[pbs-devel] [RFC proxmox-backup 09/20] fix #3174: index: add fn index list from start/end-offsets

[Christian Ebner <c.ebner@proxmox.com>]

Adds a function to get a list of DynamicEntry's from a chunk index by
given start and end offset, which should be contained within these
chunks.
This is needed in order to reference file payloads and reuse the
chunks containing them from a previous backup run.

The index entries are normalized, meaning each entrys end is equal to
the chunk size.

In addition to the list of index entries, the padding to the start of
the requested start offset from the first chunk as well as the total
size are returned, these are needed to update the encoder position
when reusing the chunks and calculating the offsets for decoding.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-datastore/src/dynamic_index.rs | 33 ++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/pbs-datastore/src/dynamic_index.rs b/pbs-datastore/src/dynamic_index.rs
index 71a5082e..59e57160 100644
--- a/pbs-datastore/src/dynamic_index.rs
+++ b/pbs-datastore/src/dynamic_index.rs
@@ -188,6 +188,39 @@ impl DynamicIndexReader {
             self.binary_search(middle_idx + 1, middle_end, end_idx, end, offset)
         }
     }
+
+    /// List of chunk indices containing the data from start_offset to end_offset
+    pub fn indices(
+        &self,
+        start_offset: u64,
+        end_offset: u64,
+    ) -> Result<(Vec<DynamicEntry>, usize, u64), Error> {
+        let end_idx = self.index.len() - 1;
+        let chunk_end = self.chunk_end(end_idx);
+        let start = self.binary_search(0, 0, end_idx, chunk_end, start_offset)?;
+        let end = self.binary_search(0, 0, end_idx, chunk_end, end_offset)?;
+
+        let offset_first = if start == 0 {
+            0
+        } else {
+            self.index[start - 1].end()
+        };
+
+        let size = (self.index[end].end() - offset_first).try_into()?;
+        let padding_start = start_offset - offset_first;
+
+        let mut indices = Vec::new();
+        let mut prev_end = offset_first;
+        for dynamic_entry in &self.index[start..end + 1] {
+            let mut dynamic_entry = dynamic_entry.clone();
+            // Normalize end to be equal to size
+            dynamic_entry.end_le -= prev_end;
+            prev_end += dynamic_entry.end_le;
+            indices.push(dynamic_entry);
+        }
+
+        Ok((indices, size, padding_start))
+    }
 }
 
 impl IndexFile for DynamicIndexReader {
-- 
2.39.2