[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #2040: Truncate IPC record batch

[GitBox <gi...@apache.org>]

HaoYang670 commented on code in PR #2040:
URL: https://github.com/apache/arrow-rs/pull/2040#discussion_r917592629


##########
arrow/src/ipc/writer.rs:
##########
@@ -861,6 +863,145 @@ fn has_validity_bitmap(data_type: &DataType, write_options: &IpcWriteOptions) ->
     }
 }
 
+/// Whether to truncate the buffer
+#[inline]
+fn buffer_need_truncate(
+    array_offset: usize,
+    buffer: &Buffer,
+    spec: &BufferSpec,
+    min_length: usize,
+) -> bool {
+    if spec == &BufferSpec::AlwaysNull {
+        false
+    } else {
+        array_offset != 0 || min_length < buffer.len()
+    }
+}
+
+/// Returns byte width for a buffer spec. Only for `BufferSpec::FixedWidth`.
+#[inline]
+fn get_buffer_byte_width(spec: &BufferSpec) -> usize {
+    match spec {
+        BufferSpec::FixedWidth { byte_width } => *byte_width,
+        _ => 0,
+    }
+}
+
+/// Returns the number of total bytes in base binary arrays.
+fn get_total_bytes(array_data: &ArrayData) -> usize {
+    if array_data.is_empty() {
+        return 0;
+    }
+    match array_data.data_type() {
+        DataType::Binary => {
+            let array: BinaryArray = array_data.clone().into();
+            let offsets = array.value_offsets();
+            (offsets[array_data.len()] - offsets[0]) as usize

Review Comment:
   Is this corrent when `array_data.offset() > 0`?



##########
arrow/src/ipc/writer.rs:
##########
@@ -861,6 +863,145 @@ fn has_validity_bitmap(data_type: &DataType, write_options: &IpcWriteOptions) ->
     }
 }
 
+/// Whether to truncate the buffer
+#[inline]
+fn buffer_need_truncate(
+    array_offset: usize,
+    buffer: &Buffer,
+    spec: &BufferSpec,
+    min_length: usize,
+) -> bool {
+    if spec == &BufferSpec::AlwaysNull {
+        false
+    } else {
+        array_offset != 0 || min_length < buffer.len()
+    }
+}

Review Comment:
   nit: (not tested)
   ```rust
   spec != &BufferSpec::AlwaysNull && (array_offset != 0 || min_length < buffer.len())
   ```



##########
arrow/src/ipc/writer.rs:
##########
@@ -1507,4 +1702,60 @@ mod tests {
             IpcWriteOptions::try_new(8, false, MetadataVersion::V5).unwrap(),
         );
     }
+
+    #[test]
+    fn truncate_ipc_record_batch() {
+        pub fn serialize(record: &RecordBatch) -> Vec<u8> {

Review Comment:
   Why do we need this function to be public?



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