feat: support per-request header override (#2631)

## Summary

This PR introduces a `HeaderProvider` which is called for all remote
HTTP calls to get the latest headers to inject. This is useful for
features like adding the latest auth tokens where the header provider
can auto-refresh tokens internally and each request always set the
refreshed token.

---------

Co-authored-by: Claude <noreply@anthropic.com>

nodejs/src/connection.rs

@@ -2,12 +2,14 @@
 // SPDX-FileCopyrightText: Copyright The LanceDB Authors
 
 use std::collections::HashMap;
+use std::sync::Arc;
 
 use lancedb::database::CreateTableMode;
 use napi::bindgen_prelude::*;
 use napi_derive::*;
 
 use crate::error::NapiErrorExt;
+use crate::header::JsHeaderProvider;
 use crate::table::Table;
 use crate::ConnectionOptions;
 use lancedb::connection::{ConnectBuilder, Connection as LanceDBConnection};
@@ -45,7 +47,11 @@ impl Connection {
 impl Connection {
     /// Create a new Connection instance from the given URI.
     #[napi(factory)]
-    pub async fn new(uri: String, options: ConnectionOptions) -> napi::Result<Self> {
+    pub async fn new(
+        uri: String,
+        options: ConnectionOptions,
+        header_provider: Option<&JsHeaderProvider>,
+    ) -> napi::Result<Self> {
         let mut builder = ConnectBuilder::new(&uri);
         if let Some(interval) = options.read_consistency_interval {
             builder =
@@ -57,8 +63,16 @@ impl Connection {
             }
         }
 
+        // Create client config, optionally with header provider
         let client_config = options.client_config.unwrap_or_default();
-        builder = builder.client_config(client_config.into());
+        let mut rust_config: lancedb::remote::ClientConfig = client_config.into();
+
+        if let Some(provider) = header_provider {
+            rust_config.header_provider =
+                Some(Arc::new(provider.clone()) as Arc<dyn lancedb::remote::HeaderProvider>);
+        }
+
+        builder = builder.client_config(rust_config);
 
         if let Some(api_key) = options.api_key {
             builder = builder.api_key(&api_key);

nodejs/src/header.rs

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+use napi::{
+    bindgen_prelude::*,
+    threadsafe_function::{ErrorStrategy, ThreadsafeFunction},
+};
+use napi_derive::napi;
+use std::collections::HashMap;
+use std::sync::Arc;
+
+/// JavaScript HeaderProvider implementation that wraps a JavaScript callback.
+/// This is the only native header provider - all header provider implementations
+/// should provide a JavaScript function that returns headers.
+#[napi]
+pub struct JsHeaderProvider {
+    get_headers_fn: Arc<ThreadsafeFunction<(), ErrorStrategy::CalleeHandled>>,
+}
+
+impl Clone for JsHeaderProvider {
+    fn clone(&self) -> Self {
+        Self {
+            get_headers_fn: self.get_headers_fn.clone(),
+        }
+    }
+}
+
+#[napi]
+impl JsHeaderProvider {
+    /// Create a new JsHeaderProvider from a JavaScript callback
+    #[napi(constructor)]
+    pub fn new(get_headers_callback: JsFunction) -> Result<Self> {
+        let get_headers_fn = get_headers_callback
+            .create_threadsafe_function(0, |ctx| Ok(vec![ctx.value]))
+            .map_err(|e| {
+                Error::new(
+                    Status::GenericFailure,
+                    format!("Failed to create threadsafe function: {}", e),
+                )
+            })?;
+
+        Ok(Self {
+            get_headers_fn: Arc::new(get_headers_fn),
+        })
+    }
+}
+
+#[cfg(feature = "remote")]
+#[async_trait::async_trait]
+impl lancedb::remote::HeaderProvider for JsHeaderProvider {
+    async fn get_headers(&self) -> lancedb::error::Result<HashMap<String, String>> {
+        // Call the JavaScript function asynchronously
+        let promise: Promise<HashMap<String, String>> =
+            self.get_headers_fn.call_async(Ok(())).await.map_err(|e| {
+                lancedb::error::Error::Runtime {
+                    message: format!("Failed to call JavaScript get_headers: {}", e),
+                }
+            })?;
+
+        // Await the promise result
+        promise.await.map_err(|e| lancedb::error::Error::Runtime {
+            message: format!("JavaScript get_headers failed: {}", e),
+        })
+    }
+}
+
+impl std::fmt::Debug for JsHeaderProvider {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "JsHeaderProvider")
+    }
+}

nodejs/src/lib.rs

@@ -8,6 +8,7 @@ use napi_derive::*;
 
 mod connection;
 mod error;
+mod header;
 mod index;
 mod iterator;
 pub mod merge;

nodejs/src/remote.rs

@@ -144,6 +144,7 @@ impl From<ClientConfig> for lancedb::remote::ClientConfig {
             extra_headers: config.extra_headers.unwrap_or_default(),
             id_delimiter: config.id_delimiter,
             tls_config: config.tls_config.map(Into::into),
+            header_provider: None, // the header provider is set separately later
         }
     }
 }