1 files changed, 82 insertions, 0 deletions
diff --git a/src/coded_input_stream/input_buf.rs b/src/coded_input_stream/input_buf.rs
new file mode 100644
index 0000000..d5d6252
--- /dev/null
+++ b/src/coded_input_stream/input_buf.rs
@@ -0,0 +1,82 @@
+use std::cmp;
+use std::mem::MaybeUninit;
+
+use crate::misc::maybe_uninit_write_slice;
+
+#[derive(Debug)]
+pub(crate) struct InputBuf<'a> {
+    // Invariants: `0 <= pos_within_buf <= limit_within_buf <= buf.len()`.
+    buf: &'a [u8],
+    pos_within_buf: usize,
+    limit_within_buf: usize,
+}
+
+impl<'a> InputBuf<'a> {
+    #[inline]
+    pub(crate) fn assertions(&self) {
+        debug_assert!(self.pos_within_buf <= self.limit_within_buf);
+        debug_assert!(self.limit_within_buf <= self.buf.len());
+    }
+
+    pub(crate) fn empty() -> InputBuf<'a> {
+        InputBuf {
+            buf: &[],
+            pos_within_buf: 0,
+            limit_within_buf: 0,
+        }
+    }
+
+    pub(crate) fn from_bytes(buf: &'a [u8]) -> InputBuf<'a> {
+        InputBuf {
+            buf,
+            pos_within_buf: 0,
+            limit_within_buf: buf.len(),
+        }
+    }
+
+    pub(crate) unsafe fn from_bytes_ignore_lifetime(buf: &[u8]) -> InputBuf<'a> {
+        let buf = &*(buf as *const [u8]);
+        Self::from_bytes(buf)
+    }
+
+    pub(crate) fn update_limit(&mut self, limit: u64) {
+        let limit_within_buf = cmp::min(self.buf.len() as u64, limit);
+        assert!(limit_within_buf >= self.pos_within_buf as u64);
+        self.limit_within_buf = limit_within_buf as usize;
+    }
+
+    pub(crate) fn pos_within_buf(&self) -> usize {
+        self.pos_within_buf
+    }
+
+    #[inline(always)]
+    pub(crate) fn remaining_in_buf(&self) -> &'a [u8] {
+        // SAFETY: Invariants.
+        unsafe {
+            self.buf
+                .get_unchecked(self.pos_within_buf..self.limit_within_buf)
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn consume(&mut self, amt: usize) {
+        assert!(amt <= self.remaining_in_buf().len());
+        self.pos_within_buf += amt;
+    }
+
+    #[inline(always)]
+    pub(crate) fn read_byte(&mut self) -> Option<u8> {
+        let r = self.remaining_in_buf().first().copied();
+        if let Some(..) = r {
+            self.pos_within_buf += 1;
+        }
+        r
+    }
+
+    pub(crate) fn read_bytes<'b>(&mut self, dest: &'b mut [MaybeUninit<u8>]) -> &'b mut [u8] {
+        // This panics if this has not enough data.
+        let r = maybe_uninit_write_slice(dest, &self.remaining_in_buf()[..dest.len()]);
+        self.pos_within_buf += r.len();
+        r
+    }
+}