feat: store backup sizes in metadata file

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,
         })