[pbs-devel] [RFC v2 proxmox-backup 24/36] index: fetch chunk form index by start/end-offset

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

In preparation for injecting reused payload chunks in payload streams
for regular files with unchanged metaddata.

Adds a function to get a list of DynamicEntry's from a chunk index by
given start and end offset, the range of which will be contained
within these returned chunks.

In addition to the list of index entries, the padding to the start of
the requested start offset from the first chunk is returned, as well
as the end padding following the requested payload to the actual
chunk end.

The padding is used for calculation of the payload reference  offset
written to the metadata archive, required for payload access during
decoding.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 1:
- s/Appendable/Reusable/ incorrect naming leftover from previous approach

 pbs-datastore/src/dynamic_index.rs | 55 ++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/pbs-datastore/src/dynamic_index.rs b/pbs-datastore/src/dynamic_index.rs
index 71a5082e..85c86b32 100644
--- a/pbs-datastore/src/dynamic_index.rs
+++ b/pbs-datastore/src/dynamic_index.rs
@@ -74,6 +74,26 @@ impl DynamicEntry {
     }
 }
 
+/// Dynamic Entry reusable by payload references
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct ReusableDynamicEntry {
+    size_le: u64,
+    digest: [u8; 32],
+}
+
+impl ReusableDynamicEntry {
+    #[inline]
+    pub fn size(&self) -> u64 {
+        u64::from_le(self.size_le)
+    }
+
+    #[inline]
+    pub fn digest(&self) -> [u8; 32] {
+        self.digest.clone()
+    }
+}
+
 pub struct DynamicIndexReader {
     _file: File,
     pub size: usize,
@@ -188,6 +208,41 @@ 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<ReusableDynamicEntry>, u64, 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 - 1)?;
+
+        let offset_first = if start == 0 {
+            0
+        } else {
+            self.index[start - 1].end()
+        };
+
+        let padding_start = start_offset - offset_first;
+        let padding_end = self.index[end].end() - end_offset;
+
+        let mut indices = Vec::new();
+        let mut prev_end = offset_first;
+        for dynamic_entry in &self.index[start..end + 1] {
+            let size = dynamic_entry.end() - prev_end;
+            let reusable_dynamic_entry = ReusableDynamicEntry {
+                size_le: size.to_le(),
+                digest: dynamic_entry.digest.clone(),
+            };
+            prev_end += size;
+            indices.push(reusable_dynamic_entry);
+        }
+
+        Ok((indices, padding_start, padding_end))
+    }
 }
 
 impl IndexFile for DynamicIndexReader {
-- 
2.39.2