Implement native and WASM WebSocket client for sigsocket communication

- Added `NativeClient` for non-WASM environments with automatic reconnection and message handling.
- Introduced `WasmClient` for WASM environments, supporting WebSocket communication and reconnection logic.
- Created protocol definitions for `SignRequest` and `SignResponse` with serialization and deserialization.
- Developed integration tests for the client functionality and sign request handling.
- Implemented WASM-specific tests to ensure compatibility and functionality in browser environments.

sigsocket_client/examples/basic_usage.rs

@@ -0,0 +1,133 @@
+//! Basic usage example for sigsocket_client
+//!
+//! This example demonstrates how to:
+//! 1. Create a sigsocket client
+//! 2. Set up a sign request handler
+//! 3. Connect to a sigsocket server
+//! 4. Handle incoming signature requests
+//!
+//! This example only runs on native (non-WASM) targets.
+
+#[cfg(not(target_arch = "wasm32"))]
+use sigsocket_client::{SigSocketClient, SignRequest, SignResponse, SignRequestHandler, Result, SigSocketError};
+
+#[cfg(not(target_arch = "wasm32"))]
+/// Example sign request handler
+///
+/// In a real application, this would:
+/// - Present the request to the user
+/// - Get user approval
+/// - Use a secure signing method (hardware wallet, etc.)
+/// - Return the signature
+struct ExampleSignHandler;
+
+#[cfg(not(target_arch = "wasm32"))]
+impl SignRequestHandler for ExampleSignHandler {
+    fn handle_sign_request(&self, request: &SignRequest) -> Result<Vec<u8>> {
+        println!("📝 Received sign request:");
+        println!("   ID: {}", request.id);
+        println!("   Message (base64): {}", request.message);
+        
+        // Decode the message to show what we're signing
+        match request.message_bytes() {
+            Ok(message_bytes) => {
+                println!("   Message (hex): {}", hex::encode(&message_bytes));
+                println!("   Message (text): {}", String::from_utf8_lossy(&message_bytes));
+            }
+            Err(e) => {
+                println!("   ⚠️  Failed to decode message: {}", e);
+                return Err(SigSocketError::Base64(e.to_string()));
+            }
+        }
+
+        // In a real implementation, you would:
+        // 1. Show this to the user
+        // 2. Get user approval
+        // 3. Sign the message using a secure method
+        
+        println!("🤔 Would you like to sign this message? (This is a simulation)");
+        println!("✅ Auto-approving for demo purposes...");
+        
+        // Simulate signing - in reality, this would be a real signature
+        let fake_signature = format!("fake_signature_for_{}", request.id);
+        Ok(fake_signature.into_bytes())
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[tokio::main]
+async fn main() -> Result<()> {
+    // Initialize logging
+    env_logger::init();
+
+    println!("🚀 SigSocket Client Example");
+    println!("============================");
+
+    // Example public key (in a real app, this would be your actual public key)
+    let public_key = hex::decode("02f9308a019258c31049344f85f89d5229b531c845836f99b08601f113bce036f9388")
+        .expect("Invalid public key hex");
+
+    println!("🔑 Public key: {}", hex::encode(&public_key));
+
+    // Create the client
+    let mut client = SigSocketClient::new("ws://localhost:8080/ws", public_key)?;
+    println!("📡 Created client for: {}", client.url());
+
+    // Set up the sign request handler
+    client.set_sign_handler(ExampleSignHandler);
+    println!("✅ Sign request handler configured");
+
+    // Connect to the server
+    println!("🔌 Connecting to sigsocket server...");
+    match client.connect().await {
+        Ok(()) => {
+            println!("✅ Connected successfully!");
+            println!("📊 Connection state: {:?}", client.state());
+        }
+        Err(e) => {
+            println!("❌ Failed to connect: {}", e);
+            println!("💡 Make sure the sigsocket server is running on localhost:8080");
+            return Err(e);
+        }
+    }
+
+    // Keep the connection alive and handle requests
+    println!("👂 Listening for signature requests...");
+    println!("   (Press Ctrl+C to exit)");
+
+    // In a real application, you might want to:
+    // - Handle reconnection
+    // - Provide a UI for user interaction
+    // - Manage multiple concurrent requests
+    // - Store and manage signatures
+
+    // For this example, we'll just wait
+    tokio::signal::ctrl_c().await.expect("Failed to listen for ctrl-c");
+
+    println!("\n🛑 Shutting down...");
+    client.disconnect().await?;
+    println!("✅ Disconnected cleanly");
+
+    Ok(())
+}
+
+// Example of how you might manually send a response (if needed)
+#[cfg(not(target_arch = "wasm32"))]
+#[allow(dead_code)]
+async fn send_manual_response(client: &SigSocketClient) -> Result<()> {
+    let response = SignResponse::new(
+        "example-request-id",
+        "dGVzdCBtZXNzYWdl", // "test message" in base64
+        "ZmFrZV9zaWduYXR1cmU=", // "fake_signature" in base64
+    );
+
+    client.send_sign_response(&response).await?;
+    println!("📤 Sent manual response: {}", response.id);
+    Ok(())
+}
+
+// WASM main function (does nothing since this example is native-only)
+#[cfg(target_arch = "wasm32")]
+fn main() {
+    // This example is designed for native use only
+}