tustvold commented on code in PR #5531:
URL: https://github.com/apache/arrow-rs/pull/5531#discussion_r1536556140
##########
arrow-ipc/src/convert.rs:
##########
@@ -806,6 +811,45 @@ pub(crate) fn get_fb_dictionary<'a>(
builder.finish()
}
+/// An owned container for a validated [`Message`]
+///
+/// Safely decoding a flatbuffer requires validating the various embedded
offsets,
+/// see [`Verifier`]. This is a potentially expensive operation, and it is
therefore desirable
+/// to only do this once. [`crate::root_as_message`] performs this validation
on construction,
+/// however, it returns a [`Message`] borrowing the provided byte slice. This
prevents
+/// storing this [`Message`] in the same data structure that owns the buffer,
as this
+/// would require self-referential borrows.
+///
+/// [`MessageBuffer`] solves this problem by providing a safe API for a
[`Message`]
+/// without a lifetime bound.
+#[derive(Clone)]
+pub struct MessageBuffer(Buffer);
+
+impl Debug for MessageBuffer {
+ fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+ self.as_ref().fmt(f)
+ }
+}
+
+impl MessageBuffer {
+ /// Try to create a [`MessageBuffer`] from the provided [`Buffer`]
+ pub fn try_new(buf: Buffer) -> Result<Self, ArrowError> {
+ let opts = VerifierOptions::default();
+ let mut v = Verifier::new(&opts, &buf);
+ <ForwardsUOffset<Message>>::run_verifier(&mut v, 0).map_err(|err| {
+ ArrowError::ParseError(format!("Unable to get root as message:
{err:?}"))
+ })?;
+ Ok(Self(buf))
+ }
+
+ /// Return the [`Message`]
+ #[inline]
+ pub fn as_ref(&self) -> Message<'_> {
Review Comment:
Unfortunately this isn't possible because of the lifetime on `Message`
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