chore: bumb version to 0.3.0

chains

.cargo/config.toml

@@ -1,3 +1,3 @@
 [alias]
-runs = "run -- paper 1.19.4-545 --config data/config --backup data/backups --world data/worlds --jar data/paper.jar"
-runrs = "run --release -- paper 1.19.4-545 --config data/config --backup data/backups --world data/worlds --jar data/paper.jar"
+runs = "run -- --config data/config --backup data/backups --world data/worlds --layers 2min,2,4,4;3min,3,2,2"
+runrs = "run --release -- --config data/config --backup data/backups --world data/worlds --layers 2min,2,4,4;3min,3,2,2"

.gitignore

@@ -19,4 +19,4 @@ target/
 
 # testing files
 *.jar
-data/
+data*/

CHANGELOG.md

@@ -7,6 +7,30 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://git.rustybever.be/Chewing_Bever/alex/src/branch/dev)
 
+## [0.3.0](https://git.rustybever.be/Chewing_Bever/alex/src/tag/0.3.0)
+
+### Added
+
+* Incremental backups
+    * 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+    * "backups to keep" has been replaced by "chains to keep"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 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)
+* CLI commands for creating, restoring & listing backups
+
+### Changed
+
+* Running the server now uses the `run` CLI subcommand
+* `server_type` and `server_version` arguments are now optional flags
+
+### Removed
+
+* `max_backups` setting
+
 ## [0.2.2](https://git.rustybever.be/Chewing_Bever/alex/src/tag/0.2.2)
 
 ### Fixed

Cargo.lock

@@ -10,11 +10,13 @@ checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
 
 [[package]]
 name = "alex"
-version = "0.2.2"
+version = "0.3.0"
 dependencies = [
  "chrono",
  "clap",
  "flate2",
+ "serde",
+ "serde_json",
  "signal-hook",
  "tar",
 ]
@@ -123,6 +125,7 @@ dependencies = [
  "iana-time-zone",
  "js-sys",
  "num-traits",
+ "serde",
  "time",
  "wasm-bindgen",
  "winapi",
@@ -292,6 +295,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "itoa"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "453ad9f582a441959e5f0d088b02ce04cfe8d51a8eaf077f12ac6d3e94164ca6"
+
 [[package]]
 name = "js-sys"
 version = "0.3.63"
@@ -384,6 +393,43 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "ryu"
+version = "1.0.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f91339c0467de62360649f8d3e185ca8de4224ff281f66000de5eb2a77a79041"
+
+[[package]]
+name = "serde"
+version = "1.0.164"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e8c8cf938e98f769bc164923b06dce91cea1751522f46f8466461af04c9027d"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.164"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9735b638ccc51c28bf6914d90a2e9725b377144fc612c49a611fddd1b631d68"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "serde_json"
+version = "1.0.96"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "057d394a50403bcac12672b2b18fb387ab6d289d957dab67dd201875391e52f1"
+dependencies = [
+ "itoa",
+ "ryu",
+ "serde",
+]
+
 [[package]]
 name = "signal-hook"
 version = "0.3.15"

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "alex"
-version = "0.2.2"
+version = "0.3.0"
 description = "Wrapper around Minecraft server processes, designed to complement Docker image installations."
 authors = ["Jef Roosens"]
 edition = "2021"
@@ -12,10 +12,11 @@ edition = "2021"
 tar = "0.4.38"
 # Used to compress said tarballs using gzip
 flate2 = "1.0.26"
-# Used for backup filenames
-chrono = "0.4.26"
+chrono = { version = "0.4.26", features = ["serde"] }
 clap = { version = "4.3.1", features = ["derive", "env"] }
 signal-hook = "0.3.15"
+serde = { version = "1.0.164", features = ["derive", "rc"] }
+serde_json = "1.0.96"
 
 [profile.release]
 lto = "fat"

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_WORLD_DIR=/app/worlds \
-    ALEX_BACKUPS_DIR=/app/backups \
-    ALEX_SERVER_VERSION="${MC_VERSION}-${PAPERMC_VERSION}"
+    ALEX_SERVER_VERSION="${MC_VERSION}-${PAPERMC_VERSION}" \
+    ALEX_LAYERS="2min,2,4,4;3min,3,2,2"
 
 # 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"]

README.md

@@ -2,7 +2,24 @@
 
 Alex is a wrapper around a typical Minecraft server process. It acts as the
 parent process, and sits in between the user's input and the server's stdin.
-This allows Alex to support additional commands that execute Rust code.
+This allows Alex to support additional commands that execute Rust code, notably
+creating periodic backups.
+
+## Installation
+
+Alex is distributed as statically compiled binaries for Linux amd64 and arm64.
+These can be found
+[here](https://git.rustybever.be/Chewing_Bever/alex/packages).
+
+### Dockerfiles
+
+You can easily install alex in your Docker images by letting Docker download it
+for you. Add the following to your Dockerfile (replace with your required
+version & architecture):
+
+```dockerfile
+ADD "https://git.rustybever.be/api/packages/Chewing_Bever/generic/alex/0.2.2/alex-linux-amd64" /bin/alex
+```
 
 ## Why
 
@@ -19,8 +36,86 @@ Afterwards, saving is enabled again with `save-on`.
 * Properly configures the process (working directory, optimisation flags)
 * Configure everything as CLI arguments or environment variables
 
-## Installation
+## Configuration
 
-Alex is distributed as statically compiled binaries for Linux amd64 and arm64.
-These can be found
-[here](https://git.rustybever.be/Chewing_Bever/alex/packages).
+Most information can be retrieved easily by looking at the help command:
+
+```
+Wrapper around Minecraft server processes, designed to complement Docker image installations.
+
+Usage: alex [OPTIONS] <COMMAND>
+
+Commands:
+  run     Run the server
+  backup  Interact with the backup system without starting a server
+  help    Print this message or the help of the given subcommand(s)
+
+Options:
+      --config <CONFIG_DIR>
+          Directory where configs are stored, and where the server will run [env: ALEX_CONFIG_DIR=] [default: .]
+      --world <WORLD_DIR>
+          Directory where world files will be saved [env: ALEX_WORLD_DIR=] [default: ../worlds]
+      --backup <BACKUP_DIR>
+          Directory where backups will be stored [env: ALEX_BACKUP_DIR=] [default: ../backups]
+      --layers <LAYERS>
+          What backup layers to employ, provided as a list of tuples name,frequency,chains,chain_len delimited by semicolons (;) [env: ALEX_LAYERS=]
+      --server <SERVER>
+          Type of server [env: ALEX_SERVER=] [default: unknown] [possible values: unknown, paper, forge, vanilla]
+      --server-version <SERVER_VERSION>
+          Version string for the server, e.g. 1.19.4-545 [env: ALEX_SERVER_VERSION=] [default: ]
+  -h, --help
+          Print help
+  -V, --version
+          Print version
+
+```
+
+### Choosing layer parameters
+
+One part of the configuration that does require some clarification is the layer
+system. Alex can manage an arbitrary number of backup layers, each having its
+own configuration. These layers can either use incremental or full backups,
+depending on how they're configured.
+
+These layers mostly correspond to the grandfather-father-son backup rotation
+scheme. For example, one could have a layer that creates incremental backups
+every 30 minutes, which are stored for 24 hours. This gives you 24 hours of
+granular rollback in case your server suffers a crash. A second layer might
+create a full backup every 24 hours, with backups being stored for 7 days. This
+gives you 7 days worth of backups with the granularity of 24 hours. This
+approach allows for greater versatility, while not having to store a large
+amount of data. Thanks to incremental backups, frequent backups don't have to
+take long at all.
+
+A layer consists of 4 pieces of metadata:
+
+* A name, which will be used in the file system and the in-game notifications
+* The frequency, which describes in minutes how frequently a backup should be
+  created
+* How many chains should be kept at all times
+* How long each chain should be
+
+These last two require some clarification. In Alex, a "chain" describes an
+initial full backup and zero or more incremental backups that are created from
+that initial full backup. This concept exists because an incremental backup has
+no real meaning if its ancestors are not known. To restore one of these chains,
+all backups in the chain need to be restored in-order. Note that a chain length
+of 1 disables incremental backups entirely.
+
+How many backups to keep is defined by how many chains should be stored.
+Because an incremental backup needs to have its ancestors in order to be
+restored, we can't simply "keep the last n backups", as this would break these
+chains. Therefore, you configure how many backups to store using these chains.
+
+For example, if you configure a layer to store 5 chains of length 4, you will
+have 20 archive files on disk, namely 5 full backups and 15 incremental
+backups. Note that Alex applies these rules to *full* chains. An in-progress
+chain does not count towards this total. Therefore, you can have up to `n-1`
+additional archive files, with `n` being the chain length, on disk.
+
+To look at it from another perspective, say we wish to have a granularity of 30
+minutes for a timespan of 24 hours. Then we could configure the layer to only
+save a single chain, with a chain length of 48. If we prefer to have a few full
+backups instead of a long chain of incremental backups, we could instead use a
+chain length of 12 and store 4 chains. Either way, the total comes out to 48,
+which spans 24 hours if we make a backup every 30 minutes.

src/backup/delta.rs

@@ -0,0 +1,86 @@
+use serde::{Deserialize, Serialize};
+use std::collections::{HashMap, HashSet};
+use std::fmt;
+use std::path::PathBuf;
+
+/// Represents the changes relative to the previous backup
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Delta {
+    /// What files were added/modified in each part of the tarball.
+    pub added: HashMap<PathBuf, HashSet<PathBuf>>,
+    /// What files were removed in this backup, in comparison to the previous backup. For full
+    /// backups, this will always be empty, as they do not consider previous backups.
+    /// The map stores a separate list for each top-level directory, as the contents of these
+    /// directories can come for different source directories.
+    pub removed: HashMap<PathBuf, HashSet<PathBuf>>,
+}
+
+impl Delta {
+    pub fn new() -> Self {
+        Self {
+            added: HashMap::new(),
+            removed: HashMap::new(),
+        }
+    }
+
+    /// Update the current state so that its result becomes the merge of itself and the other
+    /// state.
+    #[allow(dead_code)]
+    pub fn merge(&mut self, delta: &Self) {
+        for (dir, added) in delta.added.iter() {
+            // Files that were removed in the current state, but added in the new state, are no
+            // longer removed
+            if let Some(orig_removed) = self.removed.get_mut(dir) {
+                orig_removed.retain(|k| !added.contains(k));
+            }
+
+            // Newly added files are added to the state as well
+            if let Some(orig_added) = self.added.get_mut(dir) {
+                orig_added.extend(added.iter().cloned());
+            } else {
+                self.added.insert(dir.clone(), added.clone());
+            }
+        }
+
+        for (dir, removed) in delta.removed.iter() {
+            // Files that were originally added, but now deleted are removed from the added list
+            if let Some(orig_added) = self.added.get_mut(dir) {
+                orig_added.retain(|k| !removed.contains(k));
+            }
+
+            // Newly removed files are added to the state as well
+            if let Some(orig_removed) = self.removed.get_mut(dir) {
+                orig_removed.extend(removed.iter().cloned());
+            } else {
+                self.removed.insert(dir.clone(), removed.clone());
+            }
+        }
+    }
+
+    /// Modify the given state by applying this delta's changes to it
+    pub fn apply(&self, state: &mut HashMap<PathBuf, HashSet<PathBuf>>) {
+        // First we add new files, then we remove the old ones
+        for (dir, added) in self.added.iter() {
+            if let Some(current) = state.get_mut(dir) {
+                current.extend(added.iter().cloned());
+            } else {
+                state.insert(dir.clone(), added.clone());
+            }
+        }
+
+        for (dir, removed) in self.removed.iter() {
+            if let Some(current) = state.get_mut(dir) {
+                current.retain(|k| !removed.contains(k));
+            }
+        }
+    }
+}
+
+impl fmt::Display for Delta {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let added_count: usize = self.added.values().map(|s| s.len()).sum();
+        let removed_count: usize = self.removed.values().map(|s| s.len()).sum();
+
+        write!(f, "+{}-{}", added_count, removed_count)
+    }
+}

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/manager/config.rs

@@ -0,0 +1,46 @@
+use std::error::Error;
+use std::fmt;
+use std::str::FromStr;
+
+#[derive(Clone, Debug)]
+pub struct ManagerConfig {
+    pub name: String,
+    pub frequency: u32,
+    pub chains: u64,
+    pub chain_len: u64,
+}
+
+#[derive(Debug)]
+pub struct ParseManagerConfigErr;
+
+impl Error for ParseManagerConfigErr {}
+
+impl fmt::Display for ParseManagerConfigErr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "parse manager config err")
+    }
+}
+
+impl FromStr for ManagerConfig {
+    type Err = ParseManagerConfigErr;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let splits: Vec<&str> = s.split(',').collect();
+
+        if let [name, frequency, chains, chain_len] = splits[..] {
+            let name: String = name.parse().map_err(|_| ParseManagerConfigErr)?;
+            let frequency: u32 = frequency.parse().map_err(|_| ParseManagerConfigErr)?;
+            let chains: u64 = chains.parse().map_err(|_| ParseManagerConfigErr)?;
+            let chain_len: u64 = chain_len.parse().map_err(|_| ParseManagerConfigErr)?;
+
+            Ok(ManagerConfig {
+                name,
+                chains,
+                chain_len,
+                frequency,
+            })
+        } else {
+            Err(ParseManagerConfigErr)
+        }
+    }
+}

src/backup/manager/meta.rs

@@ -0,0 +1,135 @@
+use super::{Manager, ManagerConfig};
+use chrono::Utc;
+use serde::Deserialize;
+use serde::Serialize;
+use std::collections::HashMap;
+use std::io;
+use std::path::PathBuf;
+
+/// Manages a collection of backup layers, allowing them to be utilized as a single object.
+pub struct MetaManager<T>
+where
+    T: Clone + Serialize + for<'de> Deserialize<'de> + std::fmt::Debug,
+{
+    backup_dir: PathBuf,
+    dirs: Vec<(PathBuf, PathBuf)>,
+    default_metadata: T,
+    managers: HashMap<String, Manager<T>>,
+}
+
+impl<T> MetaManager<T>
+where
+    T: Clone + Serialize + for<'de> Deserialize<'de> + std::fmt::Debug,
+{
+    pub fn new<P: Into<PathBuf>>(
+        backup_dir: P,
+        dirs: Vec<(PathBuf, PathBuf)>,
+        default_metadata: T,
+    ) -> Self {
+        MetaManager {
+            backup_dir: backup_dir.into(),
+            dirs,
+            default_metadata,
+            managers: HashMap::new(),
+        }
+    }
+
+    /// Add a new manager to track, initializing it first.
+    pub fn add(&mut self, config: &ManagerConfig) -> io::Result<()> {
+        // Backup dir itself should exist, but we control its contents, so we can create
+        // separate directories for each layer
+        let path = self.backup_dir.join(&config.name);
+
+        // If the directory already exists, that's okay
+        match std::fs::create_dir(&path) {
+            Ok(()) => (),
+            Err(e) => match e.kind() {
+                io::ErrorKind::AlreadyExists => (),
+                _ => return Err(e),
+            },
+        };
+
+        let mut manager = Manager::new(
+            path,
+            self.dirs.clone(),
+            self.default_metadata.clone(),
+            config.chain_len,
+            config.chains,
+            chrono::Duration::minutes(config.frequency.into()),
+        );
+        manager.load()?;
+        self.managers.insert(config.name.clone(), manager);
+
+        Ok(())
+    }
+
+    /// Convenient wrapper for `add`.
+    pub fn add_all(&mut self, configs: &Vec<ManagerConfig>) -> io::Result<()> {
+        for config in configs {
+            self.add(config)?;
+        }
+
+        Ok(())
+    }
+
+    /// Return the name of the next scheduled layer, if one or more managers are present.
+    pub fn next_scheduled_layer(&self) -> Option<&str> {
+        self.managers
+            .iter()
+            .min_by_key(|(_, m)| m.next_scheduled_time())
+            .map(|(k, _)| k.as_str())
+    }
+
+    /// Return the earliest scheduled time for the underlying managers.
+    pub fn next_scheduled_time(&self) -> Option<chrono::DateTime<Utc>> {
+        self.managers
+            .values()
+            .map(|m| m.next_scheduled_time())
+            .min()
+    }
+
+    /// Perform a backup cycle for the earliest scheduled manager.
+    pub fn perform_backup_cycle(&mut self) -> io::Result<()> {
+        if let Some(manager) = self
+            .managers
+            .values_mut()
+            .min_by_key(|m| m.next_scheduled_time())
+        {
+            manager.create_backup()?;
+            manager.remove_old_backups()
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Create a manual backup for a specific layer
+    pub fn create_backup(&mut self, layer: &str) -> Option<io::Result<()>> {
+        if let Some(manager) = self.managers.get_mut(layer) {
+            let mut res = manager.create_backup();
+
+            if res.is_ok() {
+                res = manager.remove_old_backups();
+            }
+
+            Some(res)
+        } else {
+            None
+        }
+    }
+
+    /// Restore a backup for a specific layer
+    pub fn restore_backup(
+        &self,
+        layer: &str,
+        start_time: chrono::DateTime<Utc>,
+        dirs: &Vec<(PathBuf, PathBuf)>,
+    ) -> Option<io::Result<()>> {
+        self.managers
+            .get(layer)
+            .map(|manager| manager.restore_backup(start_time, dirs))
+    }
+
+    pub fn managers(&self) -> &HashMap<String, Manager<T>> {
+        &self.managers
+    }
+}

src/backup/manager/mod.rs

@@ -0,0 +1,194 @@
+mod config;
+mod meta;
+
+pub use config::ManagerConfig;
+pub use meta::MetaManager;
+
+use super::Backup;
+use crate::other;
+use chrono::SubsecRound;
+use chrono::Utc;
+use serde::Deserialize;
+use serde::Serialize;
+use std::fs::File;
+use std::io;
+use std::path::PathBuf;
+
+/// Manages a single backup layer consisting of one or more chains of backups.
+pub struct Manager<T>
+where
+    T: Clone + Serialize + for<'de> Deserialize<'de> + std::fmt::Debug,
+{
+    backup_dir: PathBuf,
+    dirs: Vec<(PathBuf, PathBuf)>,
+    default_metadata: T,
+    chain_len: u64,
+    chains_to_keep: u64,
+    frequency: chrono::Duration,
+    chains: Vec<Vec<Backup<T>>>,
+}
+
+impl<T> Manager<T>
+where
+    T: Clone + Serialize + for<'de> Deserialize<'de> + std::fmt::Debug,
+{
+    const METADATA_FILE: &str = "alex.json";
+
+    pub fn new<P: Into<PathBuf>>(
+        backup_dir: P,
+        dirs: Vec<(PathBuf, PathBuf)>,
+        metadata: T,
+        chain_len: u64,
+        chains_to_keep: u64,
+        frequency: chrono::Duration,
+    ) -> Self {
+        Self {
+            backup_dir: backup_dir.into(),
+            dirs,
+            default_metadata: metadata,
+            chain_len,
+            chains_to_keep,
+            frequency,
+            chains: Vec::new(),
+        }
+    }
+
+    /// Create a new backup, either full or incremental, depending on the state of the current
+    /// chain.
+    pub fn create_backup(&mut self) -> io::Result<()> {
+        // We start a new chain if the current chain is complete, or if there isn't a first chain
+        // yet
+        if let Some(current_chain) = self.chains.last() {
+            let current_chain_len: u64 = current_chain.len().try_into().unwrap();
+
+            if current_chain_len >= self.chain_len {
+                self.chains.push(Vec::new());
+            }
+        } else {
+            self.chains.push(Vec::new());
+        }
+
+        let current_chain = self.chains.last_mut().unwrap();
+
+        let mut backup = if !current_chain.is_empty() {
+            let previous_backup = current_chain.last().unwrap();
+            let state = Backup::state(current_chain);
+
+            Backup::create_from(
+                state,
+                previous_backup.start_time,
+                &self.backup_dir,
+                &self.dirs,
+            )?
+        } else {
+            Backup::create(&self.backup_dir, &self.dirs)?
+        };
+
+        backup.set_metadata(self.default_metadata.clone());
+
+        current_chain.push(backup);
+
+        self.save()?;
+
+        Ok(())
+    }
+
+    /// Delete all backups associated with outdated chains, and forget those chains.
+    pub fn remove_old_backups(&mut self) -> io::Result<()> {
+        let chains_to_store: usize = self.chains_to_keep.try_into().unwrap();
+
+        if chains_to_store < self.chains.len() {
+            let mut remove_count: usize = self.chains.len() - chains_to_store;
+
+            // We only count finished chains towards the list of stored chains
+            let chain_len: usize = self.chain_len.try_into().unwrap();
+            if self.chains.last().unwrap().len() < chain_len {
+                remove_count -= 1;
+            }
+
+            for chain in self.chains.drain(..remove_count) {
+                for backup in chain {
+                    let path = Backup::path(&self.backup_dir, backup.start_time);
+                    std::fs::remove_file(path)?;
+                }
+            }
+
+            self.save()?;
+        }
+
+        Ok(())
+    }
+
+    /// Write the in-memory state to disk.
+    pub fn save(&self) -> io::Result<()> {
+        let json_file = File::create(self.backup_dir.join(Self::METADATA_FILE))?;
+        serde_json::to_writer(json_file, &self.chains)?;
+
+        Ok(())
+    }
+
+    /// Overwrite the in-memory state with the on-disk state.
+    pub fn load(&mut self) -> io::Result<()> {
+        let json_file = match File::open(self.backup_dir.join(Self::METADATA_FILE)) {
+            Ok(f) => f,
+            Err(e) => {
+                // Don't error out if the file isn't there, it will be created when necessary
+                if e.kind() == io::ErrorKind::NotFound {
+                    self.chains = Vec::new();
+
+                    return Ok(());
+                } else {
+                    return Err(e);
+                }
+            }
+        };
+
+        self.chains = serde_json::from_reader(json_file)?;
+
+        Ok(())
+    }
+
+    /// Calculate the next time a backup should be created. If no backup has been created yet, it
+    /// will return now.
+    pub fn next_scheduled_time(&self) -> chrono::DateTime<Utc> {
+        if let Some(last_chain) = self.chains.last() {
+            if let Some(last_backup) = last_chain.last() {
+                return last_backup.start_time + self.frequency;
+            }
+        }
+
+        chrono::offset::Utc::now()
+    }
+
+    /// Restore the backup with the given start time by restoring its chain up to and including the
+    /// backup, in order.
+    pub fn restore_backup(
+        &self,
+        start_time: chrono::DateTime<Utc>,
+        dirs: &Vec<(PathBuf, PathBuf)>,
+    ) -> io::Result<()> {
+        // Iterate over each chain, skipping elements until the element with the given start time
+        // is possibly found.
+        for chain in &self.chains {
+            // If we find the element in the chain, restore the entire chain up to and including
+            // the element
+            if let Some(index) = chain
+                .iter()
+                .position(|b| b.start_time.trunc_subsecs(0) == start_time)
+            {
+                for backup in chain.iter().take(index + 1) {
+                    backup.restore(&self.backup_dir, dirs)?;
+                }
+
+                return Ok(());
+            }
+        }
+
+        Err(other("Unknown backup."))
+    }
+
+    /// Get a reference to the underlying chains
+    pub fn chains(&self) -> &Vec<Vec<Backup<T>>> {
+        &self.chains
+    }
+}

src/backup/mod.rs

@@ -0,0 +1,278 @@
+mod delta;
+mod io_ext;
+pub mod manager;
+mod path;
+
+use delta::Delta;
+pub use manager::Manager;
+pub use manager::ManagerConfig;
+pub use manager::MetaManager;
+
+use chrono::Utc;
+use flate2::read::GzDecoder;
+use flate2::write::GzEncoder;
+use flate2::Compression;
+use path::PathExt;
+use serde::{Deserialize, Serialize};
+use std::collections::{HashMap, HashSet};
+use std::fmt;
+use std::fs::File;
+use std::io;
+use std::path::{Path, PathBuf};
+
+const BYTE_SUFFIXES: [&str; 5] = ["B", "KiB", "MiB", "GiB", "TiB"];
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub enum BackupType {
+    Full,
+    Incremental,
+}
+
+/// Represents a successful backup
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Backup<T: Clone> {
+    /// When the backup was started (also corresponds to the name)
+    pub start_time: chrono::DateTime<Utc>,
+    /// When the backup finished
+    pub end_time: chrono::DateTime<Utc>,
+    pub size: usize,
+    /// Type of the backup
+    pub type_: BackupType,
+    pub delta: Delta,
+    /// Additional metadata that can be associated with a given backup
+    pub metadata: Option<T>,
+}
+
+impl Backup<()> {
+    pub const FILENAME_FORMAT: &str = "%Y-%m-%d_%H-%M-%S.tar.gz";
+
+    /// Return the path to a backup file by properly formatting the data.
+    pub fn path<P: AsRef<Path>>(backup_dir: P, start_time: chrono::DateTime<Utc>) -> PathBuf {
+        let backup_dir = backup_dir.as_ref();
+
+        let filename = format!("{}", start_time.format(Self::FILENAME_FORMAT));
+        backup_dir.join(filename)
+    }
+}
+
+impl<T: Clone> Backup<T> {
+    /// Set the backup's metadata.
+    pub fn set_metadata(&mut self, metadata: T) {
+        self.metadata = Some(metadata);
+    }
+
+    /// Resolve the state of the list of backups by applying their deltas in-order to an initially
+    /// empty state.
+    pub fn state(backups: &Vec<Self>) -> HashMap<PathBuf, HashSet<PathBuf>> {
+        let mut state: HashMap<PathBuf, HashSet<PathBuf>> = HashMap::new();
+
+        for backup in backups {
+            backup.delta.apply(&mut state);
+        }
+
+        state
+    }
+
+    /// Create a new Full backup, populated with the given directories.
+    ///
+    /// # Arguments
+    ///
+    /// * `backup_dir` - Directory to store archive in
+    /// * `dirs` - list of tuples `(path_in_tar, src_dir)` with `path_in_tar` the directory name
+    ///     under which `src_dir`'s contents should be stored in the archive
+    ///
+    /// # Returns
+    ///
+    /// The `Backup` instance describing this new backup.
+    pub fn create<P: AsRef<Path>>(
+        backup_dir: P,
+        dirs: &Vec<(PathBuf, PathBuf)>,
+    ) -> io::Result<Self> {
+        let start_time = chrono::offset::Utc::now();
+
+        let path = Backup::path(backup_dir, start_time);
+        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);
+
+        let mut delta = Delta::new();
+
+        for (dir_in_tar, src_dir) in dirs {
+            let mut added_files: HashSet<PathBuf> = HashSet::new();
+
+            for entry in src_dir.read_dir_recursive()?.ignored("cache").files() {
+                let path = entry?.path();
+                let stripped = path.strip_prefix(src_dir).unwrap();
+
+                ar.append_path_with_name(&path, dir_in_tar.join(stripped))?;
+                added_files.insert(stripped.to_path_buf());
+            }
+
+            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,
+            end_time: chrono::Utc::now(),
+            size: tar_gz.bytes_written(),
+            delta,
+            metadata: None,
+        })
+    }
+
+    /// Create a new Incremental backup from the given state, populated with the given directories.
+    ///
+    /// # Arguments
+    ///
+    /// * `previous_state` - State the file system was in during the previous backup in the chain
+    /// * `previous_start_time` - Start time of the previous backup; used to filter files
+    /// * `backup_dir` - Directory to store archive in
+    /// * `dirs` - list of tuples `(path_in_tar, src_dir)` with `path_in_tar` the directory name
+    ///     under which `src_dir`'s contents should be stored in the archive
+    ///
+    /// # Returns
+    ///
+    /// The `Backup` instance describing this new backup.
+    pub fn create_from<P: AsRef<Path>>(
+        previous_state: HashMap<PathBuf, HashSet<PathBuf>>,
+        previous_start_time: chrono::DateTime<Utc>,
+        backup_dir: P,
+        dirs: &Vec<(PathBuf, PathBuf)>,
+    ) -> io::Result<Self> {
+        let start_time = chrono::offset::Utc::now();
+
+        let path = Backup::path(backup_dir, start_time);
+        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);
+
+        let mut delta = Delta::new();
+
+        for (dir_in_tar, src_dir) in dirs {
+            let mut all_files: HashSet<PathBuf> = HashSet::new();
+            let mut added_files: HashSet<PathBuf> = HashSet::new();
+
+            for entry in src_dir.read_dir_recursive()?.ignored("cache").files() {
+                let path = entry?.path();
+                let stripped = path.strip_prefix(src_dir).unwrap();
+
+                if !path.not_modified_since(previous_start_time) {
+                    ar.append_path_with_name(&path, dir_in_tar.join(stripped))?;
+                    added_files.insert(stripped.to_path_buf());
+                }
+
+                all_files.insert(stripped.to_path_buf());
+            }
+
+            delta.added.insert(dir_in_tar.clone(), added_files);
+
+            if let Some(previous_files) = previous_state.get(dir_in_tar) {
+                delta.removed.insert(
+                    dir_in_tar.to_path_buf(),
+                    previous_files.difference(&all_files).cloned().collect(),
+                );
+            }
+        }
+
+        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,
+            end_time: chrono::Utc::now(),
+            size: tar_gz.bytes_written(),
+            delta,
+            metadata: None,
+        })
+    }
+
+    /// Restore the backup by extracting its contents to the respective directories.
+    ///
+    /// # Arguments
+    ///
+    /// * `backup_dir` - Backup directory where the file is stored
+    /// * `dirs` - list of tuples `(path_in_tar, dst_dir)` with `dst_dir` the directory on-disk
+    ///     where the files stored under `path_in_tar` inside the tarball should be extracted to.
+    pub fn restore<P: AsRef<Path>>(
+        &self,
+        backup_dir: P,
+        dirs: &Vec<(PathBuf, PathBuf)>,
+    ) -> io::Result<()> {
+        let path = Backup::path(backup_dir, self.start_time);
+        let tar_gz = File::open(path)?;
+        let enc = GzDecoder::new(tar_gz);
+        let mut ar = tar::Archive::new(enc);
+
+        // Unpack each file by matching it with one of the destination directories and extracting
+        // it to the right path
+        for entry in ar.entries()? {
+            let mut entry = entry?;
+            let entry_path_in_tar = entry.path()?.to_path_buf();
+
+            for (path_in_tar, dst_dir) in dirs {
+                if entry_path_in_tar.starts_with(path_in_tar) {
+                    let dst_path =
+                        dst_dir.join(entry_path_in_tar.strip_prefix(path_in_tar).unwrap());
+
+                    // Ensure all parent directories are present
+                    std::fs::create_dir_all(dst_path.parent().unwrap())?;
+
+                    entry.unpack(dst_path)?;
+
+                    break;
+                }
+            }
+        }
+
+        // Remove any files
+        for (path_in_tar, dst_dir) in dirs {
+            if let Some(removed) = self.delta.removed.get(path_in_tar) {
+                for path in removed {
+                    let dst_path = dst_dir.join(path);
+                    std::fs::remove_file(dst_path)?;
+                }
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl<T: Clone> fmt::Display for Backup<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let letter = match self.type_ {
+            BackupType::Full => 'F',
+            BackupType::Incremental => 'I',
+        };
+
+        // Pretty-print size
+        // If your backup is a petabyte or larger, this will crash and you need to re-evaluate your
+        // life choices
+        let index = self.size.ilog(1024) as usize;
+        let size = self.size as f64 / (1024.0_f64.powi(index as i32));
+        let duration = self.end_time - self.start_time;
+
+        write!(
+            f,
+            "{} ({}, {}m{}s, {:.2}{}, {})",
+            self.start_time.format(Backup::FILENAME_FORMAT),
+            letter,
+            duration.num_seconds() / 60,
+            duration.num_seconds() % 60,
+            size,
+            BYTE_SUFFIXES[index],
+            self.delta
+        )
+    }
+}

src/backup/path.rs

@@ -0,0 +1,147 @@
+use chrono::{Local, Utc};
+use std::collections::HashSet;
+use std::ffi::OsString;
+use std::fs::DirEntry;
+use std::path::{Path, PathBuf};
+use std::{fs, io};
+
+pub struct ReadDirRecursive {
+    ignored: HashSet<OsString>,
+    read_dir: fs::ReadDir,
+    dir_stack: Vec<PathBuf>,
+    files_only: bool,
+}
+
+impl ReadDirRecursive {
+    /// Start the iterator for a new directory
+    pub fn start<P: AsRef<Path>>(path: P) -> io::Result<Self> {
+        let path = path.as_ref();
+        let read_dir = path.read_dir()?;
+
+        Ok(ReadDirRecursive {
+            ignored: HashSet::new(),
+            read_dir,
+            dir_stack: Vec::new(),
+            files_only: false,
+        })
+    }
+
+    pub fn ignored<S: Into<OsString>>(mut self, s: S) -> Self {
+        self.ignored.insert(s.into());
+
+        self
+    }
+
+    pub fn files(mut self) -> Self {
+        self.files_only = true;
+
+        self
+    }
+
+    /// Tries to populate the `read_dir` field with a new `ReadDir` instance to consume.
+    fn next_read_dir(&mut self) -> io::Result<bool> {
+        if let Some(path) = self.dir_stack.pop() {
+            self.read_dir = path.read_dir()?;
+
+            Ok(true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    /// Convenience method to add a new directory to the stack.
+    fn push_entry(&mut self, entry: &io::Result<DirEntry>) {
+        if let Ok(entry) = entry {
+            if entry.path().is_dir() {
+                self.dir_stack.push(entry.path());
+            }
+        }
+    }
+
+    /// Determine whether an entry should be returned by the iterator.
+    fn should_return(&self, entry: &io::Result<DirEntry>) -> bool {
+        if let Ok(entry) = entry {
+            let mut res = !self.ignored.contains(&entry.file_name());
+
+            // Please just let me combine these already
+            if self.files_only {
+                if let Ok(file_type) = entry.file_type() {
+                    res = res && file_type.is_file();
+                }
+                // We  couldn't determine if it's a file, so we don't return it
+                else {
+                    res = false;
+                }
+            }
+
+            res
+        } else {
+            true
+        }
+    }
+}
+
+impl Iterator for ReadDirRecursive {
+    type Item = io::Result<DirEntry>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            // First, we try to consume the current directory's items
+            while let Some(entry) = self.read_dir.next() {
+                self.push_entry(&entry);
+
+                if self.should_return(&entry) {
+                    return Some(entry);
+                }
+            }
+
+            // If we get an error while setting up a new directory, we return this, otherwise we
+            // keep trying to consume the directories
+            match self.next_read_dir() {
+                Ok(true) => (),
+                // There's no more directories to traverse, so the iterator is done
+                Ok(false) => return None,
+                Err(e) => return Some(Err(e)),
+            }
+        }
+    }
+}
+
+pub trait PathExt {
+    /// Confirm whether the file has not been modified since the given timestamp.
+    ///
+    /// This function will only return true if it can determine with certainty that the file hasn't
+    /// been modified.
+    ///
+    /// # Args
+    ///
+    /// * `timestamp` - Timestamp to compare modified time with
+    ///
+    /// # Returns
+    ///
+    /// True if the file has not been modified for sure, false otherwise.
+    fn not_modified_since(&self, timestamp: chrono::DateTime<Utc>) -> bool;
+
+    /// An extension of the `read_dir` command that runs through the entire underlying directory
+    /// structure using breadth-first search
+    fn read_dir_recursive(&self) -> io::Result<ReadDirRecursive>;
+}
+
+impl PathExt for Path {
+    fn not_modified_since(&self, timestamp: chrono::DateTime<Utc>) -> bool {
+        if let Ok(metadata) = self.metadata() {
+            if let Ok(last_modified) = metadata.modified() {
+                let t: chrono::DateTime<Utc> = last_modified.into();
+                let t = t.with_timezone(&Local);
+
+                return t < timestamp;
+            }
+        }
+
+        false
+    }
+
+    fn read_dir_recursive(&self) -> io::Result<ReadDirRecursive> {
+        ReadDirRecursive::start(self)
+    }
+}

src/cli/backup.rs

@@ -0,0 +1,173 @@
+use crate::backup::Backup;
+use crate::cli::Cli;
+use crate::other;
+use chrono::{TimeZone, Utc};
+use clap::{Args, Subcommand};
+use std::io;
+use std::path::PathBuf;
+
+#[derive(Subcommand)]
+pub enum BackupCommands {
+    /// List all tracked backups
+    List(BackupListArgs),
+    /// Manually create a new backup
+    Create(BackupCreateArgs),
+    /// Restore a backup
+    Restore(BackupRestoreArgs),
+}
+
+#[derive(Args)]
+pub struct BackupArgs {
+    #[command(subcommand)]
+    pub command: BackupCommands,
+}
+
+#[derive(Args)]
+pub struct BackupCreateArgs {
+    /// What layer to create a backup in
+    layer: String,
+}
+
+#[derive(Args)]
+pub struct BackupListArgs {
+    /// What layer to list
+    layer: Option<String>,
+}
+
+#[derive(Args)]
+pub struct BackupRestoreArgs {
+    /// Path to the backup inside the backup directory
+    path: PathBuf,
+    /// Directory to store config in
+    output_config: PathBuf,
+    /// Directory to store worlds in
+    output_worlds: PathBuf,
+    /// Whether to overwrite the contents of the existing directories
+    #[arg(short, long, default_value_t = false)]
+    force: bool,
+    /// Create output directories if they don't exist
+    #[arg(short, long, default_value_t = false)]
+    make: bool,
+}
+
+impl BackupArgs {
+    pub fn run(&self, cli: &Cli) -> io::Result<()> {
+        match &self.command {
+            BackupCommands::Create(args) => args.run(cli),
+            BackupCommands::List(args) => args.run(cli),
+            BackupCommands::Restore(args) => args.run(cli),
+        }
+    }
+}
+
+impl BackupCreateArgs {
+    pub fn run(&self, cli: &Cli) -> io::Result<()> {
+        let mut meta = cli.meta()?;
+
+        if let Some(res) = meta.create_backup(&self.layer) {
+            res
+        } else {
+            Err(io::Error::new(io::ErrorKind::Other, "Unknown layer"))
+        }
+    }
+}
+
+impl BackupRestoreArgs {
+    pub fn run(&self, cli: &Cli) -> io::Result<()> {
+        let backup_dir = cli.backup.canonicalize()?;
+
+        // Create directories if needed
+        if self.make {
+            std::fs::create_dir_all(&self.output_config)?;
+            std::fs::create_dir_all(&self.output_worlds)?;
+        }
+
+        let output_config = self.output_config.canonicalize()?;
+        let output_worlds = self.output_worlds.canonicalize()?;
+
+        // Parse input path
+        let path = self.path.canonicalize()?;
+
+        if !path.starts_with(&backup_dir) {
+            return Err(other("Provided file is not inside the backup directory."));
+        }
+
+        let layer = if let Some(parent) = path.parent() {
+            // Backup files should be stored nested inside a layer's folder
+            if parent != backup_dir {
+                parent.file_name().unwrap().to_string_lossy()
+            } else {
+                return Err(other("Invalid path."));
+            }
+        } else {
+            return Err(other("Invalid path."));
+        };
+
+        let timestamp = if let Some(filename) = path.file_name() {
+            Utc.datetime_from_str(&filename.to_string_lossy(), Backup::FILENAME_FORMAT)
+                .map_err(|_| other("Invalid filename."))?
+        } else {
+            return Err(other("Invalid filename."));
+        };
+
+        let meta = cli.meta()?;
+
+        // Clear previous contents of directories
+        let mut entries = output_config
+            .read_dir()?
+            .chain(output_worlds.read_dir()?)
+            .peekable();
+
+        if entries.peek().is_some() && !self.force {
+            return Err(other("Output directories are not empty. If you wish to overwrite these contents, use the force flag."));
+        }
+
+        for entry in entries {
+            let path = entry?.path();
+
+            if path.is_dir() {
+                std::fs::remove_dir_all(path)?;
+            } else {
+                std::fs::remove_file(path)?;
+            }
+        }
+
+        let dirs = vec![
+            (PathBuf::from("config"), output_config),
+            (PathBuf::from("worlds"), output_worlds),
+        ];
+
+        // Restore the backup
+        if let Some(res) = meta.restore_backup(&layer, timestamp, &dirs) {
+            res
+        } else {
+            Err(other("Unknown layer"))
+        }
+    }
+}
+
+impl BackupListArgs {
+    pub fn run(&self, cli: &Cli) -> io::Result<()> {
+        let meta = cli.meta()?;
+
+        // A bit scuffed? Sure
+        for (name, manager) in meta
+            .managers()
+            .iter()
+            .filter(|(name, _)| self.layer.is_none() || &self.layer.as_ref().unwrap() == name)
+        {
+            println!("{}", name);
+
+            for chain in manager.chains().iter().filter(|c| !c.is_empty()) {
+                let mut iter = chain.iter();
+                println!("  {}", iter.next().unwrap());
+
+                for backup in iter {
+                    println!("    {}", backup);
+                }
+            }
+        }
+
+        Ok(())
+    }
+}

src/cli/mod.rs

@@ -0,0 +1,92 @@
+mod backup;
+mod run;
+
+pub use crate::backup::MetaManager;
+pub use crate::server::Metadata;
+pub use backup::{BackupArgs, BackupCommands};
+pub use run::RunArgs;
+
+use crate::backup::ManagerConfig;
+use crate::server::ServerType;
+use clap::{Parser, Subcommand};
+use std::io;
+use std::path::PathBuf;
+
+#[derive(Subcommand)]
+pub enum Commands {
+    /// Run the server
+    Run(RunArgs),
+    /// Interact with the backup system without starting a server
+    Backup(BackupArgs),
+}
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+pub struct Cli {
+    #[command(subcommand)]
+    pub command: Commands,
+    /// Directory where configs are stored, and where the server will run
+    #[arg(
+        long,
+        value_name = "CONFIG_DIR",
+        default_value = ".",
+        env = "ALEX_CONFIG_DIR",
+        global = true
+    )]
+    pub config: PathBuf,
+    /// Directory where world files will be saved
+    #[arg(
+        long,
+        value_name = "WORLD_DIR",
+        default_value = "../worlds",
+        env = "ALEX_WORLD_DIR",
+        global = true
+    )]
+    pub world: PathBuf,
+    /// Directory where backups will be stored
+    #[arg(
+        long,
+        value_name = "BACKUP_DIR",
+        default_value = "../backups",
+        env = "ALEX_BACKUP_DIR",
+        global = true
+    )]
+    pub backup: PathBuf,
+
+    /// What backup layers to employ, provided as a list of tuples name,frequency,chains,chain_len
+    /// delimited by semicolons (;).
+    #[arg(long, env = "ALEX_LAYERS", global = true, value_delimiter = ';')]
+    pub layers: Vec<ManagerConfig>,
+
+    /// Type of server
+    #[arg(long, default_value = "unknown", env = "ALEX_SERVER", global = true)]
+    pub server: ServerType,
+    /// Version string for the server, e.g. 1.19.4-545
+    #[arg(long, default_value = "", env = "ALEX_SERVER_VERSION", global = true)]
+    pub server_version: String,
+}
+
+impl Cli {
+    pub fn run(&self) -> io::Result<()> {
+        match &self.command {
+            Commands::Run(args) => args.run(self),
+            Commands::Backup(args) => args.run(self),
+        }
+    }
+
+    /// Convenience method to initialize backup manager from the cli arguments
+    pub fn meta(&self) -> io::Result<MetaManager<Metadata>> {
+        let metadata = Metadata {
+            server_type: self.server,
+            server_version: self.server_version.clone(),
+        };
+        let dirs = vec![
+            (PathBuf::from("config"), self.config.canonicalize()?),
+            (PathBuf::from("worlds"), self.world.canonicalize()?),
+        ];
+        let mut meta = MetaManager::new(self.backup.canonicalize()?, dirs, metadata);
+        meta.add_all(&self.layers)?;
+
+        Ok(meta)
+    }
+}

src/cli/run.rs

@@ -0,0 +1,94 @@
+use crate::cli::Cli;
+use crate::server;
+use crate::signals;
+use crate::stdin;
+use clap::Args;
+use std::io;
+use std::path::PathBuf;
+use std::sync::{Arc, Mutex};
+
+#[derive(Args)]
+pub struct RunArgs {
+    /// Server jar to execute
+    #[arg(
+        long,
+        value_name = "JAR_PATH",
+        default_value = "server.jar",
+        env = "ALEX_JAR"
+    )]
+    pub jar: PathBuf,
+
+    /// Java command to run the server jar with
+    #[arg(long, value_name = "JAVA_CMD", default_value_t = String::from("java"), env = "ALEX_JAVA")]
+    pub java: String,
+
+    /// XMS value in megabytes for the server instance
+    #[arg(long, default_value_t = 1024, env = "ALEX_XMS")]
+    pub xms: u64,
+    /// XMX value in megabytes for the server instance
+    #[arg(long, default_value_t = 2048, env = "ALEX_XMX")]
+    pub xmx: u64,
+
+    /// Don't actually run the server, but simply output the server configuration that would have
+    /// been ran
+    #[arg(short, long, default_value_t = false)]
+    pub dry: bool,
+}
+
+fn backups_thread(counter: Arc<Mutex<server::ServerProcess>>) {
+    loop {
+        let next_scheduled_time = {
+            let server = counter.lock().unwrap();
+            server.backups.next_scheduled_time().unwrap()
+        };
+
+        let now = chrono::offset::Utc::now();
+        if next_scheduled_time > now {
+            std::thread::sleep((next_scheduled_time - now).to_std().unwrap());
+        }
+
+        {
+            let mut server = counter.lock().unwrap();
+
+            // We explicitely ignore the error here, as we don't want the thread to fail
+            let _ = server.backup();
+        }
+    }
+}
+
+impl RunArgs {
+    pub fn run(&self, cli: &Cli) -> io::Result<()> {
+        let (_, mut signals) = signals::install_signal_handlers()?;
+
+        let mut cmd = server::ServerCommand::new(cli.server, &cli.server_version)
+            .java(&self.java)
+            .jar(self.jar.clone())
+            .config(cli.config.clone())
+            .world(cli.world.clone())
+            .backup(cli.backup.clone())
+            .managers(cli.layers.clone())
+            .xms(self.xms)
+            .xmx(self.xmx);
+        cmd.canonicalize()?;
+
+        if self.dry {
+            print!("{}", cmd);
+
+            return Ok(());
+        }
+
+        let counter = Arc::new(Mutex::new(cmd.spawn()?));
+
+        if !cli.layers.is_empty() {
+            let clone = Arc::clone(&counter);
+            std::thread::spawn(move || backups_thread(clone));
+        }
+
+        // Spawn thread that handles the main stdin loop
+        let clone = Arc::clone(&counter);
+        std::thread::spawn(move || stdin::handle_stdin(clone));
+
+        // Signal handler loop exits the process when necessary
+        signals::handle_signals(&mut signals, counter)
+    }
+}

src/main.rs

@@ -1,123 +1,38 @@
+mod backup;
+mod cli;
 mod server;
 mod signals;
 mod stdin;
 
+use crate::cli::Cli;
 use clap::Parser;
-use server::ServerType;
 use std::io;
-use std::path::PathBuf;
-use std::sync::{Arc, Mutex};
 
-#[derive(Parser)]
-#[command(author, version, about, long_about = None)]
-struct Cli {
-    /// Type of server
-    type_: ServerType,
-    /// Version string for the server, e.g. 1.19.4-545
-    #[arg(env = "ALEX_SERVER_VERSION")]
-    server_version: String,
-
-    /// Server jar to execute
-    #[arg(
-        long,
-        value_name = "JAR_PATH",
-        default_value = "server.jar",
-        env = "ALEX_JAR"
-    )]
-    jar: PathBuf,
-    /// Directory where configs are stored, and where the server will run
-    #[arg(
-        long,
-        value_name = "CONFIG_DIR",
-        default_value = ".",
-        env = "ALEX_CONFIG_DIR"
-    )]
-    config: PathBuf,
-    /// Directory where world files will be saved
-    #[arg(
-        long,
-        value_name = "WORLD_DIR",
-        default_value = "../worlds",
-        env = "ALEX_WORLD_DIR"
-    )]
-    world: PathBuf,
-    /// Directory where backups will be stored
-    #[arg(
-        long,
-        value_name = "BACKUP_DIR",
-        default_value = "../backups",
-        env = "ALEX_BACKUP_DIR"
-    )]
-    backup: PathBuf,
-    /// Java command to run the server jar with
-    #[arg(long, value_name = "JAVA_CMD", default_value_t = String::from("java"), env = "ALEX_JAVA")]
-    java: String,
-
-    /// XMS value in megabytes for the server instance
-    #[arg(long, default_value_t = 1024, env = "ALEX_XMS")]
-    xms: u64,
-    /// XMX value in megabytes for the server instance
-    #[arg(long, default_value_t = 2048, env = "ALEX_XMX")]
-    xmx: u64,
-
-    /// How many backups to keep
-    #[arg(short = 'n', long, default_value_t = 7, env = "ALEX_MAX_BACKUPS")]
-    max_backups: u64,
-    /// How frequently to perform a backup, in minutes; 0 to disable.
-    #[arg(short = 't', long, default_value_t = 0, env = "ALEX_FREQUENCY")]
-    frequency: u64,
-
-    /// Don't actually run the server, but simply output the server configuration that would have
-    /// been ran
-    #[arg(short, long, default_value_t = false)]
-    dry: bool,
+pub fn other(msg: &str) -> io::Error {
+    io::Error::new(io::ErrorKind::Other, msg)
 }
 
-fn backups_thread(counter: Arc<Mutex<server::ServerProcess>>, frequency: u64) {
-    loop {
-        std::thread::sleep(std::time::Duration::from_secs(frequency * 60));
+// fn commands_backup(cli: &Cli, args: &BackupArgs) -> io::Result<()> {
+//     let metadata = server::Metadata {
+//         server_type: cli.server,
+//         server_version: cli.server_version.clone(),
+//     };
+//     let dirs = vec![
+//         (PathBuf::from("config"), cli.config.clone()),
+//         (PathBuf::from("worlds"), cli.world.clone()),
+//     ];
+//     let mut meta = MetaManager::new(cli.backup.clone(), dirs, metadata);
+//     meta.add_all(&cli.layers)?;
 
-        {
-            let mut server = counter.lock().unwrap();
+//     match &args.command {
+//         BackupCommands::List => ()
+//     }
 
-            // We explicitely ignore the error here, as we don't want the thread to fail
-            let _ = server.backup();
-        }
-    }
-}
+//     // manager.create_backup()?;
+//     // manager.remove_old_backups()
+// }
 
 fn main() -> io::Result<()> {
-    let (_, mut signals) = signals::install_signal_handlers()?;
     let cli = Cli::parse();
-
-    let mut cmd = server::ServerCommand::new(cli.type_, &cli.server_version)
-        .java(&cli.java)
-        .jar(cli.jar)
-        .config(cli.config)
-        .world(cli.world)
-        .backup(cli.backup)
-        .xms(cli.xms)
-        .xmx(cli.xmx)
-        .max_backups(cli.max_backups);
-    cmd.canonicalize()?;
-
-    if cli.dry {
-        print!("{}", cmd);
-
-        return Ok(());
-    }
-
-    let counter = Arc::new(Mutex::new(cmd.spawn()?));
-
-    if cli.frequency > 0 {
-        let clone = Arc::clone(&counter);
-        std::thread::spawn(move || backups_thread(clone, cli.frequency));
-    }
-
-    // Spawn thread that handles the main stdin loop
-    let clone = Arc::clone(&counter);
-    std::thread::spawn(move || stdin::handle_stdin(clone));
-
-    // Signal handler loop exits the process when necessary
-    signals::handle_signals(&mut signals, counter)
+    cli.run()
 }

src/server/command.rs

@@ -1,30 +1,12 @@
-use crate::server::ServerProcess;
-use clap::ValueEnum;
+use crate::backup::ManagerConfig;
+use crate::backup::MetaManager;
+use crate::server::{Metadata, ServerProcess, ServerType};
 use std::fmt;
 use std::fs::File;
 use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, ValueEnum)]
-pub enum ServerType {
-    Paper,
-    Forge,
-    Vanilla,
-}
-
-impl fmt::Display for ServerType {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let s = match self {
-            ServerType::Paper => "PaperMC",
-            ServerType::Forge => "Forge",
-            ServerType::Vanilla => "Vanilla",
-        };
-
-        write!(f, "{}", s)
-    }
-}
-
 pub struct ServerCommand {
     type_: ServerType,
     version: String,
@@ -35,7 +17,7 @@ pub struct ServerCommand {
     backup_dir: PathBuf,
     xms: u64,
     xmx: u64,
-    max_backups: u64,
+    managers: Vec<ManagerConfig>,
 }
 
 impl ServerCommand {
@@ -50,7 +32,7 @@ impl ServerCommand {
             backup_dir: PathBuf::from("backups"),
             xms: 1024,
             xmx: 2048,
-            max_backups: 7,
+            managers: Vec::new(),
         }
     }
 
@@ -91,8 +73,9 @@ impl ServerCommand {
         self
     }
 
-    pub fn max_backups(mut self, v: u64) -> Self {
-        self.max_backups = v;
+    pub fn managers(mut self, configs: Vec<ManagerConfig>) -> Self {
+        self.managers = configs;
+
         self
     }
 
@@ -179,19 +162,24 @@ impl ServerCommand {
     }
 
     pub fn spawn(&mut self) -> std::io::Result<ServerProcess> {
+        let metadata = Metadata {
+            server_type: self.type_,
+            server_version: self.version.clone(),
+        };
+
+        let dirs = vec![
+            (PathBuf::from("config"), self.config_dir.clone()),
+            (PathBuf::from("worlds"), self.world_dir.clone()),
+        ];
+
+        let mut meta = MetaManager::new(self.backup_dir.clone(), dirs, metadata);
+        meta.add_all(&self.managers)?;
+
         let mut cmd = self.create_cmd();
         self.accept_eula()?;
         let child = cmd.spawn()?;
 
-        Ok(ServerProcess::new(
-            self.type_,
-            self.version.clone(),
-            self.config_dir.clone(),
-            self.world_dir.clone(),
-            self.backup_dir.clone(),
-            self.max_backups,
-            child,
-        ))
+        Ok(ServerProcess::new(meta, child))
     }
 }
 

src/server/mod.rs

@@ -1,5 +1,36 @@
 mod command;
 mod process;
 
-pub use command::{ServerCommand, ServerType};
+pub use command::ServerCommand;
 pub use process::ServerProcess;
+
+use clap::ValueEnum;
+use serde::{Deserialize, Serialize};
+use std::fmt;
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, ValueEnum, Serialize, Deserialize, Debug)]
+pub enum ServerType {
+    Unknown,
+    Paper,
+    Forge,
+    Vanilla,
+}
+
+impl fmt::Display for ServerType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let s = match self {
+            ServerType::Unknown => "Unknown",
+            ServerType::Paper => "PaperMC",
+            ServerType::Forge => "Forge",
+            ServerType::Vanilla => "Vanilla",
+        };
+
+        write!(f, "{}", s)
+    }
+}
+
+#[derive(Clone, Serialize, Deserialize, Debug)]
+pub struct Metadata {
+    pub server_type: ServerType,
+    pub server_version: String,
+}

src/server/process.rs

@@ -1,44 +1,18 @@
-use crate::server::ServerType;
-use flate2::write::GzEncoder;
-use flate2::Compression;
+use crate::backup::MetaManager;
+use crate::server::Metadata;
 use std::io::Write;
-use std::path::{Path, PathBuf};
 use std::process::Child;
 
-#[link(name = "c")]
-extern "C" {
-    fn geteuid() -> u32;
-    fn getegid() -> u32;
-}
-
 pub struct ServerProcess {
-    type_: ServerType,
-    version: String,
-    config_dir: PathBuf,
-    world_dir: PathBuf,
-    backup_dir: PathBuf,
-    max_backups: u64,
     child: Child,
+    pub backups: MetaManager<Metadata>,
 }
 
 impl ServerProcess {
-    pub fn new(
-        type_: ServerType,
-        version: String,
-        config_dir: PathBuf,
-        world_dir: PathBuf,
-        backup_dir: PathBuf,
-        max_backups: u64,
-        child: Child,
-    ) -> ServerProcess {
+    pub fn new(manager: MetaManager<Metadata>, child: Child) -> ServerProcess {
         ServerProcess {
-            type_,
-            version,
-            config_dir,
-            world_dir,
-            backup_dir,
-            max_backups,
             child,
+            backups: manager,
         }
     }
 
@@ -74,7 +48,8 @@ impl ServerProcess {
     /// Perform a backup by disabling the server's save feature and flushing its data, before
     /// creating an archive file.
     pub fn backup(&mut self) -> std::io::Result<()> {
-        self.custom("say backing up server")?;
+        let layer_name = String::from(self.backups.next_scheduled_layer().unwrap());
+        self.custom(&format!("say starting backup for layer '{}'", layer_name))?;
 
         // Make sure the server isn't modifying the files during the backup
         self.custom("save-off")?;
@@ -84,94 +59,32 @@ impl ServerProcess {
         // We wait some time to (hopefully) ensure the save-all call has completed
         std::thread::sleep(std::time::Duration::from_secs(10));
 
-        let res = self.create_backup_archive();
-
-        if res.is_ok() {
-            self.remove_old_backups()?;
-        }
+        let start_time = chrono::offset::Utc::now();
+        let res = self.backups.perform_backup_cycle();
 
         // The server's save feature needs to be enabled again even if the archive failed to create
         self.custom("save-on")?;
+        self.custom("save-all")?;
+
+        let duration = chrono::offset::Utc::now() - start_time;
+        let duration_str = format!(
+            "{}m{}s",
+            duration.num_seconds() / 60,
+            duration.num_seconds() % 60
+        );
 
         if res.is_ok() {
-            self.custom("say server backed up successfully")?;
+            self.custom(&format!(
+                "say backup created for layer '{}' in {}",
+                layer_name, duration_str
+            ))?;
         } else {
-            self.custom("an error occured while backing up the server")?;
+            self.custom(&format!(
+                "an error occured after {} while creating backup for layer '{}'",
+                duration_str, layer_name
+            ))?;
         }
 
         res
     }
-
-    /// Create a new compressed backup archive of the server's data.
-    fn create_backup_archive(&mut self) -> std::io::Result<()> {
-        // Create a gzip-compressed tarball of the worlds folder
-        let filename = format!(
-            "{}",
-            chrono::offset::Local::now().format("%Y-%m-%d_%H-%M-%S.tar.gz")
-        );
-        let path = self.backup_dir.join(filename);
-        let tar_gz = std::fs::File::create(path)?;
-        let enc = GzEncoder::new(tar_gz, Compression::default());
-        let mut tar = tar::Builder::new(enc);
-
-        tar.append_dir_all("worlds", &self.world_dir)?;
-
-        // Add all files from the config directory that aren't the cache
-        for entry in self
-            .config_dir
-            .read_dir()?
-            .filter_map(|e| e.ok())
-            .filter(|e| e.file_name() != "cache")
-        {
-            let tar_path = Path::new("config").join(entry.file_name());
-
-            if entry.file_type()?.is_dir() {
-                tar.append_dir_all(tar_path, entry.path())?;
-            } else {
-                tar.append_path_with_name(entry.path(), tar_path)?;
-            }
-        }
-
-        // We add a file to the backup describing for what version it was made
-        let info = format!("{} {}", self.type_, self.version);
-        let info_bytes = info.as_bytes();
-
-        let mut header = tar::Header::new_gnu();
-        header.set_size(info_bytes.len().try_into().unwrap());
-        header.set_mode(0o100644);
-        unsafe {
-            header.set_gid(getegid().into());
-            header.set_uid(geteuid().into());
-        }
-
-        tar.append_data(&mut header, "info.txt", info_bytes)?;
-
-        // Backup file gets finalized in the drop
-
-        Ok(())
-    }
-
-    /// Remove the oldest backups
-    fn remove_old_backups(&mut self) -> std::io::Result<()> {
-        // The naming format used allows us to sort the backups by name and still get a sorting by
-        // creation time
-        let mut backups = self
-            .backup_dir
-            .read_dir()?
-            .filter_map(|res| res.map(|e| e.path()).ok())
-            .collect::<Vec<PathBuf>>();
-        backups.sort();
-
-        let max_backups: usize = self.max_backups.try_into().unwrap();
-
-        if backups.len() > max_backups {
-            let excess_backups = backups.len() - max_backups;
-
-            for backup in &backups[0..excess_backups] {
-                std::fs::remove_file(backup)?;
-            }
-        }
-
-        Ok(())
-    }
 }