Implement String-like wrapper around FuriString

Author: str4d

crates/flipperzero/src/furi/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod io;
 pub mod message_queue;
+pub mod string;
 pub mod sync;
 pub mod thread;
 

crates/flipperzero/src/furi/string.rs

@@ -0,0 +1,261 @@
+//! String primitives built around `FuriString`.
+
+use core::{
+    cmp::Ordering,
+    convert::Infallible,
+    ffi::{c_char, CStr},
+    fmt,
+};
+
+#[cfg(feature = "alloc")]
+use alloc::ffi::CString;
+
+use flipperzero_sys as sys;
+
+/// A Furi string.
+///
+/// This is similar to Rust's [`CString`] in that it represents an owned, C-compatible,
+/// nul-terminated string with no nul bytes in the middle. It also has additional methods
+/// to provide the flexibility of Rust's [`String`]. It is used in various APIs of the
+/// Flipper Zero SDK.
+///
+/// This type does not requre the `alloc` feature flag, because it does not use the Rust
+/// allocator. Very short strings (7 bytes or fewer) are stored directly inside the
+/// `FuriString` struct (which is stored on the heap), while longer strings are allocated
+/// on the heap by the Flipper Zero firmware.
+#[derive(Eq)]
+pub struct String(*mut sys::FuriString);
+
+impl Drop for String {
+    fn drop(&mut self) {
+        unsafe { sys::furi_string_free(self.0) };
+    }
+}
+
+// Implementations matching `std::string::String`.
+impl String {
+    /// Creates a new empty `String`.
+    #[inline]
+    #[must_use]
+    pub fn new() -> Self {
+        String(unsafe { sys::furi_string_alloc() })
+    }
+
+    /// Creates a new empty `String` with at least the specified capacity.
+    #[inline]
+    #[must_use]
+    pub fn with_capacity(capacity: usize) -> Self {
+        let s = Self::new();
+        // The size passed to `sys::furi_string_reserve` needs to include the nul
+        // terminator.
+        unsafe { sys::furi_string_reserve(s.0, capacity + 1) };
+        s
+    }
+
+    /// Extracts a `CStr` containing the entire string slice, with nul termination.
+    #[inline]
+    #[must_use]
+    pub fn as_c_str(&self) -> &CStr {
+        unsafe { CStr::from_ptr(sys::furi_string_get_cstr(self.0)) }
+    }
+
+    /// Appends a given `String` onto the end of this `String`.
+    #[inline]
+    pub fn push_string(&mut self, string: &String) {
+        unsafe { sys::furi_string_cat(self.0, string.0) }
+    }
+
+    /// Appends a given Rust `str` onto the end of this `String`.
+    #[inline]
+    pub fn push_rust_str(&mut self, string: &str) {
+        self.reserve(string.len());
+        for ch in string.chars() {
+            self.push(ch);
+        }
+    }
+
+    /// Appends a given `CStr` onto the end of this `String`.
+    #[inline]
+    pub fn push_c_str(&mut self, string: &CStr) {
+        unsafe { sys::furi_string_cat_str(self.0, string.as_ptr()) }
+    }
+
+    /// Reserves capacity for at least `additional` bytes more than the current length.
+    #[inline]
+    pub fn reserve(&mut self, additional: usize) {
+        // `self.len()` counts the number of bytes excluding the terminating nul, but the
+        // size passed to `sys::furi_string_reserve` needs to include the nul terminator.
+        unsafe { sys::furi_string_reserve(self.0, self.len() + additional + 1) };
+    }
+
+    /// Appends the given [`char`] to the end of this `String`.
+    #[inline]
+    pub fn push(&mut self, ch: char) {
+        match ch.len_utf8() {
+            1 => unsafe { sys::furi_string_push_back(self.0, ch as c_char) },
+            _ => unsafe { sys::furi_string_utf8_push(self.0, ch as u32) },
+        }
+    }
+
+    /// Returns a byte slice of this `String`'s contents.
+    ///
+    /// The returned slice will **not** contain the trailing nul terminator that the
+    /// underlying C string has.
+    #[inline]
+    #[must_use]
+    pub fn to_bytes(&self) -> &[u8] {
+        self.as_c_str().to_bytes()
+    }
+
+    /// Returns a byte slice of this `String`'s contents with the trailing nul byte.
+    ///
+    /// This function is the equivalent of [`String::to_bytes`] except that it will retain
+    /// the trailing nul terminator instead of chopping it off.
+    #[inline]
+    #[must_use]
+    pub fn to_bytes_with_nul(&self) -> &[u8] {
+        self.as_c_str().to_bytes_with_nul()
+    }
+
+    /// Shortens this `String` to the specified length.
+    ///
+    /// If `new_len` is greater than the string's current length, this has no effect.
+    #[inline]
+    pub fn truncate(&mut self, new_len: usize) {
+        unsafe { sys::furi_string_left(self.0, new_len) };
+    }
+
+    /// Returns the length of this `String`.
+    ///
+    /// This length is in bytes, not [`char`]s or graphemes. In other words, it might not
+    /// be what a human considers the length of the string.
+    #[inline]
+    #[must_use]
+    pub fn len(&self) -> usize {
+        unsafe { sys::furi_string_size(self.0) }
+    }
+
+    /// Returns `true` if this `String` has a length of zero, and `false` otherwise.
+    #[inline]
+    #[must_use]
+    pub fn is_empty(&self) -> bool {
+        unsafe { sys::furi_string_empty(self.0) }
+    }
+
+    /// Splits the string into two at the given byte index.
+    ///
+    /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and the
+    /// returned `String` contains bytes `[at, len)`.
+    ///
+    /// Note that the capacity of `self` does not change.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at` is beyond the last byte of the string.
+    #[inline]
+    #[must_use = "use `.truncate()` if you don't need the other half"]
+    pub fn split_off(&mut self, at: usize) -> String {
+        // SAFETY: Trimming the beginning of a C string results in a valid C string, as
+        // long as the nul byte is not trimmed.
+        assert!(at <= self.len());
+        let ret =
+            String(unsafe { sys::furi_string_alloc_set_str(self.as_c_str().as_ptr().add(at)) });
+        self.truncate(at);
+        ret
+    }
+
+    /// Truncates this `String`, removing all contents.
+    ///
+    /// While this means the `String` will have a length of zero, it does not touch its
+    /// capacity.
+    #[inline]
+    pub fn clear(&mut self) {
+        unsafe { sys::furi_string_reset(self.0) };
+    }
+}
+
+impl Default for String {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl AsRef<CStr> for String {
+    fn as_ref(&self) -> &CStr {
+        self.as_c_str()
+    }
+}
+
+impl PartialEq for String {
+    fn eq(&self, other: &Self) -> bool {
+        unsafe { sys::furi_string_equal(self.0, other.0) }
+    }
+}
+
+impl PartialEq<CStr> for String {
+    fn eq(&self, other: &CStr) -> bool {
+        unsafe { sys::furi_string_equal_str(self.0, other.as_ptr()) }
+    }
+}
+
+impl PartialEq<String> for CStr {
+    fn eq(&self, other: &String) -> bool {
+        other.eq(self)
+    }
+}
+
+#[cfg(feature = "alloc")]
+impl PartialEq<CString> for String {
+    fn eq(&self, other: &CString) -> bool {
+        self.eq(other.as_c_str())
+    }
+}
+
+#[cfg(feature = "alloc")]
+impl PartialEq<String> for CString {
+    fn eq(&self, other: &String) -> bool {
+        other.eq(self.as_c_str())
+    }
+}
+
+impl Ord for String {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match unsafe { sys::furi_string_cmp(self.0, other.0) } {
+            ..=-1 => Ordering::Less,
+            0 => Ordering::Equal,
+            1.. => Ordering::Greater,
+        }
+    }
+}
+
+impl PartialOrd for String {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl fmt::Write for String {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.push_rust_str(s);
+        Ok(())
+    }
+
+    fn write_char(&mut self, c: char) -> fmt::Result {
+        self.push(c);
+        Ok(())
+    }
+}
+
+impl ufmt::uWrite for String {
+    type Error = Infallible;
+
+    fn write_str(&mut self, s: &str) -> Result<(), Self::Error> {
+        self.push_rust_str(s);
+        Ok(())
+    }
+
+    fn write_char(&mut self, c: char) -> Result<(), Self::Error> {
+        self.push(c);
+        Ok(())
+    }
+}