config: Implement percent TOKEN substitution

config.go

@@ -370,6 +370,102 @@ type Config struct {
 	position Position
 }
 
+// %%    A literal `%'.
+// %C    Shorthand for %l%h%p%r.
+// %d    Local user's home directory.
+// %h    The remote hostname.
+// %i    The local user ID.
+// %L    The local hostname.
+// %l    The local hostname, including the domain name.
+// %n    The original remote hostname, as given on the command line.
+// %p    The remote port.
+// %r    The remote username.
+// %u    The local username.
+func (host *Host) percent(alias, val string) string {
+	var (
+		b          bytes.Buffer
+		sawPercent bool
+	)
+	for _, c := range val {
+		if sawPercent {
+			sawPercent = false
+			switch c {
+			case 'd':
+				b.WriteString(homedir())
+			case 'h':
+				b.WriteString(host.tryKV(alias, "HostName"))
+			case 'i':
+				b.WriteString(fmt.Sprintf("%d", os.Getuid()))
+			case 'L':
+				if h, err := os.Hostname(); err != nil {
+					b.WriteString(fmt.Sprintf("%%!L(%v)", err))
+				} else {
+					b.WriteString(h)
+				}
+			case 'n':
+				b.WriteString(alias)
+			case 'p':
+				b.WriteString(host.tryKV(alias, "Port"))
+			case 'r':
+				b.WriteString(host.tryKV(alias, "User"))
+			case 'u':
+				b.WriteString(os.Getenv("USER"))
+			case '%':
+				b.WriteString("%")
+			default:
+				// In the event of a bad format char, fmt returns
+				// the mangled string and no error.
+				// It may be best to follow that practice, as
+				// it gives you a much better idea where things
+				// went wrong.
+				b.WriteString(`%!` + string(c))
+			}
+			continue
+		}
+		if c != '%' {
+			b.WriteByte(byte(c))
+			continue
+		}
+		sawPercent = true
+	}
+	if sawPercent {
+		b.WriteString("%!(NOVERB)")
+	}
+	return b.String()
+}
+
+func (host *Host) findKV(alias, key string) (string, error) {
+	lowerKey := strings.ToLower(key)
+	for _, node := range host.Nodes {
+		switch t := node.(type) {
+		case *Empty:
+			continue
+		case *KV:
+			// "keys are case insensitive" per the spec
+			lkey := strings.ToLower(t.Key)
+			if lkey == "match" {
+				panic("can't handle Match directives")
+			}
+			if lkey == lowerKey {
+				return t.Value, nil
+			}
+		case *Include:
+			val := t.Get(alias, key)
+			if val != "" {
+				return val, nil
+			}
+		default:
+			return "", fmt.Errorf("unknown Node type %v", t)
+		}
+	}
+	return "", fmt.Errorf("%v has no key %v", alias, key)
+}
+
+func (host *Host) tryKV(alias, key string) string {
+	v, _ := host.findKV(alias, key)
+	return v
+}
+
 // Get finds the first value in the configuration that matches the alias and
 // contains key. Get returns the empty string if no value was found, or if the
 // Config contains an invalid conditional Include value.
@@ -831,7 +927,7 @@ func init() {
 func newConfig() *Config {
 	return &Config{
 		Hosts: []*Host{
-			&Host{
+			{
 				implicit: true,
 				Patterns: []*Pattern{matchAll},
 				Nodes:    make([]Node, 0),

config_test.go

@@ -482,6 +482,41 @@ func TestNoTrailingNewline(t *testing.T) {
 	}
 }
 
+func TestPercent(t *testing.T) {
+	b := bytes.NewBufferString(`Host wap
+	HostName wap.example.org
+	Port 22
+	User root
+	KexAlgorithms diffie-hellman-group1-sha1
+`)
+	cfg, err := Decode(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+	host := cfg.Hosts[1]
+	t.Logf("cfg is %v, %d hosts, Hosts %v, host %v", cfg, len(cfg.Hosts), cfg.Hosts, host)
+	home := os.Getenv("HOME")
+	user := os.Getenv("USER")
+
+	for _, tt := range []struct {
+		in  string
+		out string
+	}{
+		{"hi", "hi"},
+		{"%dhi", home + "hi"},
+		{"%uhi", user + "hi"},
+		{"%h.%n.%p.%r.%u", "wap.example.org.wap.22.root." + user},
+		{"%Z", "%!Z"},
+		{"%", "%!(NOVERB)"},
+		{"%d%", home + "%!(NOVERB)"},
+	} {
+		o := host.percent("wap", tt.in)
+		if o != tt.out {
+			t.Errorf("%q: got %q, want %q", tt.in, o, tt.out)
+		}
+	}
+}
+
 func TestCustomFinder(t *testing.T) {
 	us := &UserSettings{}
 	us.ConfigFinder(func() string {