rust-libp2p/protocols/kad/src/record.rs

// Copyright 2019 Parity Technologies (UK) Ltd.
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//! Records and record storage abstraction of the libp2p Kademlia DHT.

use fnv::FnvHashMap;
use multihash::Multihash;
use std::borrow::Cow;

/// The records that are kept in the dht.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Record {
    /// Key of the record.
    pub key: Multihash,
    /// Value of the record.
    pub value: Vec<u8>,
}

/// Trait for a record store.
pub trait RecordStore {
    fn get(&self, k: &Multihash) -> Option<Cow<Record>>;
    fn put(&mut self, r: Record) -> Result<(), RecordStorageError>;
}

/// The error record store may return
#[derive(Clone, Debug, PartialEq)]
pub enum RecordStorageError {
    /// Store reached the capacity limit.
    AtCapacity,
    /// Value being put is larger than the limit.
    ValueTooLarge,
}

/// In-memory implementation of the record store.
pub struct MemoryRecordStorage {
    /// Maximum number of records we will store.
    max_records: usize,
    /// Maximum size of the record we will store.
    max_record_size: usize,
    /// The records.
    records: FnvHashMap<Multihash, Record>
}

impl MemoryRecordStorage {
    const MAX_RECORDS: usize = 1024;
    const MAX_RECORD_SIZE: usize = 65535;

    /// Creates a new `MemoryRecordStorage`.
    pub fn new(max_records: usize, max_record_size: usize) -> Self {
        MemoryRecordStorage{
            max_records,
            max_record_size,
            records: FnvHashMap::default()
        }
    }
}

impl Default for MemoryRecordStorage {
    fn default() -> Self {
        MemoryRecordStorage::new(Self::MAX_RECORDS, Self::MAX_RECORD_SIZE)
    }
}

impl RecordStore for MemoryRecordStorage {
    fn get(&self, k: &Multihash) -> Option<Cow<Record>> {
        match self.records.get(k) {
            Some(rec) => Some(Cow::Borrowed(rec)),
            None => None,
        }
    }

    fn put(&mut self, r: Record) -> Result<(), RecordStorageError> {
        if self.records.len() >= self.max_records {
            return Err(RecordStorageError::AtCapacity);
        }

        if r.value.len() >= self.max_record_size {
            return Err(RecordStorageError::ValueTooLarge)
        }

        self.records.insert(r.key.clone(), r);

        Ok(())
    }
}