feat: parse and validate events from websockets

Establishes a websocket listener, parses events, and performs
validation to ensure valid signatures.

src/error.rs

@@ -0,0 +1,39 @@
+//! Error handling.
+
+use std::result;
+use thiserror::Error;
+use tungstenite::error::Error as WsError;
+
+pub type Result<T, E = Error> = result::Result<T, E>;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("Protocol parse error")]
+    ProtoParseError,
+    #[error("Connection error")]
+    ConnError,
+    #[error("Client write error")]
+    ConnWriteError,
+    #[error("Event parse failed")]
+    EventParseFailed,
+    #[error("Event validation failed")]
+    EventInvalid,
+    #[error("JSON parsing failed")]
+    JsonParseFailed(serde_json::Error),
+    #[error("WebSocket proto error")]
+    WebsocketError(WsError),
+    #[error("Command unknown")]
+    CommandUnknownError,
+}
+
+impl From<serde_json::Error> for Error {
+    fn from(r: serde_json::Error) -> Self {
+        Error::JsonParseFailed(r)
+    }
+}
+
+impl From<WsError> for Error {
+    fn from(r: WsError) -> Self {
+        Error::WebsocketError(r)
+    }
+}