get rid of os/exec and talk with sway directly via IPC

main.go

@@ -18,14 +18,15 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package main
 
 import (
-	"bytes"
+	"encoding/binary"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io"
 	"log"
 	"log/slog"
+	"net"
 	"os"
-	"os/exec"
 	"runtime/debug"
 
 	"github.com/lmittmann/tint"
@@ -47,6 +48,12 @@ type Node struct {
 	Current_workspace string `json:"current_workspace"`
 }
 
+type Response struct {
+	Success    bool   `json:"success"`
+	ParseError bool   `json:"parse_error"`
+	Error      string `json:"error"`
+}
+
 const (
 	root = iota + 1
 	output
@@ -56,7 +63,14 @@ const (
 
 	LevelNotice = slog.Level(2)
 
-	VERSION = "v0.1.3"
+	VERSION = "v0.2.0"
+
+	IPC_HEADER_SIZE = 14
+	IPC_MAGIC       = "i3-ipc"
+
+	// message types
+	IPC_GET_TREE    = 4
+	IPC_RUN_COMMAND = 0
 )
 
 var (
@@ -73,15 +87,14 @@ var (
 
 const Usage string = `This is swaycycle - cycle focus through all visible windows on a sway workspace.
 
-Usage: swaycycle [-vVdDn] [-l <log>]
+Usage: swaycycle [-vdDn] [-l <log>]
 
 Options:
   -n, --no-switch        do not switch windows
   -d, --debug            enable debugging
   -D, --dump             dump the sway tree (needs -d as well)
   -l, --logfile string   write output to logfile
-  -v, --verbose          enable verbose logging
+  -v, --version          show program version
-  -V, --version          show program version
 
 Copyleft (L) 2025 Thomas von Dein.
 Licensed under the terms of the GNU GPL version 3.
@@ -90,9 +103,8 @@ Licensed under the terms of the GNU GPL version 3.
 func main() {
 	flag.BoolVarP(&Debug, "debug", "d", false, "enable debugging")
 	flag.BoolVarP(&Dumptree, "dump", "D", false, "dump the sway tree (needs -d as well)")
-	flag.BoolVarP(&Verbose, "verbose", "v", false, "enable verbose logging")
 	flag.BoolVarP(&Notswitch, "no-switch", "n", false, "do not switch windows")
-	flag.BoolVarP(&Version, "version", "V", false, "show program version")
+	flag.BoolVarP(&Version, "version", "v", false, "show program version")
 	flag.BoolVarP(&Showhelp, "help", "h", Showhelp, "show help")
 
 	flag.StringVarP(&Logfile, "logfile", "l", "", "write output to logfile")
@@ -120,156 +132,124 @@ func main() {
 		setupLogging(os.Stdout)
 	}
 
-	// fills Visibles node list
+	// connect to sway unix socket
-	fetchSwayTree()
+	unixsock, err := setupIPC()
+	if err != nil {
+		log.Fatalf("Failed to connect to sway unix socket: %s", err)
+	}
+
+	// retrieve the raw json tree
+	rawjson, err := getTree(unixsock)
+	if err != nil {
+		log.Fatalf("Failed to retrieve raw json tree: %s", err)
+	}
+
+	// traverse the tree and find visible windows
+	if err := processJSON(rawjson); err != nil {
+		log.Fatalf("%s", err)
+	}
 
 	if len(Visibles) == 0 {
 		os.Exit(0)
 	}
 
 	id := findNextWindow()
+	slog.Debug("findNextWindow", "nextid", id)
 
 	if id > 0 && !Notswitch {
-		switchFocus(id)
+		switchFocus(id, unixsock)
 	}
 }
 
-func setupLogging(output io.Writer) {
+// connect to unix socket
-	logLevel := &slog.LevelVar{}
+func setupIPC() (net.Conn, error) {
+	sockfile := os.Getenv("SWAYSOCK")
 
-	if !Debug {
+	if sockfile == "" {
-		// default logging
+		return nil, fmt.Errorf("Environment variable SWAYSOCK does not exist or is empty")
-		opts := &tint.Options{
-			Level:     logLevel,
-			AddSource: false,
-			NoColor:   IsNoTty(),
-		}
-
-		if Verbose {
-			logLevel.Set(slog.LevelInfo)
-		} else {
-			logLevel.Set(LevelNotice)
-		}
-
-		handler := tint.NewHandler(output, opts)
-		logger := slog.New(handler)
-
-		slog.SetDefault(logger)
-	} else {
-		// we're using a more verbose logger in debug mode
-		buildInfo, _ := debug.ReadBuildInfo()
-		opts := &yadu.Options{
-			Level:     logLevel,
-			AddSource: true,
-		}
-
-		logLevel.Set(slog.LevelDebug)
-
-		handler := yadu.NewHandler(output, opts)
-		debuglogger := slog.New(handler).With(
-			slog.Group("program_info",
-				slog.Int("pid", os.Getpid()),
-				slog.String("go_version", buildInfo.GoVersion),
-			),
-		)
-		slog.SetDefault(debuglogger)
 	}
+
+	conn, err := net.Dial("unix", sockfile)
+	if err != nil {
+		return nil, err
+	}
+
+	return conn, nil
 }
 
-// find the next window after the  one with current focus. if the last
+// send a sway message header
-// one has focus, return the first
+func sendHeaderIPC(sock net.Conn, messageType uint32, len uint32) error {
-func findNextWindow() int {
+	sendPayload := make([]byte, IPC_HEADER_SIZE)
-	if len(Visibles) == 0 {
+	copy(sendPayload, []byte(IPC_MAGIC))
-		return 0
+	binary.LittleEndian.PutUint32(sendPayload[6:], len)
-	}
+	binary.LittleEndian.PutUint32(sendPayload[10:], messageType)
 
-	seenfocused := false
+	_, err := sock.Write(sendPayload)
-
-	for _, node := range Visibles {
-		if node.Focused {
-			seenfocused = true
-			continue
-		}
-
-		if seenfocused {
-			return node.Id
-		}
-	}
-
-	if seenfocused {
-		return Visibles[0].Id
-	}
-
-	return 0
-}
-
-// actually switch focus using a swaymsg command
-func switchFocus(id int) {
-	var cmd *exec.Cmd
-	arg := fmt.Sprintf("[con_id=%d]", id)
-
-	slog.Debug("executing", "command", "swaymsg "+arg+" focus")
-
-	cmd = exec.Command("swaymsg", arg, "focus")
-
-	errbuf := &bytes.Buffer{}
-	cmd.Stderr = errbuf
-
-	out, err := cmd.Output()
 
 	if err != nil {
-		slog.Debug("failed to execute swaymsg", "output", out)
+		return fmt.Errorf("failed to send header to IPC %w", err)
-		log.Fatalf("Failed to execute swaymsg to switch focus: %s", err)
 	}
 
-	if errbuf.String() != "" {
+	return nil
-		log.Fatalf("swaymsg error: %s", errbuf.String())
-	}
-
-	slog.Info("switched focus", "con_id", id)
 }
 
-// execute swaymsg to get its internal tree
+// send a payload, header had to be sent before
-func fetchSwayTree() {
+func sendPayloadIPC(sock net.Conn, payload []byte) error {
-	var cmd *exec.Cmd
+	_, err := sock.Write(payload)
-
-	slog.Debug("executing", "command", "swaymsg -t get_tree -r")
-
-	cmd = exec.Command("swaymsg", "-t", "get_tree", "-r")
-
-	errbuf := &bytes.Buffer{}
-	cmd.Stderr = errbuf
-
-	out, err := cmd.Output()
 
 	if err != nil {
-		log.Fatalf("Failed to execute swaymsg to get json tree: %s", err)
+		return fmt.Errorf("failed to send payload to IPC %w", err)
 	}
 
-	if errbuf.String() != "" {
+	return nil
-		log.Fatalf("swaymsg error: %s", errbuf.String())
-	}
-
-	if err := processJSON(out); err != nil {
-		log.Fatalf("%s", err)
-	}
 }
 
-func istype(nd Node, which int) bool {
+// read a response, reads response header and returns payload only
-	switch nd.Nodetype {
+func readResponseIPC(sock net.Conn) ([]byte, error) {
-	case "root":
+	// read header
-		return which == root
+	buf := make([]byte, IPC_HEADER_SIZE)
-	case "output":
+
-		return which == output
+	_, err := sock.Read(buf)
-	case "workspace":
+	if err != nil {
-		return which == workspace
+		return nil, fmt.Errorf("failed to read header from socket: %s", err)
-	case "con":
-		return which == con
-	case "floating_con":
-		return which == floating
 	}
 
-	return false
+	slog.Debug("got IPC header", "header", hex.EncodeToString(buf))
+
+	if string(buf[:6]) != IPC_MAGIC {
+		return nil, fmt.Errorf("got invalid IPC response from sway socket")
+	}
+
+	payloadLen := binary.LittleEndian.Uint32(buf[6:10])
+
+	if payloadLen == 0 {
+		return nil, fmt.Errorf("got empty payload IPC response from sway socket")
+	}
+
+	// read payload
+	payload := make([]byte, payloadLen)
+
+	_, err = sock.Read(payload)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read payload from socket: %s", err)
+	}
+
+	return payload, nil
+}
+
+// get raw JSON tree via sway IPC
+func getTree(sock net.Conn) ([]byte, error) {
+	err := sendHeaderIPC(sock, IPC_GET_TREE, 0)
+	if err != nil {
+		return nil, err
+	}
+
+	payload, err := readResponseIPC(sock)
+	if err != nil {
+		return nil, err
+	}
+
+	return payload, nil
 }
 
 // get into the sway tree, determine current workspace and extract all
@@ -303,6 +283,80 @@ func processJSON(jsoncode []byte) error {
 	return nil
 }
 
+// find the next window after the  one with current focus. if the last
+// one has focus, return the first
+func findNextWindow() int {
+	if len(Visibles) == 0 {
+		return 0
+	}
+
+	seenfocused := false
+
+	for _, node := range Visibles {
+		if node.Focused {
+			seenfocused = true
+			continue
+		}
+
+		if seenfocused {
+			return node.Id
+		}
+	}
+
+	if seenfocused {
+		return Visibles[0].Id
+	}
+
+	return 0
+}
+
+// actually switch focus using a swaymsg command
+func switchFocus(id int, sock net.Conn) error {
+	command := fmt.Sprintf("[con_id=%d] focus", id)
+
+	slog.Debug("executing", "command", command)
+
+	// send switch focus command
+	err := sendHeaderIPC(sock, IPC_RUN_COMMAND, uint32(len(command)))
+	if err != nil {
+		return err
+	}
+
+	if err != nil {
+		return fmt.Errorf("failed to send run_command to IPC %w", err)
+	}
+
+	err = sendPayloadIPC(sock, []byte(command))
+	if err != nil {
+		return fmt.Errorf("failed to send switch focus command: %w", err)
+	}
+
+	// check response from sway
+	payload, err := readResponseIPC(sock)
+	if err != nil {
+		return err
+	}
+
+	responses := []Response{}
+
+	if err := json.Unmarshal(payload, &responses); err != nil {
+		return fmt.Errorf("Failed to unmarshal json response: %w", err)
+	}
+
+	if len(responses) == 0 {
+		return fmt.Errorf("Got invalid IPC zero response")
+	}
+
+	if !responses[0].Success {
+		slog.Debug("IPC response to switch focus command", "response", responses)
+		return fmt.Errorf("Failed to switch focus: %s", responses[0].Error)
+	}
+
+	slog.Info("switched focus", "con_id", id)
+
+	return nil
+}
+
 // iterate recursively over given node list extracting visible windows
 func recurseNodes(nodes []Node) {
 	for _, node := range nodes {
@@ -330,6 +384,64 @@ func recurseNodes(nodes []Node) {
 	}
 }
 
+// we use line wise logging, unless debugging is enabled
+func setupLogging(output io.Writer) {
+	logLevel := &slog.LevelVar{}
+
+	if !Debug {
+		// default logging
+		opts := &tint.Options{
+			Level:     logLevel,
+			AddSource: false,
+			NoColor:   IsNoTty(),
+		}
+
+		logLevel.Set(slog.LevelInfo)
+
+		handler := tint.NewHandler(output, opts)
+		logger := slog.New(handler)
+
+		slog.SetDefault(logger)
+	} else {
+		// we're using a more verbose logger in debug mode
+		buildInfo, _ := debug.ReadBuildInfo()
+		opts := &yadu.Options{
+			Level:     logLevel,
+			AddSource: true,
+		}
+
+		logLevel.Set(slog.LevelDebug)
+
+		handler := yadu.NewHandler(output, opts)
+		debuglogger := slog.New(handler).With(
+			slog.Group("program_info",
+				slog.Int("pid", os.Getpid()),
+				slog.String("go_version", buildInfo.GoVersion),
+			),
+		)
+
+		slog.SetDefault(debuglogger)
+	}
+}
+
+// little helper to distinguish sway tree node types
+func istype(nd Node, which int) bool {
+	switch nd.Nodetype {
+	case "root":
+		return which == root
+	case "output":
+		return which == output
+	case "workspace":
+		return which == workspace
+	case "con":
+		return which == con
+	case "floating_con":
+		return which == floating
+	}
+
+	return false
+}
+
 // returns TRUE if stdout is NOT a tty or windows
 func IsNoTty() bool {
 	if !isatty.IsTerminal(os.Stdout.Fd()) {