I should probably make more commits

src/subslice.rs

@@ -0,0 +1,117 @@
+use std::io::{Read, Write};
+
+use crate::{FatFs, SliceLike};
+
+pub struct SubSliceMut<'a, S: SliceLike> {
+    fat_fs: &'a mut FatFs<S>,
+
+    offset: u64,
+    len: usize,
+}
+
+impl<S: SliceLike> SubSliceMut<'_, S> {
+    pub fn new(fat_fs: &mut FatFs<S>, offset: u64, len: usize) -> SubSliceMut<'_, S> {
+        SubSliceMut {
+            fat_fs,
+            offset,
+            len,
+        }
+    }
+}
+
+impl<S: SliceLike> SubSliceMut<'_, S> {
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+}
+
+impl<S: SliceLike> Read for SubSliceMut<'_, S> {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let bytes_to_read = self.len.min(buf.len());
+
+        self.fat_fs
+            .data
+            .read_at_offset(self.offset, &mut buf[..bytes_to_read])?;
+
+        self.offset += bytes_to_read as u64;
+        self.len -= bytes_to_read;
+
+        Ok(bytes_to_read)
+    }
+}
+
+impl<S: SliceLike> Write for SubSliceMut<'_, S> {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let bytes_to_write = self.len.min(buf.len());
+
+        self.fat_fs
+            .data
+            .write_at_offset(self.offset, &buf[..bytes_to_write])?;
+
+        self.offset += bytes_to_write as u64;
+        self.len -= bytes_to_write;
+
+        Ok(bytes_to_write)
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
+pub struct SubSlice<'a, S: SliceLike> {
+    fat_fs: &'a mut FatFs<S>,
+
+    offset: u64,
+    len: usize,
+}
+
+impl<S: SliceLike> SubSlice<'_, S> {
+    pub fn new(fat_fs: &mut FatFs<S>, offset: u64, len: usize) -> SubSlice<'_, S> {
+        SubSlice {
+            fat_fs,
+            offset,
+            len,
+        }
+    }
+
+    pub fn fat_fs(&self) -> &FatFs<S> {
+        self.fat_fs
+    }
+
+    pub fn fat_fs_mut(&self) -> &FatFs<S> {
+        self.fat_fs
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+    pub fn len(&self) -> usize {
+        self.len
+    }
+}
+
+impl<'a, S: SliceLike> SubSlice<'a, S> {
+    pub fn release(self) -> &'a mut FatFs<S> {
+        self.fat_fs
+    }
+}
+
+impl<S: SliceLike> Read for SubSlice<'_, S> {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let bytes_to_read = self.len.min(buf.len());
+
+        self.fat_fs
+            .data
+            .read_at_offset(self.offset, &mut buf[..bytes_to_read])?;
+
+        self.offset += bytes_to_read as u64;
+        self.len -= bytes_to_read;
+
+        Ok(bytes_to_read)
+    }
+}