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//! Store chunks on-disk on server.
use crate::chunk::DataChunk;
use crate::chunkid::ChunkId;
use std::path::{Path, PathBuf};
/// Store chunks, with metadata, persistently.
///
/// The chunks and their metadata are stored persistently on disk
/// under a directory specified as the Store struct is created. To
/// store or retrieve a chunk its identifier must be used.
pub struct Store {
dir: PathBuf,
}
/// An error from a `Store` operation.
pub type StoreError = std::io::Error;
impl Store {
/// Create a new Store to represent on-disk storage of chunks.x
pub fn new(dir: &Path) -> Self {
Store {
dir: dir.to_path_buf(),
}
}
// Construct name for a files in the store from chunk id.
//
// The name of directory containing the file is returned
// separately to make it easier to create it if needed.
fn filenames(&self, id: &ChunkId) -> (PathBuf, PathBuf, PathBuf) {
let bytes = id.as_bytes();
assert!(bytes.len() > 3);
let a = bytes[0];
let b = bytes[1];
let c = bytes[2];
let dir = self.dir.join(format!("{}/{}/{}", a, b, c));
let meta = dir.join(format!("{}.{}", id, "meta"));
let data = dir.join(format!("{}.{}", id, "data"));
(dir, meta, data)
}
/// Save a chunk into a store.
pub fn save(&self, id: &ChunkId, chunk: &DataChunk) -> Result<(), StoreError> {
let (dir, metaname, dataname) = &self.filenames(id);
if !dir.exists() {
std::fs::create_dir_all(dir)?;
}
std::fs::write(metaname, chunk.meta().to_json())?;
std::fs::write(dataname, chunk.data())?;
Ok(())
}
/// Load a chunk from a store.
pub fn load(&self, id: &ChunkId) -> Result<DataChunk, StoreError> {
let (_, metaname, dataname) = &self.filenames(id);
let meta = std::fs::read(metaname)?;
let meta = serde_json::from_slice(&meta)?;
let data = std::fs::read(dataname)?;
let data = DataChunk::new(data, meta);
Ok(data)
}
/// Delete a chunk from a store.
pub fn delete(&self, id: &ChunkId) -> Result<(), StoreError> {
let (_, metaname, dataname) = &self.filenames(id);
std::fs::remove_file(metaname)?;
std::fs::remove_file(dataname)?;
Ok(())
}
}
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