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