files
 
 import (
+	"bytes"
+	"fmt"
 	"os"
+	"os/exec"
+	"strings"
 )
 
 func osGetHostname() (string, error) {
-	hostname, err := os.Hostname()
-	return hostname, err
+	host, err := os.Hostname()
+	if err != nil {
+		return host, fmt.Errorf("failed to get hostname: %w", err)
+	}
+
+	domain, err := getDomainName()
+	if err != nil || domain == "" {
+		return host, err
+	}
+
+	return fmt.Sprintf("%s.%s", host, domain), nil
+}
+
+// getDomainName executes the 'domainname' command and returns its output.
+func getDomainName() (string, error) {
+	cmd := exec.Command("domainname")
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	if err := cmd.Run(); err != nil {
+		return "", fmt.Errorf("failed to execute 'domainname': %w", err)
+	}
+	domain := strings.TrimSpace(out.String())
+	if domain == "(none)" {
+		return "", ErrorDomainNameMisconfigured
+	}
+
+	return domain, nil
 }