Issue 128: Convert frame::Reason to struct (#142)

Alter frame::Reason to a struct with a single u32 member.
Introduce Constants to the impl for existing Reasons. Change all usage
in the library and its tests to adopt this change,
using the new constants.

src/frame/reason.rs

@@ -1,99 +1,58 @@
 use std::fmt;
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-pub enum Reason {
-    NoError,
-    ProtocolError,
-    InternalError,
-    FlowControlError,
-    SettingsTimeout,
-    StreamClosed,
-    FrameSizeError,
-    RefusedStream,
-    Cancel,
-    CompressionError,
-    ConnectError,
-    EnhanceYourCalm,
-    InadequateSecurity,
-    Http11Required,
-    Other(u32),
-    // TODO: reserve additional variants
-}
 
-// ===== impl Reason =====
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub struct Reason(u32);
 
 impl Reason {
-    pub fn description(&self) -> &str {
-        use self::Reason::*;
+    pub const NO_ERROR: Reason = Reason(0);
+    pub const PROTOCOL_ERROR: Reason = Reason(1);
+    pub const INTERNAL_ERROR: Reason = Reason(2);
+    pub const FLOW_CONTROL_ERROR: Reason = Reason(3);
+    pub const SETTINGS_TIMEOUT: Reason = Reason(4);
+    pub const STREAM_CLOSED: Reason = Reason(5);
+    pub const FRAME_SIZE_ERROR: Reason = Reason(6);
+    pub const REFUSED_STREAM: Reason = Reason(7);
+    pub const CANCEL: Reason = Reason(8);
+    pub const COMPRESSION_ERROR: Reason = Reason(9);
+    pub const CONNECT_ERROR: Reason = Reason(10);
+    pub const ENHANCE_YOUR_CALM: Reason = Reason(11);
+    pub const INADEQUATE_SECURITY: Reason = Reason(12);
+    pub const HTTP11_REQUIRED: Reason = Reason(13);
 
-        match *self {
-            NoError => "not a result of an error",
-            ProtocolError => "unspecific protocol error detected",
-            InternalError => "unexpected internal error encountered",
-            FlowControlError => "flow-control protocol violated",
-            SettingsTimeout => "settings ACK not received in timely manner",
-            StreamClosed => "received frame when stream half-closed",
-            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",
-            ConnectError => {
-                "connection established in response to a CONNECT request \
-                 was reset or abnormally closed"
+    pub fn description(&self) -> &str {
+        match self.0 {
+            0 => "not a result of an error",
+            1 => "unspecific protocol error detected",
+            2 => "unexpected internal error encountered",
+            3 => "flow-control protocol violated",
+            4 => "settings ACK not received in timely manner",
+            5 => "received frame when stream half-closed",
+            6 => "frame with invalid size",
+            7 => "refused stream before processing any application logic",
+            8 => "stream no longer needed",
+            9 => "unable to maintain the header compression context",
+            10 => {
+                "connection established in response to a CONNECT request was reset or abnormally \
+                 closed"
             },
-            EnhanceYourCalm => "detected excessive load generating behavior",
-            InadequateSecurity => "security properties do not meet minimum requirements",
-            Http11Required => "endpoint requires HTTP/1.1",
-            Other(_) => "other reason (ain't no tellin')",
+            11 => "detected excessive load generating behavior",
+            12 => "security properties do not meet minimum requirements",
+            13 => "endpoint requires HTTP/1.1",
+            _ => "unknown reason",
         }
     }
 }
 
 impl From<u32> for Reason {
     fn from(src: u32) -> Reason {
-        use self::Reason::*;
-
-        match src {
-            0x0 => NoError,
-            0x1 => ProtocolError,
-            0x2 => InternalError,
-            0x3 => FlowControlError,
-            0x4 => SettingsTimeout,
-            0x5 => StreamClosed,
-            0x6 => FrameSizeError,
-            0x7 => RefusedStream,
-            0x8 => Cancel,
-            0x9 => CompressionError,
-            0xa => ConnectError,
-            0xb => EnhanceYourCalm,
-            0xc => InadequateSecurity,
-            0xd => Http11Required,
-            _ => Other(src),
-        }
+        Reason(src)
     }
 }
 
 impl From<Reason> for u32 {
     fn from(src: Reason) -> u32 {
-        use self::Reason::*;
-
-        match src {
-            NoError => 0x0,
-            ProtocolError => 0x1,
-            InternalError => 0x2,
-            FlowControlError => 0x3,
-            SettingsTimeout => 0x4,
-            StreamClosed => 0x5,
-            FrameSizeError => 0x6,
-            RefusedStream => 0x7,
-            Cancel => 0x8,
-            CompressionError => 0x9,
-            ConnectError => 0xa,
-            EnhanceYourCalm => 0xb,
-            InadequateSecurity => 0xc,
-            Http11Required => 0xd,
-            Other(v) => v,
-        }
+        src.0
     }
 }