fs/path: Add Path and PathBuf abstractions

uefi/src/fs/path/mod.rs

@@ -0,0 +1,54 @@
+//! This module offers the [`Path`] and [`PathBuf`] abstractions.
+//!
+//! # Interoperability with Rust strings
+//!
+//! For the interoperability with Rust strings, i.e., `String` and `str` from
+//! the standard library, the API is intended to transform these types first to
+//! `CString16` respectively `CStr16`. They do not directly translate to
+//! [`Path`] and [`PathBuf`].
+//!
+//! # Path Structure
+//!
+//! Paths use the [`SEPARATOR`] character as separator. Paths are absolute and
+//! do not contain `.` or `..` components. However, this can be implemented in
+//! the future.
+
+mod path;
+mod pathbuf;
+mod validation;
+
+pub use path::Path;
+pub use path::Components;
+pub use pathbuf::PathBuf;
+
+use uefi::{CStr16, Char16};
+pub(super) use validation::validate_path;
+pub use validation::PathError;
+
+/// The default separator for paths.
+pub const SEPARATOR: char = '\\';
+/// [`SEPARATOR`] but as useful UEFI type.
+pub const SEPARATOR_C16: Char16 = unsafe { Char16::from_u16_unchecked('\\' as u16) };
+
+/// Stringified version of [`SEPARATOR`].
+pub const SEPARATOR_STR: &str = "\\";
+/// [`SEPARATOR_STR`] but as useful UEFI type.
+pub const SEPARATOR_CSTR16: &CStr16 = uefi_macros::cstr16!("\\");
+
+/// Deny list of characters for path components. UEFI supports FAT-like file
+/// systems. According to <https://en.wikipedia.org/wiki/Comparison_of_file_systems>,
+/// paths should not contain the following symbols.
+pub const CHARACTER_DENY_LIST: [Char16; 10] = unsafe {
+    [
+        Char16::from_u16_unchecked('\0' as u16),
+        Char16::from_u16_unchecked('"' as u16),
+        Char16::from_u16_unchecked('*' as u16),
+        Char16::from_u16_unchecked('/' as u16),
+        Char16::from_u16_unchecked(':' as u16),
+        Char16::from_u16_unchecked('<' as u16),
+        Char16::from_u16_unchecked('>' as u16),
+        Char16::from_u16_unchecked('?' as u16),
+        Char16::from_u16_unchecked('\\' as u16),
+        Char16::from_u16_unchecked('|' as u16),
+    ]
+};

uefi/src/fs/path/path.rs

@@ -0,0 +1,266 @@
+// allow "path.rs" in "path"
+#![allow(clippy::module_inception)]
+
+use crate::fs::path::{PathBuf, SEPARATOR_C16};
+use crate::CStr16;
+use core::fmt::{Display, Formatter};
+use uefi::CString16;
+
+/// A path similar to the `Path` of the standard library, but based on
+/// [`CStr16`] strings and [`SEPARATOR`] as separator.
+///
+/// [`SEPARATOR`]: super::SEPARATOR
+#[derive(Debug, PartialEq, Eq)]
+pub struct Path(CStr16);
+
+impl Path {
+    /// Constructor.
+    #[must_use]
+    pub fn new<S: AsRef<CStr16> + ?Sized>(s: &S) -> &Self {
+        unsafe { &*(s.as_ref() as *const CStr16 as *const Self) }
+    }
+
+    /// Returns the underlying string.
+    #[must_use]
+    pub fn to_cstr16(&self) -> &CStr16 {
+        &self.0
+    }
+
+    /// Returns a path buf from that type.
+    #[must_use]
+    pub fn to_path_buf(&self) -> PathBuf {
+        let cstring = CString16::from(&self.0);
+        PathBuf::from(cstring)
+    }
+
+    /// Iterator over the components of a path.
+    #[must_use]
+    pub fn components(&self) -> Components {
+        Components {
+            path: self.as_ref(),
+            i: 0,
+        }
+    }
+
+    /// Returns the parent directory as [`PathBuf`].
+    ///
+    /// If the path is a top-level component, this returns None.
+    #[must_use]
+    pub fn parent(&self) -> Option<PathBuf> {
+        let components_count = self.components().count();
+        if components_count == 0 {
+            return None;
+        }
+
+        // Return None, as we do not treat "\\" as dedicated component.
+        let sep_count = self
+            .0
+            .as_slice()
+            .iter()
+            .filter(|char| **char == SEPARATOR_C16)
+            .count();
+        if sep_count == 0 {
+            return None;
+        }
+
+        let path =
+            self.components()
+                .take(components_count - 1)
+                .fold(CString16::new(), |mut acc, next| {
+                    // Add separator, as needed.
+                    if !acc.is_empty() && *acc.as_slice().last().unwrap() != SEPARATOR_C16 {
+                        acc.push(SEPARATOR_C16);
+                    }
+                    acc.push_str(next.as_ref());
+                    acc
+                });
+        let path = PathBuf::from(path);
+        Some(path)
+    }
+
+    /// Returns of the path is empty.
+    #[must_use]
+    pub fn is_empty(&self) -> bool {
+        self.to_cstr16().is_empty()
+    }
+}
+
+impl Display for Path {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        Display::fmt(self.to_cstr16(), f)
+    }
+}
+
+/// Iterator over the components of a path. For example, the path `\\a\\b\\c`
+/// has the components `[a, b, c]`. This is a more basic approach than the
+/// components type of the standard library.
+#[derive(Debug)]
+pub struct Components<'a> {
+    path: &'a CStr16,
+    i: usize,
+}
+
+impl<'a> Iterator for Components<'a> {
+    // Attention. We can't iterate over &'Ctr16, as we would break any guarantee
+    // made for the terminating null character.
+    type Item = CString16;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.path.is_empty() {
+            return None;
+        }
+        if self.path.num_chars() == 1 && self.path.as_slice()[0] == SEPARATOR_C16 {
+            // The current implementation does not handle the root dir as
+            // dedicated component so far. We just return nothing.
+            return None;
+        }
+
+        // If the path is not empty and starts with a separator, skip it.
+        if self.i == 0 && *self.path.as_slice().first().unwrap() == SEPARATOR_C16 {
+            self.i = 1;
+        }
+
+        // Count how many characters are there until the next separator is
+        // found.
+        let len = self
+            .path
+            .iter()
+            .skip(self.i)
+            .take_while(|c| **c != SEPARATOR_C16)
+            .count();
+
+        let progress = self.i + len;
+        if progress > self.path.num_chars() {
+            None
+        } else {
+            // select the next component and build an owned string
+            let part = &self.path.as_slice()[self.i..self.i + len];
+            let mut string = CString16::new();
+            part.iter().for_each(|c| string.push(*c));
+
+            // +1: skip the separator
+            self.i = progress + 1;
+            Some(string)
+        }
+    }
+}
+
+mod convenience_impls {
+    use super::*;
+    use core::borrow::Borrow;
+
+    impl AsRef<Path> for &Path {
+        fn as_ref(&self) -> &Path {
+            self
+        }
+    }
+
+    impl<'a> From<&'a CStr16> for &'a Path {
+        fn from(value: &'a CStr16) -> Self {
+            Path::new(value)
+        }
+    }
+
+    impl AsRef<CStr16> for Path {
+        fn as_ref(&self) -> &CStr16 {
+            &self.0
+        }
+    }
+
+    impl Borrow<CStr16> for Path {
+        fn borrow(&self) -> &CStr16 {
+            &self.0
+        }
+    }
+
+    impl AsRef<Path> for CStr16 {
+        fn as_ref(&self) -> &Path {
+            Path::new(self)
+        }
+    }
+
+    impl Borrow<Path> for CStr16 {
+        fn borrow(&self) -> &Path {
+            Path::new(self)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use alloc::vec::Vec;
+    use uefi_macros::cstr16;
+
+    #[test]
+    fn from_cstr16() {
+        let source: &CStr16 = cstr16!("\\hello\\foo\\bar");
+        let _path: &Path = source.into();
+        let _path: &Path = Path::new(source);
+    }
+
+    #[test]
+    fn from_cstring16() {
+        let source = CString16::try_from("\\hello\\foo\\bar").unwrap();
+        let _path: &Path = source.as_ref().into();
+        let _path: &Path = Path::new(source.as_ref());
+    }
+
+    #[test]
+    fn components_iter() {
+        let path = Path::new(cstr16!("foo\\bar\\hello"));
+        let components = path.components().collect::<Vec<_>>();
+        let components: Vec<&CStr16> = components.iter().map(|x| x.as_ref()).collect::<Vec<_>>();
+        let expected: &[&CStr16] = &[cstr16!("foo"), cstr16!("bar"), cstr16!("hello")];
+        assert_eq!(components.as_slice(), expected);
+
+        // In case there is a leading slash, it should be ignored.
+        let path = Path::new(cstr16!("\\foo\\bar\\hello"));
+        let components = path.components().collect::<Vec<_>>();
+        let components: Vec<&CStr16> = components.iter().map(|x| x.as_ref()).collect::<Vec<_>>();
+        let expected: &[&CStr16] = &[cstr16!("foo"), cstr16!("bar"), cstr16!("hello")];
+        assert_eq!(components.as_slice(), expected);
+
+        // empty path iteration should be just fine
+        let empty_cstring16 = CString16::try_from("").unwrap();
+        let path = Path::new(empty_cstring16.as_ref());
+        let components = path.components().collect::<Vec<_>>();
+        let expected: &[CString16] = &[];
+        assert_eq!(components.as_slice(), expected);
+
+        // test empty path
+        let _path = Path::new(cstr16!());
+        let path = Path::new(cstr16!(""));
+        let components = path.components().collect::<Vec<_>>();
+        let components: Vec<&CStr16> = components.iter().map(|x| x.as_ref()).collect::<Vec<_>>();
+        let expected: &[&CStr16] = &[];
+        assert_eq!(components.as_slice(), expected);
+
+        // test path that has only root component. Treated as empty path by
+        // the components iterator.
+        let path = Path::new(cstr16!("\\"));
+        let components = path.components().collect::<Vec<_>>();
+        let components: Vec<&CStr16> = components.iter().map(|x| x.as_ref()).collect::<Vec<_>>();
+        let expected: &[&CStr16] = &[];
+        assert_eq!(components.as_slice(), expected);
+    }
+
+    #[test]
+    fn test_parent() {
+        assert_eq!(None, Path::new(cstr16!("")).parent());
+        assert_eq!(None, Path::new(cstr16!("\\")).parent());
+        assert_eq!(
+            Path::new(cstr16!("a\\b")).parent(),
+            Some(PathBuf::from(cstr16!("a"))),
+        );
+        assert_eq!(
+            Path::new(cstr16!("\\a\\b")).parent(),
+            Some(PathBuf::from(cstr16!("a"))),
+        );
+        assert_eq!(
+            Path::new(cstr16!("a\\b\\c\\d")).parent(),
+            Some(PathBuf::from(cstr16!("a\\b\\c"))),
+        );
+        assert_eq!(Path::new(cstr16!("abc")).parent(), None,);
+    }
+}