fix: propagate errors and harden mount path handling

Addresses audit findings from 2026-04-19:

- Q-H1: replace Println with Printf for %s-formatted error (line 42)
- Q-H2/Q-M2/Q-M3: verify_mount_dir and mount_sshfs now return error;
  main exits on failure instead of continuing with invalid state
- Q-M1: default Port to "22" when ssh_config has no entry
- S-M1: create mount dir with 0700 instead of 0777
- S-M2: filepath.Clean + base-prefix check rejects HostName values
  that would escape ~/Servers/
- Q-L1: correct "~/.ssh_config" typo to "~/.ssh/config"

Also: use os.Exit(2) for usage error (was 80), route user-facing
errors to stderr.

main.go

@@ -1,12 +1,15 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	"os"
 	"os/exec"
-	"github.com/moby/sys/mountinfo"
+	"path/filepath"
+	"strings"
+
 	"github.com/kevinburke/ssh_config"
-	"flag"
+	"github.com/moby/sys/mountinfo"
 )
 
 var eFlag = flag.Bool("e", false, "open mountpoint in your editor")
@@ -16,21 +19,30 @@ func main() {
 	args := flag.Args()
 
 	if len(args) == 0 {
-		fmt.Println("No hostname specified.")
-		os.Exit(80)
-	} else {
+		fmt.Fprintln(os.Stderr, "No hostname specified.")
+		os.Exit(2)
+	}
+
 	hostname := ssh_config.Get(args[0], "HostName")
 	user := ssh_config.Get(args[0], "User")
 	port := ssh_config.Get(args[0], "Port")
 	ifile := ssh_config.Get(args[0], "IdentityFile")
 
 	if len(hostname) == 0 || len(user) == 0 || len(ifile) == 0 {
-			fmt.Println("Hostname not found in ~/.ssh_config")
+		fmt.Fprintln(os.Stderr, "Hostname not found in ~/.ssh/config")
 		os.Exit(3)
-		} else {
-			mount := verify_mount_dir(hostname)
+	}
+	if len(port) == 0 {
+		port = "22"
+	}
 
-			fmt.Println("Hostname:	",hostname)
+	mount, err := verify_mount_dir(hostname)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "verify_mount_dir() failed:", err)
+		os.Exit(4)
+	}
+
+	fmt.Println("Hostname:	", hostname)
 	fmt.Println("User:		", user)
 	fmt.Println("Port:		", port)
 	fmt.Println("Ifile:		", ifile)
@@ -39,42 +51,49 @@ func main() {
 
 	chkmount, chkmount_err := mountinfo.Mounted(mount)
 	if chkmount_err != nil {
-				fmt.Println("mountinfo.Mounted() failed with %s\n", chkmount_err)
+		fmt.Fprintf(os.Stderr, "mountinfo.Mounted() failed with %s\n", chkmount_err)
+		os.Exit(5)
+	}
+	if !chkmount {
+		if err := mount_sshfs(hostname, user, ifile, port, mount); err != nil {
+			fmt.Fprintln(os.Stderr, "mount_sshfs() failed:", err)
+			os.Exit(6)
 		}
-			if chkmount == false {
-				mount_sshfs(hostname, user, ifile, port, mount)
 	} else {
 		fmt.Println("!!! Already mounted")
 	}
 	run_editor(mount)
-		}
-	}
 }
 
 func run_editor(mount string) {
-	if(*eFlag == true) {
+	if *eFlag {
 		cmd := exec.Command("subl", mount)
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
 		err := cmd.Run()
 		if err != nil {
-			fmt.Println("run_editor() failed with\n",err)
+			fmt.Fprintln(os.Stderr, "run_editor() failed with", err)
 		}
 	}
 }
 
-func verify_mount_dir(hostname string)(mount string) {
-	homedir, homedirerr := os.UserHomeDir()
-	if homedirerr != nil {
-		fmt.Println( homedirerr )
+func verify_mount_dir(hostname string) (string, error) {
+	homedir, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("resolve home dir: %w", err)
 	}
-	mount = homedir+"/Servers/"+hostname
-	os.MkdirAll(mount, os.ModePerm)
-
-	return
+	base := filepath.Join(homedir, "Servers")
+	mount := filepath.Clean(filepath.Join(base, hostname))
+	if !strings.HasPrefix(mount, base+string(os.PathSeparator)) {
+		return "", fmt.Errorf("hostname %q escapes mount base %q", hostname, base)
+	}
+	if err := os.MkdirAll(mount, 0700); err != nil {
+		return "", fmt.Errorf("create mount dir %q: %w", mount, err)
+	}
+	return mount, nil
 }
 
-func mount_sshfs(hostname string, user string, ifile string, port string, mount string) {
+func mount_sshfs(hostname string, user string, ifile string, port string, mount string) error {
 	cmd := exec.Command("sshfs", "-p", port,
 		"-o", "IdentityFile="+ifile,
 		"-o", "idmap=user",
@@ -91,8 +110,5 @@ func mount_sshfs(hostname string, user string, ifile string, port string, mount
 		user+"@"+hostname+":/", mount)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
-	err := cmd.Run()
-	if err != nil {
-		fmt.Println("mount_sshfs() failed with\n",err)
-	}
+	return cmd.Run()
 }