[PATCH v1 proxmox-backup 2/3] datastore: check that .i.bad files from S3 actually match that pattern

[Robert Obkircher <r.obkircher@proxmox.com>]

Compare the characters, not just the length, and introduce a helper
that can be tested in isolation.

Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
---
 pbs-datastore/src/chunk_store.rs | 21 ++++++++++++++-------
 pbs-datastore/src/datastore.rs   |  7 +++----
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index a936f5034..f40c58f7e 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -360,13 +360,7 @@ impl ChunkStore {
                             }
 
                             // i-th bad chunk
-                            if bytes.len() == 64 + ".i.bad".len()
-                                && bytes[64] == b'.'
-                                && bytes[65] >= b'0'
-                                && bytes[65] <= b'9'
-                                && bytes[66] == b'.'
-                                && bytes.ends_with(b"bad")
-                            {
+                            if is_bad_chunk_suffix(&bytes[64..]) {
                                 return Some((Ok(entry), percentage, ChunkExt::Bad));
                             }
 
@@ -1028,6 +1022,19 @@ impl ChunkExt {
     }
 }
 
+pub fn is_bad_chunk_suffix(s: &[u8]) -> bool {
+    s.len() == ".i.bad".len() && s[0] == b'.' && s[1].is_ascii_digit() && &s[2..] == b".bad"
+}
+
+#[test]
+fn test_is_bad_chunk_suffix() {
+    assert!(is_bad_chunk_suffix(".0.bad".as_bytes()));
+    assert!(is_bad_chunk_suffix(".9.bad".as_bytes()));
+    for s in [".10.bad", ".a.bad", ".bad", "0.bad", ""] {
+        assert!(!is_bad_chunk_suffix(s.as_bytes()));
+    }
+}
+
 #[test]
 fn test_chunk_store1() {
     use tempfile::TempDir;
diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index 3079fe833..bac5ce3b4 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -43,7 +43,7 @@ use proxmox_section_config::SectionConfigData;
 use crate::backup_info::{
     BackupDir, BackupGroup, BackupInfo, OLD_LOCKING, PROTECTED_MARKER_FILENAME,
 };
-use crate::chunk_store::ChunkStore;
+use crate::chunk_store::{ChunkStore, is_bad_chunk_suffix};
 use crate::dynamic_index::{DynamicIndexReader, DynamicIndexWriter};
 use crate::fixed_index::{FixedIndexReader, FixedIndexWriter};
 use crate::hierarchy::{ListGroups, ListGroupsType, ListNamespaces, ListNamespacesRecursive};
@@ -2680,13 +2680,12 @@ impl DataStore {
         // file_name() should always be Some, as objects will have a filename
         let file_name = path.file_name()?;
         let bytes = file_name.as_bytes();
-        let bad_ext_len = ".0.bad".len();
-        let bad_chunk = if bytes.len() == 64 + bad_ext_len {
+        let bad_chunk = if is_bad_chunk_suffix(&bytes[64..]) {
             true
         } else if bytes.len() == 64 {
             false
         } else {
-            return None;
+            return None; // unexpected suffix
         };
         if !bytes.iter().take(64).all(u8::is_ascii_hexdigit) {
             return None;
-- 
2.47.3