Implement std::error::Error for our custom errors

For allowing a more ergonomic use and better integration on the
ecosystem, this adds the `std::error::Error` `impl` for our custom
errors.

We intent to drop this hand made code once `derive_more` finishes the
addition of the Error derive support[1]. Until that is available, we
need to live with that.

1. https://github.com/JelteF/derive_more/issues/92

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

actix-http/CHANGES.md

@@ -1,5 +1,13 @@
 # Changes
 
+## [Unreleased]
+
+### Changed
+
+* Implement `std::error::Error` for our custom errors [#1422]
+
+[#1422]: https://github.com/actix/actix-web/pull/1422
+
 ## [2.0.0-alpha.2] - 2020-03-07
 
 ### Changed

actix-http/src/client/error.rs

@@ -55,6 +55,8 @@ pub enum ConnectError {
     Io(io::Error),
 }
 
+impl std::error::Error for ConnectError {}
+
 impl From<actix_connect::ConnectError> for ConnectError {
     fn from(err: actix_connect::ConnectError) -> ConnectError {
         match err {
@@ -86,6 +88,8 @@ pub enum InvalidUrl {
     HttpError(http::Error),
 }
 
+impl std::error::Error for InvalidUrl {}
+
 /// A set of errors that can occur during request sending and response reading
 #[derive(Debug, Display, From)]
 pub enum SendRequestError {
@@ -115,6 +119,8 @@ pub enum SendRequestError {
     Body(Error),
 }
 
+impl std::error::Error for SendRequestError {}
+
 /// Convert `SendRequestError` to a server `Response`
 impl ResponseError for SendRequestError {
     fn status_code(&self) -> StatusCode {
@@ -139,6 +145,8 @@ pub enum FreezeRequestError {
     Http(HttpError),
 }
 
+impl std::error::Error for FreezeRequestError {}
+
 impl From<FreezeRequestError> for SendRequestError {
     fn from(e: FreezeRequestError) -> Self {
         match e {

actix-http/src/error.rs

@@ -333,6 +333,8 @@ pub enum PayloadError {
     Io(io::Error),
 }
 
+impl std::error::Error for PayloadError {}
+
 impl From<h2::Error> for PayloadError {
     fn from(err: h2::Error) -> Self {
         PayloadError::Http2Payload(err)
@@ -441,6 +443,8 @@ pub enum ContentTypeError {
     UnknownEncoding,
 }
 
+impl std::error::Error for ContentTypeError {}
+
 /// Return `BadRequest` for `ContentTypeError`
 impl ResponseError for ContentTypeError {
     fn status_code(&self) -> StatusCode {

actix-http/src/ws/mod.rs

@@ -58,6 +58,8 @@ pub enum ProtocolError {
     Io(io::Error),
 }
 
+impl std::error::Error for ProtocolError {}
+
 impl ResponseError for ProtocolError {}
 
 /// Websocket handshake errors