Avoid useless memory copies in IPC reader.

arrow/src/ipc/compression/codec.rs

@@ -92,18 +92,16 @@ impl CompressionCodec {
     /// [8 bytes]:         uncompressed length
     /// [remaining bytes]: compressed data stream
     /// ```
-    pub(crate) fn decompress_to_buffer(&self, input: &[u8]) -> Result<Buffer> {
+    pub(crate) fn decompress_to_buffer(&self, input: &Buffer) -> Result<Buffer> {
         // read the first 8 bytes to determine if the data is
         // compressed
         let decompressed_length = read_uncompressed_size(input);
         let buffer = if decompressed_length == 0 {
             // emtpy
-            let empty = Vec::<u8>::new();
-            Buffer::from(empty)
+            Buffer::from([])
         } else if decompressed_length == LENGTH_NO_COMPRESSED_DATA {
             // no compression
-            let data = &input[(LENGTH_OF_PREFIX_DATA as usize)..];
-            Buffer::from(data)
+            input.slice(LENGTH_OF_PREFIX_DATA as usize)
         } else {
             // decompress data using the codec
             let mut uncompressed_buffer =

arrow/src/ipc/reader.rs

@@ -53,14 +53,11 @@ fn read_buffer(
 ) -> Result<Buffer> {
     let start_offset = buf.offset() as usize;
     let end_offset = start_offset + buf.length() as usize;
-    let buf_data = &a_data[start_offset..end_offset];
+    let buf_data = Buffer::from(&a_data[start_offset..end_offset]);
     // corner case: empty buffer
-    if buf_data.is_empty() {
-        return Ok(Buffer::from(buf_data));
-    }
-    match compression_codec {
-        Some(decompressor) => decompressor.decompress_to_buffer(buf_data),
-        None => Ok(Buffer::from(buf_data)),
+    match (buf_data.is_empty(), compression_codec) {
+        (true, _) | (_, None) => Ok(buf_data),
+        (false, Some(decompressor)) => decompressor.decompress_to_buffer(&buf_data),
     }
 }