Add protocol error types

src/client.rs

@@ -52,7 +52,7 @@ mod encryption {
     use std::net::TcpStream;
 
     use crate::{
-        error::{Error, UrlErrorType, Result},
+        error::{Error, Result, UrlErrorType},
         stream::Mode,
     };
 
@@ -71,7 +71,7 @@ use self::encryption::wrap_stream;
 pub use self::encryption::AutoStream;
 
 use crate::{
-    error::{Error, UrlErrorType, Result},
+    error::{Error, Result, UrlErrorType},
     handshake::{client::ClientHandshake, HandshakeError},
     protocol::WebSocket,
     stream::{Mode, NoDelay},
@@ -103,8 +103,7 @@ pub fn connect_with_config<Req: IntoClientRequest>(
     ) -> Result<(WebSocket<AutoStream>, Response)> {
         let uri = request.uri();
         let mode = uri_mode(uri)?;
-        let host =
-            request.uri().host().ok_or_else(|| Error::Url(UrlErrorType::NoHostName))?;
+        let host = request.uri().host().ok_or_else(|| Error::Url(UrlErrorType::NoHostName))?;
         let port = uri.port_u16().unwrap_or(match mode {
             Mode::Plain => 80,
             Mode::Tls => 443,

src/error.rs

@@ -2,7 +2,7 @@
 
 use std::{borrow::Cow, error::Error as ErrorTrait, fmt, io, result, str, string};
 
-use crate::protocol::Message;
+use crate::protocol::{frame::coding::Data, Message};
 use http::Response;
 
 #[cfg(feature = "tls")]
@@ -41,14 +41,14 @@ pub enum Error {
     /// underlying connection and you should probably consider them fatal.
     Io(io::Error),
     #[cfg(feature = "tls")]
-    /// TLS error
+    /// TLS error.
     Tls(tls::Error),
     /// - When reading: buffer capacity exhausted.
     /// - When writing: your message is bigger than the configured max message size
     ///   (64MB by default).
     Capacity(Cow<'static, str>),
     /// Protocol violation.
-    Protocol(Cow<'static, str>),
+    Protocol(ProtocolErrorType),
     /// Message send queue full.
     SendQueueFull(Message),
     /// UTF coding error
@@ -147,13 +147,13 @@ impl From<httparse::Error> for Error {
     fn from(err: httparse::Error) -> Self {
         match err {
             httparse::Error::TooManyHeaders => Error::Capacity("Too many headers".into()),
-            e => Error::Protocol(e.to_string().into()),
+            e => Error::Protocol(ProtocolErrorType::HttparseError(e)),
         }
     }
 }
 
 /// Indicates the specific type/cause of URL error.
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 pub enum UrlErrorType {
     /// TLS is used despite not being compiled with the TLS feature enabled.
     TlsFeatureNotEnabled,
@@ -166,7 +166,7 @@ pub enum UrlErrorType {
     /// The URL host name, though included, is empty.
     EmptyHostName,
     /// The URL does not include a path/query.
-    NoPathOrQuery
+    NoPathOrQuery,
 }
 
 impl fmt::Display for UrlErrorType {
@@ -177,7 +177,128 @@ impl fmt::Display for UrlErrorType {
             UrlErrorType::UnableToConnect(uri) => write!(f, "Unable to connect to {}", uri),
             UrlErrorType::UnsupportedUrlScheme => write!(f, "URL scheme not supported"),
             UrlErrorType::EmptyHostName => write!(f, "URL contains empty host name"),
-            UrlErrorType::NoPathOrQuery => write!(f, "No path/query in URL")
+            UrlErrorType::NoPathOrQuery => write!(f, "No path/query in URL"),
+        }
+    }
+}
+
+/// Indicates the specific type/cause of a protocol error.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum ProtocolErrorType {
+    /// Use of the wrong HTTP method (the WebSocket protocol requires the GET method be used).
+    WrongHttpMethod,
+    /// Wrong HTTP version used (the WebSocket protocol requires version 1.1 or higher).
+    WrongHttpVersion,
+    /// Missing `Connection: upgrade` HTTP header.
+    MissingConnectionUpgradeHeader,
+    /// Missing `Upgrade: websocket` HTTP header.
+    MissingUpgradeWebSocketHeader,
+    /// Missing `Sec-WebSocket-Version: 13` HTTP header.
+    MissingSecWebSocketVersionHeader,
+    /// Missing `Sec-WebSocket-Key` HTTP header.
+    MissingSecWebSocketKey,
+    /// The `Sec-WebSocket-Accept` header is either not present or does not specify the correct key value.
+    SecWebSocketAcceptKeyMismatch,
+    /// Garbage data encountered after client request.
+    JunkAfterRequest,
+    /// Custom responses must be unsuccessful.
+    CustomResponseSuccessful,
+    /// No more data while still performing handshake.
+    HandshakeIncomplete,
+    /// Wrapper around a [`httparse::Error`] value.
+    HttparseError(httparse::Error),
+    /// Not allowed to send after having sent a closing frame.
+    SendAfterClosing,
+    /// Remote sent data after sending a closing frame.
+    ReceivedAfterClosing,
+    /// Reserved bits in frame header are non-zero.
+    NonZeroReservedBits,
+    /// The server must close the connection when an unmasked frame is received.
+    UnmaskedFrameFromClient,
+    /// The client must close the connection when a masked frame is received.
+    MaskedFrameFromServer,
+    /// Control frames must not be fragmented.
+    FragmentedControlFrame,
+    /// Control frames must have a payload of 125 bytes or less.
+    ControlFrameTooBig,
+    /// Type of control frame not recognised.
+    UnknownControlFrameType(u8),
+    /// Type of data frame not recognised.
+    UnknownDataFrameType(u8),
+    /// Received a continue frame despite there being nothing to continue.
+    UnexpectedContinueFrame,
+    /// Received data while waiting for more fragments.
+    ExpectedFragment(Data),
+    /// Connection closed without performing the closing handshake.
+    ResetWithoutClosingHandshake,
+    /// Encountered an invalid opcode.
+    InvalidOpcode(u8),
+    /// The payload for the closing frame is invalid.
+    InvalidCloseSequence,
+}
+
+impl fmt::Display for ProtocolErrorType {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ProtocolErrorType::WrongHttpMethod => {
+                write!(f, "Unsupported HTTP method used, only GET is allowed")
+            }
+            ProtocolErrorType::WrongHttpVersion => write!(f, "HTTP version must be 1.1 or higher"),
+            ProtocolErrorType::MissingConnectionUpgradeHeader => {
+                write!(f, "No \"Connection: upgrade\" header")
+            }
+            ProtocolErrorType::MissingUpgradeWebSocketHeader => {
+                write!(f, "No \"Upgrade: websocket\" header")
+            }
+            ProtocolErrorType::MissingSecWebSocketVersionHeader => {
+                write!(f, "No \"Sec-WebSocket-Version: 13\" header")
+            }
+            ProtocolErrorType::MissingSecWebSocketKey => {
+                write!(f, "No \"Sec-WebSocket-Key\" header")
+            }
+            ProtocolErrorType::SecWebSocketAcceptKeyMismatch => {
+                write!(f, "Key mismatch in \"Sec-WebSocket-Accept\" header")
+            }
+            ProtocolErrorType::JunkAfterRequest => write!(f, "Junk after client request"),
+            ProtocolErrorType::CustomResponseSuccessful => {
+                write!(f, "Custom response must not be successful")
+            }
+            ProtocolErrorType::HandshakeIncomplete => write!(f, "Handshake not finished"),
+            ProtocolErrorType::HttparseError(e) => write!(f, "httparse error: {}", e),
+            ProtocolErrorType::SendAfterClosing => {
+                write!(f, "Sending after closing is not allowed")
+            }
+            ProtocolErrorType::ReceivedAfterClosing => write!(f, "Remote sent after having closed"),
+            ProtocolErrorType::NonZeroReservedBits => write!(f, "Reserved bits are non-zero"),
+            ProtocolErrorType::UnmaskedFrameFromClient => {
+                write!(f, "Received an unmasked frame from client")
+            }
+            ProtocolErrorType::MaskedFrameFromServer => {
+                write!(f, "Received a masked frame from server")
+            }
+            ProtocolErrorType::FragmentedControlFrame => write!(f, "Fragmented control frame"),
+            ProtocolErrorType::ControlFrameTooBig => {
+                write!(f, "Control frame too big (payload must be 125 bytes or less)")
+            }
+            ProtocolErrorType::UnknownControlFrameType(i) => {
+                write!(f, "Unknown control frame type: {}", i)
+            }
+            ProtocolErrorType::UnknownDataFrameType(i) => {
+                write!(f, "Unknown data frame type: {}", i)
+            }
+            ProtocolErrorType::UnexpectedContinueFrame => {
+                write!(f, "Continue frame but nothing to continue")
+            }
+            ProtocolErrorType::ExpectedFragment(c) => {
+                write!(f, "While waiting for more fragments received: {}", c)
+            }
+            ProtocolErrorType::ResetWithoutClosingHandshake => {
+                write!(f, "Connection reset without closing handshake")
+            }
+            ProtocolErrorType::InvalidOpcode(opcode) => {
+                write!(f, "Encountered invalid opcode: {}", opcode)
+            }
+            ProtocolErrorType::InvalidCloseSequence => write!(f, "Invalid close sequence"),
         }
     }
-}
+}

src/handshake/client.rs

@@ -16,7 +16,7 @@ use super::{
     HandshakeRole, MidHandshake, ProcessingResult,
 };
 use crate::{
-    error::{Error, UrlErrorType, Result},
+    error::{Error, ProtocolErrorType, Result, UrlErrorType},
     protocol::{Role, WebSocket, WebSocketConfig},
 };
 
@@ -42,11 +42,11 @@ impl<S: Read + Write> ClientHandshake<S> {
         config: Option<WebSocketConfig>,
     ) -> Result<MidHandshake<Self>> {
         if request.method() != http::Method::GET {
-            return Err(Error::Protocol("Invalid HTTP method, only GET supported".into()));
+            return Err(Error::Protocol(ProtocolErrorType::WrongHttpMethod));
         }
 
         if request.version() < http::Version::HTTP_11 {
-            return Err(Error::Protocol("HTTP version should be 1.1 or higher".into()));
+            return Err(Error::Protocol(ProtocolErrorType::WrongHttpVersion));
         }
 
         // Check the URI scheme: only ws or wss are supported
@@ -97,8 +97,7 @@ fn generate_request(request: Request, key: &str) -> Result<Vec<u8>> {
     let mut req = Vec::new();
     let uri = request.uri();
 
-    let authority =
-        uri.authority().ok_or_else(|| Error::Url(UrlErrorType::NoHostName))?.as_str();
+    let authority = uri.authority().ok_or_else(|| Error::Url(UrlErrorType::NoHostName))?.as_str();
     let host = if let Some(idx) = authority.find('@') {
         // handle possible name:password@
         authority.split_at(idx + 1).1
@@ -165,7 +164,7 @@ impl VerifyData {
             .map(|h| h.eq_ignore_ascii_case("websocket"))
             .unwrap_or(false)
         {
-            return Err(Error::Protocol("No \"Upgrade: websocket\" in server reply".into()));
+            return Err(Error::Protocol(ProtocolErrorType::MissingUpgradeWebSocketHeader));
         }
         // 3.  If the response lacks a |Connection| header field or the
         // |Connection| header field doesn't contain a token that is an
@@ -177,14 +176,14 @@ impl VerifyData {
             .map(|h| h.eq_ignore_ascii_case("Upgrade"))
             .unwrap_or(false)
         {
-            return Err(Error::Protocol("No \"Connection: upgrade\" in server reply".into()));
+            return Err(Error::Protocol(ProtocolErrorType::MissingConnectionUpgradeHeader));
         }
         // 4.  If the response lacks a |Sec-WebSocket-Accept| header field or
         // the |Sec-WebSocket-Accept| contains a value other than the
         // base64-encoded SHA-1 of ... the client MUST _Fail the WebSocket
         // Connection_. (RFC 6455)
         if !headers.get("Sec-WebSocket-Accept").map(|h| h == &self.accept_key).unwrap_or(false) {
-            return Err(Error::Protocol("Key mismatch in Sec-WebSocket-Accept".into()));
+            return Err(Error::Protocol(ProtocolErrorType::SecWebSocketAcceptKeyMismatch));
         }
         // 5.  If the response includes a |Sec-WebSocket-Extensions| header
         // field and this header field indicates the use of an extension
@@ -218,7 +217,7 @@ impl TryParse for Response {
 impl<'h, 'b: 'h> FromHttparse<httparse::Response<'h, 'b>> for Response {
     fn from_httparse(raw: httparse::Response<'h, 'b>) -> Result<Self> {
         if raw.version.expect("Bug: no HTTP version") < /*1.*/1 {
-            return Err(Error::Protocol("HTTP version should be 1.1 or higher".into()));
+            return Err(Error::Protocol(ProtocolErrorType::WrongHttpMethod));
         }
 
         let headers = HeaderMap::from_httparse(raw.headers)?;

src/handshake/machine.rs

@@ -3,7 +3,7 @@ use log::*;
 use std::io::{Cursor, Read, Write};
 
 use crate::{
-    error::{Error, Result},
+    error::{Error, ProtocolErrorType, Result},
     util::NonBlockingResult,
 };
 use input_buffer::{InputBuffer, MIN_READ};
@@ -50,7 +50,7 @@ impl<Stream: Read + Write> HandshakeMachine<Stream> {
                     .read_from(&mut self.stream)
                     .no_block()?;
                 match read {
-                    Some(0) => Err(Error::Protocol("Handshake not finished".into())),
+                    Some(0) => Err(Error::Protocol(ProtocolErrorType::HandshakeIncomplete)),
                     Some(_) => Ok(if let Some((size, obj)) = Obj::try_parse(Buf::chunk(&buf))? {
                         buf.advance(size);
                         RoundResult::StageFinished(StageResult::DoneReading {

src/handshake/server.rs

@@ -19,7 +19,7 @@ use super::{
     HandshakeRole, MidHandshake, ProcessingResult,
 };
 use crate::{
-    error::{Error, Result},
+    error::{Error, ProtocolErrorType, Result},
     protocol::{Role, WebSocket, WebSocketConfig},
 };
 
@@ -34,11 +34,11 @@ pub type ErrorResponse = HttpResponse<Option<String>>;
 
 fn create_parts<T>(request: &HttpRequest<T>) -> Result<Builder> {
     if request.method() != http::Method::GET {
-        return Err(Error::Protocol("Method is not GET".into()));
+        return Err(Error::Protocol(ProtocolErrorType::WrongHttpMethod));
     }
 
     if request.version() < http::Version::HTTP_11 {
-        return Err(Error::Protocol("HTTP version should be 1.1 or higher".into()));
+        return Err(Error::Protocol(ProtocolErrorType::WrongHttpVersion));
     }
 
     if !request
@@ -48,7 +48,7 @@ fn create_parts<T>(request: &HttpRequest<T>) -> Result<Builder> {
         .map(|h| h.split(|c| c == ' ' || c == ',').any(|p| p.eq_ignore_ascii_case("Upgrade")))
         .unwrap_or(false)
     {
-        return Err(Error::Protocol("No \"Connection: upgrade\" in client request".into()));
+        return Err(Error::Protocol(ProtocolErrorType::MissingConnectionUpgradeHeader));
     }
 
     if !request
@@ -58,17 +58,17 @@ fn create_parts<T>(request: &HttpRequest<T>) -> Result<Builder> {
         .map(|h| h.eq_ignore_ascii_case("websocket"))
         .unwrap_or(false)
     {
-        return Err(Error::Protocol("No \"Upgrade: websocket\" in client request".into()));
+        return Err(Error::Protocol(ProtocolErrorType::MissingUpgradeWebSocketHeader));
     }
 
     if !request.headers().get("Sec-WebSocket-Version").map(|h| h == "13").unwrap_or(false) {
-        return Err(Error::Protocol("No \"Sec-WebSocket-Version: 13\" in client request".into()));
+        return Err(Error::Protocol(ProtocolErrorType::MissingSecWebSocketVersionHeader));
     }
 
     let key = request
         .headers()
         .get("Sec-WebSocket-Key")
-        .ok_or_else(|| Error::Protocol("Missing Sec-WebSocket-Key".into()))?;
+        .ok_or_else(|| Error::Protocol(ProtocolErrorType::MissingSecWebSocketKey))?;
 
     let builder = Response::builder()
         .status(StatusCode::SWITCHING_PROTOCOLS)
@@ -125,11 +125,11 @@ impl TryParse for Request {
 impl<'h, 'b: 'h> FromHttparse<httparse::Request<'h, 'b>> for Request {
     fn from_httparse(raw: httparse::Request<'h, 'b>) -> Result<Self> {
         if raw.method.expect("Bug: no method in header") != "GET" {
-            return Err(Error::Protocol("Method is not GET".into()));
+            return Err(Error::Protocol(ProtocolErrorType::WrongHttpMethod));
         }
 
         if raw.version.expect("Bug: no HTTP version") < /*1.*/1 {
-            return Err(Error::Protocol("HTTP version should be 1.1 or higher".into()));
+            return Err(Error::Protocol(ProtocolErrorType::WrongHttpVersion));
         }
 
         let headers = HeaderMap::from_httparse(raw.headers)?;
@@ -237,7 +237,7 @@ impl<S: Read + Write, C: Callback> HandshakeRole for ServerHandshake<S, C> {
         Ok(match finish {
             StageResult::DoneReading { stream, result, tail } => {
                 if !tail.is_empty() {
-                    return Err(Error::Protocol("Junk after client request".into()));
+                    return Err(Error::Protocol(ProtocolErrorType::JunkAfterRequest));
                 }
 
                 let response = create_response(&result)?;
@@ -257,7 +257,7 @@ impl<S: Read + Write, C: Callback> HandshakeRole for ServerHandshake<S, C> {
                     Err(resp) => {
                         if resp.status().is_success() {
                             return Err(Error::Protocol(
-                                "Custom response must not be successful".into(),
+                                ProtocolErrorType::CustomResponseSuccessful,
                             ));
                         }
 

src/protocol/frame/frame.rs

@@ -13,7 +13,7 @@ use super::{
     coding::{CloseCode, Control, Data, OpCode},
     mask::{apply_mask, generate_mask},
 };
-use crate::error::{Error, Result};
+use crate::error::{Error, ProtocolErrorType, Result};
 
 /// A struct representing the close command.
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -186,9 +186,7 @@ impl FrameHeader {
         // Disallow bad opcode
         match opcode {
             OpCode::Control(Control::Reserved(_)) | OpCode::Data(Data::Reserved(_)) => {
-                return Err(Error::Protocol(
-                    format!("Encountered invalid opcode: {}", first & 0x0F).into(),
-                ))
+                return Err(Error::Protocol(ProtocolErrorType::InvalidOpcode(first & 0x0F)))
             }
             _ => (),
         }
@@ -286,7 +284,7 @@ impl Frame {
     pub(crate) fn into_close(self) -> Result<Option<CloseFrame<'static>>> {
         match self.payload.len() {
             0 => Ok(None),
-            1 => Err(Error::Protocol("Invalid close sequence".into())),
+            1 => Err(Error::Protocol(ProtocolErrorType::InvalidCloseSequence)),
             _ => {
                 let mut data = self.payload;
                 let code = NetworkEndian::read_u16(&data[0..2]).into();

src/protocol/mod.rs

@@ -21,7 +21,7 @@ use self::{
     message::{IncompleteMessage, IncompleteMessageType},
 };
 use crate::{
-    error::{Error, Result},
+    error::{Error, ProtocolErrorType, Result},
     util::NonBlockingResult,
 };
 
@@ -331,7 +331,7 @@ impl WebSocketContext {
 
         // Do not write after sending a close frame.
         if !self.state.is_active() {
-            return Err(Error::Protocol("Sending after closing is not allowed".into()));
+            return Err(Error::Protocol(ProtocolErrorType::SendAfterClosing));
         }
 
         if let Some(max_send_queue) = self.config.max_send_queue {
@@ -431,9 +431,7 @@ impl WebSocketContext {
             .check_connection_reset(self.state)?
         {
             if !self.state.can_read() {
-                return Err(Error::Protocol(
-                    "Remote sent frame after having sent a Close Frame".into(),
-                ));
+                return Err(Error::Protocol(ProtocolErrorType::ReceivedAfterClosing));
             }
             // MUST be 0 unless an extension is negotiated that defines meanings
             // for non-zero values.  If a nonzero value is received and none of
@@ -443,7 +441,7 @@ impl WebSocketContext {
             {
                 let hdr = frame.header();
                 if hdr.rsv1 || hdr.rsv2 || hdr.rsv3 {
-                    return Err(Error::Protocol("Reserved bits are non-zero".into()));
+                    return Err(Error::Protocol(ProtocolErrorType::NonZeroReservedBits));
                 }
             }
 
@@ -458,15 +456,13 @@ impl WebSocketContext {
                         // frame that is not masked. (RFC 6455)
                         // The only exception here is if the user explicitly accepts given
                         // stream by setting WebSocketConfig.accept_unmasked_frames to true
-                        return Err(Error::Protocol(
-                            "Received an unmasked frame from client".into(),
-                        ));
+                        return Err(Error::Protocol(ProtocolErrorType::UnmaskedFrameFromClient));
                     }
                 }
                 Role::Client => {
                     if frame.is_masked() {
                         // A client MUST close a connection if it detects a masked frame. (RFC 6455)
-                        return Err(Error::Protocol("Received a masked frame from server".into()));
+                        return Err(Error::Protocol(ProtocolErrorType::MaskedFrameFromServer));
                     }
                 }
             }
@@ -477,14 +473,14 @@ impl WebSocketContext {
                         // All control frames MUST have a payload length of 125 bytes or less
                         // and MUST NOT be fragmented. (RFC 6455)
                         _ if !frame.header().is_final => {
-                            Err(Error::Protocol("Fragmented control frame".into()))
+                            Err(Error::Protocol(ProtocolErrorType::FragmentedControlFrame))
                         }
                         _ if frame.payload().len() > 125 => {
-                            Err(Error::Protocol("Control frame too big".into()))
+                            Err(Error::Protocol(ProtocolErrorType::ControlFrameTooBig))
                         }
                         OpCtl::Close => Ok(self.do_close(frame.into_close()?).map(Message::Close)),
                         OpCtl::Reserved(i) => {
-                            Err(Error::Protocol(format!("Unknown control frame type {}", i).into()))
+                            Err(Error::Protocol(ProtocolErrorType::UnknownControlFrameType(i)))
                         }
                         OpCtl::Ping => {
                             let data = frame.into_data();
@@ -506,7 +502,7 @@ impl WebSocketContext {
                                 msg.extend(frame.into_data(), self.config.max_message_size)?;
                             } else {
                                 return Err(Error::Protocol(
-                                    "Continue frame but nothing to continue".into(),
+                                    ProtocolErrorType::UnexpectedContinueFrame,
                                 ));
                             }
                             if fin {
@@ -515,9 +511,9 @@ impl WebSocketContext {
                                 Ok(None)
                             }
                         }
-                        c if self.incomplete.is_some() => Err(Error::Protocol(
-                            format!("Received {} while waiting for more fragments", c).into(),
-                        )),
+                        c if self.incomplete.is_some() => {
+                            Err(Error::Protocol(ProtocolErrorType::ExpectedFragment(c)))
+                        }
                         OpData::Text | OpData::Binary => {
                             let msg = {
                                 let message_type = match data {
@@ -537,7 +533,7 @@ impl WebSocketContext {
                             }
                         }
                         OpData::Reserved(i) => {
-                            Err(Error::Protocol(format!("Unknown data frame type {}", i).into()))
+                            Err(Error::Protocol(ProtocolErrorType::UnknownDataFrameType(i)))
                         }
                     }
                 }
@@ -548,7 +544,7 @@ impl WebSocketContext {
                 WebSocketState::ClosedByPeer | WebSocketState::CloseAcknowledged => {
                     Err(Error::ConnectionClosed)
                 }
-                _ => Err(Error::Protocol("Connection reset without closing handshake".into())),
+                _ => Err(Error::Protocol(ProtocolErrorType::ResetWithoutClosingHandshake)),
             }
         }
     }

tests/no_send_after_close.rs

@@ -8,7 +8,7 @@ use std::{
     time::Duration,
 };
 
-use tungstenite::{accept, connect, Error, Message};
+use tungstenite::{accept, connect, error::ProtocolErrorType, Error, Message};
 use url::Url;
 
 #[test]
@@ -46,7 +46,7 @@ fn test_no_send_after_close() {
     assert!(err.is_err());
 
     match err.unwrap_err() {
-        Error::Protocol(s) => assert_eq!("Sending after closing is not allowed", s),
+        Error::Protocol(s) => assert_eq!(s, ProtocolErrorType::SendAfterClosing),
         e => panic!("unexpected error: {:?}", e),
     }