# beer-protocols The terminal-protocol building blocks beer is built on: byte codecs, the terminfo capability table, character-set translation, SGR parsing, and the keyboard/mouse wire encoders. Everything here is a pure function or a plain data type, with no terminal state, so each protocol detail can be read and tested on its own. beer feeds these into its `vte`-driven dispatcher and its grid model. This README doubles as the reference for **which escape sequences, OSC commands, and POSIX behaviours beer actually implements** - the parts a user notices. Sequences not listed here are parsed and ignored rather than passed through. Notation: `ESC` is `0x1b`, `CSI` is `ESC [`, `OSC` is `ESC ]`, `DCS` is `ESC P`, `ST` is the string terminator `ESC \` (a `BEL` is also accepted to end an OSC). `Ps` is a numeric parameter, `Pt` a text parameter. ## Crate layout | Module | What it covers | | --------- | ------------------------------------------------------------------------------ | | `codec` | base64 (OSC 52), hex (XTGETTCAP names), `file://` URI percent-decoding (OSC 7) | | `caps` | terminfo capabilities answered over XTGETTCAP | | `charset` | G0/G1 designation and DEC special-graphics line drawing | | `sgr` | the multi-parameter SGR colour and underline forms | | `key` | legacy xterm/VT and kitty keyboard-protocol key encoding | | `mouse` | X10 / UTF-8 / SGR mouse-report encoding | | `style` | the enums an SGR/DECSET stream selects | ## C0 control characters | Byte | Name | Effect | | ------------- | -------- | ------------------------------------------------------------- | | `0x07` | BEL | rings the bell (visual flash / command / urgency, per config) | | `0x08` | BS | backspace | | `0x09` | HT | tab to next stop | | `0x0A`-`0x0C` | LF/VT/FF | line feed | | `0x0D` | CR | carriage return | | `0x0E` | SO | invoke G1 (shift out) | | `0x0F` | SI | invoke G0 (shift in) | ## Cursor movement and editing (CSI) | Sequence | Name | Effect | | ------------------------ | ----------- | ------------------------------------------ | | `CSI Ps A` | CUU | cursor up | | `CSI Ps B` / `CSI Ps e` | CUD | cursor down | | `CSI Ps C` / `CSI Ps a` | CUF | cursor forward | | `CSI Ps D` | CUB | cursor back | | `CSI Ps E` | CNL | cursor down, to column 1 | | `CSI Ps F` | CPL | cursor up, to column 1 | | `CSI Ps G` / `CSI Ps \`` | CHA | move to column | | `CSI Ps d` | VPA | move to row | | `CSI Ps ; Ps H` / `f` | CUP/HVP | move to row;col | | `CSI Ps J` | ED | erase in display (0 below, 1 above, 2 all) | | `CSI Ps K` | EL | erase in line (0 right, 1 left, 2 all) | | `CSI Ps @` | ICH | insert blank characters | | `CSI Ps P` | DCH | delete characters | | `CSI Ps L` | IL | insert lines | | `CSI Ps M` | DL | delete lines | | `CSI Ps X` | ECH | erase characters | | `CSI Ps S` | SU | scroll up | | `CSI Ps T` | SD | scroll down | | `CSI Ps ; Ps r` | DECSTBM | set scroll region (top;bottom) | | `CSI Ps g` | TBC | clear tab stop (0) or all tabs (3) | | `CSI s` / `CSI u` | SCOSC/SCORC | save / restore cursor | ## ESC (non-CSI) | Sequence | Name | Effect | | --------------------- | ----------- | ------------------------------------------------------------------- | | `ESC D` | IND | line feed | | `ESC M` | RI | reverse index | | `ESC E` | NEL | next line | | `ESC 7` / `ESC 8` | DECSC/DECRC | save / restore cursor | | `ESC H` | HTS | set tab stop | | `ESC c` | RIS | full reset | | `ESC ( c` / `ESC ) c` | SCS | designate G0 / G1 charset (`0` = DEC special graphics, `B` = ASCII) | ## Graphic rendition (SGR, `CSI Ps m`) Bold (1), dim (2), italic (3), underline (4), blink (5/6), reverse (7), hidden (8), strike (9), and their resets (22-29). Overline (53) and its reset (55). Underline styles via `4:x` and SGR 21: single, double, curly, dotted, dashed. Colours: the 16 ANSI colours (30-37, 90-97 foreground; 40-47, 100-107 background) and default (39/49). Extended colour for foreground (38), background (48), and underline (58/59), in both the legacy semicolon form (`38;5;n`, `38;2;r;g;b`) and the colon-subparameter form (`38:5:n`, `38:2:r:g:b`, with an ignored colour-space id). 256-colour and 24-bit truecolor are fully supported. ## Modes (DECSET/DECRST `CSI [?] Ps h` / `l`) | Mode | Name | Effect | | --------------- | ------- | -------------------------------------- | | `4` (ANSI) | IRM | insert/replace | | `?1` | DECCKM | application cursor keys | | `?6` | DECOM | origin mode | | `?7` | DECAWM | autowrap | | `?25` | DECTCEM | cursor visibility | | `?9` | - | X10 mouse reporting | | `?1000` | - | normal mouse (press/release) | | `?1002` | - | button-event mouse (drag) | | `?1003` | - | any-event mouse (all motion) | | `?1004` | - | focus in/out reporting | | `?1005` | - | UTF-8 mouse coordinates | | `?1006` | - | SGR mouse coordinates | | `?47` / `?1047` | - | alternate screen | | `?1049` | - | alternate screen + save/restore cursor | | `?2004` | - | bracketed paste | | `?2026` | - | synchronized output | Mode state is reportable with **DECRQM** (`CSI [?] Ps $ p`), which replies `CSI [?] Ps ; state $ y` (1 set, 2 reset, 0 unrecognized). ## Cursor style (DECSCUSR, `CSI Ps SP q`) `0`/`1` blinking block, `2` steady block, `3` blinking underline, `4` steady underline, `5` blinking bar, `6` steady bar. The configured default applies until an application overrides it. ## Device reports | Sequence | Name | Reply | | -------------------- | --------- | ---------------------------------------------------------- | | `CSI c` | DA1 | `CSI ?62;22c` (VT220 + ANSI colour) | | `CSI > c` | DA2 | `CSI >0;276;0c` | | `CSI = c` | DA3 | `DCS !\|00000000 ST` | | `CSI 5 n` | DSR | `CSI 0n` (terminal OK) | | `CSI 6 n` | CPR | `CSI row;col R` (cursor position) | | `CSI > q` | XTVERSION | `DCS >\|beer(version) ST` | | `DCS + q ST` | XTGETTCAP | per name, `DCS 1 + r name=value ST` or `DCS 0 + r name ST` | XTGETTCAP answers `TN` (terminal name `beer`), `Co`/`colors` (256), and `RGB` (`8/8/8`, i.e. truecolor). ## Window title `OSC 0 ; Pt` and `OSC 2 ; Pt` set the title. The title stack (`CSI 22 t` push, `CSI 23 t` pop) is supported, so full-screen programs can save and restore it. ## OSC commands | Command | Effect | | --------------------------------- | ------------------------------------------------ | | `OSC 0` / `OSC 2` | set window title | | `OSC 4 ; idx ; spec` | set / query palette entry (`?` queries) | | `OSC 104 [; idx ...]` | reset palette (all, or listed entries) | | `OSC 10` / `OSC 11` | set / query default foreground / background | | `OSC 110` / `OSC 111` | reset foreground / background | | `OSC 12` / `OSC 112` | set / reset cursor colour | | `OSC 17` / `OSC 19` | set / query selection background / foreground | | `OSC 7 ; file://host/path` | report working directory (used for new windows) | | `OSC 8 ; params ; URI` | hyperlink (empty URI ends it) | | `OSC 9 ; Pt` | desktop notification (iTerm2 style) | | `OSC 777 ; notify ; title ; body` | desktop notification (rxvt style) | | `OSC 99 ; metadata ; body` | desktop notification (kitty style, single-chunk) | | `OSC 52 ; target ; data` | clipboard set (base64) or query (`?`) | | `OSC 133 ; A/B/C/D` | shell-integration prompt marks | Colour specs follow the X11 forms `#rrggbb` and `rgb:rr/gg/bb` (1-4 hex digits per channel). Colour queries reply in the `rgb:rrrr/gggg/bbbb` form. ### Clipboard (OSC 52) `OSC 52 ; c ; ` sets the clipboard, `; p ;` the primary selection; `; c ; ?` queries. For privacy, a query is answered from the text beer itself last placed there, **not** the live system clipboard - so a remote program cannot read what another application copied. ### Shell integration (OSC 133 / OSC 7) Prompt marks `A` (prompt start), `B` (command start), `C` (output start), and `D` (command end) drive prompt-jumping and "pipe last command output". `OSC 7` tracks the working directory so a new window opens in the same place. ## Keyboard The legacy xterm/VT encoding covers cursor keys (with DECCKM application mode), the editing keypad (Insert/Delete/PageUp/PageDown), F1-F12, and the xterm modifier parameter (`CSI 1 ; m `), with Alt sending an ESC (meta) prefix. The **kitty keyboard protocol** (`CSI > flags u` push, `CSI < flags u` pop, `CSI = flags ; mode u` set, `CSI ? u` query) is implemented with the disambiguate, report-event-types, report-alternate-keys, report-all-keys, and report-associated-text enhancement flags. Keys are encoded as `CSI code[:shifted] ; mod[:event] [; text] u`, with a 32-deep push/pop stack. The common keys (Enter, Tab, Backspace) keep their legacy bytes when unmodified so a plain shell stays usable. ## Mouse Reports are framed in the legacy byte form (`CSI M Cb Cx Cy`), the UTF-8 coordinate form (DECSET 1005), or the SGR form (`CSI < Cb ; Cx ; Cy M/m`, DECSET 1006). Shift/Alt/Ctrl modifier bits and the motion bit are encoded; legacy releases collapse to button code 3. Reporting level is chosen by the application via the mouse modes above; with reporting off the pointer drives local selection and scrollback. ## POSIX / terminal behaviour - A real PTY pair (`rustix` `openpt`/`grantpt`/`unlockpt`), with the child's `TERM` set to the configured value (default `beer`) and the window size kept in sync via `TIOCSWINSZ` (`SIGWINCH` reaches the child). - The child's exit status is propagated as beer's own exit code. - Alternate screen, scroll regions, autowrap and reflow on resize, and a scrollback buffer. - Bracketed paste (DECSET 2004) and synchronized output (DECSET 2026) so applications can paste safely and update atomically.