some semblance of an event loop

Cargo.lock

@@ -73,6 +73,17 @@ version = "2.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
 
+[[package]]
+name = "bstr"
+version = "1.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63044e1ae8e69f3b5a92c736ca6269b8d12fa7efe39bf34ddb06d102cf0e2cab"
+dependencies = [
+ "memchr",
+ "regex-automata",
+ "serde",
+]
+
 [[package]]
 name = "cfg-if"
 version = "1.0.4"
@@ -85,6 +96,12 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
 
+[[package]]
+name = "circular-buffer"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14c638459986b83c2b885179bd4ea6a2cbb05697b001501a56adb3a3d230803b"
+
 [[package]]
 name = "clap"
 version = "4.5.60"
@@ -153,16 +170,21 @@ checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
 name = "dynix"
 version = "0.1.0"
 dependencies = [
+ "bitflags",
+ "bstr",
+ "circular-buffer",
  "clap",
  "command-error",
  "fs-err",
  "itertools",
  "libc",
+ "mio",
  "regex",
  "regex-lite",
  "rustix",
  "serde",
  "serde_json",
+ "sync-fd",
  "tap",
  "tracing",
  "tracing-human-layer",
@@ -314,6 +336,18 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "mio"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a69bcab0ad47271a0234d9422b131806bf3968021e5dc9328caf2d4cd58557fc"
+dependencies = [
+ "libc",
+ "log",
+ "wasi",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "nix"
 version = "0.30.1"
@@ -585,6 +619,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "sync-fd"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5666edb8017247cac3f25fe3f2a8c889177d8adda7ce7d29a1f7278e2858aee2"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "tap"
 version = "1.0.1"
@@ -734,6 +777,12 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
 
+[[package]]
+name = "wasi"
+version = "0.11.1+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+
 [[package]]
 name = "windows"
 version = "0.61.3"

Cargo.toml

@@ -22,16 +22,21 @@ regex-full = ["dep:regex"]
 regex-lite = ["dep:regex-lite"]
 
 [dependencies]
+bitflags = { version = "2.11.0", features = ["std"] }
+bstr = "1.12.1"
+circular-buffer = "1.2.0"
 clap = { version = "4.5.54", features = ["color", "derive"] }
 command-error = "0.8.0"
 fs-err = "3.2.2"
 itertools = "0.14.0"
 libc = { version = "0.2.180", features = ["extra_traits"] }
+mio = { version = "1.1.1", features = ["os-ext", "os-poll"] }
 regex = { version = "1.12.3", optional = true }
 regex-lite = { version = "0.1.9", optional = true }
-rustix = { version = "1.1.4", features = ["event", "fs"] }
+rustix = { version = "1.1.4", features = ["event", "fs", "termios"] }
-serde = { version = "1.0.228", features = ["derive"] }
+serde = { version = "1.0.228", features = ["derive", "rc"] }
 serde_json = "1.0.149"
+sync-fd = "0.1.0"
 tap = "1.0.1"
 tracing = { version = "0.1.44", features = ["attributes"] }
 tracing-human-layer = "0.2.1"

rustfmt.toml

@@ -0,0 +1,6 @@
+# SPDX-FileCopyrightText: 2026 Qyriad <qyriad@qyriad.me>
+#
+# SPDX-License-Identifier: EUPL-1.1
+
+match_block_trailing_comma = true
+merge_derives = false

src/args.rs

@@ -12,6 +12,7 @@ use clap::ColorChoice;
 use crate::prelude::*;
 
 #[derive(Debug, Clone, PartialEq, clap::Parser)]
+#[command(long_about = None)]
 pub struct AppendCmd {
     #[arg(required = true)]
     pub name: Arc<str>,
@@ -20,10 +21,17 @@ pub struct AppendCmd {
     pub value: Arc<str>,
 }
 
+/// Accept commands over (default stdin).
+#[derive(Debug, Clone, PartialEq, clap::Parser)]
+#[command(long_about = None)]
+pub struct DaemonCmd {
+    // FIXME: support Unix sockets.
+}
+
 #[derive(Debug, Clone, PartialEq, clap::Subcommand)]
-#[command(flatten_help = true)]
 pub enum Subcommand {
     Append(AppendCmd),
+    Daemon(DaemonCmd),
 }
 
 static DEFAULT_PATH: LazyLock<Box<OsStr>> = LazyLock::new(|| {

src/daemon.rs

@@ -0,0 +1,244 @@
+use std::{
+    io,
+    ops::Deref,
+    os::fd::{AsFd, BorrowedFd, OwnedFd},
+    time::Duration,
+};
+
+use circular_buffer::CircularBuffer;
+
+use mio::{Events, Interest, Poll, Token, unix::SourceFd};
+
+use rustix::{
+    buffer::{Buffer, spare_capacity},
+    fs::{OFlags, fcntl_setfl},
+    io::Errno,
+    termios::{
+        ControlModes, InputModes, LocalModes, OptionalActions, OutputModes, SpecialCodeIndex,
+        SpecialCodes, Termios, tcgetattr, tcsetattr,
+    },
+};
+
+use serde::{Deserialize, Serialize};
+use serde_json::StreamDeserializer;
+
+use crate::prelude::*;
+
+use crate::OwnedFdWithFlags;
+
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum ConvenientAttrPath {
+    Dotted(Box<str>),
+    Split(Box<[Box<str>]>),
+}
+
+impl ConvenientAttrPath {
+    pub fn clone_from_dotted(s: &str) -> Self {
+        Self::Dotted(Box::from(s))
+    }
+
+    pub fn clone_from_split(s: &[&str]) -> Self {
+        Self::from_str_iter(s.into_iter().map(Deref::deref))
+    }
+
+    pub fn from_str_iter<'i, I>(iter: I) -> Self
+    where
+        I: Iterator<Item = &'i str>,
+    {
+        let boxed = iter.map(|s| Box::from(s));
+        Self::Split(Box::from_iter(boxed))
+    }
+}
+
+impl<'i> FromIterator<&'i str> for ConvenientAttrPath {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = &'i str>,
+    {
+        Self::from_str_iter(iter.into_iter())
+    }
+}
+
+impl FromIterator<Box<str>> for ConvenientAttrPath {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = Box<str>>,
+    {
+        Self::Split(Box::from_iter(iter))
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+#[derive(serde::Deserialize, serde::Serialize)]
+#[serde(tag = "action", content = "args", rename_all = "snake_case")]
+pub enum DaemonCmd {
+    Append {
+        name: ConvenientAttrPath,
+        value: Box<str>,
+    },
+}
+
+const TIMEOUT_NEVER: Option<Duration> = None;
+
+#[derive(Debug)]
+pub struct Daemon {
+    fd: OwnedFdWithFlags,
+    poll_error_buffer: CircularBuffer<ERROR_BUFFER_LEN, IoError>,
+    fd_error_buffer: CircularBuffer<ERROR_BUFFER_LEN, IoError>,
+
+    cmd_buffer: Vec<u8>,
+    next_timeout: Option<Duration>,
+}
+
+impl Daemon {
+    /// Panics if we cannot make `fd` non-blocking.
+    pub fn new(fd: OwnedFd) -> Self {
+        let fd = OwnedFdWithFlags::new_with_fallback(fd);
+
+        // Make non-blocking.
+        //fcntl_setfl(fd.as_fd(), fd.oflags().union(OFlags::NONBLOCK))
+        //    .tap_err(|e| error!("F_SETFL O_NONBLOCK failed on fd {:?}: {e}", fd.as_fd()))
+        //    .unwrap();
+
+        Self {
+            fd,
+            poll_error_buffer: Default::default(),
+            fd_error_buffer: Default::default(),
+            cmd_buffer: Vec::with_capacity(1024),
+            next_timeout: TIMEOUT_NEVER,
+        }
+    }
+
+    /// This panics if stdin cannot be opened.
+    ///
+    /// If you want to handle that error, use [`Daemon::from_raw_parts()`].
+    pub fn from_stdin() -> Self {
+        let stdin = io::stdin();
+        let fd = stdin
+            .as_fd()
+            .try_clone_to_owned()
+            .expect("dynix daemon could not open stdin; try a Unix socket?");
+
+        debug!("opened daemon to stdin file descriptor {fd:?}");
+
+        Self::new(fd)
+    }
+
+    //pub unsafe fn from_raw_parts(fd: OwnedFd) -> Self {
+    //    Self {
+    //        fd: OwnedFdWithFlags::new_with_fallback(fd),
+    //    }
+    //}
+
+    pub fn fd(&self) -> BorrowedFd<'_> {
+        self.fd.as_fd()
+    }
+}
+
+const ERROR_BUFFER_LEN: usize = 8;
+
+/// Private helpers.
+impl Daemon {
+    fn read_cmd(&mut self) -> Result<(), IoError> {
+        if self.cmd_buffer.len() == self.cmd_buffer.capacity() {
+            self.cmd_buffer.reserve(1024);
+        }
+
+        let _count = rustix::io::read(&self.fd, spare_capacity(&mut self.cmd_buffer))?;
+
+        // The buffer might have existing data from the last read.
+        let deserializer = serde_json::Deserializer::from_slice(&self.cmd_buffer);
+        let stream: StreamDeserializer<_, DaemonCmd> = deserializer.into_iter();
+        for cmd in stream {
+            let cmd = match cmd {
+                Ok(cmd) => cmd,
+                Err(e) if e.is_eof() => {
+                    self.next_timeout = Some(Duration::from_secs(4));
+                    warn!("Didn't get a valid daemon command; giving the other side 4 seconds...");
+                    return Ok(());
+                },
+                Err(e) => {
+                    warn!("error deserializing command: {e}");
+                    warn!("error count: {}", self.fd_error_buffer.len());
+                    self.cmd_buffer.clear();
+                    // Don't propagate the error unless we have too many.
+                    self.fd_error_buffer.try_push_back(e.into()).tap_err(|e| {
+                        error!(
+                            "Accumulated too many errors for daemon fd {:?}: {e}",
+                            self.fd(),
+                        )
+                    })?;
+                    return Ok(());
+                },
+            };
+            debug!("got cmd: {cmd:?}");
+        }
+
+        self.cmd_buffer.clear();
+
+        Ok(())
+    }
+
+    pub(crate) fn enter_loop(&mut self) -> Result<Option<()>, IoError> {
+        let raw_fd = self.fd.as_raw_fd();
+        let mut daemon_source = SourceFd(&raw_fd);
+        const DAEMON: Token = Token(0);
+        let mut poll = Poll::new().unwrap_or_else(|e| unreachable!("creating new mio Poll: {e}"));
+
+        poll.registry()
+            .register(&mut daemon_source, DAEMON, Interest::READABLE)
+            .unwrap_or_else(|e| unreachable!("registering mio Poll for daemon fd {raw_fd:?}: {e}"));
+
+        let mut events = Events::with_capacity(1024);
+
+        let example = DaemonCmd::Append {
+            //name: ConvenientAttrPath::Dotted(Box::from(
+            //    "services.gotosocial.settings.application-name",
+            //)),
+            //name: ConvenientAttrPath::Split(Box::from([
+            //    Box::from("services"),
+            //    Box::from("gotosocial"),
+            //])),
+            name: ConvenientAttrPath::clone_from_split(&[
+                "services",
+                "gotosocial",
+                "settings",
+                "application-name",
+            ]),
+            value: Box::from("foo"),
+        };
+
+        //let example_as_json = serde_json::to_string_pretty(&example).unwrap();
+        //info!("{}", example_as_json);
+
+        loop {
+            match poll.poll(&mut events, self.next_timeout.take()) {
+                Ok(_) => {
+                    if events.is_empty() {
+                        warn!("timeout expired");
+                        self.cmd_buffer.clear();
+                    } else {
+                        let _ = self.poll_error_buffer.pop_front();
+                    }
+                },
+                Err(e) => {
+                    warn!("mio Poll::poll() error: {e}");
+                    self.poll_error_buffer.try_push_back(e).tap_err(|e| {
+                        error!("accumulated too many errors for mio::Poll::poll(): {e}")
+                    })?;
+                },
+            }
+
+            for event in &events {
+                match event.token() {
+                    DAEMON => {
+                        self.read_cmd().unwrap();
+                    },
+                    _ => unreachable!(),
+                }
+            }
+        }
+    }
+}

src/daemon_io.rs

@@ -17,7 +17,6 @@ use crate::prelude::*;
 ///
 /// - [`IntoRawFd`]
 /// - [`drop()`]
-#[derive(Debug)]
 pub struct OwnedFdWithFlags {
     fd: OwnedFd,
     oflags: OFlags,
@@ -29,14 +28,34 @@ impl OwnedFdWithFlags {
         Ok(Self { fd, oflags })
     }
 
+    pub fn as_ref_owned(&self) -> &OwnedFd {
+        &self.fd
+    }
+
     /// If, for some ungodly reason, `fcntl(F_GETFL)` fails, then empty flags are used.
     /// Empty flags should not be restored on close.
     ///
     /// I'm pretty sure this should never happen if the program is IO-safe.
     pub fn new_with_fallback(fd: OwnedFd) -> Self {
-        let oflags = Self::get_flags_or_log(fd.as_fd());
+        let oflags = Self::get_flags_or_log(&fd);
         Self { fd, oflags }
     }
+
+    pub fn oflags(&self) -> OFlags {
+        self.oflags
+    }
+}
+
+impl Debug for OwnedFdWithFlags {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        let mut flags_str: String = Default::default();
+        bitflags::parser::to_writer(&self.oflags, &mut flags_str)?;
+
+        f.debug_struct("OwnedFdWithFlags")
+            .field("fd", &self.fd)
+            .field("oflags", &flags_str)
+            .finish()
+    }
 }
 
 impl Drop for OwnedFdWithFlags {
@@ -56,15 +75,19 @@ impl OwnedFdWithFlags {
             return;
         }
 
-        if let Err(e) = fcntl_setfl(&self.fd, self.oflags) {
+        match fcntl_setfl(&self.fd, self.oflags) {
-            error!(
+            Ok(_) => (),
+            // EBADF
+            //Err(Errno::BADF) => (),
+            Err(e) => error!(
                 "fcntl(F_SETFL) to restore flags {:?} on fd {:?} failed: {e}\nIO safety violation?",
                 self.oflags, self.fd,
-            );
+            ),
-        };
+        }
     }
 
-    fn get_flags_or_log(fd: BorrowedFd) -> OFlags {
+    fn get_flags_or_log<Fd: AsFd>(fd: Fd) -> OFlags {
+        let fd = fd.as_fd();
         fcntl_getfl(fd)
             .tap_err(|e| error!("fcntl(F_GETFL) failed on fd {fd:?}: {e}\nIO-safety violation?"))
             .unwrap_or(OFlags::empty())
@@ -87,7 +110,7 @@ impl IntoRawFd for OwnedFdWithFlags {
 impl FromRawFd for OwnedFdWithFlags {
     unsafe fn from_raw_fd(fd: RawFd) -> Self {
         let fd = unsafe { OwnedFd::from_raw_fd(fd) };
-        let oflags = Self::get_flags_or_log(fd.as_fd());
+        let oflags = Self::get_flags_or_log(&fd);
         Self { fd, oflags }
     }
 }
@@ -104,3 +127,24 @@ impl From<OwnedFd> for OwnedFdWithFlags {
         Self { fd, oflags }
     }
 }
+
+impl Read for &OwnedFdWithFlags {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, IoError> {
+        debug_assert!(buf.len() > 0);
+        loop {
+            buf.fill(0);
+            match rustix::io::read(self.as_ref_owned(), &mut *buf) {
+                Ok(count) => {
+                    debug_assert!(count <= buf.len());
+                    return Ok(count);
+                },
+                Err(e) if e.kind() == IoErrorKind::Interrupted => continue,
+                Err(e) if e.kind() == IoErrorKind::WouldBlock => return Ok(0),
+                Err(e) => {
+                    let e = IoError::from_raw_os_error(e.raw_os_error());
+                    return Err(e);
+                },
+            }
+        }
+    }
+}

src/lib.rs

@@ -13,8 +13,8 @@ pub(crate) mod prelude {
     pub use std::{
         error::Error as StdError,
         ffi::{OsStr, OsString},
-        fmt::{Display, Formatter, Result as FmtResult},
+        fmt::{Debug, Display, Formatter, Result as FmtResult},
-        io::{Error as IoError, Read, Seek, SeekFrom, Write},
+        io::{Error as IoError, ErrorKind as IoErrorKind, Read, Seek, SeekFrom, Write},
         path::{Path, PathBuf},
         process::{Command, ExitCode},
         str::FromStr,
@@ -33,6 +33,8 @@ pub(crate) mod prelude {
     #[cfg(unix)]
     pub use fs_err::os::unix::fs::{FileExt, OpenOptionsExt};
 
+    pub use bstr::ByteSlice;
+
     pub use tap::{Pipe, Tap, TapFallible};
 
     pub use tracing::{Level, debug, error, info, trace, warn};
@@ -44,11 +46,13 @@ pub mod args;
 pub use args::{AppendCmd, Args};
 mod color;
 pub use color::{_CLI_ENABLE_COLOR, SHOULD_COLOR};
+mod daemon;
+pub use daemon::Daemon;
 mod daemon_io;
 pub use daemon_io::OwnedFdWithFlags;
 pub mod line;
-mod nixcmd;
 pub use line::Line;
+mod nixcmd;
 pub mod source;
 pub use source::{SourceFile, SourceLine};
 
@@ -67,6 +71,8 @@ use _regex::Regex;
 use itertools::Itertools;
 use serde::{Deserialize, Serialize};
 
+use crate::args::DaemonCmd;
+
 pub const ASCII_WHITESPACE: &[char] = &['\t', '\n', '\x0C', '\r', ' '];
 
 /// Regex pattern to extract the priority in a `lib.mkOverride` call.
@@ -118,6 +124,13 @@ pub fn do_append(args: Arc<Args>, append_args: AppendCmd) -> Result<(), BoxDynEr
     Ok(())
 }
 
+//#[tracing::instrument(level = "debug")]
+pub fn do_daemon(args: Arc<Args>, daemon_args: DaemonCmd) -> Result<(), BoxDynError> {
+    let mut daemon = Daemon::from_stdin();
+    daemon.enter_loop().unwrap();
+    todo!();
+}
+
 #[derive(Debug, Clone, PartialEq, Hash, Serialize, Deserialize)]
 pub struct DefinitionWithLocation {
     pub file: Box<Path>,

src/main.rs

@@ -34,6 +34,7 @@ fn main_wrapped() -> Result<(), Box<dyn StdError + Send + Sync + 'static>> {
         use dynix::args::Subcommand::*;
         match &args.subcommand {
             Append(append_args) => dynix::do_append(args.clone(), append_args.clone())?,
+            Daemon(daemon_args) => dynix::do_daemon(args.clone(), daemon_args.clone())?,
         };
     }