| 1 | //! OSC 11 terminal-background query. |
| 2 | //! |
| 3 | //! `COLORFGBG` is the only background signal the palette had before this |
| 4 | //! module, and most modern terminals never set it — Windows Terminal, conhost, |
| 5 | //! VS Code, GNOME Terminal, Alacritty and Ghostty all omit it. Without it a |
| 6 | //! white terminal was indistinguishable from a black one, so detection fell |
| 7 | //! back to `Dark` and painted dark-tuned text onto a light surface (#4833). |
| 8 | //! |
| 9 | //! OSC 11 (`ESC ] 11 ; ? BEL`) asks the terminal for its actual background |
| 10 | //! color and is answered by every terminal listed above. The reply is an |
| 11 | //! `xterm`-style color spec, e.g. |
| 12 | //! |
| 13 | //! ```text |
| 14 | //! ESC ] 11 ; rgb:ffff/ffff/ffff ESC \ |
| 15 | //! ``` |
| 16 | //! |
| 17 | //! The parse is a pure function so it can be tested without a terminal; the |
| 18 | //! query itself is Unix-only, bounded by a short deadline, and never runs when |
| 19 | //! stdin/stdout are not both TTYs. |
| 20 | |
| 21 | /// Upper bound on how long startup will wait for a terminal that never |
| 22 | /// answers. A terminal that supports OSC 11 replies in well under a |
| 23 | /// millisecond; anything past this is a terminal that will never reply, and |
| 24 | /// startup latency matters more than the answer. |
| 25 | pub const OSC11_QUERY_TIMEOUT: std::time::Duration = std::time::Duration::from_millis(120); |
| 26 | |
| 27 | /// The query sequence. `ESC \` (ST) is the terminator we prefer in the reply, |
| 28 | /// but terminals may answer with BEL instead, so the reader accepts both. |
| 29 | /// |
| 30 | /// Only the Unix query path writes it — see the note on [`parse_osc11_reply`]. |
| 31 | #[cfg_attr(not(unix), allow(dead_code))] |
| 32 | const OSC11_QUERY: &[u8] = b"\x1b]11;?\x1b\\"; |
| 33 | |
| 34 | /// Extract an RGB triple from an OSC 11 reply body. |
| 35 | /// |
| 36 | /// Accepts the shapes terminals actually emit: |
| 37 | /// - `rgb:RRRR/GGGG/BBBB` (xterm, 1–4 hex digits per channel, any width) |
| 38 | /// - `#RRGGBB` / `#RGB` / `#RRRRGGGGBBBB` |
| 39 | /// |
| 40 | /// Leading `ESC ] 11 ;` and the trailing BEL/ST are optional — anything |
| 41 | /// outside the color spec is ignored, so a reply that arrived interleaved with |
| 42 | /// other terminal chatter still parses. |
| 43 | /// |
| 44 | /// Returns `None` when no color spec is present or a channel is malformed. |
| 45 | /// Channels wider than 8 bits are scaled down, not truncated, so `ffff` is |
| 46 | /// `255` rather than `0`. |
| 47 | // The parser is deliberately cross-platform while the query is Unix-only: |
| 48 | // there is no portable way to read a raw OSC reply off a Windows console |
| 49 | // handle yet, so on Windows nothing calls these. They are kept (rather than |
| 50 | // cfg'd out) because they are pure, fully tested on every platform, and are |
| 51 | // exactly what a future Windows read path would need — but that leaves them |
| 52 | // dead in a non-test Windows build, which `-D warnings` rejects. |
| 53 | #[cfg_attr(not(unix), allow(dead_code))] |
| 54 | #[must_use] |
| 55 | pub fn parse_osc11_reply(reply: &str) -> Option<(u8, u8, u8)> { |
| 56 | if let Some(idx) = reply.find("rgb:") { |
| 57 | return parse_slash_separated(&reply[idx + 4..]); |
| 58 | } |
| 59 | if let Some(idx) = reply.find('#') { |
| 60 | return parse_hash_hex(&reply[idx + 1..]); |
| 61 | } |
| 62 | None |
| 63 | } |
| 64 | |
| 65 | #[cfg_attr(not(unix), allow(dead_code))] |
| 66 | fn parse_slash_separated(spec: &str) -> Option<(u8, u8, u8)> { |
| 67 | let spec: String = spec |
| 68 | .chars() |
| 69 | .take_while(|c| c.is_ascii_hexdigit() || *c == '/') |
| 70 | .collect(); |
| 71 | let mut parts = spec.split('/'); |
| 72 | let r = scale_hex_channel(parts.next()?)?; |
| 73 | let g = scale_hex_channel(parts.next()?)?; |
| 74 | let b = scale_hex_channel(parts.next()?)?; |
| 75 | if parts.next().is_some() { |
| 76 | return None; |
| 77 | } |
| 78 | Some((r, g, b)) |
| 79 | } |
| 80 | |
| 81 | #[cfg_attr(not(unix), allow(dead_code))] |
| 82 | fn parse_hash_hex(spec: &str) -> Option<(u8, u8, u8)> { |
| 83 | let digits: String = spec.chars().take_while(char::is_ascii_hexdigit).collect(); |
| 84 | if !digits.len().is_multiple_of(3) || digits.is_empty() || digits.len() > 12 { |
| 85 | return None; |
| 86 | } |
| 87 | let width = digits.len() / 3; |
| 88 | let r = scale_hex_channel(&digits[..width])?; |
| 89 | let g = scale_hex_channel(&digits[width..width * 2])?; |
| 90 | let b = scale_hex_channel(&digits[width * 2..])?; |
| 91 | Some((r, g, b)) |
| 92 | } |
| 93 | |
| 94 | /// Normalize a hex channel of arbitrary width (1–4 digits) to 8 bits by |
| 95 | /// rescaling across the channel's full range: `f` → `255`, `ffff` → `255`, |
| 96 | /// `8000` → `128`. |
| 97 | #[cfg_attr(not(unix), allow(dead_code))] |
| 98 | fn scale_hex_channel(digits: &str) -> Option<u8> { |
| 99 | if digits.is_empty() || digits.len() > 4 || !digits.chars().all(|c| c.is_ascii_hexdigit()) { |
| 100 | return None; |
| 101 | } |
| 102 | let value = u32::from_str_radix(digits, 16).ok()?; |
| 103 | let max = (1u32 << (4 * digits.len() as u32)) - 1; |
| 104 | Some(((value * 255 + max / 2) / max) as u8) |
| 105 | } |
| 106 | |
| 107 | /// Ask the terminal for its background color, giving up after `timeout`. |
| 108 | /// |
| 109 | /// Returns `None` — never blocks past `timeout`, never panics — when: |
| 110 | /// - stdin and stdout are not both TTYs (piped output, CI, `codewhale < file`), |
| 111 | /// - the platform has no supported query path (non-Unix; see the module docs), |
| 112 | /// - the terminal does not answer, or answers with something unparsable. |
| 113 | /// |
| 114 | /// # Caveat |
| 115 | /// |
| 116 | /// This reads from stdin, so it must only be called while the terminal is in |
| 117 | /// raw mode and before the event loop starts. Bytes that arrive during the |
| 118 | /// window and are not part of the reply are discarded — at startup that window |
| 119 | /// is sub-millisecond on any terminal that answers at all. |
| 120 | #[must_use] |
| 121 | pub fn query_terminal_background(timeout: std::time::Duration) -> Option<(u8, u8, u8)> { |
| 122 | query_impl(timeout) |
| 123 | } |
| 124 | |
| 125 | #[cfg(unix)] |
| 126 | fn query_impl(timeout: std::time::Duration) -> Option<(u8, u8, u8)> { |
| 127 | use std::io::{Read, Write}; |
| 128 | use std::os::fd::AsRawFd; |
| 129 | use std::time::Instant; |
| 130 | |
| 131 | let stdin = std::io::stdin(); |
| 132 | let stdout = std::io::stdout(); |
| 133 | let in_fd = stdin.as_raw_fd(); |
| 134 | let out_fd = stdout.as_raw_fd(); |
| 135 | |
| 136 | // SAFETY: `isatty` only inspects the descriptor; both fds are owned by the |
| 137 | // std handles held above for the duration of the call. |
| 138 | let both_tty = unsafe { libc::isatty(in_fd) == 1 && libc::isatty(out_fd) == 1 }; |
| 139 | if !both_tty { |
| 140 | return None; |
| 141 | } |
| 142 | |
| 143 | { |
| 144 | let mut out = stdout.lock(); |
| 145 | out.write_all(OSC11_QUERY).ok()?; |
| 146 | out.flush().ok()?; |
| 147 | } |
| 148 | |
| 149 | let deadline = Instant::now() + timeout; |
| 150 | let mut reply = Vec::with_capacity(32); |
| 151 | let mut stdin = stdin.lock(); |
| 152 | let mut byte = [0u8; 1]; |
| 153 | loop { |
| 154 | let remaining = deadline.saturating_duration_since(Instant::now()); |
| 155 | if remaining.is_zero() { |
| 156 | return None; |
| 157 | } |
| 158 | if !wait_readable(in_fd, remaining) { |
| 159 | return None; |
| 160 | } |
| 161 | match stdin.read(&mut byte) { |
| 162 | Ok(1) => {} |
| 163 | _ => return None, |
| 164 | } |
| 165 | // BEL, or the ESC of a `ESC \` string terminator, ends the reply. |
| 166 | if byte[0] == 0x07 || (byte[0] == 0x1b && !reply.is_empty()) { |
| 167 | break; |
| 168 | } |
| 169 | reply.push(byte[0]); |
| 170 | if reply.len() >= 128 { |
| 171 | return None; |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | parse_osc11_reply(&String::from_utf8_lossy(&reply)) |
| 176 | } |
| 177 | |
| 178 | /// Block until `fd` has data or `timeout` elapses. `true` means readable. |
| 179 | #[cfg(unix)] |
| 180 | fn wait_readable(fd: std::os::fd::RawFd, timeout: std::time::Duration) -> bool { |
| 181 | let mut pollfd = libc::pollfd { |
| 182 | fd, |
| 183 | events: libc::POLLIN, |
| 184 | revents: 0, |
| 185 | }; |
| 186 | let millis = i32::try_from(timeout.as_millis()) |
| 187 | .unwrap_or(i32::MAX) |
| 188 | .max(1); |
| 189 | // SAFETY: `pollfd` is a live, correctly-initialized single-element array |
| 190 | // and the count matches. |
| 191 | let rc = unsafe { libc::poll(std::ptr::addr_of_mut!(pollfd), 1, millis) }; |
| 192 | rc > 0 && (pollfd.revents & libc::POLLIN) != 0 |
| 193 | } |
| 194 | |
| 195 | /// Non-Unix platforms have no portable way to read a raw OSC reply back off |
| 196 | /// the console handle, so detection falls through to the environment-based |
| 197 | /// sources. Callers treat `None` as "no evidence", never as "dark". |
| 198 | #[cfg(not(unix))] |
| 199 | fn query_impl(_timeout: std::time::Duration) -> Option<(u8, u8, u8)> { |
| 200 | None |
| 201 | } |
| 202 |