src/backup/chunk_store.rs: use zstd compression insteadf of lz4

Provides better compressionm rate, and is still fast.

Cargo.toml

@@ -41,7 +41,7 @@ md5 = "0.6"
 base64 = "0.10"
 pam-sys = "0.5"
 pam = "0.7"
-lz4 = "1.23"
+zstd = "0.4"
 xdg = "2.2"
 
 [patch.crates-io]

debian/control

@@ -6,7 +6,7 @@ Build-Depends: bash-completion,
                debhelper (>= 10),
                python3-docutils,
 	       python3-sphinx,
-               liblz4-dev,
+               libzstd-dev,
                libpam0g-dev,
                pkg-config,
 Standards-Version: 3.9.5
@@ -18,6 +18,6 @@ Depends: ${shlibs:Depends}, ${misc:Depends},
 	 libjs-extjs (>= 6.0.1),
 	 fonts-font-awesome,
 	 proxmox-widget-toolkit,
-	 liblz4-1,
+	 libzstd1,
 Description: Proxmox Backup Server
  This is experimental code used to test Rust.

src/backup/chunk_store.rs

@@ -183,7 +183,7 @@ impl ChunkStore {
 
         buffer.clear();
         let f = std::fs::File::open(&chunk_path)?;
-        let mut decoder = lz4::Decoder::new(f)?;
+        let mut decoder = zstd::stream::Decoder::new(f)?;
 
         decoder.read_to_end(buffer)?;
 
@@ -333,12 +333,10 @@ impl ChunkStore {
 
         let f = std::fs::File::create(&tmp_path)?;
 
-        // fixme: what is the fasted lz4 encoder available (see lzbench)?
-        let mut encoder = lz4::EncoderBuilder::new().level(1).build(f)?;
+        let mut encoder = zstd::stream::Encoder::new(f, 1)?;
 
         encoder.write_all(chunk)?;
-        let (f, encode_result) = encoder.finish();
-        encode_result?;
+        let f = encoder.finish()?;
 
         if let Err(err) = std::fs::rename(&tmp_path, &chunk_path) {
             if let Err(_) = std::fs::remove_file(&tmp_path)  { /* ignore */ }