scovich commented on code in PR #7535:
URL: https://github.com/apache/arrow-rs/pull/7535#discussion_r2104449497


##########
parquet-variant/src/utils.rs:
##########
@@ -0,0 +1,42 @@
+use std::{array::TryFromSliceError, ops::Range};
+
+use arrow_schema::ArrowError;
+
+#[inline]
+pub(crate) fn slice_from_slice(bytes: &[u8], range: Range<usize>) -> 
Result<&[u8], ArrowError> {
+    bytes.get(range.clone()).ok_or_else(|| {
+        ArrowError::InvalidArgumentError(format!(
+            "Tried to extract {} bytes at offset {} from {}-byte buffer",
+            range.end - range.start,
+            range.start,
+            bytes.len(),
+        ))
+    })
+}
+pub(crate) fn array_from_slice<const N: usize>(
+    bytes: &[u8],
+    offset: usize,
+) -> Result<[u8; N], ArrowError> {
+    let bytes = slice_from_slice(bytes, offset..offset + N)?;
+    bytes.try_into().map_err(map_try_from_slice_error)
+}
+
+/// To be used in `map_err` when unpacking an integer from a slice of bytes.
+pub(crate) fn map_try_from_slice_error(e: TryFromSliceError) -> ArrowError {
+    ArrowError::InvalidArgumentError(e.to_string())
+}
+
+pub(crate) fn non_empty_slice(slice: &[u8]) -> Result<&[u8], ArrowError> {
+    if slice.is_empty() {
+        return Err(ArrowError::InvalidArgumentError(
+            "Received empty bytes".to_string(),
+        ));
+    } else {
+        return Ok(slice);
+    }

Review Comment:
   Could also just add `.map(Copy::copy)` to the chain to make callers' lives 
easier?



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