meta: split protocol codecs and encoders into a beer-protocols crate

Signed-off-by: NotAShelf <raf@notashelf.dev> Change-Id: Ib7706308c892e43d2044fbb766505e9e6a6a6964
2026-06-26 11:44:20 +03:00 · 2026-06-26 11:44:20 +03:00 · 1f1451f108
commit 1f1451f108
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+# 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 <names> 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 ; <base64>` 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 <letter>`), 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.