Wire in recv flow control (#26)

src/frame/go_away.rs

@@ -3,13 +3,20 @@ use frame::{self, Head, Error, Kind, StreamId};
 
 use bytes::{BufMut, BigEndian};
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy)]
 pub struct GoAway {
     last_stream_id: StreamId,
     error_code: u32,
 }
 
 impl GoAway {
+    pub fn new(last_stream_id: StreamId, reason: Reason) -> Self {
+        GoAway {
+            last_stream_id,
+            error_code: reason.into(),
+        }
+    }
+
     pub fn reason(&self) -> Reason {
         self.error_code.into()
     }

src/frame/mod.rs

@@ -165,6 +165,9 @@ pub enum Error {
     /// An invalid setting value was provided
     InvalidSettingValue,
 
+    /// An invalid window update value
+    InvalidWindowUpdateValue,
+
     /// The payload length specified by the frame header was not the
     /// value necessary for the specific frame type.
     InvalidPayloadLength,

src/frame/window_update.rs

@@ -38,7 +38,9 @@ impl WindowUpdate {
         // when received.
         let size_increment = unpack_octets_4!(payload, 0, u32) & !SIZE_INCREMENT_MASK;
 
-        // TODO: the size_increment must be greater than 0
+        if size_increment == 0 {
+            return Err(Error::InvalidWindowUpdateValue.into());
+        }
 
         Ok(WindowUpdate {
             stream_id: head.stream_id(),