Initial commit

vendor/go.i3wm.org/i3/byteorder.go

@@ -0,0 +1,63 @@
+package i3
+
+import (
+	"encoding/binary"
+	"io"
+	"strings"
+)
+
+// detectByteOrder sends messages to i3 to determine the byte order it uses.
+// For details on this technique, see:
+// https://build.i3wm.org/docs/ipc.html#_appendix_a_detecting_byte_order_in_memory_safe_languages
+func detectByteOrder(conn io.ReadWriter) (binary.ByteOrder, error) {
+	const (
+		// targetLen is 0x00 01 01 00 in both, big and little endian
+		targetLen = 65536 + 256
+
+		// SUBSCRIBE was introduced in 3.e (2010-03-30)
+		prefixSubscribe = "[]"
+
+		// RUN_COMMAND was always present
+		prefixCmd = "nop byte-order detection. padding: "
+	)
+
+	// 2. Send a big endian encoded message of type SUBSCRIBE:
+	payload := []byte(prefixSubscribe + strings.Repeat(" ", targetLen-len(prefixSubscribe)))
+	if err := binary.Write(conn, binary.BigEndian, &header{magic, uint32(len(payload)), messageTypeSubscribe}); err != nil {
+		return nil, err
+	}
+	if _, err := conn.Write(payload); err != nil {
+		return nil, err
+	}
+
+	// 3. Send a byte order independent RUN_COMMAND message:
+	payload = []byte(prefixCmd + strings.Repeat("a", targetLen-len(prefixCmd)))
+	if err := binary.Write(conn, binary.BigEndian, &header{magic, uint32(len(payload)), messageTypeRunCommand}); err != nil {
+		return nil, err
+	}
+	if _, err := conn.Write(payload); err != nil {
+		return nil, err
+	}
+
+	// 4. Receive a message header, decode the message type as big endian:
+	var header [14]byte
+	if _, err := io.ReadFull(conn, header[:]); err != nil {
+		return nil, err
+	}
+	if messageType(binary.BigEndian.Uint32(header[10:14])) == messageReplyTypeCommand {
+		order := binary.LittleEndian // our big endian message was not answered
+		// Read remaining payload
+		_, err := io.ReadFull(conn, make([]byte, order.Uint32(header[6:10])))
+		return order, err
+	}
+	order := binary.BigEndian // our big endian message was answered
+	// Read remaining payload
+	if _, err := io.ReadFull(conn, make([]byte, order.Uint32(header[6:10]))); err != nil {
+		return order, err
+	}
+
+	// Slurp the pending RUN_COMMAND reply.
+	sock := &socket{conn: conn, order: order}
+	_, err := sock.recvMsg()
+	return binary.BigEndian, err
+}