From 4c29007f111a6a147f532c408fbb84761e722dd7 Mon Sep 17 00:00:00 2001
From: Xiangpeng Hao <me@haoxp.xyz>
Date: Sun, 17 Mar 2024 22:48:03 +0000
Subject: [PATCH] fix variadic counting

---
 arrow-ipc/src/reader.rs | 3 ++-
 arrow-ipc/src/writer.rs | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arrow-ipc/src/reader.rs b/arrow-ipc/src/reader.rs
index c4d9703847e5..d9d474d5d3f4 100644
--- a/arrow-ipc/src/reader.rs
+++ b/arrow-ipc/src/reader.rs
@@ -87,7 +87,7 @@ fn create_array(
             let count = variadic_counts
                 .pop_front()
                 .expect("Incorrect variadic count!");
-            let count = count + 1; // add the null buffer.
+            let count = count + 2; // view and null buffer.
             let buffers = (0..count)
                 .map(|_| reader.next_buffer())
                 .collect::<Result<Vec<_>, _>>()?;
@@ -360,6 +360,7 @@ impl<'a> ArrayReader<'a> {
                 let count = variadic_count
                     .pop_front()
                     .expect("Incorrect variadic count!");
+                let count = count + 2; // view and null buffer.
                 for _i in 0..count {
                     self.skip_buffer()
                 }
diff --git a/arrow-ipc/src/writer.rs b/arrow-ipc/src/writer.rs
index c5632f0ddc34..46dd17c3e805 100644
--- a/arrow-ipc/src/writer.rs
+++ b/arrow-ipc/src/writer.rs
@@ -567,7 +567,10 @@ impl IpcDataGenerator {
 fn set_variadic_buffer_counts(counts: &mut Vec<i64>, array: &dyn Array) {
     match array.data_type() {
         DataType::BinaryView | DataType::Utf8View => {
-            counts.push(array.to_data().buffers().len() as i64);
+            // The spec is not clear on whether the view/null buffer should be included in the variadic buffer count.
+            // But from C++ impl https://github.com/apache/arrow/blob/b448b33808f2dd42866195fa4bb44198e2fc26b9/cpp/src/arrow/ipc/writer.cc#L477
+            // we know they are not included.
+            counts.push(array.to_data().buffers().len() as i64 - 1);
         }
         DataType::Struct(_) => {
             let array = array.as_any().downcast_ref::<StructArray>().unwrap();