redis_rocksdb 0.3.9

rust implement structure kv(key/value) embedded database, storage by rocksdb
Documentation 
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use std::ops::Deref;
use std::ptr;

use crate::{read_int, write_int, Bytes, RedisRocksdb, RrError, Stack};

impl Stack for RedisRocksdb {
	fn index<K: Bytes>(&self, key: &K, _index: i64) -> Result<Vec<u8>, RrError> {
		let stack = StackHeader::get_stack(&self.db, key.as_ref())?;
		match stack {
			None => Ok(vec![]),
			Some(v) => Ok(v.size.to_vec()),
		}
	}

	fn len<K: Bytes>(&self, _key: &K) -> Result<i64, RrError> {
		todo!()
	}

	fn push<K: Bytes, V: Bytes>(&mut self, _key: &K, _value: &V) -> Result<i64, RrError> {
		todo!()
	}

	fn pushs<K: Bytes, V: Bytes>(&mut self, _key: &K, _values: &[&V]) -> Result<i64, RrError> {
		todo!()
	}

	fn push_exists<K: Bytes, V: Bytes>(&mut self, _key: &K, _value: &V) -> Result<i64, RrError> {
		todo!()
	}

	fn range<K: Bytes>(&self, _key: &K, _start: i64, _stop: i64) -> Result<Vec<Vec<u8>>, RrError> {
		todo!()
	}

	fn set<K: Bytes, V: Bytes>(&mut self, _key: &K, _index: i64, _value: &V) -> Result<Vec<u8>, RrError> {
		todo!()
	}

	fn pop<K: Bytes>(&self, _key: &K) -> Result<Vec<u8>, RrError> {
		todo!()
	}

	fn pops<K: Bytes>(&self, _key: &K, _amount: u64) -> Result<Vec<Vec<u8>>, RrError> {
		todo!()
	}

	fn poplpush<K: Bytes, V: Bytes>(&mut self, _key: &K, _dstkey: &K) -> Result<V, RrError> {
		todo!()
	}

	fn clear<K: Bytes>(&mut self, _key: &K) -> Result<i64, RrError> {
		todo!()
	}
}

struct StackHeader {
	size: [u8; 8],
	// key: &'a [u8],
}

impl StackHeader {
	fn size_i64(&self) -> i64 {
		read_int(&self.size)
	}
	fn add_1(&mut self) -> i64 {
		let mut t = read_int(&self.size);
		t += 1;
		write_int(&mut self.size, t);
		t
	}

	fn add(&mut self, v: i64) -> i64 {
		let mut t = read_int(&self.size);
		t += v;
		write_int(&mut self.size, t);
		t
	}

	fn make_key_index(key: &[u8], index: i64) -> Vec<u8> {
		let mut v = Vec::with_capacity(key.len() + 9);
		unsafe {
			v.set_len(v.capacity());
			ptr::copy(key.as_ptr(), v.as_mut_ptr(), key.len());
		}
		let vv = v.as_mut_slice();
		vv[key.len()] = b'_';
		write_int(&mut vv[key.len() + 1..], index);
		v
	}

	fn get_stack(db: &rocksdb::TransactionDB, key: &[u8]) -> Result<Option<Self>, RrError> {
		let v = db.get(key)?;
		match v {
			None => Ok(None),
			Some(v) => {
				if v.len() < 8 {
					Err(RrError::data_error("key < 8"))
				} else {
					Ok(Some(StackHeader::from(v.deref())))
				}
			},
		}
	}
	fn get_index(&self, db: &rocksdb::TransactionDB, key: &[u8], _index: i64) -> Result<Vec<u8>, RrError> {
		let v = db.get(key)?;
		match v {
			None => Ok(vec![]),
			Some(v) => {
				if v.len() < 8 {
					Err(RrError::data_error("key < 8"))
				} else {
					Ok(v.to_vec())
				}
			},
		}
	}
}

impl From<i64> for StackHeader {
	fn from(value: i64) -> Self {
		let mut s = StackHeader { size: [0; 8] };
		write_int(&mut s.size, value);
		s
	}
}

impl From<&[u8]> for StackHeader {
	fn from(value: &[u8]) -> Self {
		let mut s = StackHeader { size: [0; 8] };
		s.size.copy_from_slice(value);
		s
	}
}

impl AsRef<[u8]> for StackHeader {
	fn as_ref(&self) -> &[u8] {
		&self.size
	}
}

impl Bytes for StackHeader {}