1 files changed, 113 insertions, 0 deletions
diff --git a/src/common/sized_buffer.rs b/src/common/sized_buffer.rs
new file mode 100644
index 0000000..ebfcab5
--- /dev/null
+++ b/src/common/sized_buffer.rs
@@ -0,0 +1,113 @@
+use memchr::memchr;
+use std::io;
+use std::io::Write;
+
+pub struct SizedBuffer<T> {
+    len: usize,
+    pos: usize,
+    pub inner: T,
+}
+
+#[derive(Debug)]
+pub enum Error {
+    IO(io::Error),
+    ReadPastEnd,
+    WrongByte { expected: u8, got: u8 },
+}
+
+impl<const N: usize> SizedBuffer<[u8; N]> {
+    pub fn new() -> Self {
+        Self {
+            len: 0,
+            pos: 0,
+            inner: [0; N],
+        }
+    }
+
+    pub fn append(&mut self, bytes: &mut [u8]) -> Result<(), Error> {
+        self.write_all(bytes).map_err(Error::IO)
+    }
+
+    pub fn peek(&self) -> u8 {
+        self.inner[self.pos]
+    }
+
+    pub fn read(&mut self) -> Result<u8, Error> {
+        self.seek(1)?;
+        Ok(self.inner[self.pos - 1])
+    }
+
+    /* Reads n bytes from the buffer, and moves the cursor right after the last byte read.
+     *
+     * Example with n=3:
+     *
+     *     pos = 2
+     *      v
+     * [0,1,2,3,4,5,6,7,8,9]
+     *     |-----|^
+     *      read  new pos
+     */
+    pub fn read_count(&mut self, n: usize) -> Result<&[u8], Error> {
+        self.seek(n)?;
+        Ok(&self.inner[self.pos - n..self.pos])
+    }
+
+    pub fn read_count_unchecked(&mut self, n: usize) -> &[u8] {
+        self.seek_unchecked(n);
+        &self.inner[self.pos - n..self.pos]
+    }
+
+    pub fn skip_byte(&mut self, byte: u8) -> Result<(), Error> {
+        let x = self.read()?;
+        if x != byte {
+            return Err(Error::WrongByte {
+                expected: byte,
+                got: x,
+            });
+        }
+        Ok(())
+    }
+
+    pub fn seek(&mut self, n: usize) -> Result<(), Error> {
+        /* Allows to seek 1 past the end of the buffer. Subsequent reads will still fail but this
+         * allows to read the last byte. Otherwise trying to read the last byte would fail after
+         * reading it, when trying to advance the position of the cursor. */
+        if self.pos + n > self.len {
+            return Err(Error::ReadPastEnd);
+        }
+        self.pos += n;
+
+        Ok(())
+    }
+
+    pub fn seek_unchecked(&mut self, n: usize) {
+        self.pos += n;
+    }
+
+    pub fn find_offset(&mut self, x: u8) -> Option<usize> {
+        memchr(x, &self.inner[self.pos..self.len])
+    }
+
+    pub fn empty(&self) -> bool {
+        self.len == self.pos
+    }
+
+    pub fn reset(&mut self) {
+        self.len = 0;
+        self.pos = 0;
+    }
+}
+
+impl<const N: usize> Write for SizedBuffer<[u8; N]> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let amt = (&mut self.inner[self.len..]).write(buf)?;
+        self.len += amt;
+        Ok(amt)
+    }
+
+    #[inline]
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}