feat(client): complete sshi ssh on (unhashed) known hosts

cliclient/cmd/ssh.go

@@ -1,9 +1,85 @@
 package cmd
 
 import (
+	"bufio"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
 	"github.com/spf13/cobra"
+	"golang.org/x/crypto/ssh"
 )
 
+func expandFilename(fn string) string {
+	if strings.HasPrefix(fn, "~/") {
+		if hd, err := os.UserHomeDir(); err == nil {
+			fn = filepath.Join(hd, fn[2:])
+		}
+	}
+	return fn
+}
+
+func sshKnownHostnames(in []byte) []string {
+	var hosts, ret []string
+	var err error
+	for {
+		_, hosts, _, _, in, err = ssh.ParseKnownHosts(in)
+		if err != nil {
+			break
+		}
+		for _, h := range hosts {
+			if i := strings.IndexRune(h, ']'); i != -1 && strings.HasPrefix(h, "[") {
+				h = h[1:i]
+			}
+			// Skip wildcards, negations, and hashed entries
+			if !strings.ContainsAny(h, "*?!|") {
+				ret = append(ret, h)
+			}
+		}
+	}
+	return ret
+}
+
+func sshHostnames(cmd *cobra.Command, args []string, toComplete string) (ret []string, compDir cobra.ShellCompDirective) {
+	compDir = cobra.ShellCompDirectiveNoFileComp
+	if len(args) != 0 {
+		return
+	}
+
+	ssh := exec.CommandContext(cmd.Context(), "ssh", "-G", toComplete)
+	stdout, err := ssh.StdoutPipe()
+	if err != nil || ssh.Start() != nil {
+		return
+	}
+	var fns []string
+	s := bufio.NewScanner(stdout)
+	for s.Scan() {
+		flds := strings.Fields(s.Text())
+		if len(flds) > 1 && (flds[0] == "globalknownhostsfile" || flds[0] == "userknownhostsfile") {
+			// These seem to be output space separated, with no escaping, so we're out of luck with filenames containing spaces
+			for _, fn := range flds[1:] {
+				if fn = expandFilename(fn); fn != "" {
+					fns = append(fns, fn)
+				}
+			}
+		}
+	}
+	_ = ssh.Wait()
+
+	buf := make([]byte, 1024*1024)
+	for _, fn := range fns {
+		if f, err := os.Open(fn); err == nil {
+			n, err := f.Read(buf)
+			_ = f.Close()
+			if err == nil {
+				ret = append(ret, sshKnownHostnames(buf[:n])...)
+			}
+		}
+	}
+	return
+}
+
 var SshCmd = &cobra.Command{
 	Use:                "ssh",
 	Short:              "Invoke ssh command with signed certificate on ssh-agent",
@@ -12,7 +88,7 @@ var SshCmd = &cobra.Command{
 		ignoreFlagsAfter("ssh")
 		return runExecCommand(RootCmd.Flags().Args()[1:])
 	},
-	ValidArgsFunction: noCompletion,
+	ValidArgsFunction: sshHostnames,
 }
 
 func init() {