Optionally require alignment when reading IPC, respect alignment when…

… writing (#5554)

* fix

* Remove redundant alignment check

* fix typo

* Add comment about randomized testing

* add doc comment on enforce_zero_copy

* address alamb feedback

* be explicit

* fix unit tests

* fix arrow-flight tests

* clippy

* hide api change + add require_alignment to StreamDecoder too

* Preserve docs

---------

Co-authored-by: Raphael Taylor-Davies <r.taylordavies@googlemail.com>

arrow-buffer/src/buffer/scalar.rs

@@ -63,7 +63,7 @@ impl<T: ArrowNativeType> ScalarBuffer<T> {
     /// This method will panic if
     ///
     /// * `offset` or `len` would result in overflow
-    /// * `buffer` is not aligned to a multiple of `std::mem::size_of::<T>`
+    /// * `buffer` is not aligned to a multiple of `std::mem::align_of::<T>`
     /// * `bytes` is not large enough for the requested slice
     pub fn new(buffer: Buffer, offset: usize, len: usize) -> Self {
         let size = std::mem::size_of::<T>();

arrow-flight/src/encode.rs

@@ -627,6 +627,7 @@ mod tests {
     use arrow_array::{cast::downcast_array, types::*};
     use arrow_buffer::Buffer;
     use arrow_cast::pretty::pretty_format_batches;
+    use arrow_ipc::MetadataVersion;
     use arrow_schema::UnionMode;
     use std::collections::HashMap;
 
@@ -638,7 +639,8 @@ mod tests {
     /// ensure only the batch's used data (not the allocated data) is sent
     /// <https://github.com/apache/arrow-rs/issues/208>
     fn test_encode_flight_data() {
-        let options = IpcWriteOptions::default();
+        // use 8-byte alignment - default alignment is 64 which produces bigger ipc data
+        let options = IpcWriteOptions::try_new(8, false, MetadataVersion::V5).unwrap();
         let c1 = UInt32Array::from(vec![1, 2, 3, 4, 5, 6]);
 
         let batch = RecordBatch::try_from_iter(vec![("a", Arc::new(c1) as ArrayRef)])
@@ -1343,6 +1345,8 @@ mod tests {
 
             let mut stream = FlightDataEncoderBuilder::new()
                 .with_max_flight_data_size(max_flight_data_size)
+                // use 8-byte alignment - default alignment is 64 which produces bigger ipc data
+                .with_options(IpcWriteOptions::try_new(8, false, MetadataVersion::V5).unwrap())
                 .build(futures::stream::iter([Ok(batch.clone())]));
 
             let mut i = 0;