feat(client): allow constructing without connecting

src/client.rs

@@ -34,7 +34,7 @@ pub enum ClientType {
 /// Generalized Electrum client that supports multiple backends. Can re-instantiate client_type if connections
 /// drops
 pub struct Client {
-    client_type: RwLock<ClientType>,
+    client_type: RwLock<Option<ClientType>>,
     config: Config,
     url: String,
 }
@@ -44,8 +44,9 @@ macro_rules! impl_inner_call {
     {
         let mut errors = vec![];
         loop {
+            $self.connect()?;
             let read_client = $self.client_type.read().unwrap();
-            let res = match &*read_client {
+            let res = match read_client.as_ref().expect("connect populated client") {
                 ClientType::TCP(inner) => inner.$name( $($args, )* ),
                 #[cfg(any(feature = "openssl", feature = "rustls", feature = "rustls-ring"))]
                 ClientType::SSL(inner) => inner.$name( $($args, )* ),
@@ -79,7 +80,7 @@ macro_rules! impl_inner_call {
                             match ClientType::from_config(&$self.url, &$self.config) {
                                 Ok(new_client) => {
                                     info!("Succesfully created new client");
-                                    *write_client = new_client;
+                                    *write_client = Some(new_client);
                                     break;
                                 },
                                 Err(e) => {
@@ -199,15 +200,41 @@ impl Client {
 
     /// Generic constructor that supports multiple backends and allows configuration through
     /// the [Config]
+    ///
+    /// This stores the URL and configuration without opening a network connection.
     pub fn from_config(url: &str, config: Config) -> Result<Self, Error> {
-        let client_type = RwLock::new(ClientType::from_config(url, &config)?);
+        #[cfg(not(any(feature = "openssl", feature = "rustls", feature = "rustls-ring")))]
+        if url.starts_with("ssl://") {
+            return Err(Error::Message(
+                "SSL connections require one of the following features to be enabled: openssl, rustls, or rustls-ring".to_string()
+            ));
+        }
 
         Ok(Client {
-            client_type,
+            client_type: RwLock::new(None),
             config,
             url: url.to_string(),
         })
     }
+
+    /// Establishes the Electrum connection and negotiates the protocol version.
+    ///
+    /// Does nothing if the client is already connected.
+    pub fn connect(&self) -> Result<(), Error> {
+        {
+            let client_type = self.client_type.read().unwrap();
+            if client_type.is_some() {
+                return Ok(());
+            }
+        }
+
+        let mut client_type = self.client_type.write().unwrap();
+        if client_type.is_none() {
+            *client_type = Some(ClientType::from_config(&self.url, &self.config)?);
+        }
+
+        Ok(())
+    }
 }
 
 impl ElectrumApi for Client {
@@ -434,6 +461,28 @@ impl ElectrumApi for Client {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::io::{BufRead, BufReader, ErrorKind, Write};
+    use std::net::TcpListener;
+    use std::thread;
+
+    const VERSION_RESPONSE: &[u8] = br#"{"jsonrpc":"2.0","result":["test-server","1.6"],"id":0}"#;
+    const FEATURES_RESPONSE: &[u8] =
+        br#"{"jsonrpc":"2.0","result":{"server_version":"test-server","genesis_hash":"0000000000000000000000000000000000000000000000000000000000000000","protocol_min":"1.4","protocol_max":"1.6","hash_function":"sha256","pruning":null},"id":1}"#;
+
+    fn listener_url(listener: &TcpListener) -> String {
+        format!("tcp://{}", listener.local_addr().unwrap())
+    }
+
+    fn read_request(reader: &mut impl BufRead) -> String {
+        let mut request = String::new();
+        reader.read_line(&mut request).unwrap();
+        request
+    }
+
+    fn write_response(stream: &mut impl Write, response: &[u8]) {
+        stream.write_all(response).unwrap();
+        stream.write_all(b"\n").unwrap();
+    }
 
     #[test]
     fn more_failed_attempts_than_retries_means_exhausted() {
@@ -464,4 +513,69 @@ mod tests {
 
         assert!(!exhausted)
     }
+
+    #[test]
+    fn client_constructor_does_not_connect() {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        listener.set_nonblocking(true).unwrap();
+        let url = listener_url(&listener);
+
+        let client = Client::new(&url).unwrap();
+
+        assert!(client.client_type.read().unwrap().is_none());
+        match listener.accept() {
+            Ok(_) => panic!("constructor opened a connection"),
+            Err(err) if err.kind() == ErrorKind::WouldBlock => {}
+            Err(err) => panic!("unexpected accept error: {err}"),
+        }
+    }
+
+    #[test]
+    fn client_connect_opens_connection_and_negotiates_protocol() {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let url = listener_url(&listener);
+        let server = thread::spawn(move || {
+            let (mut stream, _) = listener.accept().unwrap();
+            let mut reader = BufReader::new(stream.try_clone().unwrap());
+            let request = read_request(&mut reader);
+            write_response(&mut stream, VERSION_RESPONSE);
+
+            request
+        });
+
+        let client = Client::new(&url).unwrap();
+
+        client.connect().unwrap();
+
+        assert!(client.client_type.read().unwrap().is_some());
+        let request = server.join().unwrap();
+        assert!(request.contains(r#""method":"server.version""#));
+    }
+
+    #[test]
+    fn first_api_call_connects_before_dispatching_request() {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let url = listener_url(&listener);
+        let server = thread::spawn(move || {
+            let (mut stream, _) = listener.accept().unwrap();
+            let mut reader = BufReader::new(stream.try_clone().unwrap());
+
+            let version_request = read_request(&mut reader);
+            write_response(&mut stream, VERSION_RESPONSE);
+
+            let features_request = read_request(&mut reader);
+            write_response(&mut stream, FEATURES_RESPONSE);
+
+            (version_request, features_request)
+        });
+
+        let client = Client::new(&url).unwrap();
+
+        let features = client.server_features().unwrap();
+
+        assert_eq!(features.server_version, "test-server");
+        let (version_request, features_request) = server.join().unwrap();
+        assert!(version_request.contains(r#""method":"server.version""#));
+        assert!(features_request.contains(r#""method":"server.features""#));
+    }
 }