From e7457e61432e7a8259405e6fdaf5c952267d4296 Mon Sep 17 00:00:00 2001
From: Richard <richard.baah@datadoghq.com>
Date: Tue, 21 Jul 2026 16:03:23 -0400
Subject: [PATCH 1/2] fix off by one error for slice accounting

---
 arrow-data/src/data.rs | 52 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/arrow-data/src/data.rs b/arrow-data/src/data.rs
index 0e0ef9e9a482..08162e5977c9 100644
--- a/arrow-data/src/data.rs
+++ b/arrow-data/src/data.rs
@@ -530,7 +530,19 @@ impl ArrayData {
         for spec in layout.buffers.iter() {
             match spec {
                 BufferSpec::FixedWidth { byte_width, .. } => {
-                    let buffer_size = self.len.checked_mul(*byte_width).ok_or_else(|| {
+                    // Offset buffers contain len+1 elements: one boundary per element
+                    // plus a final boundary marking the end of the last element.
+                    let len = match self.data_type {
+                        DataType::Utf8
+                        | DataType::LargeUtf8
+                        | DataType::Binary
+                        | DataType::LargeBinary
+                        | DataType::List(_)
+                        | DataType::LargeList(_)
+                        | DataType::Map(_, _) => self.len + 1,
+                        _ => self.len,
+                    };
+                    let buffer_size = len.checked_mul(*byte_width).ok_or_else(|| {
                         ArrowError::ComputeError(
                             "Integer overflow computing buffer size".to_string(),
                         )
@@ -2616,6 +2628,44 @@ mod tests {
         assert!(!string_data_slice.ptr_eq(&string_data))
     }
 
+    #[test]
+    fn test_slice_memory_size_utf8_offset_buffer_len_plus_one() {
+        // 2-element array ["hello", "world"]: array len = 2, 10 bytes
+        let data_buffer = Buffer::from_slice_ref("helloworld".as_bytes());
+        // offsets need array_len+1 entries to mark the end of every string:
+        //   [0, 5, 10] -> 3 i32s = 12 bytes
+        let offsets_buffer = Buffer::from_slice_ref([0_i32, 5_i32, 10_i32]);
+        let array = ArrayData::try_new(
+            DataType::Utf8,
+            2,
+            None,
+            0,
+            vec![offsets_buffer, data_buffer],
+            vec![],
+        )
+        .unwrap();
+        assert_eq!(array.get_slice_memory_size().unwrap(), 22); // 12 + 10
+    }
+
+    #[test]
+    fn test_slice_memory_size_binary_offset_buffer_len_plus_one() {
+        // 2-element array: array len = 2, not 3
+        // values: 5 bytes
+        let data_buffer = Buffer::from_slice_ref(&[0u8, 1, 2, 3, 4]);
+        // offsets need array_len+1 entries to mark the end of every element:
+        let offsets_buffer = Buffer::from_slice_ref([0_i32, 2_i32, 5_i32]);
+        let array = ArrayData::try_new(
+            DataType::Binary,
+            2,
+            None,
+            0,
+            vec![offsets_buffer, data_buffer],
+            vec![],
+        )
+        .unwrap();
+        assert_eq!(array.get_slice_memory_size().unwrap(), 17); // 12 + 5
+    }
+
     #[test]
     fn test_slice_memory_size() {
         let mut bit_v: [u8; 2] = [0; 2];

From ee32ab0d82047a0b24c4bbe4b8a2fa2bf2d71bd0 Mon Sep 17 00:00:00 2001
From: Richard <richard.baah@datadoghq.com>
Date: Tue, 21 Jul 2026 16:24:03 -0400
Subject: [PATCH 2/2] fix clippy

---
 arrow-data/src/data.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arrow-data/src/data.rs b/arrow-data/src/data.rs
index 08162e5977c9..8a037bc0f54c 100644
--- a/arrow-data/src/data.rs
+++ b/arrow-data/src/data.rs
@@ -2651,7 +2651,7 @@ mod tests {
     fn test_slice_memory_size_binary_offset_buffer_len_plus_one() {
         // 2-element array: array len = 2, not 3
         // values: 5 bytes
-        let data_buffer = Buffer::from_slice_ref(&[0u8, 1, 2, 3, 4]);
+        let data_buffer = Buffer::from_slice_ref([0u8, 1, 2, 3, 4]);
         // offsets need array_len+1 entries to mark the end of every element:
         let offsets_buffer = Buffer::from_slice_ref([0_i32, 2_i32, 5_i32]);
         let array = ArrayData::try_new(