fix: EC encode reads .idx from separate index directory

write_ec_files now accepts an idx_dir parameter so it can find the .idx
file when --dir.idx is configured. Previously it looked for .idx in the
data directory, which failed when a separate index directory was in use.

seaweed-volume/src/server/grpc_server.rs

@@ -1649,7 +1649,7 @@ impl VolumeServer for VolumeGrpcService {
         let collection = &req.collection;
 
         // Find the volume's directory and validate collection
-        let (dir, vol_version, dat_file_size) = {
+        let (dir, idx_dir, vol_version, dat_file_size) = {
             let store = self.state.store.read().unwrap();
             let (loc_idx, vol) = store
                 .find_volume(vid)
@@ -1664,6 +1664,7 @@ impl VolumeServer for VolumeGrpcService {
             let dat_size = vol.dat_file_size().unwrap_or(0) as i64;
             (
                 store.locations[loc_idx].directory.clone(),
+                store.locations[loc_idx].idx_directory.clone(),
                 version,
                 dat_size,
             )
@@ -1692,6 +1693,7 @@ impl VolumeServer for VolumeGrpcService {
 
         crate::storage::erasure_coding::ec_encoder::write_ec_files(
             &dir,
+            &idx_dir,
             collection,
             vid,
             data_shards as usize,

seaweed-volume/src/storage/erasure_coding/ec_decoder.rs

@@ -216,7 +216,7 @@ mod tests {
         // Encode to EC
         let data_shards = 10;
         let parity_shards = 4;
-        ec_encoder::write_ec_files(dir, "", VolumeId(1), data_shards, parity_shards).unwrap();
+        ec_encoder::write_ec_files(dir, dir, "", VolumeId(1), data_shards, parity_shards).unwrap();
 
         // Delete original .dat and .idx
         std::fs::remove_file(format!("{}/1.dat", dir)).unwrap();

seaweed-volume/src/storage/erasure_coding/ec_encoder.rs

@@ -21,6 +21,7 @@ use crate::storage::volume::volume_file_name;
 /// Also creates a sorted .ecx index from the .idx file.
 pub fn write_ec_files(
     dir: &str,
+    idx_dir: &str,
     collection: &str,
     volume_id: VolumeId,
     data_shards: usize,
@@ -28,7 +29,8 @@ pub fn write_ec_files(
 ) -> io::Result<()> {
     let base = volume_file_name(dir, collection, volume_id);
     let dat_path = format!("{}.dat", base);
-    let idx_path = format!("{}.idx", base);
+    let idx_base = volume_file_name(idx_dir, collection, volume_id);
+    let idx_path = format!("{}.idx", idx_base);
 
     // Create sorted .ecx from .idx
     write_sorted_ecx_from_idx(&idx_path, &format!("{}.ecx", base))?;
@@ -481,7 +483,7 @@ mod tests {
         let data_shards = 10;
         let parity_shards = 4;
         let total_shards = data_shards + parity_shards;
-        write_ec_files(dir, "", VolumeId(1), data_shards, parity_shards).unwrap();
+        write_ec_files(dir, dir, "", VolumeId(1), data_shards, parity_shards).unwrap();
 
         // Verify shard files exist
         for i in 0..total_shards {