subxt: Expose light client under experimental feature-flag

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

Cargo.toml

@@ -73,6 +73,11 @@ wabt = "0.10.0"
 wasm-bindgen-test = "0.3.24"
 which = "4.4.0"
 
+# Light client support:
+smoldot-light = { git = "https://github.com/smol-dot/smoldot.git", default-features = false }
+tokio-stream = "0.1.14"
+futures-util = "0.3.28"
+
 # Substrate crates:
 sp-core = { version = "20.0.0", default-features = false }
 sp-core-hashing = "8.0.0"

subxt/Cargo.toml

@@ -40,6 +40,16 @@ jsonrpsee-web = ["jsonrpsee/async-wasm-client", "jsonrpsee/client-web-transport"
 # latest features exposed by the metadata.
 unstable-metadata = []
 
+# Activate this to expose the Light Client functionality.
+# Note that this feature is experimental and things may break or not work as expected.
+experimental-light-client = [
+    "smoldot-light/std",
+    "tokio-stream",
+    "tokio/sync",
+    "tokio/rt",
+    "futures-util",
+]
+
 [dependencies]
 codec = { package = "parity-scale-codec", workspace = true, features = ["derive"] }
 scale-info = { workspace = true }
@@ -78,6 +88,12 @@ sp-runtime = { workspace = true, optional = true }
 subxt-macro = { workspace = true }
 subxt-metadata = { workspace = true }
 
+# Light client support:
+smoldot-light = { workspace = true, optional = true }
+tokio = { workspace = true, optional = true }
+tokio-stream = { workspace = true, optional = true }
+futures-util = { workspace = true, optional = true }
+
 [target.wasm32-unknown-unknown.dependencies]
 getrandom = { workspace = true, features = ["js"] }
 

subxt/src/rpc/mod.rs

@@ -47,6 +47,9 @@
 #[cfg(feature = "jsonrpsee")]
 mod jsonrpsee_impl;
 
+#[cfg(feature = "experimental-light-client")]
+mod lightclient;
+
 mod rpc;
 mod rpc_client;
 mod rpc_client_t;
@@ -62,3 +65,6 @@ pub use rpc_client_t::{
 };
 
 pub use rpc_client::{rpc_params, RpcClient, RpcParams, Subscription};
+
+#[cfg(feature = "experimental-light-client")]
+pub use lightclient::{LightClient, LightClientError};