lightclient: Add light client Error

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

subxt/src/error/mod.rs

@@ -8,6 +8,9 @@ mod dispatch_error;
 
 use core::fmt::Debug;
 
+#[cfg(feature = "experimental-light-client")]
+pub use crate::rpc::LightClientError;
+
 // Re-export dispatch error types:
 pub use dispatch_error::{
     ArithmeticError, DispatchError, ModuleError, RawModuleError, TokenError, TransactionalError,
@@ -63,6 +66,10 @@ pub enum Error {
     /// The bytes representing an error that we were unable to decode.
     #[error("An error occurred but it could not be decoded: {0:?}")]
     Unknown(Vec<u8>),
+    /// Light client error.
+    #[cfg(feature = "experimental-light-client")]
+    #[error("An error occurred but it could not be decoded: {0:?}")]
+    LightClient(#[from] LightClientError),
     /// Other error.
     #[error("Other error: {0}")]
     Other(String),

subxt/src/rpc/lightclient/mod.rs

@@ -0,0 +1,32 @@
+mod background;
+mod client;
+
+pub use client::LightClient;
+
+/// Light client error.
+#[derive(Debug, thiserror::Error)]
+pub enum LightClientError {
+    /// Error encountered while adding the chain to the light-client.
+    #[error("Failed to add the chain to the light client: {0}")]
+    AddChainError(String),
+    /// The background task is closed.
+    #[error("Failed to communicate with the background task.")]
+    BackgroundClosed,
+    /// Invalid RPC parameters cannot be serialized as JSON string.
+    #[error("RPC parameters cannot be serialized as JSON string.")]
+    InvalidParams,
+    /// Error originated while trying to submit a RPC request.
+    #[error("RPC request cannot be sent: {0}")]
+    Request(String),
+    /// The provided URL scheme is invalid.
+    ///
+    /// Supported versions: WS, WSS.
+    #[error("The provided URL scheme is invalid.")]
+    InvalidScheme,
+    /// The provided URL is invalid.
+    #[error("The provided URL scheme is invalid.")]
+    InvalidUrl,
+    /// Handshake error while connecting to a node.
+    #[error("WS handshake failed")]
+    Handshake,
+}