8. Encoding of Terminal Modes

8. Encoding of Terminal Modes

All encoded terminal modes (as passed in a pty request) are encoded into a byte stream. It is intended that the coding be portable across different environments. The stream consists of opcode-argument pairs wherein the opcode is a byte value. Opcodes 1 to 159 have a single uint32 argument. Opcodes 160 to 255 are not yet defined, and cause parsing to stop (they should only be used after any other data). The stream is terminated by opcode TTY_OP_END (0x00).

The client SHOULD put any modes it knows about in the stream, and the server MAY ignore any modes it does not know about. This allows some degree of machine-independence, at least between systems that use a POSIX-like tty interface. The protocol can support other systems as well, but the client may need to fill reasonable values for a number of parameters so the server pty gets set to a reasonable mode (the server leaves all unspecified mode bits in their default values, and only some combinations make sense).

The naming of opcode values mostly follows the POSIX terminal mode flags. The following opcode values have been defined. Note that the values given below are in decimal format for readability, but they are actually byte values.

opcode	mnemonic	description
0	TTY_OP_END	Indicates end of options.
1	VINTR	Interrupt character; 255 if none. Similarly for the other characters. Not all of these characters are supported on all systems.
2	VQUIT	The quit character (sends SIGQUIT signal on POSIX systems).
3	VERASE	Erase the character to left of the cursor.
4	VKILL	Kill the current input line.
5	VEOF	End-of-file character (sends EOF from the terminal).
6	VEOL	End-of-line character in addition to carriage return and/or linefeed.
7	VEOL2	Additional end-of-line character.
8	VSTART	Continues paused output (normally control-Q).
9	VSTOP	Pauses output (normally control-S).
10	VSUSP	Suspends the current program.
11	VDSUSP	Another suspend character.
12	VREPRINT	Reprints the current input line.
13	VWERASE	Erases a word left of cursor.
14	VLNEXT	Enter the next character typed literally, even if it is a special character
15	VFLUSH	Character to flush output.
16	VSWTCH	Switch to a different shell layer.
17	VSTATUS	Prints system status line (load, command, pid, etc).
18	VDISCARD	Toggles the flushing of terminal output.
30	IGNPAR	The ignore parity flag. The parameter SHOULD be 0 if this flag is FALSE, and 1 if it is TRUE.
31	PARMRK	Mark parity and framing errors.
32	INPCK	Enable checking of parity errors.
33	ISTRIP	Strip 8th bit off characters.
34	INLCR	Map NL into CR on input.
35	IGNCR	Ignore CR on input.
36	ICRNL	Map CR to NL on input.
37	IUCLC	Translate uppercase characters to lowercase.
38	IXON	Enable output flow control.
39	IXANY	Any char will restart after stop.
40	IXOFF	Enable input flow control.
41	IMAXBEL	Ring bell on input queue full.
50	ISIG	Enable signals INTR, QUIT, [D]SUSP.
51	ICANON	Canonicalize input lines.
52	XCASE	Enable input and output of uppercase characters by preceding their lowercase equivalents with "\".
53	ECHO	Enable echoing.
54	ECHOE	Visually erase chars.
55	ECHOK	Kill character discards current line.
56	ECHONL	Echo NL even if ECHO is off.
57	NOFLSH	Don't flush after interrupt.
58	TOSTOP	Stop background jobs from output.
59	IEXTEN	Enable extensions.
60	ECHOCTL	Echo control characters as ^(Char).
61	ECHOKE	Visual erase for line kill.
62	PENDIN	Retype pending input.
70	OPOST	Enable output processing.
71	OLCUC	Convert lowercase to uppercase.
72	ONLCR	Map NL to CR-NL.
73	OCRNL	Translate carriage return to newline (output).
74	ONOCR	Translate newline to carriage return-newline (output).
75	ONLRET	Newline performs a carriage return (output).
90	CS7	7 bit mode.
91	CS8	8 bit mode.
92	PARENB	Parity enable.
93	PARODD	Odd parity, else even.
128	TTY_OP_ISPEED	Specifies the input baud rate in bits per second.
129	TTY_OP_OSPEED	Specifies the output baud rate in bits per second.

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