1 files changed, 71 insertions, 0 deletions

diff --git a/rsnix/src/strbuf.rs b/rsnix/src/strbuf.rs
new file mode 100644
index 0000000..262720d
--- /dev/null
+++ b/rsnix/src/strbuf.rs
@@ -0,0 +1,71 @@
+//! Fixed-capacity ASCII string, allocated entirely on the stack.
+//! Shared by the line discipline (`tty`) and the shell.
+
+use core::fmt;
+
+/// A fixed-capacity string allocated entirely on the stack.
+pub struct String<const N: usize> {
+    buf: [u8; N],
+    len: usize,
+}
+
+impl<const N: usize> Default for String<N> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<const N: usize> String<N> {
+    pub const fn new() -> Self {
+        String {
+            buf: [0u8; N],
+            len: 0,
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        // SAFETY: we only write valid ASCII bytes.
+        unsafe { core::str::from_utf8_unchecked(&self.buf[..self.len]) }
+    }
+
+    pub fn push(&mut self, c: char) -> Result<(), ()> {
+        if self.len >= N {
+            return Err(());
+        }
+        self.buf[self.len] = c as u8;
+        self.len += 1;
+        Ok(())
+    }
+
+    pub fn pop(&mut self) -> Option<char> {
+        if self.len == 0 {
+            return None;
+        }
+        self.len -= 1;
+        Some(self.buf[self.len] as char)
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    pub fn clear(&mut self) {
+        self.len = 0;
+    }
+
+    pub fn trim(&self) -> &str {
+        self.as_str().trim()
+    }
+}
+
+impl<const N: usize> fmt::Display for String<N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}
+
+impl<const N: usize> fmt::Debug for String<N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", self.as_str())
+    }
+}