Split things into different files, to optimize future work

rustfmt.toml

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+style_edition = "2024"

src/arrays.rs

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+use crate::LOGGING_TAG_MAX_LEN;
+use std::ffi::CStr;
+use std::mem::MaybeUninit;
+
+// FIXME: When `maybe_uninit_uninit_array` is stabilized, use it instead of this helper
+pub fn uninit_array<const N: usize, T>() -> [MaybeUninit<T>; N] {
+    // SAFETY: Array contains MaybeUninit, which is fine to be uninit
+    unsafe { MaybeUninit::uninit().assume_init() }
+}
+
+// FIXME: Remove when maybe_uninit_slice is stabilized to provide MaybeUninit::slice_assume_init_ref()
+pub unsafe fn slice_assume_init_ref<T>(slice: &[MaybeUninit<T>]) -> &[T] {
+    &*(slice as *const [MaybeUninit<T>] as *const [T])
+}
+
+/// Fills up `storage` with `tag` and a necessary NUL terminator, optionally ellipsizing the input
+/// `tag` if it's too large.
+///
+/// Returns a [`CStr`] containing the initialized portion of `storage`, including its NUL
+/// terminator.
+pub fn fill_tag_bytes<'a>(
+    storage: &'a mut [MaybeUninit<u8>; LOGGING_TAG_MAX_LEN + 1],
+    tag: &[u8],
+) -> &'a CStr {
+    // FIXME: Simplify when maybe_uninit_fill with MaybeUninit::fill_from() is stabilized
+    let initialized = if tag.len() > LOGGING_TAG_MAX_LEN {
+        for (input, output) in tag
+            .iter()
+            // Elipsize the last two characters (TODO: use special … character)?
+            .take(LOGGING_TAG_MAX_LEN - 2)
+            .chain(b"..\0")
+            .zip(storage.iter_mut())
+        {
+            output.write(*input);
+        }
+        storage.as_slice()
+    } else {
+        for (input, output) in tag.iter().chain(b"\0").zip(storage.iter_mut()) {
+            output.write(*input);
+        }
+        &storage[..tag.len() + 1]
+    };
+
+    // SAFETY: The above code ensures that `initialized` only refers to a portion of the `array`
+    // slice that was initialized, thus it is safe to cast those `MaybeUninit<u8>`s to `u8`:
+    let initialized = unsafe { slice_assume_init_ref(initialized) };
+    CStr::from_bytes_with_nul(initialized).expect("Unreachable: we wrote a nul terminator")
+}

src/config.rs

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+use crate::{FormatFn, LogId};
+use log::{Level, LevelFilter, Record};
+use std::ffi::CString;
+use std::fmt;
+
+/// Filter for android logger.
+#[derive(Default)]
+pub struct Config {
+    pub(crate) log_level: Option<LevelFilter>,
+    pub(crate) buf_id: Option<LogId>,
+    filter: Option<env_filter::Filter>,
+    pub(crate) tag: Option<CString>,
+    pub(crate) custom_format: Option<FormatFn>,
+}
+
+impl fmt::Debug for Config {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Config")
+            .field("log_level", &self.log_level)
+            .field("buf_id", &self.buf_id)
+            .field("filter", &self.filter)
+            .field("tag", &self.tag)
+            .field("custom_format", match &self.custom_format {
+                Some(_) => &"Some(_)",
+                None => &"None",
+            })
+            .finish()
+    }
+}
+
+impl Config {
+    /// Changes the maximum log level.
+    ///
+    /// Note, that `Trace` is the maximum level, because it provides the
+    /// maximum amount of detail in the emitted logs.
+    ///
+    /// If `Off` level is provided, then nothing is logged at all.
+    ///
+    /// [`log::max_level()`] is considered as the default level.
+    pub fn with_max_level(mut self, level: LevelFilter) -> Self {
+        self.log_level = Some(level);
+        self
+    }
+
+    /// Changes the Android logging system buffer to be used.
+    ///
+    /// By default, logs are sent to the [`Main`] log. Other logging buffers may
+    /// only be accessible to certain processes.
+    ///
+    /// [`Main`]: LogId::Main
+    pub fn with_log_buffer(mut self, buf_id: LogId) -> Self {
+        self.buf_id = Some(buf_id);
+        self
+    }
+
+    pub(crate) fn filter_matches(&self, record: &Record) -> bool {
+        if let Some(ref filter) = self.filter {
+            filter.matches(record)
+        } else {
+            true
+        }
+    }
+
+    pub(crate) fn is_loggable(&self, level: Level) -> bool {
+        // todo: consider __android_log_is_loggable.
+        level <= self.log_level.unwrap_or_else(log::max_level)
+    }
+
+    pub fn with_filter(mut self, filter: env_filter::Filter) -> Self {
+        self.filter = Some(filter);
+        self
+    }
+
+    pub fn with_tag<S: Into<Vec<u8>>>(mut self, tag: S) -> Self {
+        self.tag = Some(CString::new(tag).expect("Can't convert tag to CString"));
+        self
+    }
+
+    /// Sets the format function for formatting the log output.
+    /// ```
+    /// # use android_logger::Config;
+    /// android_logger::init_once(
+    ///     Config::default()
+    ///         .with_max_level(log::LevelFilter::Trace)
+    ///         .format(|f, record| write!(f, "my_app: {}", record.args()))
+    /// )
+    /// ```
+    pub fn format<F>(mut self, format: F) -> Self
+    where
+        F: Fn(&mut dyn fmt::Write, &Record) -> fmt::Result + Sync + Send + 'static,
+    {
+        self.custom_format = Some(Box::new(format));
+        self
+    }
+}

src/id.rs

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+/// Possible identifiers of a specific buffer of Android logging system for
+/// logging a message.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum LogId {
+    /// Main log buffer.
+    ///
+    /// This is the only log buffer available to apps.
+    Main,
+
+    /// Radio log buffer.
+    Radio,
+
+    /// Event log buffer.
+    Events,
+
+    /// System log buffer.
+    System,
+
+    /// Crash log buffer.
+    Crash,
+
+    /// Kernel log buffer.
+    Kernel,
+
+    /// Security log buffer.
+    Security,
+
+    /// Statistics log buffer.
+    Stats,
+}
+
+#[cfg(target_os = "android")]
+impl LogId {
+    pub(crate) const fn to_native(log_id: Option<Self>) -> Option<log_ffi::log_id_t> {
+        match log_id {
+            Some(Self::Main) => Some(log_ffi::log_id_t::MAIN),
+            Some(Self::Radio) => Some(log_ffi::log_id_t::RADIO),
+            Some(Self::Events) => Some(log_ffi::log_id_t::EVENTS),
+            Some(Self::System) => Some(log_ffi::log_id_t::SYSTEM),
+            Some(Self::Crash) => Some(log_ffi::log_id_t::CRASH),
+            Some(Self::Kernel) => Some(log_ffi::log_id_t::KERNEL),
+            Some(Self::Security) => Some(log_ffi::log_id_t::SECURITY),
+            Some(Self::Stats) => Some(log_ffi::log_id_t::STATS),
+            None => None,
+        }
+    }
+}