perf(h1): remove book keeping on final body writes

src/common/buf.rs

@@ -0,0 +1,34 @@
+use bytes::Buf;
+use iovec::IoVec;
+
+/// A `Buf` wrapping a static byte slice.
+#[derive(Debug)]
+pub(crate) struct StaticBuf(pub(crate) &'static [u8]);
+
+impl Buf for StaticBuf {
+    #[inline]
+    fn remaining(&self) -> usize {
+        self.0.len()
+    }
+
+    #[inline]
+    fn bytes(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        self.0 = &self.0[cnt..];
+    }
+
+    #[inline]
+    fn bytes_vec<'t>(&'t self, dst: &mut [&'t IoVec]) -> usize {
+        if dst.is_empty() {
+            return 0;
+        } else {
+            dst[0] = self.0.into();
+            return 1;
+        }
+    }
+}
+

src/common/mod.rs

@@ -1,5 +1,7 @@
+mod buf;
 mod exec;
 mod never;
 
+pub(crate) use self::buf::StaticBuf;
 pub(crate) use self::exec::Exec;
 pub use self::never::Never;