utilities for archiving snapshots (#3224)

# Description of Changes

Adds utilities for marking and deleting snapshot directories that have
been archived

# API and ABI breaking changes

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corresponding GitHub label. -->

None

# Expected complexity level and risk

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1

# Testing

<!-- Describe any testing you've done, and any testing you'd like your
reviewers to do,
so that you're confident that all the changes work as expected! -->

Testing will be handled by the patch that adds archival

Author: joshua-spacetime

crates/paths/src/server.rs

@@ -206,6 +206,11 @@ path_type! {
     SnapshotDirPath: dir
 }
 
+path_type! {
+    /// An archived snapshot directory. `{data-dir}/replica/$replica_id/snapshots/$tx_offset.archived_snapshot`
+    ArchivedSnapshotDirPath: dir
+}
+
 impl SnapshotDirPath {
     pub fn snapshot_file(&self, tx_offset: u64) -> SnapshotFilePath {
         let file_name = format!("{tx_offset:0>20}.snapshot_bsatn");
@@ -221,6 +226,12 @@ impl SnapshotDirPath {
         fs::rename(self, invalid_path)
     }
 
+    pub fn rename_as_archived(&self) -> io::Result<ArchivedSnapshotDirPath> {
+        let path = self.0.with_extension("archived_snapshot");
+        fs::rename(self, &path)?;
+        Ok(ArchivedSnapshotDirPath(path))
+    }
+
     pub fn tx_offset(&self) -> Option<u64> {
         self.0
             .file_stem()

crates/snapshot/src/lib.rs

@@ -30,7 +30,7 @@ use spacetimedb_fs_utils::{
     lockfile::{Lockfile, LockfileError},
 };
 use spacetimedb_lib::Identity;
-use spacetimedb_paths::server::{SnapshotDirPath, SnapshotFilePath, SnapshotsPath};
+use spacetimedb_paths::server::{ArchivedSnapshotDirPath, SnapshotDirPath, SnapshotFilePath, SnapshotsPath};
 use spacetimedb_paths::FromPathUnchecked;
 use spacetimedb_primitives::TableId;
 use spacetimedb_sats::{bsatn, de::Deserialize, ser::Serialize};
@@ -40,6 +40,7 @@ use spacetimedb_table::{
     page_pool::PagePool,
     table::Table,
 };
+use std::fs;
 use std::{
     collections::BTreeMap,
     collections::HashMap,
@@ -145,6 +146,9 @@ pub const SNAPSHOT_FILE_EXT: &str = "snapshot_bsatn";
 /// File extension of snapshots which have been marked invalid by [`SnapshotRepository::invalidate_newer_snapshots`].
 pub const INVALID_SNAPSHOT_DIR_EXT: &str = "invalid_snapshot";
 
+/// File extension of snapshots which have been archived
+pub const ARCHIVED_SNAPSHOT_EXT: &str = "archived_snapshot";
+
 #[derive(Clone, Serialize, Deserialize)]
 /// The hash and refcount of a single blob in the blob store.
 struct BlobEntry {
@@ -890,6 +894,27 @@ impl SnapshotRepository {
             }))
     }
 
+    /// Return an interator of [`ArchivedSnapshotDirPath`] for all the archived snapshot directories on disk
+    pub fn all_archived_snapshots(&self) -> Result<impl Iterator<Item = ArchivedSnapshotDirPath>, SnapshotError> {
+        Ok(self
+            .root
+            // Item = Result<DirEntry>
+            .read_dir()?
+            // Item = DirEntry
+            .filter_map(Result::ok)
+            // Item = PathBuf
+            .map(|dirent| dirent.path())
+            // Ignore entries not shaped like snapshot directories.
+            .filter(|path| path.extension() == Some(OsStr::new(ARCHIVED_SNAPSHOT_EXT)))
+            // Item = ArchivedSnapshotDirPath
+            .map(ArchivedSnapshotDirPath::from_path_unchecked))
+    }
+
+    /// Delete an archived snapshot from disk
+    pub fn remove_archived_snapshot(path: &ArchivedSnapshotDirPath) -> Result<(), SnapshotError> {
+        fs::remove_dir_all(path).map_err(SnapshotError::Io)
+    }
+
     /// Return the `TxOffset` of the highest-offset complete snapshot in the repository.
     ///
     /// Does not verify that the snapshot of the returned `TxOffset` is valid and uncorrupted,