feat(writer): add delta writer (#18)

Co-authored-by: ZENOTME <st810918843@gmail.com>

Author: ZENOTME

crates/iceberg/src/writer/base_writer/data_file_writer.rs

@@ -20,7 +20,7 @@
 use arrow_array::RecordBatch;
 use itertools::Itertools;
 
-use crate::spec::{DataContentType, DataFile, Struct};
+use crate::spec::{DataContentType, DataFile, SchemaRef, Struct};
 use crate::writer::file_writer::{FileWriter, FileWriterBuilder};
 use crate::writer::{CurrentFileStatus, IcebergWriter, IcebergWriterBuilder};
 use crate::Result;
@@ -99,6 +99,10 @@ impl<B: FileWriterBuilder> CurrentFileStatus for DataFileWriter<B> {
     fn current_written_size(&self) -> usize {
         self.inner_writer.as_ref().unwrap().current_written_size()
     }
+
+    fn current_schema(&self) -> SchemaRef {
+        self.inner_writer.as_ref().unwrap().current_schema()
+    }
 }
 
 #[cfg(test)]

crates/iceberg/src/writer/file_writer/parquet_writer.rs

@@ -548,6 +548,10 @@ impl CurrentFileStatus for ParquetWriter {
     fn current_written_size(&self) -> usize {
         self.written_size.load(std::sync::atomic::Ordering::Relaxed) as usize
     }
+
+    fn current_schema(&self) -> SchemaRef {
+        self.schema.clone()
+    }
 }
 
 /// AsyncFileWriter is a wrapper of FileWrite to make it compatible with tokio::io::AsyncWrite.