add support for configuring max frame size

- Adds `max_frame_size` to client and server builders
- Pushes max_frame_size into Codec
- Detects when the Codec triggers an error from a frame too big
- Sends a GOAWAY when FRAME_SIZE_ERROR is encountered reading a frame

src/frame/reason.rs

@@ -33,7 +33,7 @@ impl Reason {
             FlowControlError => "flow-control protocol violated",
             SettingsTimeout => "settings ACK not received in timely manner",
             StreamClosed => "received frame when stream half-closed",
-            FrameSizeError => "frame sent with invalid size",
+            FrameSizeError => "frame with invalid size",
             RefusedStream => "refused stream before processing any application logic",
             Cancel => "stream no longer needed",
             CompressionError => "unable to maintain the header compression context",

src/frame/settings.rs

@@ -46,7 +46,7 @@ pub const DEFAULT_MAX_FRAME_SIZE: FrameSize = 16_384;
 pub const MAX_INITIAL_WINDOW_SIZE: usize = (1 << 31) - 1;
 
 /// MAX_FRAME_SIZE upper bound
-pub const MAX_MAX_FRAME_SIZE: usize = (1 << 24) - 1;
+pub const MAX_MAX_FRAME_SIZE: FrameSize = (1 << 24) - 1;
 
 // ===== impl Settings =====
 
@@ -78,6 +78,13 @@ impl Settings {
         self.max_frame_size
     }
 
+    pub fn set_max_frame_size(&mut self, size: Option<u32>) {
+        if let Some(val) = size {
+            assert!(DEFAULT_MAX_FRAME_SIZE <= val && val <= MAX_MAX_FRAME_SIZE);
+        }
+        self.max_frame_size = size;
+    }
+
     pub fn load(head: Head, payload: &[u8]) -> Result<Settings, Error> {
         use self::Setting::*;
 
@@ -131,7 +138,7 @@ impl Settings {
                     settings.initial_window_size = Some(val);
                 },
                 Some(MaxFrameSize(val)) => {
-                    if val < DEFAULT_MAX_FRAME_SIZE || val as usize > MAX_MAX_FRAME_SIZE {
+                    if val < DEFAULT_MAX_FRAME_SIZE || val > MAX_MAX_FRAME_SIZE {
                         return Err(Error::InvalidSettingValue);
                     } else {
                         settings.max_frame_size = Some(val);