From 18ad2173816bf455c2dabece9009aae29133b3d3 Mon Sep 17 00:00:00 2001
From: Jonas Maier <>
Date: Wed, 11 Mar 2026 15:32:51 +0100
Subject: first draft of cancellable builtins, kinda shit

---
 src/rw.rs | 231 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 231 insertions(+)
 create mode 100644 src/rw.rs

(limited to 'src/rw.rs')

diff --git a/src/rw.rs b/src/rw.rs
new file mode 100644
index 0000000..31808fb
--- /dev/null
+++ b/src/rw.rs
@@ -0,0 +1,231 @@
+use core::fmt;
+use std::{
+    fs::File,
+    io::{self, PipeReader, PipeWriter, Read, Write},
+    os::fd::{AsFd, BorrowedFd},
+    process::Stdio,
+};
+
+use nix::poll::{PollFd, PollFlags};
+
+pub enum Input {
+    Stdin,
+    Pipe(PipeReader),
+    File(File),
+}
+
+pub enum Output {
+    Stdout,
+    Pipe(PipeWriter),
+    File(File),
+}
+
+impl From<Input> for Stdio {
+    fn from(value: Input) -> Self {
+        match value {
+            Input::Stdin => Stdio::inherit(),
+            Input::Pipe(reader) => reader.into(),
+            Input::File(file) => file.into(),
+        }
+    }
+}
+
+impl From<Output> for Stdio {
+    fn from(value: Output) -> Stdio {
+        match value {
+            Output::Stdout => Stdio::inherit(),
+            Output::Pipe(writer) => writer.into(),
+            Output::File(file) => file.into(),
+        }
+    }
+}
+
+pub struct Canceler {
+    tx: PipeWriter,
+}
+
+impl Canceler {
+    pub fn cancel(&mut self) {
+        let _ = self.tx.write(b".");
+    }
+}
+
+pub struct InputReader {
+    input: Input,
+    cancel: PipeReader,
+    canceled: bool,
+}
+
+impl InputReader {
+    pub fn new(input: Input) -> (InputReader, Canceler) {
+        let (cancel, tx) = std::io::pipe().unwrap();
+        (
+            Self {
+                input,
+                cancel,
+                canceled: false,
+            },
+            Canceler { tx },
+        )
+    }
+}
+
+const TIMEOUT_MS: u16 = 20;
+
+enum PollStatus {
+    Cancel,
+    Ready,
+    Wait,
+}
+
+fn check<'a>(
+    canceled: &mut bool,
+    cancel: &PipeReader,
+    fd: BorrowedFd<'a>,
+    flags: PollFlags,
+) -> PollStatus {
+    if *canceled {
+        return PollStatus::Cancel;
+    }
+
+    let mut poll_fds = [
+        PollFd::new(cancel.as_fd(), PollFlags::POLLIN),
+        PollFd::new(fd, flags),
+    ];
+
+    if nix::poll::poll(&mut poll_fds, TIMEOUT_MS).is_err() {
+        *canceled = true;
+        return PollStatus::Cancel;
+    };
+
+    if let Some(event) = poll_fds[0].revents() {
+        if event.contains(PollFlags::POLLIN) {
+            *canceled = true;
+            return PollStatus::Cancel;
+        }
+    }
+
+    if let Some(event) = poll_fds[1].revents() {
+        if event.contains(flags) {
+            return PollStatus::Ready;
+        }
+    }
+
+    PollStatus::Wait
+}
+
+impl InputReader {
+    fn cancel(&mut self) -> PollStatus {
+        self.canceled = true;
+        PollStatus::Cancel
+    }
+
+    fn poll(&mut self) -> PollStatus {
+        let stdin = io::stdin();
+        let read_fd = match &self.input {
+            Input::Stdin => stdin.as_fd(),
+            Input::Pipe(pipe) => pipe.as_fd(),
+            Input::File(file) => file.as_fd(),
+        };
+        check(&mut self.canceled, &self.cancel, read_fd, PollFlags::POLLIN)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Canceled;
+
+impl fmt::Display for Canceled {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "canceled")
+    }
+}
+
+impl std::error::Error for Canceled {}
+
+impl Read for InputReader {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        loop {
+            match self.poll() {
+                PollStatus::Cancel => return Err(io::Error::new(io::ErrorKind::Other, Canceled)),
+                PollStatus::Ready => (),
+                PollStatus::Wait => continue,
+            }
+            return match &mut self.input {
+                Input::Stdin => io::stdin().read(buf),
+                Input::Pipe(reader) => reader.read(buf),
+                Input::File(file) => file.read(buf),
+            };
+        }
+    }
+}
+
+pub struct OutputWriter {
+    output: Output,
+    cancel: PipeReader,
+    canceled: bool,
+}
+
+impl OutputWriter {
+    pub fn new(output: Output) -> (Self, Canceler) {
+        let (cancel, tx) = std::io::pipe().unwrap();
+        (
+            Self {
+                output,
+                cancel,
+                canceled: false,
+            },
+            Canceler { tx },
+        )
+    }
+    fn poll(&mut self) -> PollStatus {
+        let stdout = io::stdout();
+        let write_fd = match &self.output {
+            Output::Stdout => stdout.as_fd(),
+            Output::Pipe(pipe) => pipe.as_fd(),
+            Output::File(file) => file.as_fd(),
+        };
+        check(
+            &mut self.canceled,
+            &self.cancel,
+            write_fd,
+            PollFlags::POLLOUT,
+        )
+    }
+}
+
+impl Write for OutputWriter {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        loop {
+            match self.poll() {
+                PollStatus::Cancel => return Err(io::Error::new(io::ErrorKind::Other, Canceled)),
+                PollStatus::Ready => (),
+                PollStatus::Wait => continue,
+            }
+            return match &mut self.output {
+                Output::Stdout => io::stdout().write(buf),
+                Output::Pipe(writer) => writer.write(buf),
+                Output::File(file) => file.write(buf),
+            };
+        }
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        match &mut self.output {
+            Output::Stdout => io::stdout().flush(),
+            Output::Pipe(writer) => writer.flush(),
+            Output::File(file) => file.flush(),
+        }
+    }
+}
+
+impl From<InputReader> for Input {
+    fn from(value: InputReader) -> Self {
+        value.input
+    }
+}
+
+impl From<OutputWriter> for Output {
+    fn from(value: OutputWriter) -> Self {
+        value.output
+    }
+}
-- 
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