Start working on prioritization

src/proto/streams/prioritize.rs

@@ -0,0 +1,61 @@
+use super::*;
+
+#[derive(Debug)]
+pub(super) struct Prioritize<B> {
+    pending_send: Option<Indices>,
+
+    /// Holds frames that are waiting to be written to the socket
+    buffer: Buffer<B>,
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Indices {
+    head: store::Key,
+    tail: store::Key,
+}
+
+impl<B> Prioritize<B> {
+    pub fn new() -> Prioritize<B> {
+        Prioritize {
+            pending_send: None,
+            buffer: Buffer::new(),
+        }
+    }
+
+    pub fn queue_frame(&mut self,
+                       frame: Frame<B>,
+                       stream: &mut store::Ptr<B>)
+    {
+        // queue the frame in the buffer
+        stream.pending_send.push_back(&mut self.buffer, frame);
+
+        if stream.is_pending_send {
+            debug_assert!(self.pending_send.is_some());
+
+            // Already queued to have frame processed.
+            return;
+        }
+
+        // The next pointer shouldn't be set
+        debug_assert!(stream.next_pending_send.is_none());
+
+        // Queue the stream
+        match self.pending_send {
+            Some(ref mut idxs) => {
+                // Update the current tail node to point to `stream`
+                stream.resolve(idxs.tail).next_pending_send = Some(stream.key());
+
+                // Update the tail pointer
+                idxs.tail = stream.key();
+            }
+            None => {
+                self.pending_send = Some(Indices {
+                    head: stream.key(),
+                    tail: stream.key(),
+                });
+            }
+        }
+
+        stream.is_pending_send = true;
+    }
+}