[pbs-devel] [PATCH v9 proxmox-backup 36/58] client: pxar: add helper to handle optional preludes

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

Pxar archives with format version 2 allows to store optional
information file format version and prelude entries.

Cover the case for these entries, the file format version entry being
introduced to distinguish between different file formats used for
encoding as well as the prelude entry used to store optional metadata
such as the pxar cli exlude parameters.

Add the logic to accept and decode these prelude entries when
accessing the archive via a decoder instance.

For now simply ignore them.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 8:
- add debug log output of encountered pxar format version

 pbs-client/src/pxar/create.rs             |  2 +-
 pbs-client/src/pxar/extract.rs            |  7 +++--
 pbs-client/src/pxar/tools.rs              |  7 +++++
 pbs-client/src/tools/mod.rs               | 36 +++++++++++++++++++++++
 src/api2/tape/restore.rs                  | 17 ++++-------
 src/tape/file_formats/snapshot_archive.rs |  1 +
 6 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 53c8a5307..56931dad7 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -226,7 +226,7 @@ where
     }
 
     let metadata_mode = options.previous_ref.is_some() && writers.archive.payload().is_some();
-    let mut encoder = Encoder::new(writers.archive, &metadata).await?;
+    let mut encoder = Encoder::new(writers.archive, &metadata, None).await?;
 
     let mut patterns = options.patterns;
 
diff --git a/pbs-client/src/pxar/extract.rs b/pbs-client/src/pxar/extract.rs
index 5f5ac6188..e22390606 100644
--- a/pbs-client/src/pxar/extract.rs
+++ b/pbs-client/src/pxar/extract.rs
@@ -29,6 +29,7 @@ use proxmox_compression::zip::{ZipEncoder, ZipEntry};
 use crate::pxar::dir_stack::PxarDirStack;
 use crate::pxar::metadata;
 use crate::pxar::Flags;
+use crate::tools::handle_root_with_optional_format_version_prelude;
 
 pub struct PxarExtractOptions<'a> {
     pub match_list: &'a [MatchEntry],
@@ -124,9 +125,7 @@ where
         // we use this to keep track of our directory-traversal
         decoder.enable_goodbye_entries(true);
 
-        let root = decoder
-            .next()
-            .context("found empty pxar archive")?
+        let (root, _) = handle_root_with_optional_format_version_prelude(&mut decoder)
             .context("error reading pxar archive")?;
 
         if !root.is_dir() {
@@ -267,6 +266,8 @@ where
         };
 
         let extract_res = match (did_match, entry.kind()) {
+            (_, EntryKind::Version(_version)) => Ok(()),
+            (_, EntryKind::Prelude(_prelude)) => Ok(()),
             (_, EntryKind::Directory) => {
                 self.callback(entry.path());
 
diff --git a/pbs-client/src/pxar/tools.rs b/pbs-client/src/pxar/tools.rs
index 459951d50..27e5185a3 100644
--- a/pbs-client/src/pxar/tools.rs
+++ b/pbs-client/src/pxar/tools.rs
@@ -172,6 +172,13 @@ pub fn format_multi_line_entry(entry: &Entry) -> String {
     let meta = entry.metadata();
 
     let (size, link, type_name, payload_offset) = match entry.kind() {
+        EntryKind::Version(version) => (format!("{version:?}"), String::new(), "version", None),
+        EntryKind::Prelude(prelude) => (
+            "0".to_string(),
+            format!("raw data: {:?} bytes", prelude.data.len()),
+            "prelude",
+            None,
+        ),
         EntryKind::File {
             size,
             payload_offset,
diff --git a/pbs-client/src/tools/mod.rs b/pbs-client/src/tools/mod.rs
index 6680dc475..d62b651ee 100644
--- a/pbs-client/src/tools/mod.rs
+++ b/pbs-client/src/tools/mod.rs
@@ -589,3 +589,39 @@ pub fn has_pxar_filename_extension(name: &str, with_didx_extension: bool) -> boo
         name.ends_with(".pxar") || name.ends_with(".mpxar") || name.ends_with(".ppxar")
     }
 }
+
+/// Decode possible format version and prelude entries before getting the root directory
+/// entry.
+///
+/// Returns the root directory entry and, if present, the prelude entry
+pub fn handle_root_with_optional_format_version_prelude<R: pxar::decoder::SeqRead>(
+    decoder: &mut pxar::decoder::sync::Decoder<R>,
+) -> Result<(pxar::Entry, Option<pxar::Entry>), Error> {
+    let first = decoder
+        .next()
+        .ok_or_else(|| format_err!("missing root entry"))??;
+    match first.kind() {
+        pxar::EntryKind::Directory => {
+            let version = pxar::format::FormatVersion::Version1;
+            log::debug!("pxar format version '{version:?}'");
+            Ok((first, None))
+        }
+        pxar::EntryKind::Version(version) => {
+            log::debug!("pxar format version '{version:?}'");
+            let second = decoder
+                .next()
+                .ok_or_else(|| format_err!("missing root entry"))??;
+            match second.kind() {
+                pxar::EntryKind::Directory => Ok((second, None)),
+                pxar::EntryKind::Prelude(_prelude) => {
+                    let third = decoder
+                        .next()
+                        .ok_or_else(|| format_err!("missing root entry"))??;
+                    Ok((third, Some(second)))
+                }
+                _ => bail!("unexpected entry kind {:?}", second.kind()),
+            }
+        }
+        _ => bail!("unexpected entry kind {:?}", first.kind()),
+    }
+}
diff --git a/src/api2/tape/restore.rs b/src/api2/tape/restore.rs
index 9184ff934..382909647 100644
--- a/src/api2/tape/restore.rs
+++ b/src/api2/tape/restore.rs
@@ -23,6 +23,7 @@ use pbs_api_types::{
     PRIV_DATASTORE_MODIFY, PRIV_TAPE_READ, TAPE_RESTORE_NAMESPACE_SCHEMA,
     TAPE_RESTORE_SNAPSHOT_SCHEMA, UPID_SCHEMA,
 };
+use pbs_client::tools::handle_root_with_optional_format_version_prelude;
 use pbs_config::CachedUserInfo;
 use pbs_datastore::dynamic_index::DynamicIndexReader;
 use pbs_datastore::fixed_index::FixedIndexReader;
@@ -1713,17 +1714,11 @@ fn try_restore_snapshot_archive<R: pxar::decoder::SeqRead>(
     decoder: &mut pxar::decoder::sync::Decoder<R>,
     snapshot_path: &Path,
 ) -> Result<BackupManifest, Error> {
-    let _root = match decoder.next() {
-        None => bail!("missing root entry"),
-        Some(root) => {
-            let root = root?;
-            match root.kind() {
-                pxar::EntryKind::Directory => { /* Ok */ }
-                _ => bail!("wrong root entry type"),
-            }
-            root
-        }
-    };
+    let (root, _) = handle_root_with_optional_format_version_prelude(decoder)?;
+    match root.kind() {
+        pxar::EntryKind::Directory => { /* Ok */ }
+        _ => bail!("wrong root entry type"),
+    }
 
     let root_path = Path::new("/");
     let manifest_file_name = OsStr::new(MANIFEST_BLOB_NAME);
diff --git a/src/tape/file_formats/snapshot_archive.rs b/src/tape/file_formats/snapshot_archive.rs
index 82f466980..f5a588f4e 100644
--- a/src/tape/file_formats/snapshot_archive.rs
+++ b/src/tape/file_formats/snapshot_archive.rs
@@ -61,6 +61,7 @@ pub fn tape_write_snapshot_archive<'a>(
         let mut encoder = pxar::encoder::sync::Encoder::new(
             pxar::PxarVariant::Unified(PxarTapeWriter::new(writer)),
             &root_metadata,
+            None,
         )?;
 
         for filename in file_list.iter() {
-- 
2.39.2



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