feat: store backup sizes in metadata file

CHANGELOG.md

@@ -13,7 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     * Chain length describes how many incremental backups to create from the
       same full backup
     * "backups to keep" has been replaced by "chains to keep"
-* Server type & version is now stored as metadata in the metadata file
+* Server type & version and backup size are now stored as metadata in the
+  metadata file
 * Backup layers
     * Store multiple chains of backups in parallel, configuring each with
       different parameters (son-father-grandfather principle)

Dockerfile

@@ -47,13 +47,15 @@ COPY --from=builder /app/target/debug/alex /bin/alex
 RUN chmod +x /bin/alex
 
 # Default value to keep users from eating up all ram accidentally
-ENV ALEX_XMS=1024 \
+ENV ALEX_CONFIG_DIR=/app/config \
+    ALEX_WORLD_DIR=/app/worlds \
+    ALEX_BACKUP_DIR=/app/backups \
+    ALEX_SERVER=paper \
+    ALEX_XMS=1024 \
     ALEX_XMX=2048 \
     ALEX_JAR=/app/server.jar \
-    ALEX_CONFIG_DIR=/app/config \
+    ALEX_SERVER_VERSION="${MC_VERSION}-${PAPERMC_VERSION}" \
-    ALEX_WORLD_DIR=/app/worlds \
+    ALEX_LAYERS="2min,2,4,4;3min,3,2,2"
-    ALEX_BACKUPS_DIR=/app/backups \
-    ALEX_SERVER_VERSION="${MC_VERSION}-${PAPERMC_VERSION}"
 
 # Document exposed ports
 EXPOSE 25565
@@ -62,4 +64,4 @@ EXPOSE 25565
 USER paper:paper
 
 ENTRYPOINT ["/bin/dumb-init", "--"]
-CMD ["/bin/alex", "paper"]
+CMD ["/bin/alex", "run"]

src/backup/io_ext.rs

@@ -0,0 +1,43 @@
+use std::io::{self, Write};
+
+/// Wrapper around the Write trait that counts how many bytes have been written in total.
+/// Heavily inspired by https://stackoverflow.com/a/42189386
+pub struct CountingWrite<W> {
+    inner: W,
+    count: usize,
+}
+
+impl<W> CountingWrite<W>
+where
+    W: Write,
+{
+    pub fn new(writer: W) -> Self {
+        Self {
+            inner: writer,
+            count: 0,
+        }
+    }
+
+    pub fn bytes_written(&self) -> usize {
+        self.count
+    }
+}
+
+impl<W> Write for CountingWrite<W>
+where
+    W: Write,
+{
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let res = self.inner.write(buf);
+
+        if let Ok(count) = res {
+            self.count += count;
+        }
+
+        res
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.inner.flush()
+    }
+}

src/backup/mod.rs

@@ -1,4 +1,5 @@
 mod delta;
+mod io_ext;
 pub mod manager;
 mod path;
 
@@ -30,6 +31,7 @@ pub enum BackupType {
 pub struct Backup<T: Clone> {
     /// When the backup was started (also corresponds to the name)
     pub start_time: chrono::DateTime<Utc>,
+    pub size: usize,
     /// Type of the backup
     pub type_: BackupType,
     pub delta: Delta,
@@ -84,7 +86,7 @@ impl<T: Clone> Backup<T> {
         let start_time = chrono::offset::Utc::now();
 
         let path = Backup::path(backup_dir, start_time);
-        let tar_gz = File::create(path)?;
+        let tar_gz = io_ext::CountingWrite::new(File::create(path)?);
         let enc = GzEncoder::new(tar_gz, Compression::default());
         let mut ar = tar::Builder::new(enc);
 
@@ -104,9 +106,16 @@ impl<T: Clone> Backup<T> {
             delta.added.insert(dir_in_tar.to_path_buf(), added_files);
         }
 
+        let mut enc = ar.into_inner()?;
+
+        // The docs recommend running try_finish before unwrapping using finish
+        enc.try_finish()?;
+        let tar_gz = enc.finish()?;
+
         Ok(Backup {
             type_: BackupType::Full,
             start_time,
+            size: tar_gz.bytes_written(),
             delta,
             metadata: None,
         })
@@ -122,7 +131,7 @@ impl<T: Clone> Backup<T> {
         let start_time = chrono::offset::Utc::now();
 
         let path = Backup::path(backup_dir, start_time);
-        let tar_gz = File::create(path)?;
+        let tar_gz = io_ext::CountingWrite::new(File::create(path)?);
         let enc = GzEncoder::new(tar_gz, Compression::default());
         let mut ar = tar::Builder::new(enc);
 
@@ -154,9 +163,16 @@ impl<T: Clone> Backup<T> {
             }
         }
 
+        let mut enc = ar.into_inner()?;
+
+        // The docs recommend running try_finish before unwrapping using finish
+        enc.try_finish()?;
+        let tar_gz = enc.finish()?;
+
         Ok(Backup {
             type_: BackupType::Incremental,
             start_time,
+            size: tar_gz.bytes_written(),
             delta,
             metadata: None,
         })