1 files changed, 77 insertions, 0 deletions
diff --git a/src/buf/ext/limit.rs b/src/buf/ext/limit.rs
new file mode 100644
index 0000000..f86e011
--- /dev/null
+++ b/src/buf/ext/limit.rs
@@ -0,0 +1,77 @@
+use crate::BufMut;
+
+use core::{cmp, mem::MaybeUninit};
+
+/// A `BufMut` adapter which limits the amount of bytes that can be written
+/// to an underlying buffer.
+#[derive(Debug)]
+pub struct Limit<T> {
+    inner: T,
+    limit: usize,
+}
+
+pub(super) fn new<T>(inner: T, limit: usize) -> Limit<T> {
+    Limit {
+        inner,
+        limit,
+    }
+}
+
+impl<T> Limit<T> {
+    /// Consumes this `Limit`, returning the underlying value.
+    pub fn into_inner(self) -> T {
+        self.inner
+    }
+
+    /// Gets a reference to the underlying `BufMut`.
+    ///
+    /// It is inadvisable to directly write to the underlying `BufMut`.
+    pub fn get_ref(&self) -> &T {
+        &self.inner
+    }
+
+    /// Gets a mutable reference to the underlying `BufMut`.
+    ///
+    /// It is inadvisable to directly write to the underlying `BufMut`.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.inner
+    }
+
+    /// Returns the maximum number of bytes that can be written
+    ///
+    /// # Note
+    ///
+    /// If the inner `BufMut` has fewer bytes than indicated by this method then
+    /// that is the actual number of available bytes.
+    pub fn limit(&self) -> usize {
+        self.limit
+    }
+
+    /// Sets the maximum number of bytes that can be written.
+    ///
+    /// # Note
+    ///
+    /// If the inner `BufMut` has fewer bytes than `lim` then that is the actual
+    /// number of available bytes.
+    pub fn set_limit(&mut self, lim: usize) {
+        self.limit = lim
+    }
+}
+
+impl<T: BufMut> BufMut for Limit<T> {
+    fn remaining_mut(&self) -> usize {
+        cmp::min(self.inner.remaining_mut(), self.limit)
+    }
+
+    fn bytes_mut(&mut self) -> &mut [MaybeUninit<u8>] {
+        let bytes = self.inner.bytes_mut();
+        let end = cmp::min(bytes.len(), self.limit);
+        &mut bytes[..end]
+    }
+
+    unsafe fn advance_mut(&mut self, cnt: usize) {
+        assert!(cnt <= self.limit);
+        self.inner.advance_mut(cnt);
+        self.limit -= cnt;
+    }
+}