feat(client): opt-in connection check on Qdrant::build()

src/qdrant_client/config.rs

@@ -39,6 +39,14 @@ pub struct QdrantConfig {
     /// Whether to check compatibility between the client and server versions
     pub check_compatibility: bool,
 
+    /// Whether to verify connectivity to the Qdrant server when building the client.
+    ///
+    /// gRPC connections are established lazily, so by default building a client
+    /// succeeds even when the server is unreachable; connection errors only surface
+    /// on the first request. When enabled, [`build`](Self::build) performs a health
+    /// check and returns an error if the server cannot be reached.
+    pub check_connection: bool,
+
     /// Amount of concurrent connections.
     /// If set to 0 or 1, connection pools will be disabled.
     pub pool_size: usize,
@@ -207,11 +215,37 @@ impl QdrantConfig {
         self
     }
 
+    /// Verify connectivity to the Qdrant server when building the client.
+    ///
+    /// gRPC connections are established lazily, so [`build`](Self::build) normally
+    /// succeeds even when the server is unreachable; connection failures would only
+    /// be observed on the first API call. Enabling this makes `build` perform a
+    /// health check and return an error if the server cannot be reached.
+    ///
+    /// ```rust,no_run
+    /// use qdrant_client::Qdrant;
+    ///
+    /// let client = Qdrant::from_url("http://localhost:6334")
+    ///     .check_connection()
+    ///     .build();
+    /// ```
+    pub fn check_connection(mut self) -> Self {
+        self.check_connection = true;
+        self
+    }
+
     /// Set the pool size of concurrent connections.
     /// If set to 0 or 1, connection pools will be disabled.
     pub fn set_pool_size(&mut self, pool_size: usize) {
         self.pool_size = pool_size;
     }
+
+    /// Set whether to verify connectivity to the server when building the client.
+    ///
+    /// Also see [`check_connection()`](fn@Self::check_connection).
+    pub fn set_check_connection(&mut self, check_connection: bool) {
+        self.check_connection = check_connection;
+    }
 }
 
 /// Default Qdrant client configuration.
@@ -227,6 +261,7 @@ impl Default for QdrantConfig {
             api_key: None,
             compression: None,
             check_compatibility: true,
+            check_connection: false,
             pool_size: 3,
             custom_headers: Vec::new(),
         }

src/qdrant_client/mod.rs

@@ -99,22 +99,22 @@ impl Qdrant {
     ///
     /// Constructs the client and connects based on the given [`QdrantConfig`](config::QdrantConfig).
     pub fn new(config: QdrantConfig) -> QdrantResult<Self> {
-        if config.check_compatibility {
-            // create a temporary client to check compatibility
+        if config.check_compatibility || config.check_connection {
+            // create a temporary client to check connectivity and/or compatibility
             let channel = ChannelPool::new(
                 config.uri.parse::<Uri>()?,
                 config.timeout,
                 config.connect_timeout,
                 config.keep_alive_while_idle,
-                1, // No need to create a pool for the compatibility check.
+                1, // No need to create a pool for the health check.
             );
             let client = Self {
                 channel: Arc::new(channel),
                 config: config.clone(),
             };
 
             // We're in sync context, spawn temporary runtime in thread to do async health check
-            let server_version = thread::scope(|s| {
+            let health_check = thread::scope(|s| {
                 s.spawn(|| {
                     tokio::runtime::Builder::new_current_thread()
                         .enable_io()
@@ -125,24 +125,36 @@ impl Qdrant {
                 })
                 .join()
                 .expect("Failed to join health check thread")
-            })
-            .ok()
-            .map(|info| info.version);
-
-            let client_version = env!("CARGO_PKG_VERSION").to_string();
-            if let Some(server_version) = server_version {
-                let is_compatible = is_compatible(Some(&client_version), Some(&server_version));
-                if !is_compatible {
-                    println!("Client version {client_version} is not compatible with server version {server_version}. \
-                    Major versions should match and minor version difference must not exceed 1. \
-                    Set check_compatibility=false to skip version check.");
+            });
+
+            // When connection checking is requested, surface connection errors eagerly
+            // instead of silently deferring them to the first API call.
+            let server_version = match health_check {
+                Ok(info) => Some(info.version),
+                Err(err) => {
+                    if config.check_connection {
+                        return Err(err);
+                    }
+                    None
+                }
+            };
+
+            if config.check_compatibility {
+                let client_version = env!("CARGO_PKG_VERSION").to_string();
+                if let Some(server_version) = server_version {
+                    let is_compatible = is_compatible(Some(&client_version), Some(&server_version));
+                    if !is_compatible {
+                        println!("Client version {client_version} is not compatible with server version {server_version}. \
+                        Major versions should match and minor version difference must not exceed 1. \
+                        Set check_compatibility=false to skip version check.");
+                    }
+                } else {
+                    println!(
+                        "Failed to obtain server version. \
+                        Unable to check client-server compatibility. \
+                        Set check_compatibility=false to skip version check."
+                    );
                 }
-            } else {
-                println!(
-                    "Failed to obtain server version. \
-                    Unable to check client-server compatibility. \
-                    Set check_compatibility=false to skip version check."
-                );
             }
         }
 
@@ -253,3 +265,35 @@ impl Qdrant {
         .await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use super::*;
+
+    // Nothing listens on this port, so a connection attempt is refused quickly;
+    // these tests do not require a running Qdrant server.
+    const UNREACHABLE_URL: &str = "http://127.0.0.1:6999";
+
+    #[test]
+    fn build_without_connection_check_succeeds_when_server_is_down() {
+        // gRPC connects lazily; without a connection check, building the client
+        // must succeed even when no server is reachable.
+        let client = Qdrant::from_url(UNREACHABLE_URL)
+            .skip_compatibility_check()
+            .build();
+        assert!(client.is_ok());
+    }
+
+    #[test]
+    fn build_with_connection_check_fails_when_server_is_down() {
+        // With connection checking enabled, building must fail eagerly when the
+        // server is unreachable (issue #258).
+        let result = Qdrant::from_url(UNREACHABLE_URL)
+            .check_connection()
+            .connect_timeout(Duration::from_secs(1))
+            .build();
+        assert!(result.is_err());
+    }
+}