splix commented on code in PR #530:
URL: https://github.com/apache/avro-rs/pull/530#discussion_r3038876846
##########
avro/src/reader/block.rs:
##########
@@ -35,10 +35,57 @@ use crate::{
util,
};
+/// Byte offset and record count of a single Avro data block.
+///
+/// Captured automatically as blocks are read during forward iteration.
+/// Use with [`super::Reader::seek_to_block`] to jump back to a
previously-read block.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct BlockPosition {
+ /// Byte offset in the stream where this block starts (before the
object-count varint).
+ pub offset: u64,
+ /// Total number of records in this block.
+ pub message_count: usize,
+}
+
+/// Wraps an inner reader and tracks the current byte position.
+///
+/// Avoids requiring `Seek` just to know how many bytes have been consumed.
+/// When the inner reader also implements `Seek`, seeking updates the tracked
position.
+#[derive(Debug, Clone)]
+struct PositionTracker<R> {
+ inner: R,
+ pos: u64,
+}
+
+impl<R> PositionTracker<R> {
+ fn new(inner: R) -> Self {
+ Self { inner, pos: 0 }
+ }
+
+ fn position(&self) -> u64 {
+ self.pos
+ }
+}
+
+impl<R: Read> Read for PositionTracker<R> {
+ fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+ let n = self.inner.read(buf)?;
+ self.pos += n as u64;
+ Ok(n)
+ }
Review Comment:
Is there any common examples for this behavior?
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