Implement new file device interface

This is a complete redesign of the file device. The most notable
addition is the ability to ascend and descend the file tree.

1 files changed, 66 insertions, 0 deletions

diff --git a/src/devices/file/circular_path_buffer.rs b/src/devices/file/circular_path_buffer.rs
new file mode 100644
index 0000000..f828f73
--- /dev/null
+++ b/src/devices/file/circular_path_buffer.rs
@@ -0,0 +1,66 @@
+use std::ffi::OsString;
+use std::os::unix::ffi::OsStringExt;
+use std::path::PathBuf;
+
+pub struct CircularPathBuffer {
+    buffer: [u8; 256],
+    pointer: u8,
+}
+
+impl CircularPathBuffer {
+    pub fn new() -> Self {
+        Self { buffer: [0; 256] , pointer: 0 }
+    }
+
+    pub fn clear(&mut self) {
+        self.buffer.fill(0);
+        self.pointer = 0;
+    }
+
+    pub fn populate(&mut self, bytes: &[u8]) {
+        self.clear();
+        if bytes.len() > 255 {
+            unreachable!(
+                "Attempted to populate CircularPathBuffer with {} bytes: {:?}",
+                bytes.len(), String::from_utf8_lossy(bytes)
+            )
+        }
+        let self_slice = &mut self.buffer[..bytes.len()];
+        self_slice.copy_from_slice(&bytes);
+    }
+
+    pub fn set_pointer(&mut self, value: u8) {
+        self.pointer = 0;
+        if value != 0x00 {
+            for (i, c) in self.buffer.iter().enumerate() {
+                match c {
+                    b'/' => self.pointer = (i + 1) as u8,
+                    0x00 => break,
+                    _ => continue,
+                }
+            }
+        }
+    }
+
+    pub fn read_byte(&mut self) -> u8 {
+        let pointer = self.pointer as usize;
+        self.pointer = self.pointer.wrapping_add(1);
+        self.buffer[pointer]
+    }
+
+    // Returns an unsanitized relative path.
+    pub fn push_byte(&mut self, value: u8) -> Option<PathBuf> {
+        if value == 0x00 {
+            let pointer = self.pointer as usize;
+            let vec = self.buffer[..pointer].to_vec();
+            self.clear();
+            let os_string: OsString = OsStringExt::from_vec(vec);
+            Some(os_string.into())
+        } else {
+            let pointer = self.pointer as usize;
+            self.pointer = self.pointer.wrapping_add(1);
+            self.buffer[pointer] = value;
+            None
+        }
+    }
+}