1 files changed, 156 insertions, 0 deletions
diff --git a/library/proc_macro/src/bridge/buffer.rs b/library/proc_macro/src/bridge/buffer.rs
new file mode 100644
index 000000000..48030f8d8
--- /dev/null
+++ b/library/proc_macro/src/bridge/buffer.rs
@@ -0,0 +1,156 @@
+//! Buffer management for same-process client<->server communication.
+
+use std::io::{self, Write};
+use std::mem;
+use std::ops::{Deref, DerefMut};
+use std::slice;
+
+#[repr(C)]
+pub struct Buffer {
+    data: *mut u8,
+    len: usize,
+    capacity: usize,
+    reserve: extern "C" fn(Buffer, usize) -> Buffer,
+    drop: extern "C" fn(Buffer),
+}
+
+unsafe impl Sync for Buffer {}
+unsafe impl Send for Buffer {}
+
+impl Default for Buffer {
+    #[inline]
+    fn default() -> Self {
+        Self::from(vec![])
+    }
+}
+
+impl Deref for Buffer {
+    type Target = [u8];
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.data as *const u8, self.len) }
+    }
+}
+
+impl DerefMut for Buffer {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut [u8] {
+        unsafe { slice::from_raw_parts_mut(self.data, self.len) }
+    }
+}
+
+impl Buffer {
+    #[inline]
+    pub(super) fn new() -> Self {
+        Self::default()
+    }
+
+    #[inline]
+    pub(super) fn clear(&mut self) {
+        self.len = 0;
+    }
+
+    #[inline]
+    pub(super) fn take(&mut self) -> Self {
+        mem::take(self)
+    }
+
+    // We have the array method separate from extending from a slice. This is
+    // because in the case of small arrays, codegen can be more efficient
+    // (avoiding a memmove call). With extend_from_slice, LLVM at least
+    // currently is not able to make that optimization.
+    #[inline]
+    pub(super) fn extend_from_array<const N: usize>(&mut self, xs: &[u8; N]) {
+        if xs.len() > (self.capacity - self.len) {
+            let b = self.take();
+            *self = (b.reserve)(b, xs.len());
+        }
+        unsafe {
+            xs.as_ptr().copy_to_nonoverlapping(self.data.add(self.len), xs.len());
+            self.len += xs.len();
+        }
+    }
+
+    #[inline]
+    pub(super) fn extend_from_slice(&mut self, xs: &[u8]) {
+        if xs.len() > (self.capacity - self.len) {
+            let b = self.take();
+            *self = (b.reserve)(b, xs.len());
+        }
+        unsafe {
+            xs.as_ptr().copy_to_nonoverlapping(self.data.add(self.len), xs.len());
+            self.len += xs.len();
+        }
+    }
+
+    #[inline]
+    pub(super) fn push(&mut self, v: u8) {
+        // The code here is taken from Vec::push, and we know that reserve()
+        // will panic if we're exceeding isize::MAX bytes and so there's no need
+        // to check for overflow.
+        if self.len == self.capacity {
+            let b = self.take();
+            *self = (b.reserve)(b, 1);
+        }
+        unsafe {
+            *self.data.add(self.len) = v;
+            self.len += 1;
+        }
+    }
+}
+
+impl Write for Buffer {
+    #[inline]
+    fn write(&mut self, xs: &[u8]) -> io::Result<usize> {
+        self.extend_from_slice(xs);
+        Ok(xs.len())
+    }
+
+    #[inline]
+    fn write_all(&mut self, xs: &[u8]) -> io::Result<()> {
+        self.extend_from_slice(xs);
+        Ok(())
+    }
+
+    #[inline]
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl Drop for Buffer {
+    #[inline]
+    fn drop(&mut self) {
+        let b = self.take();
+        (b.drop)(b);
+    }
+}
+
+impl From<Vec<u8>> for Buffer {
+    fn from(mut v: Vec<u8>) -> Self {
+        let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity());
+        mem::forget(v);
+
+        // This utility function is nested in here because it can *only*
+        // be safely called on `Buffer`s created by *this* `proc_macro`.
+        fn to_vec(b: Buffer) -> Vec<u8> {
+            unsafe {
+                let Buffer { data, len, capacity, .. } = b;
+                mem::forget(b);
+                Vec::from_raw_parts(data, len, capacity)
+            }
+        }
+
+        extern "C" fn reserve(b: Buffer, additional: usize) -> Buffer {
+            let mut v = to_vec(b);
+            v.reserve(additional);
+            Buffer::from(v)
+        }
+
+        extern "C" fn drop(b: Buffer) {
+            mem::drop(to_vec(b));
+        }
+
+        Buffer { data, len, capacity, reserve, drop }
+    }
+}