Add WASM support to lightwalletd-tonic feature flag (#1270)

The transport-specific code is moved behind a new `lightwalletd-tonic-transport` feature flag.

.github/workflows/ci.yml

@@ -195,7 +195,7 @@ jobs:
         run: cargo add --no-default-features --path ../crates/zcash_proofs
       - name: Add zcash_client_backend as a dependency of the synthetic crate
         working-directory: ./ci-build
-        run: cargo add --no-default-features --path ../crates/zcash_client_backend
+        run: cargo add --features lightwalletd-tonic --path ../crates/zcash_client_backend
       - name: Copy pinned dependencies into synthetic crate
         run: cp crates/Cargo.lock ci-build/
       - name: Add target

Cargo.toml

@@ -94,8 +94,8 @@ rayon = "1.5"
 
 # Protobuf and gRPC
 prost = "0.12"
-tonic = "0.10"
-tonic-build = "0.10"
+tonic = { version = "0.10", default-features = false }
+tonic-build = { version = "0.10", default-features = false }
 
 # Secret management
 secrecy = "0.8"

zcash_client_backend/Cargo.toml

@@ -66,7 +66,7 @@ tracing.workspace = true
 # - Protobuf interfaces and gRPC bindings
 hex.workspace = true
 prost.workspace = true
-tonic = { workspace = true, optional = true }
+tonic = { workspace = true, optional = true, features = ["prost", "codegen"]}
 
 # - Secret management
 secrecy.workspace = true
@@ -102,7 +102,7 @@ crossbeam-channel.workspace = true
 rayon.workspace = true
 
 [build-dependencies]
-tonic-build.workspace = true
+tonic-build = { workspace = true, features = ["prost"]}
 which = "4"
 
 [dev-dependencies]
@@ -123,6 +123,9 @@ time = ">=0.3.22, <0.3.24" # time 0.3.24 has MSRV 1.67
 ## Enables the `tonic` gRPC client bindings for connecting to a `lightwalletd` server.
 lightwalletd-tonic = ["dep:tonic"]
 
+## Enables the `transport` feature of `tonic` producing a fully-featured client and server implementation
+lightwalletd-tonic-transport = ["lightwalletd-tonic", "tonic?/transport"]
+
 ## Enables receiving transparent funds and shielding them.
 transparent-inputs = [
     "dep:hdwallet",

zcash_client_backend/src/proto.rs

@@ -779,3 +779,16 @@ impl proposal::Proposal {
         }
     }
 }
+
+#[cfg(feature = "lightwalletd-tonic-transport")]
+impl service::compact_tx_streamer_client::CompactTxStreamerClient<tonic::transport::Channel> {
+    /// Attempt to create a new client by connecting to a given endpoint.
+    pub async fn connect<D>(dst: D) -> Result<Self, tonic::transport::Error>
+    where
+        D: TryInto<tonic::transport::Endpoint>,
+        D::Error: Into<tonic::codegen::StdError>,
+    {
+        let conn = tonic::transport::Endpoint::new(dst)?.connect().await?;
+        Ok(Self::new(conn))
+    }
+}