// Copyright 2014 Tyler Neely
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

use crate::{
    ffi, ffi_util::opt_bytes_to_ptr, ColumnFamily, ColumnFamilyDescriptor, Error, FlushOptions,
    Options, WriteOptions, DB,
};

use libc::{self, c_char, c_int, c_uchar, c_void, size_t};
use std::collections::BTreeMap;
use std::ffi::{CStr, CString};
use std::fmt;
use std::fs;
use std::marker::PhantomData;
use std::ops::Deref;
use std::path::Path;
use std::ptr;
use std::slice;
use std::str;

unsafe impl Send for DB {}
unsafe impl Sync for DB {}

#[derive(Debug, Copy, Clone, PartialEq)]
pub enum DBCompressionType {
    None = ffi::rocksdb_no_compression as isize,
    Snappy = ffi::rocksdb_snappy_compression as isize,
    Zlib = ffi::rocksdb_zlib_compression as isize,
    Bz2 = ffi::rocksdb_bz2_compression as isize,
    Lz4 = ffi::rocksdb_lz4_compression as isize,
    Lz4hc = ffi::rocksdb_lz4hc_compression as isize,
    Zstd = ffi::rocksdb_zstd_compression as isize,
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub enum DBCompactionStyle {
    Level = ffi::rocksdb_level_compaction as isize,
    Universal = ffi::rocksdb_universal_compaction as isize,
    Fifo = ffi::rocksdb_fifo_compaction as isize,
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub enum DBRecoveryMode {
    TolerateCorruptedTailRecords = ffi::rocksdb_tolerate_corrupted_tail_records_recovery as isize,
    AbsoluteConsistency = ffi::rocksdb_absolute_consistency_recovery as isize,
    PointInTime = ffi::rocksdb_point_in_time_recovery as isize,
    SkipAnyCorruptedRecord = ffi::rocksdb_skip_any_corrupted_records_recovery as isize,
}

/// An atomic batch of write operations.
///
/// Making an atomic commit of several writes:
///
/// ```
/// use rocksdb::{DB, Options, WriteBatch};
///
/// let path = "_path_for_rocksdb_storage1";
/// {
///     let db = DB::open_default(path).unwrap();
///     let mut batch = WriteBatch::default();
///     batch.put(b"my key", b"my value");
///     batch.put(b"key2", b"value2");
///     batch.put(b"key3", b"value3");
///     db.write(batch); // Atomically commits the batch
/// }
/// let _ = DB::destroy(&Options::default(), path);
/// ```
pub struct WriteBatch {
    inner: *mut ffi::rocksdb_writebatch_t,
}

pub struct ReadOptions {
    inner: *mut ffi::rocksdb_readoptions_t,
}

/// A consistent view of the database at the point of creation.
///
/// ```
/// use rocksdb::{DB, IteratorMode, Options};
///
/// let path = "_path_for_rocksdb_storage3";
/// {
///     let db = DB::open_default(path).unwrap();
///     let snapshot = db.snapshot(); // Creates a longer-term snapshot of the DB, but closed when goes out of scope
///     let mut iter = snapshot.iterator(IteratorMode::Start); // Make as many iterators as you'd like from one snapshot
/// }
/// let _ = DB::destroy(&Options::default(), path);
/// ```
///
pub struct Snapshot<'a> {
    db: &'a DB,
    inner: *const ffi::rocksdb_snapshot_t,
}

/// `Send` and `Sync` implementations for `Snapshot` are safe, because `Snapshot` is
/// immutable and can be safely shared between threads.
unsafe impl<'a> Send for Snapshot<'a> {}
unsafe impl<'a> Sync for Snapshot<'a> {}

/// An iterator over a database or column family, with specifiable
/// ranges and direction.
///
/// This iterator is different to the standard ``DBIterator`` as it aims Into
/// replicate the underlying iterator API within RocksDB itself. This should
/// give access to more performance and flexibility but departs from the
/// widely recognised Rust idioms.
///
/// ```
/// use rocksdb::{DB, Options};
///
/// let path = "_path_for_rocksdb_storage4";
/// {
///     let db = DB::open_default(path).unwrap();
///     let mut iter = db.raw_iterator();
///
///     // Forwards iteration
///     iter.seek_to_first();
///     while iter.valid() {
///         println!("Saw {:?} {:?}", iter.key(), iter.value());
///         iter.next();
///     }
///
///     // Reverse iteration
///     iter.seek_to_last();
///     while iter.valid() {
///         println!("Saw {:?} {:?}", iter.key(), iter.value());
///         iter.prev();
///     }
///
///     // Seeking
///     iter.seek(b"my key");
///     while iter.valid() {
///         println!("Saw {:?} {:?}", iter.key(), iter.value());
///         iter.next();
///     }
///
///     // Reverse iteration from key
///     // Note, use seek_for_prev when reversing because if this key doesn't exist,
///     // this will make the iterator start from the previous key rather than the next.
///     iter.seek_for_prev(b"my key");
///     while iter.valid() {
///         println!("Saw {:?} {:?}", iter.key(), iter.value());
///         iter.prev();
///     }
/// }
/// let _ = DB::destroy(&Options::default(), path);
/// ```
pub struct DBRawIterator<'a> {
    inner: *mut ffi::rocksdb_iterator_t,
    db: PhantomData<&'a DB>,
}

/// Iterates the batches of writes since a given sequence number.
///
/// `DBWALIterator` is returned by `DB::get_updates_since()` and will return the
/// batches of write operations that have occurred since a given sequence number
/// (see `DB::latest_sequence_number()`). This iterator cannot be constructed by
/// the application.
///
/// The iterator item type is a tuple of (`u64`, `WriteBatch`) where the first
/// value is the sequence number of the associated write batch.
///
pub struct DBWALIterator {
    inner: *mut ffi::rocksdb_wal_iterator_t,
}

impl DBWALIterator {
    /// Returns `true` if the iterator is valid. An iterator is invalidated when
    /// it reaches the end of its defined range, or when it encounters an error.
    ///
    /// To check whether the iterator encountered an error after `valid` has
    /// returned `false`, use the [`status`](DBWALIterator::status) method.
    /// `status` will never return an error when `valid` is `true`.
    pub fn valid(&self) -> bool {
        unsafe { ffi::rocksdb_wal_iter_valid(self.inner) != 0 }
    }

    /// Returns an error `Result` if the iterator has encountered an error
    /// during operation. When an error is encountered, the iterator is
    /// invalidated and [`valid`](DBWALIterator::valid) will return `false` when
    /// called.
    pub fn status(&self) -> Result<(), Error> {
        unsafe {
            ffi_try!(ffi::rocksdb_wal_iter_status(self.inner));
        }
        Ok(())
    }
}

impl Iterator for DBWALIterator {
    type Item = (u64, WriteBatch);

    fn next(&mut self) -> Option<(u64, WriteBatch)> {
        // Seek to the next write batch.
        unsafe {
            ffi::rocksdb_wal_iter_next(self.inner);
        }
        if self.valid() {
            let mut seq: u64 = 0;
            let inner = unsafe { ffi::rocksdb_wal_iter_get_batch(self.inner, &mut seq) };
            Some((seq, WriteBatch { inner }))
        } else {
            None
        }
    }
}

impl Drop for DBWALIterator {
    fn drop(&mut self) {
        unsafe {
            ffi::rocksdb_wal_iter_destroy(self.inner);
        }
    }
}

/// An iterator over a database or column family, with specifiable
/// ranges and direction.
///
/// ```
/// use rocksdb::{DB, Direction, IteratorMode, Options};
///
/// let path = "_path_for_rocksdb_storage2";
/// {
///     let db = DB::open_default(path).unwrap();
///     let mut iter = db.iterator(IteratorMode::Start); // Always iterates forward
///     for (key, value) in iter {
///         println!("Saw {:?} {:?}", key, value);
///     }
///     iter = db.iterator(IteratorMode::End);  // Always iterates backward
///     for (key, value) in iter {
///         println!("Saw {:?} {:?}", key, value);
///     }
///     iter = db.iterator(IteratorMode::From(b"my key", Direction::Forward)); // From a key in Direction::{forward,reverse}
///     for (key, value) in iter {
///         println!("Saw {:?} {:?}", key, value);
///     }
///
///     // You can seek with an existing Iterator instance, too
///     iter = db.iterator(IteratorMode::Start);
///     iter.set_mode(IteratorMode::From(b"another key", Direction::Reverse));
///     for (key, value) in iter {
///         println!("Saw {:?} {:?}", key, value);
///     }
/// }
/// let _ = DB::destroy(&Options::default(), path);
/// ```
pub struct DBIterator<'a> {
    raw: DBRawIterator<'a>,
    direction: Direction,
    just_seeked: bool,
}

pub enum Direction {
    Forward,
    Reverse,
}

pub type KVBytes = (Box<[u8]>, Box<[u8]>);

pub enum IteratorMode<'a> {
    Start,
    End,
    From(&'a [u8], Direction),
}

impl<'a> DBRawIterator<'a> {
    fn new(db: &DB, readopts: &ReadOptions) -> DBRawIterator<'a> {
        unsafe {
            DBRawIterator {
                inner: ffi::rocksdb_create_iterator(db.inner, readopts.inner),
                db: PhantomData,
            }
        }
    }

    fn new_cf(
        db: &DB,
        cf_handle: &ColumnFamily,
        readopts: &ReadOptions,
    ) -> Result<DBRawIterator<'a>, Error> {
        unsafe {
            Ok(DBRawIterator {
                inner: ffi::rocksdb_create_iterator_cf(db.inner, readopts.inner, cf_handle.inner),
                db: PhantomData,
            })
        }
    }

    /// Returns `true` if the iterator is valid. An iterator is invalidated when
    /// it reaches the end of its defined range, or when it encounters an error.
    ///
    /// To check whether the iterator encountered an error after `valid` has
    /// returned `false`, use the [`status`](DBRawIterator::status) method. `status` will never
    /// return an error when `valid` is `true`.
    pub fn valid(&self) -> bool {
        unsafe { ffi::rocksdb_iter_valid(self.inner) != 0 }
    }

    /// Returns an error `Result` if the iterator has encountered an error
    /// during operation. When an error is encountered, the iterator is
    /// invalidated and [`valid`](DBRawIterator::valid) will return `false` when called.
    ///
    /// Performing a seek will discard the current status.
    pub fn status(&self) -> Result<(), Error> {
        unsafe {
            ffi_try!(ffi::rocksdb_iter_get_error(self.inner));
        }
        Ok(())
    }

    /// Seeks to the first key in the database.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use rocksdb::{DB, Options};
    ///
    /// let path = "_path_for_rocksdb_storage5";
    /// {
    ///     let db = DB::open_default(path).unwrap();
    ///     let mut iter = db.raw_iterator();
    ///
    ///     // Iterate all keys from the start in lexicographic order
    ///     iter.seek_to_first();
    ///
    ///     while iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///         iter.next();
    ///     }
    ///
    ///     // Read just the first key
    ///     iter.seek_to_first();
    ///
    ///     if iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///     } else {
    ///         // There are no keys in the database
    ///     }
    /// }
    /// let _ = DB::destroy(&Options::default(), path);
    /// ```
    pub fn seek_to_first(&mut self) {
        unsafe {
            ffi::rocksdb_iter_seek_to_first(self.inner);
        }
    }

    /// Seeks to the last key in the database.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use rocksdb::{DB, Options};
    ///
    /// let path = "_path_for_rocksdb_storage6";
    /// {
    ///     let db = DB::open_default(path).unwrap();
    ///     let mut iter = db.raw_iterator();
    ///
    ///     // Iterate all keys from the end in reverse lexicographic order
    ///     iter.seek_to_last();
    ///
    ///     while iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///         iter.prev();
    ///     }
    ///
    ///     // Read just the last key
    ///     iter.seek_to_last();
    ///
    ///     if iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///     } else {
    ///         // There are no keys in the database
    ///     }
    /// }
    /// let _ = DB::destroy(&Options::default(), path);
    /// ```
    pub fn seek_to_last(&mut self) {
        unsafe {
            ffi::rocksdb_iter_seek_to_last(self.inner);
        }
    }

    /// Seeks to the specified key or the first key that lexicographically follows it.
    ///
    /// This method will attempt to seek to the specified key. If that key does not exist, it will
    /// find and seek to the key that lexicographically follows it instead.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use rocksdb::{DB, Options};
    ///
    /// let path = "_path_for_rocksdb_storage7";
    /// {
    ///     let db = DB::open_default(path).unwrap();
    ///     let mut iter = db.raw_iterator();
    ///
    ///     // Read the first key that starts with 'a'
    ///     iter.seek(b"a");
    ///
    ///     if iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///     } else {
    ///         // There are no keys in the database
    ///     }
    /// }
    /// let _ = DB::destroy(&Options::default(), path);
    /// ```
    pub fn seek<K: AsRef<[u8]>>(&mut self, key: K) {
        let key = key.as_ref();

        unsafe {
            ffi::rocksdb_iter_seek(
                self.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            );
        }
    }

    /// Seeks to the specified key, or the first key that lexicographically precedes it.
    ///
    /// Like ``.seek()`` this method will attempt to seek to the specified key.
    /// The difference with ``.seek()`` is that if the specified key do not exist, this method will
    /// seek to key that lexicographically precedes it instead.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use rocksdb::{DB, Options};
    ///
    /// let path = "_path_for_rocksdb_storage8";
    /// {
    ///     let db = DB::open_default(path).unwrap();
    ///     let mut iter = db.raw_iterator();
    ///
    ///     // Read the last key that starts with 'a'
    ///     iter.seek_for_prev(b"b");
    ///
    ///     if iter.valid() {
    ///         println!("{:?} {:?}", iter.key(), iter.value());
    ///     } else {
    ///         // There are no keys in the database
    ///     }
    /// }
    /// let _ = DB::destroy(&Options::default(), path);
    /// ```
    pub fn seek_for_prev<K: AsRef<[u8]>>(&mut self, key: K) {
        let key = key.as_ref();

        unsafe {
            ffi::rocksdb_iter_seek_for_prev(
                self.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            );
        }
    }

    /// Seeks to the next key.
    ///
    /// Returns true if the iterator is valid after this operation.
    pub fn next(&mut self) {
        unsafe {
            ffi::rocksdb_iter_next(self.inner);
        }
    }

    /// Seeks to the previous key.
    ///
    /// Returns true if the iterator is valid after this operation.
    pub fn prev(&mut self) {
        unsafe {
            ffi::rocksdb_iter_prev(self.inner);
        }
    }

    /// Returns a slice of the current key.
    pub fn key(&self) -> Option<&[u8]> {
        if self.valid() {
            // Safety Note: This is safe as all methods that may invalidate the buffer returned
            // take `&mut self`, so borrow checker will prevent use of buffer after seek.
            unsafe {
                let mut key_len: size_t = 0;
                let key_len_ptr: *mut size_t = &mut key_len;
                let key_ptr = ffi::rocksdb_iter_key(self.inner, key_len_ptr) as *const c_uchar;

                Some(slice::from_raw_parts(key_ptr, key_len as usize))
            }
        } else {
            None
        }
    }

    /// Returns a slice of the current value.
    pub fn value(&self) -> Option<&[u8]> {
        if self.valid() {
            // Safety Note: This is safe as all methods that may invalidate the buffer returned
            // take `&mut self`, so borrow checker will prevent use of buffer after seek.
            unsafe {
                let mut val_len: size_t = 0;
                let val_len_ptr: *mut size_t = &mut val_len;
                let val_ptr = ffi::rocksdb_iter_value(self.inner, val_len_ptr) as *const c_uchar;

                Some(slice::from_raw_parts(val_ptr, val_len as usize))
            }
        } else {
            None
        }
    }
}

impl<'a> Drop for DBRawIterator<'a> {
    fn drop(&mut self) {
        unsafe {
            ffi::rocksdb_iter_destroy(self.inner);
        }
    }
}

impl<'a> DBIterator<'a> {
    fn new(db: &DB, readopts: &ReadOptions, mode: IteratorMode) -> DBIterator<'a> {
        let mut rv = DBIterator {
            raw: DBRawIterator::new(db, readopts),
            direction: Direction::Forward, // blown away by set_mode()
            just_seeked: false,
        };
        rv.set_mode(mode);
        rv
    }

    fn new_cf(
        db: &DB,
        cf_handle: &ColumnFamily,
        readopts: &ReadOptions,
        mode: IteratorMode,
    ) -> Result<DBIterator<'a>, Error> {
        let mut rv = DBIterator {
            raw: DBRawIterator::new_cf(db, cf_handle, readopts)?,
            direction: Direction::Forward, // blown away by set_mode()
            just_seeked: false,
        };
        rv.set_mode(mode);
        Ok(rv)
    }

    pub fn set_mode(&mut self, mode: IteratorMode) {
        match mode {
            IteratorMode::Start => {
                self.raw.seek_to_first();
                self.direction = Direction::Forward;
            }
            IteratorMode::End => {
                self.raw.seek_to_last();
                self.direction = Direction::Reverse;
            }
            IteratorMode::From(key, Direction::Forward) => {
                self.raw.seek(key);
                self.direction = Direction::Forward;
            }
            IteratorMode::From(key, Direction::Reverse) => {
                self.raw.seek_for_prev(key);
                self.direction = Direction::Reverse;
            }
        };

        self.just_seeked = true;
    }

    /// See [`valid`](DBRawIterator::valid)
    pub fn valid(&self) -> bool {
        self.raw.valid()
    }

    /// See [`status`](DBRawIterator::status)
    pub fn status(&self) -> Result<(), Error> {
        self.raw.status()
    }
}

impl<'a> Iterator for DBIterator<'a> {
    type Item = KVBytes;

    fn next(&mut self) -> Option<KVBytes> {
        if !self.raw.valid() {
            return None;
        }

        // Initial call to next() after seeking should not move the iterator
        // or the first item will not be returned
        if !self.just_seeked {
            match self.direction {
                Direction::Forward => self.raw.next(),
                Direction::Reverse => self.raw.prev(),
            }
        } else {
            self.just_seeked = false;
        }

        if self.raw.valid() {
            // .key() and .value() only ever return None if valid == false, which we've just cheked
            Some((
                Box::from(self.raw.key().unwrap()),
                Box::from(self.raw.value().unwrap()),
            ))
        } else {
            None
        }
    }
}

impl<'a> Into<DBRawIterator<'a>> for DBIterator<'a> {
    fn into(self) -> DBRawIterator<'a> {
        self.raw
    }
}

impl<'a> Snapshot<'a> {
    pub fn new(db: &DB) -> Snapshot {
        let snapshot = unsafe { ffi::rocksdb_create_snapshot(db.inner) };
        Snapshot {
            db,
            inner: snapshot,
        }
    }

    pub fn iterator(&self, mode: IteratorMode) -> DBIterator<'a> {
        let readopts = ReadOptions::default();
        self.iterator_opt(mode, readopts)
    }

    pub fn iterator_cf(
        &self,
        cf_handle: &ColumnFamily,
        mode: IteratorMode,
    ) -> Result<DBIterator, Error> {
        let readopts = ReadOptions::default();
        self.iterator_cf_opt(cf_handle, readopts, mode)
    }

    pub fn iterator_opt(&self, mode: IteratorMode, mut readopts: ReadOptions) -> DBIterator<'a> {
        readopts.set_snapshot(self);
        DBIterator::new(self.db, &readopts, mode)
    }

    pub fn iterator_cf_opt(
        &self,
        cf_handle: &ColumnFamily,
        mut readopts: ReadOptions,
        mode: IteratorMode,
    ) -> Result<DBIterator, Error> {
        readopts.set_snapshot(self);
        DBIterator::new_cf(self.db, cf_handle, &readopts, mode)
    }

    /// Opens a raw iterator over the data in this snapshot, using the default read options.
    pub fn raw_iterator(&self) -> DBRawIterator {
        let readopts = ReadOptions::default();
        self.raw_iterator_opt(readopts)
    }

    /// Opens a raw iterator over the data in this snapshot under the given column family, using the default read options.
    pub fn raw_iterator_cf(&self, cf_handle: &ColumnFamily) -> Result<DBRawIterator, Error> {
        let readopts = ReadOptions::default();
        self.raw_iterator_cf_opt(cf_handle, readopts)
    }

    /// Opens a raw iterator over the data in this snapshot, using the given read options.
    pub fn raw_iterator_opt(&self, mut readopts: ReadOptions) -> DBRawIterator {
        readopts.set_snapshot(self);
        DBRawIterator::new(self.db, &readopts)
    }

    /// Opens a raw iterator over the data in this snapshot under the given column family, using the given read options.
    pub fn raw_iterator_cf_opt(
        &self,
        cf_handle: &ColumnFamily,
        mut readopts: ReadOptions,
    ) -> Result<DBRawIterator, Error> {
        readopts.set_snapshot(self);
        DBRawIterator::new_cf(self.db, cf_handle, &readopts)
    }

    pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Vec<u8>>, Error> {
        let readopts = ReadOptions::default();
        self.get_opt(key, readopts)
    }

    pub fn get_cf<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
    ) -> Result<Option<Vec<u8>>, Error> {
        let readopts = ReadOptions::default();
        self.get_cf_opt(cf, key.as_ref(), readopts)
    }

    pub fn get_opt<K: AsRef<[u8]>>(
        &self,
        key: K,
        mut readopts: ReadOptions,
    ) -> Result<Option<Vec<u8>>, Error> {
        readopts.set_snapshot(self);
        self.db.get_opt(key.as_ref(), &readopts)
    }

    pub fn get_cf_opt<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
        mut readopts: ReadOptions,
    ) -> Result<Option<Vec<u8>>, Error> {
        readopts.set_snapshot(self);
        self.db.get_cf_opt(cf, key.as_ref(), &readopts)
    }
}

impl<'a> Drop for Snapshot<'a> {
    fn drop(&mut self) {
        unsafe {
            ffi::rocksdb_release_snapshot(self.db.inner, self.inner);
        }
    }
}

impl ColumnFamilyDescriptor {
    // Create a new column family descriptor with the specified name and options.
    pub fn new<S>(name: S, options: Options) -> Self
    where
        S: Into<String>,
    {
        ColumnFamilyDescriptor {
            name: name.into(),
            options,
        }
    }
}

impl DB {
    /// Open a database with default options.
    pub fn open_default<P: AsRef<Path>>(path: P) -> Result<DB, Error> {
        let mut opts = Options::default();
        opts.create_if_missing(true);
        DB::open(&opts, path)
    }

    /// Open the database with the specified options.
    pub fn open<P: AsRef<Path>>(opts: &Options, path: P) -> Result<DB, Error> {
        DB::open_cf(opts, path, None::<&str>)
    }

    /// Open a database with the given database options and column family names.
    ///
    /// Column families opened using this function will be created with default `Options`.
    pub fn open_cf<P, I, N>(opts: &Options, path: P, cfs: I) -> Result<DB, Error>
    where
        P: AsRef<Path>,
        I: IntoIterator<Item = N>,
        N: AsRef<str>,
    {
        let cfs = cfs
            .into_iter()
            .map(|name| ColumnFamilyDescriptor::new(name.as_ref(), Options::default()));

        DB::open_cf_descriptors(opts, path, cfs)
    }

    /// Open a database with the given database options and column family descriptors.
    pub fn open_cf_descriptors<P, I>(opts: &Options, path: P, cfs: I) -> Result<DB, Error>
    where
        P: AsRef<Path>,
        I: IntoIterator<Item = ColumnFamilyDescriptor>,
    {
        let cfs: Vec<_> = cfs.into_iter().collect();

        let cpath = to_cpath(&path)?;

        if let Err(e) = fs::create_dir_all(&path) {
            return Err(Error::new(format!(
                "Failed to create RocksDB directory: `{:?}`.",
                e
            )));
        }

        let db: *mut ffi::rocksdb_t;
        let mut cf_map = BTreeMap::new();

        if cfs.is_empty() {
            unsafe {
                db = ffi_try!(ffi::rocksdb_open(opts.inner, cpath.as_ptr() as *const _));
            }
        } else {
            let mut cfs_v = cfs;
            // Always open the default column family.
            if !cfs_v.iter().any(|cf| cf.name == "default") {
                cfs_v.push(ColumnFamilyDescriptor {
                    name: String::from("default"),
                    options: Options::default(),
                });
            }
            // We need to store our CStrings in an intermediate vector
            // so that their pointers remain valid.
            let c_cfs: Vec<CString> = cfs_v
                .iter()
                .map(|cf| CString::new(cf.name.as_bytes()).unwrap())
                .collect();

            let mut cfnames: Vec<_> = c_cfs.iter().map(|cf| cf.as_ptr()).collect();

            // These handles will be populated by DB.
            let mut cfhandles: Vec<_> = cfs_v.iter().map(|_| ptr::null_mut()).collect();

            let mut cfopts: Vec<_> = cfs_v
                .iter()
                .map(|cf| cf.options.inner as *const _)
                .collect();

            unsafe {
                db = ffi_try!(ffi::rocksdb_open_column_families(
                    opts.inner,
                    cpath.as_ptr(),
                    cfs_v.len() as c_int,
                    cfnames.as_mut_ptr(),
                    cfopts.as_mut_ptr(),
                    cfhandles.as_mut_ptr(),
                ));
            }

            for handle in &cfhandles {
                if handle.is_null() {
                    return Err(Error::new(
                        "Received null column family handle from DB.".to_owned(),
                    ));
                }
            }

            for (cf_desc, inner) in cfs_v.iter().zip(cfhandles) {
                cf_map.insert(cf_desc.name.clone(), ColumnFamily { inner });
            }
        }

        if db.is_null() {
            return Err(Error::new("Could not initialize database.".to_owned()));
        }

        Ok(DB {
            inner: db,
            cfs: cf_map,
            path: path.as_ref().to_path_buf(),
        })
    }

    pub fn list_cf<P: AsRef<Path>>(opts: &Options, path: P) -> Result<Vec<String>, Error> {
        let cpath = to_cpath(path)?;
        let mut length = 0;

        unsafe {
            let ptr = ffi_try!(ffi::rocksdb_list_column_families(
                opts.inner,
                cpath.as_ptr() as *const _,
                &mut length,
            ));

            let vec = slice::from_raw_parts(ptr, length)
                .iter()
                .map(|ptr| CStr::from_ptr(*ptr).to_string_lossy().into_owned())
                .collect();
            ffi::rocksdb_list_column_families_destroy(ptr, length);
            Ok(vec)
        }
    }

    pub fn destroy<P: AsRef<Path>>(opts: &Options, path: P) -> Result<(), Error> {
        let cpath = to_cpath(path)?;
        unsafe {
            ffi_try!(ffi::rocksdb_destroy_db(opts.inner, cpath.as_ptr()));
        }
        Ok(())
    }

    pub fn repair<P: AsRef<Path>>(opts: &Options, path: P) -> Result<(), Error> {
        let cpath = to_cpath(path)?;
        unsafe {
            ffi_try!(ffi::rocksdb_repair_db(opts.inner, cpath.as_ptr()));
        }
        Ok(())
    }

    pub fn path(&self) -> &Path {
        &self.path.as_path()
    }

    /// Flushes database memtables to SST files on the disk.
    pub fn flush_opt(&self, flushopts: &FlushOptions) -> Result<(), Error> {
        unsafe {
            ffi_try!(ffi::rocksdb_flush(self.inner, flushopts.inner));
        }
        Ok(())
    }

    /// Flushes database memtables to SST files on the disk using default options.
    pub fn flush(&self) -> Result<(), Error> {
        self.flush_opt(&FlushOptions::default())
    }

    /// Flushes database memtables to SST files on the disk for a given column family.
    pub fn flush_cf_opt(&self, cf: &ColumnFamily, flushopts: &FlushOptions) -> Result<(), Error> {
        unsafe {
            ffi_try!(ffi::rocksdb_flush_cf(self.inner, flushopts.inner, cf.inner));
        }
        Ok(())
    }

    /// Flushes database memtables to SST files on the disk for a given column family using default
    /// options.
    pub fn flush_cf(&self, cf: &ColumnFamily) -> Result<(), Error> {
        self.flush_cf_opt(cf, &FlushOptions::default())
    }

    pub fn write_opt(&self, batch: WriteBatch, writeopts: &WriteOptions) -> Result<(), Error> {
        unsafe {
            ffi_try!(ffi::rocksdb_write(self.inner, writeopts.inner, batch.inner));
        }
        Ok(())
    }

    pub fn write(&self, batch: WriteBatch) -> Result<(), Error> {
        self.write_opt(batch, &WriteOptions::default())
    }

    pub fn write_without_wal(&self, batch: WriteBatch) -> Result<(), Error> {
        let mut wo = WriteOptions::new();
        wo.disable_wal(true);
        self.write_opt(batch, &wo)
    }

    /// Return the bytes associated with a key value with read options. If you only intend to use
    /// the vector returned temporarily, consider using [`get_pinned_opt`](#method.get_pinned_opt)
    /// to avoid unnecessary memory copy.
    pub fn get_opt<K: AsRef<[u8]>>(
        &self,
        key: K,
        readopts: &ReadOptions,
    ) -> Result<Option<Vec<u8>>, Error> {
        self.get_pinned_opt(key, readopts)
            .map(|x| x.map(|v| v.as_ref().to_vec()))
    }

    /// Return the bytes associated with a key value. If you only intend to use the vector returned
    /// temporarily, consider using [`get_pinned`](#method.get_pinned) to avoid unnecessary memory
    /// copy.
    pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Vec<u8>>, Error> {
        self.get_opt(key.as_ref(), &ReadOptions::default())
    }

    /// Return the bytes associated with a key value and the given column family with read options.
    /// If you only intend to use the vector returned temporarily, consider using
    /// [`get_pinned_cf_opt`](#method.get_pinned_cf_opt) to avoid unnecessary memory.
    pub fn get_cf_opt<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
        readopts: &ReadOptions,
    ) -> Result<Option<Vec<u8>>, Error> {
        self.get_pinned_cf_opt(cf, key, readopts)
            .map(|x| x.map(|v| v.as_ref().to_vec()))
    }

    /// Return the bytes associated with a key value and the given column family. If you only
    /// intend to use the vector returned temporarily, consider using
    /// [`get_pinned_cf`](#method.get_pinned_cf) to avoid unnecessary memory.
    pub fn get_cf<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
    ) -> Result<Option<Vec<u8>>, Error> {
        self.get_cf_opt(cf, key.as_ref(), &ReadOptions::default())
    }

    /// Return the value associated with a key using RocksDB's PinnableSlice
    /// so as to avoid unnecessary memory copy.
    pub fn get_pinned_opt<K: AsRef<[u8]>>(
        &self,
        key: K,
        readopts: &ReadOptions,
    ) -> Result<Option<DBPinnableSlice>, Error> {
        if readopts.inner.is_null() {
            return Err(Error::new(
                "Unable to create RocksDB read options. This is a fairly trivial call, and its \
                 failure may be indicative of a mis-compiled or mis-loaded RocksDB library."
                    .to_owned(),
            ));
        }

        let key = key.as_ref();
        unsafe {
            let val = ffi_try!(ffi::rocksdb_get_pinned(
                self.inner,
                readopts.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            ));
            if val.is_null() {
                Ok(None)
            } else {
                Ok(Some(DBPinnableSlice::from_c(val)))
            }
        }
    }

    /// Return the value associated with a key using RocksDB's PinnableSlice
    /// so as to avoid unnecessary memory copy. Similar to get_pinned_opt but
    /// leverages default options.
    pub fn get_pinned<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<DBPinnableSlice>, Error> {
        self.get_pinned_opt(key, &ReadOptions::default())
    }

    /// Return the value associated with a key using RocksDB's PinnableSlice
    /// so as to avoid unnecessary memory copy. Similar to get_pinned_opt but
    /// allows specifying ColumnFamily
    pub fn get_pinned_cf_opt<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
        readopts: &ReadOptions,
    ) -> Result<Option<DBPinnableSlice>, Error> {
        if readopts.inner.is_null() {
            return Err(Error::new(
                "Unable to create RocksDB read options. This is a fairly trivial call, and its \
                 failure may be indicative of a mis-compiled or mis-loaded RocksDB library."
                    .to_owned(),
            ));
        }

        let key = key.as_ref();
        unsafe {
            let val = ffi_try!(ffi::rocksdb_get_pinned_cf(
                self.inner,
                readopts.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            ));
            if val.is_null() {
                Ok(None)
            } else {
                Ok(Some(DBPinnableSlice::from_c(val)))
            }
        }
    }

    /// Return the value associated with a key using RocksDB's PinnableSlice
    /// so as to avoid unnecessary memory copy. Similar to get_pinned_cf_opt but
    /// leverages default options.
    pub fn get_pinned_cf<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
    ) -> Result<Option<DBPinnableSlice>, Error> {
        self.get_pinned_cf_opt(cf, key, &ReadOptions::default())
    }

    pub fn create_cf<N: AsRef<str>>(&mut self, name: N, opts: &Options) -> Result<(), Error> {
        let cname = match CString::new(name.as_ref().as_bytes()) {
            Ok(c) => c,
            Err(_) => {
                return Err(Error::new(
                    "Failed to convert path to CString when creating cf".to_owned(),
                ));
            }
        };
        unsafe {
            let inner = ffi_try!(ffi::rocksdb_create_column_family(
                self.inner,
                opts.inner,
                cname.as_ptr(),
            ));

            self.cfs
                .insert(name.as_ref().to_string(), ColumnFamily { inner });
        };
        Ok(())
    }

    pub fn drop_cf(&mut self, name: &str) -> Result<(), Error> {
        if let Some(cf) = self.cfs.remove(name) {
            unsafe {
                ffi_try!(ffi::rocksdb_drop_column_family(self.inner, cf.inner));
            }
            Ok(())
        } else {
            Err(Error::new(
                format!("Invalid column family: {}", name).to_owned(),
            ))
        }
    }

    /// Return the underlying column family handle.
    pub fn cf_handle(&self, name: &str) -> Option<&ColumnFamily> {
        self.cfs.get(name)
    }

    pub fn iterator<'a, 'b: 'a>(&'a self, mode: IteratorMode) -> DBIterator<'b> {
        let readopts = ReadOptions::default();
        self.iterator_opt(mode, &readopts)
    }

    pub fn iterator_opt<'a, 'b: 'a>(
        &'a self,
        mode: IteratorMode,
        readopts: &ReadOptions,
    ) -> DBIterator<'b> {
        DBIterator::new(self, &readopts, mode)
    }

    /// Opens an iterator using the provided ReadOptions.
    /// This is used when you want to iterate over a specific ColumnFamily with a modified ReadOptions
    pub fn iterator_cf_opt(
        &self,
        cf_handle: &ColumnFamily,
        readopts: &ReadOptions,
        mode: IteratorMode,
    ) -> Result<DBIterator, Error> {
        DBIterator::new_cf(self, cf_handle, &readopts, mode)
    }

    /// Opens an iterator with `set_total_order_seek` enabled.
    /// This must be used to iterate across prefixes when `set_memtable_factory` has been called
    /// with a Hash-based implementation.
    pub fn full_iterator<'a, 'b: 'a>(&'a self, mode: IteratorMode) -> DBIterator<'b> {
        let mut opts = ReadOptions::default();
        opts.set_total_order_seek(true);
        DBIterator::new(self, &opts, mode)
    }

    pub fn prefix_iterator<'a, 'b: 'a, P: AsRef<[u8]>>(&'a self, prefix: P) -> DBIterator<'b> {
        let mut opts = ReadOptions::default();
        opts.set_prefix_same_as_start(true);
        DBIterator::new(
            self,
            &opts,
            IteratorMode::From(prefix.as_ref(), Direction::Forward),
        )
    }

    pub fn iterator_cf(
        &self,
        cf_handle: &ColumnFamily,
        mode: IteratorMode,
    ) -> Result<DBIterator, Error> {
        let opts = ReadOptions::default();
        DBIterator::new_cf(self, cf_handle, &opts, mode)
    }

    pub fn full_iterator_cf(
        &self,
        cf_handle: &ColumnFamily,
        mode: IteratorMode,
    ) -> Result<DBIterator, Error> {
        let mut opts = ReadOptions::default();
        opts.set_total_order_seek(true);
        DBIterator::new_cf(self, cf_handle, &opts, mode)
    }

    pub fn prefix_iterator_cf<P: AsRef<[u8]>>(
        &self,
        cf_handle: &ColumnFamily,
        prefix: P,
    ) -> Result<DBIterator, Error> {
        let mut opts = ReadOptions::default();
        opts.set_prefix_same_as_start(true);
        DBIterator::new_cf(
            self,
            cf_handle,
            &opts,
            IteratorMode::From(prefix.as_ref(), Direction::Forward),
        )
    }

    /// Opens a raw iterator over the database, using the default read options
    pub fn raw_iterator(&self) -> DBRawIterator {
        let opts = ReadOptions::default();
        DBRawIterator::new(self, &opts)
    }

    /// Opens a raw iterator over the given column family, using the default read options
    pub fn raw_iterator_cf(&self, cf_handle: &ColumnFamily) -> Result<DBRawIterator, Error> {
        let opts = ReadOptions::default();
        DBRawIterator::new_cf(self, cf_handle, &opts)
    }

    /// Opens a raw iterator over the database, using the given read options
    pub fn raw_iterator_opt(&self, readopts: &ReadOptions) -> DBRawIterator {
        DBRawIterator::new(self, readopts)
    }

    /// Opens a raw iterator over the given column family, using the given read options
    pub fn raw_iterator_cf_opt(
        &self,
        cf_handle: &ColumnFamily,
        readopts: &ReadOptions,
    ) -> Result<DBRawIterator, Error> {
        DBRawIterator::new_cf(self, cf_handle, readopts)
    }

    pub fn snapshot(&self) -> Snapshot {
        Snapshot::new(self)
    }

    pub fn put_opt<K, V>(&self, key: K, value: V, writeopts: &WriteOptions) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_put(
                self.inner,
                writeopts.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn put_cf_opt<K, V>(
        &self,
        cf: &ColumnFamily,
        key: K,
        value: V,
        writeopts: &WriteOptions,
    ) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_put_cf(
                self.inner,
                writeopts.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn merge_opt<K, V>(&self, key: K, value: V, writeopts: &WriteOptions) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_merge(
                self.inner,
                writeopts.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn merge_cf_opt<K, V>(
        &self,
        cf: &ColumnFamily,
        key: K,
        value: V,
        writeopts: &WriteOptions,
    ) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_merge_cf(
                self.inner,
                writeopts.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn delete_opt<K: AsRef<[u8]>>(
        &self,
        key: K,
        writeopts: &WriteOptions,
    ) -> Result<(), Error> {
        let key = key.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_delete(
                self.inner,
                writeopts.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn delete_cf_opt<K: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        key: K,
        writeopts: &WriteOptions,
    ) -> Result<(), Error> {
        let key = key.as_ref();

        unsafe {
            ffi_try!(ffi::rocksdb_delete_cf(
                self.inner,
                writeopts.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            ));
            Ok(())
        }
    }

    pub fn put<K, V>(&self, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        self.put_opt(key.as_ref(), value.as_ref(), &WriteOptions::default())
    }

    pub fn put_cf<K, V>(&self, cf: &ColumnFamily, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        self.put_cf_opt(cf, key.as_ref(), value.as_ref(), &WriteOptions::default())
    }

    pub fn merge<K, V>(&self, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        self.merge_opt(key.as_ref(), value.as_ref(), &WriteOptions::default())
    }

    pub fn merge_cf<K, V>(&self, cf: &ColumnFamily, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        self.merge_cf_opt(cf, key.as_ref(), value.as_ref(), &WriteOptions::default())
    }

    pub fn delete<K: AsRef<[u8]>>(&self, key: K) -> Result<(), Error> {
        self.delete_opt(key.as_ref(), &WriteOptions::default())
    }

    pub fn delete_cf<K: AsRef<[u8]>>(&self, cf: &ColumnFamily, key: K) -> Result<(), Error> {
        self.delete_cf_opt(cf, key.as_ref(), &WriteOptions::default())
    }

    pub fn compact_range<S: AsRef<[u8]>, E: AsRef<[u8]>>(&self, start: Option<S>, end: Option<E>) {
        unsafe {
            let start = start.as_ref().map(|s| s.as_ref());
            let end = end.as_ref().map(|e| e.as_ref());

            ffi::rocksdb_compact_range(
                self.inner,
                opt_bytes_to_ptr(start),
                start.map_or(0, |s| s.len()) as size_t,
                opt_bytes_to_ptr(end),
                end.map_or(0, |e| e.len()) as size_t,
            );
        }
    }

    pub fn compact_range_cf<S: AsRef<[u8]>, E: AsRef<[u8]>>(
        &self,
        cf: &ColumnFamily,
        start: Option<S>,
        end: Option<E>,
    ) {
        unsafe {
            let start = start.as_ref().map(|s| s.as_ref());
            let end = end.as_ref().map(|e| e.as_ref());

            ffi::rocksdb_compact_range_cf(
                self.inner,
                cf.inner,
                opt_bytes_to_ptr(start),
                start.map_or(0, |s| s.len()) as size_t,
                opt_bytes_to_ptr(end),
                end.map_or(0, |e| e.len()) as size_t,
            );
        }
    }

    pub fn set_options(&self, opts: &[(&str, &str)]) -> Result<(), Error> {
        let copts = opts
            .iter()
            .map(|(name, value)| {
                let cname = match CString::new(name.as_bytes()) {
                    Ok(cname) => cname,
                    Err(e) => return Err(Error::new(format!("Invalid option name `{}`", e))),
                };
                let cvalue = match CString::new(value.as_bytes()) {
                    Ok(cvalue) => cvalue,
                    Err(e) => return Err(Error::new(format!("Invalid option value: `{}`", e))),
                };
                Ok((cname, cvalue))
            })
            .collect::<Result<Vec<(CString, CString)>, Error>>()?;

        let cnames: Vec<*const c_char> = copts.iter().map(|opt| opt.0.as_ptr()).collect();
        let cvalues: Vec<*const c_char> = copts.iter().map(|opt| opt.1.as_ptr()).collect();
        let count = opts.len() as i32;
        unsafe {
            ffi_try!(ffi::rocksdb_set_options(
                self.inner,
                count,
                cnames.as_ptr(),
                cvalues.as_ptr(),
            ));
        }
        Ok(())
    }

    /// Retrieves a RocksDB property by name.
    ///
    /// For a full list of properties, see
    /// https://github.com/facebook/rocksdb/blob/08809f5e6cd9cc4bc3958dd4d59457ae78c76660/include/rocksdb/db.h#L428-L634
    pub fn property_value(&self, name: &str) -> Result<Option<String>, Error> {
        let prop_name = match CString::new(name) {
            Ok(c) => c,
            Err(e) => {
                return Err(Error::new(format!(
                    "Failed to convert property name to CString: {}",
                    e
                )));
            }
        };

        unsafe {
            let value = ffi::rocksdb_property_value(self.inner, prop_name.as_ptr());
            if value.is_null() {
                return Ok(None);
            }

            let str_value = match CStr::from_ptr(value).to_str() {
                Ok(s) => s.to_owned(),
                Err(e) => {
                    return Err(Error::new(format!(
                        "Failed to convert property value to string: {}",
                        e
                    )));
                }
            };

            libc::free(value as *mut c_void);
            Ok(Some(str_value))
        }
    }

    /// Retrieves a RocksDB property by name, for a specific column family.
    ///
    /// For a full list of properties, see
    /// https://github.com/facebook/rocksdb/blob/08809f5e6cd9cc4bc3958dd4d59457ae78c76660/include/rocksdb/db.h#L428-L634
    pub fn property_value_cf(
        &self,
        cf: &ColumnFamily,
        name: &str,
    ) -> Result<Option<String>, Error> {
        let prop_name = match CString::new(name) {
            Ok(c) => c,
            Err(e) => {
                return Err(Error::new(format!(
                    "Failed to convert property name to CString: {}",
                    e
                )));
            }
        };

        unsafe {
            let value = ffi::rocksdb_property_value_cf(self.inner, cf.inner, prop_name.as_ptr());
            if value.is_null() {
                return Ok(None);
            }

            let str_value = match CStr::from_ptr(value).to_str() {
                Ok(s) => s.to_owned(),
                Err(e) => {
                    return Err(Error::new(format!(
                        "Failed to convert property value to string: {}",
                        e
                    )));
                }
            };

            libc::free(value as *mut c_void);
            Ok(Some(str_value))
        }
    }

    /// Retrieves a RocksDB property and casts it to an integer.
    ///
    /// For a full list of properties that return int values, see
    /// https://github.com/facebook/rocksdb/blob/08809f5e6cd9cc4bc3958dd4d59457ae78c76660/include/rocksdb/db.h#L654-L689
    pub fn property_int_value(&self, name: &str) -> Result<Option<u64>, Error> {
        match self.property_value(name) {
            Ok(Some(value)) => match value.parse::<u64>() {
                Ok(int_value) => Ok(Some(int_value)),
                Err(e) => Err(Error::new(format!(
                    "Failed to convert property value to int: {}",
                    e
                ))),
            },
            Ok(None) => Ok(None),
            Err(e) => Err(e),
        }
    }

    /// Retrieves a RocksDB property for a specific column family and casts it to an integer.
    ///
    /// For a full list of properties that return int values, see
    /// https://github.com/facebook/rocksdb/blob/08809f5e6cd9cc4bc3958dd4d59457ae78c76660/include/rocksdb/db.h#L654-L689
    pub fn property_int_value_cf(
        &self,
        cf: &ColumnFamily,
        name: &str,
    ) -> Result<Option<u64>, Error> {
        match self.property_value_cf(cf, name) {
            Ok(Some(value)) => match value.parse::<u64>() {
                Ok(int_value) => Ok(Some(int_value)),
                Err(e) => Err(Error::new(format!(
                    "Failed to convert property value to int: {}",
                    e
                ))),
            },
            Ok(None) => Ok(None),
            Err(e) => Err(e),
        }
    }

    /// The sequence number of the most recent transaction.
    pub fn latest_sequence_number(&self) -> u64 {
        unsafe { ffi::rocksdb_get_latest_sequence_number(self.inner) }
    }

    /// Iterate over batches of write operations since a given sequence.
    ///
    /// Produce an iterator that will provide the batches of write operations
    /// that have occurred since the given sequence (see
    /// `latest_sequence_number()`). Use the provided iterator to retrieve each
    /// (`u64`, `WriteBatch`) tuple, and then gather the individual puts and
    /// deletes using the `WriteBatch::iterate()` function.
    ///
    /// Calling `get_updates_since()` with a sequence number that is out of
    /// bounds will return an error.
    pub fn get_updates_since(&self, seq_number: u64) -> Result<DBWALIterator, Error> {
        unsafe {
            // rocksdb_wal_readoptions_t does not appear to have any functions
            // for creating and destroying it; fortunately we can pass a nullptr
            // here to get the default behavior
            let opts: *const ffi::rocksdb_wal_readoptions_t = ptr::null();
            let iter = ffi_try!(ffi::rocksdb_get_updates_since(self.inner, seq_number, opts));
            Ok(DBWALIterator { inner: iter })
        }
    }
}

/// Receives the puts and deletes of a write batch.
///
/// The application must provide an implementation of this trait when
/// iterating the operations within a `WriteBatch`
pub trait WriteBatchIterator {
    /// Called with a key and value that were `put` into the batch.
    fn put(&mut self, key: Box<[u8]>, value: Box<[u8]>);
    /// Called with a key that was `delete`d from the batch.
    fn delete(&mut self, key: Box<[u8]>);
}

unsafe extern "C" fn writebatch_put_callback(
    state: *mut c_void,
    k: *const c_char,
    klen: usize,
    v: *const c_char,
    vlen: usize,
) {
    // coerce the raw pointer back into a box, but "leak" it so we prevent
    // freeing the resource before we are done with it
    let boxed_cb = Box::from_raw(state as *mut &mut dyn WriteBatchIterator);
    let leaked_cb = Box::leak(boxed_cb);
    let key = slice::from_raw_parts(k as *const u8, klen as usize);
    let value = slice::from_raw_parts(v as *const u8, vlen as usize);
    leaked_cb.put(
        key.to_vec().into_boxed_slice(),
        value.to_vec().into_boxed_slice(),
    );
}

unsafe extern "C" fn writebatch_delete_callback(state: *mut c_void, k: *const c_char, klen: usize) {
    // coerce the raw pointer back into a box, but "leak" it so we prevent
    // freeing the resource before we are done with it
    let boxed_cb = Box::from_raw(state as *mut &mut dyn WriteBatchIterator);
    let leaked_cb = Box::leak(boxed_cb);
    let key = slice::from_raw_parts(k as *const u8, klen as usize);
    leaked_cb.delete(key.to_vec().into_boxed_slice());
}

impl WriteBatch {
    pub fn len(&self) -> usize {
        unsafe { ffi::rocksdb_writebatch_count(self.inner) as usize }
    }

    /// Return WriteBatch serialized size (in bytes).
    pub fn size_in_bytes(&self) -> usize {
        unsafe {
            let mut batch_size: size_t = 0;
            ffi::rocksdb_writebatch_data(self.inner, &mut batch_size);
            batch_size as usize
        }
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Iterate the put and delete operations within this write batch. Note that
    /// this does _not_ return an `Iterator` but instead will invoke the `put()`
    /// and `delete()` member functions of the provided `WriteBatchIterator`
    /// trait implementation.
    pub fn iterate(&self, callbacks: &mut dyn WriteBatchIterator) {
        let state = Box::into_raw(Box::new(callbacks));
        unsafe {
            ffi::rocksdb_writebatch_iterate(
                self.inner,
                state as *mut c_void,
                Some(writebatch_put_callback),
                Some(writebatch_delete_callback),
            );
            // we must manually set the raw box free since there is no
            // associated "destroy" callback for this object
            Box::from_raw(state);
        }
    }

    /// Insert a value into the database under the given key.
    pub fn put<K, V>(&mut self, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_put(
                self.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            );
            Ok(())
        }
    }

    pub fn put_cf<K, V>(&mut self, cf: &ColumnFamily, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_put_cf(
                self.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            );
            Ok(())
        }
    }

    pub fn merge<K, V>(&mut self, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_merge(
                self.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            );
            Ok(())
        }
    }

    pub fn merge_cf<K, V>(&mut self, cf: &ColumnFamily, key: K, value: V) -> Result<(), Error>
    where
        K: AsRef<[u8]>,
        V: AsRef<[u8]>,
    {
        let key = key.as_ref();
        let value = value.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_merge_cf(
                self.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
                value.as_ptr() as *const c_char,
                value.len() as size_t,
            );
            Ok(())
        }
    }

    /// Remove the database entry for key.
    ///
    /// Returns an error if the key was not found.
    pub fn delete<K: AsRef<[u8]>>(&mut self, key: K) -> Result<(), Error> {
        let key = key.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_delete(
                self.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            );
            Ok(())
        }
    }

    pub fn delete_cf<K: AsRef<[u8]>>(&mut self, cf: &ColumnFamily, key: K) -> Result<(), Error> {
        let key = key.as_ref();

        unsafe {
            ffi::rocksdb_writebatch_delete_cf(
                self.inner,
                cf.inner,
                key.as_ptr() as *const c_char,
                key.len() as size_t,
            );
            Ok(())
        }
    }

    /// Remove database entries from start key to end key.
    ///
    /// Removes the database entries in the range ["begin_key", "end_key"), i.e.,
    /// including "begin_key" and excluding "end_key". It is not an error if no
    /// keys exist in the range ["begin_key", "end_key").
    pub fn delete_range<K: AsRef<[u8]>>(&mut self, from: K, to: K) -> Result<(), Error> {
        let (start_key, end_key) = (from.as_ref(), to.as_ref());

        unsafe {
            ffi::rocksdb_writebatch_delete_range(
                self.inner,
                start_key.as_ptr() as *const c_char,
                start_key.len() as size_t,
                end_key.as_ptr() as *const c_char,
                end_key.len() as size_t,
            );
            Ok(())
        }
    }

    /// Remove database entries in column family from start key to end key.
    ///
    /// Removes the database entries in the range ["begin_key", "end_key"), i.e.,
    /// including "begin_key" and excluding "end_key". It is not an error if no
    /// keys exist in the range ["begin_key", "end_key").
    pub fn delete_range_cf<K: AsRef<[u8]>>(
        &mut self,
        cf: &ColumnFamily,
        from: K,
        to: K,
    ) -> Result<(), Error> {
        let (start_key, end_key) = (from.as_ref(), to.as_ref());

        unsafe {
            ffi::rocksdb_writebatch_delete_range_cf(
                self.inner,
                cf.inner,
                start_key.as_ptr() as *const c_char,
                start_key.len() as size_t,
                end_key.as_ptr() as *const c_char,
                end_key.len() as size_t,
            );
            Ok(())
        }
    }

    /// Clear all updates buffered in this batch.
    pub fn clear(&mut self) -> Result<(), Error> {
        unsafe {
            ffi::rocksdb_writebatch_clear(self.inner);
        }
        Ok(())
    }
}

impl Default for WriteBatch {
    fn default() -> WriteBatch {
        WriteBatch {
            inner: unsafe { ffi::rocksdb_writebatch_create() },
        }
    }
}

impl Drop for WriteBatch {
    fn drop(&mut self) {
        unsafe { ffi::rocksdb_writebatch_destroy(self.inner) }
    }
}

impl Drop for DB {
    fn drop(&mut self) {
        unsafe {
            for cf in self.cfs.values() {
                ffi::rocksdb_column_family_handle_destroy(cf.inner);
            }
            ffi::rocksdb_close(self.inner);
        }
    }
}

impl fmt::Debug for DB {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "RocksDB {{ path: {:?} }}", self.path())
    }
}

impl Drop for ReadOptions {
    fn drop(&mut self) {
        unsafe { ffi::rocksdb_readoptions_destroy(self.inner) }
    }
}

impl ReadOptions {
    // TODO add snapshot setting here
    // TODO add snapshot wrapper structs with proper destructors;
    // that struct needs an "iterator" impl too.
    #[allow(dead_code)]
    fn fill_cache(&mut self, v: bool) {
        unsafe {
            ffi::rocksdb_readoptions_set_fill_cache(self.inner, v as c_uchar);
        }
    }

    fn set_snapshot(&mut self, snapshot: &Snapshot) {
        unsafe {
            ffi::rocksdb_readoptions_set_snapshot(self.inner, snapshot.inner);
        }
    }

    /// Set the upper bound for an iterator.
    /// The upper bound itself is not included on the iteration result.
    ///
    /// # Safety
    ///
    /// This function will store a clone of key and will give a raw pointer of it to the
    /// underlying C++ API, therefore, when given to any other [`DB`] method you must ensure
    /// that this [`ReadOptions`] value does not leave the scope too early (e.g. `DB::iterator_cf_opt`).
    pub unsafe fn set_iterate_upper_bound<K: AsRef<[u8]>>(&mut self, key: K) {
        let key = key.as_ref();
        ffi::rocksdb_readoptions_set_iterate_upper_bound(
            self.inner,
            key.as_ptr() as *const c_char,
            key.len() as size_t,
        );
    }

    pub fn set_prefix_same_as_start(&mut self, v: bool) {
        unsafe { ffi::rocksdb_readoptions_set_prefix_same_as_start(self.inner, v as c_uchar) }
    }

    pub fn set_total_order_seek(&mut self, v: bool) {
        unsafe { ffi::rocksdb_readoptions_set_total_order_seek(self.inner, v as c_uchar) }
    }

    /// If true, all data read from underlying storage will be
    /// verified against corresponding checksums.
    ///
    /// Default: true
    pub fn set_verify_checksums(&mut self, v: bool) {
        unsafe {
            ffi::rocksdb_readoptions_set_verify_checksums(self.inner, v as c_uchar);
        }
    }

    /// If non-zero, an iterator will create a new table reader which
    /// performs reads of the given size. Using a large size (> 2MB) can
    /// improve the performance of forward iteration on spinning disks.
    /// Default: 0
    ///
    /// ```
    /// use rocksdb::{ReadOptions};
    ///
    /// let mut opts = ReadOptions::default();
    /// opts.set_readahead_size(4_194_304); // 4mb
    /// ```
    pub fn set_readahead_size(&mut self, v: usize) {
        unsafe {
            ffi::rocksdb_readoptions_set_readahead_size(self.inner, v as size_t);
        }
    }

    /// If true, create a tailing iterator. Note that tailing iterators
    /// only support moving in the forward direction. Iterating in reverse
    /// or seek_to_last are not supported.
    pub fn set_tailing(&mut self, v: bool) {
        unsafe {
            ffi::rocksdb_readoptions_set_tailing(self.inner, v as c_uchar);
        }
    }
}

impl Default for ReadOptions {
    fn default() -> ReadOptions {
        unsafe {
            ReadOptions {
                inner: ffi::rocksdb_readoptions_create(),
            }
        }
    }
}

// Safety note: auto-implementing Send on most db-related types is prevented by the inner FFI
// pointer. In most cases, however, this pointer is Send-safe because it is never aliased and
// rocksdb internally does not rely on thread-local information for its user-exposed types.
unsafe impl<'a> Send for DBRawIterator<'a> {}
unsafe impl Send for ReadOptions {}

// Sync is similarly safe for many types because they do not expose interior mutability, and their
// use within the rocksdb library is generally behind a const reference
unsafe impl<'a> Sync for DBRawIterator<'a> {}
unsafe impl Sync for ReadOptions {}

fn to_cpath<P: AsRef<Path>>(path: P) -> Result<CString, Error> {
    match CString::new(path.as_ref().to_string_lossy().as_bytes()) {
        Ok(c) => Ok(c),
        Err(e) => Err(Error::new(format!(
            "Failed to convert path to CString: {}",
            e,
        ))),
    }
}

/// Wrapper around RocksDB PinnableSlice struct.
///
/// With a pinnable slice, we can directly leverage in-memory data within
/// RocksDB to avoid unnecessary memory copies. The struct here wraps the
/// returned raw pointer and ensures proper finalization work.
pub struct DBPinnableSlice<'a> {
    ptr: *mut ffi::rocksdb_pinnableslice_t,
    db: PhantomData<&'a DB>,
}

// Safety note: auto-implementing Send on most db-related types is prevented by the inner FFI
// pointer. In most cases, however, this pointer is Send-safe because it is never aliased and
// rocksdb internally does not rely on thread-local information for its user-exposed types.
unsafe impl<'a> Send for DBPinnableSlice<'a> {}

// Sync is similarly safe for many types because they do not expose interior mutability, and their
// use within the rocksdb library is generally behind a const reference
unsafe impl<'a> Sync for DBPinnableSlice<'a> {}

impl<'a> AsRef<[u8]> for DBPinnableSlice<'a> {
    fn as_ref(&self) -> &[u8] {
        // Implement this via Deref so as not to repeat ourselves
        &*self
    }
}

impl<'a> Deref for DBPinnableSlice<'a> {
    type Target = [u8];

    fn deref(&self) -> &[u8] {
        unsafe {
            let mut val_len: size_t = 0;
            let val = ffi::rocksdb_pinnableslice_value(self.ptr, &mut val_len) as *mut u8;
            slice::from_raw_parts(val, val_len)
        }
    }
}

impl<'a> Drop for DBPinnableSlice<'a> {
    fn drop(&mut self) {
        unsafe {
            ffi::rocksdb_pinnableslice_destroy(self.ptr);
        }
    }
}

impl<'a> DBPinnableSlice<'a> {
    /// Used to wrap a PinnableSlice from rocksdb to avoid unnecessary memcpy
    ///
    /// # Unsafe
    /// Requires that the pointer must be generated by rocksdb_get_pinned
    unsafe fn from_c(ptr: *mut ffi::rocksdb_pinnableslice_t) -> DBPinnableSlice<'a> {
        DBPinnableSlice {
            ptr,
            db: PhantomData,
        }
    }
}

#[test]
fn external() {
    let path = "_rust_rocksdb_externaltest";
    {
        let db = DB::open_default(path).unwrap();
        let p = db.put(b"k1", b"v1111");
        assert!(p.is_ok());
        let r: Result<Option<Vec<u8>>, Error> = db.get(b"k1");
        assert_eq!(r.unwrap().unwrap(), b"v1111");
        assert!(db.delete(b"k1").is_ok());
        assert!(db.get(b"k1").unwrap().is_none());
    }
    let opts = Options::default();
    let result = DB::destroy(&opts, path);
    assert!(result.is_ok());
}

#[test]
fn errors_do_stuff() {
    let path = "_rust_rocksdb_error";
    {
        let _db = DB::open_default(path).unwrap();
        let opts = Options::default();
        // The DB will still be open when we try to destroy it and the lock should fail.
        match DB::destroy(&opts, path) {
            Err(s) => {
                let message = s.to_string();
                assert!(message.find("IO error:").is_some());
                assert!(message.find("_rust_rocksdb_error/LOCK:").is_some());
            }
            Ok(_) => panic!("should fail"),
        }
    }
    let opts = Options::default();
    let result = DB::destroy(&opts, path);
    assert!(result.is_ok());
}

#[test]
fn writebatch_works() {
    let path = "_rust_rocksdb_writebacktest";
    {
        let db = DB::open_default(path).unwrap();
        {
            // test putx
            let mut batch = WriteBatch::default();
            assert!(db.get(b"k1").unwrap().is_none());
            assert_eq!(batch.len(), 0);
            assert!(batch.is_empty());
            let _ = batch.put(b"k1", b"v1111");
            let _ = batch.put(b"k2", b"v2222");
            let _ = batch.put(b"k3", b"v3333");
            assert_eq!(batch.len(), 3);
            assert!(!batch.is_empty());
            assert!(db.get(b"k1").unwrap().is_none());
            let p = db.write(batch);
            assert!(p.is_ok());
            let r: Result<Option<Vec<u8>>, Error> = db.get(b"k1");
            assert_eq!(r.unwrap().unwrap(), b"v1111");
        }
        {
            // test delete
            let mut batch = WriteBatch::default();
            let _ = batch.delete(b"k1");
            assert_eq!(batch.len(), 1);
            assert!(!batch.is_empty());
            let p = db.write(batch);
            assert!(p.is_ok());
            assert!(db.get(b"k1").unwrap().is_none());
        }
        {
            // test delete_range
            let mut batch = WriteBatch::default();
            let _ = batch.delete_range(b"k2", b"k4");
            assert_eq!(batch.len(), 1);
            assert!(!batch.is_empty());
            let p = db.write(batch);
            assert!(p.is_ok());
            assert!(db.get(b"k2").unwrap().is_none());
            assert!(db.get(b"k3").unwrap().is_none());
        }
        {
            // test size_in_bytes
            let mut batch = WriteBatch::default();
            let before = batch.size_in_bytes();
            let _ = batch.put(b"k1", b"v1234567890");
            let after = batch.size_in_bytes();
            assert!(before + 10 <= after);
        }
    }
    let opts = Options::default();
    assert!(DB::destroy(&opts, path).is_ok());
}

#[test]
fn iterator_test() {
    let path = "_rust_rocksdb_iteratortest";
    {
        let db = DB::open_default(path).unwrap();
        let p = db.put(b"k1", b"v1111");
        assert!(p.is_ok());
        let p = db.put(b"k2", b"v2222");
        assert!(p.is_ok());
        let p = db.put(b"k3", b"v3333");
        assert!(p.is_ok());
        let iter = db.iterator(IteratorMode::Start);
        for (k, v) in iter {
            println!(
                "Hello {}: {}",
                str::from_utf8(&*k).unwrap(),
                str::from_utf8(&*v).unwrap()
            );
        }
    }
    let opts = Options::default();
    assert!(DB::destroy(&opts, path).is_ok());
}

#[test]
fn iterator_test_past_end() {
    let path = "_rust_rocksdb_iteratortest_past_end";
    {
        let db = DB::open_default(path).unwrap();
        db.put(b"k1", b"v1111").unwrap();
        let mut iter = db.iterator(IteratorMode::Start);
        assert!(iter.next().is_some());
        assert!(iter.next().is_none());
        assert!(iter.next().is_none());
    }
    let opts = Options::default();
    DB::destroy(&opts, path).unwrap();
}

#[test]
fn iterator_test_tailing() {
    let path = "_rust_rocksdb_iteratortest_tailing";
    {
        let data = [(b"k1", b"v1"), (b"k2", b"v2"), (b"k3", b"v3")];
        let mut ro = ReadOptions::default();
        ro.set_tailing(true);
        let db = DB::open_default(path).unwrap();

        let mut data_iter = data.iter();
        let (k, v) = data_iter.next().unwrap();
        let r = db.put(k, v);
        assert!(r.is_ok());

        let tail_iter = db.iterator_opt(IteratorMode::Start, &ro);
        for (k, v) in data_iter {
            let r = db.put(k, v);
            assert!(r.is_ok());
        }

        let mut tot = 0;
        for (i, (k, v)) in tail_iter.enumerate() {
            assert_eq!(
                (k.to_vec(), v.to_vec()),
                (data[i].0.to_vec(), data[i].1.to_vec())
            );
            tot = tot + 1;
        }
        assert_eq!(tot, data.len());
    }
    let opts = Options::default();
    assert!(DB::destroy(&opts, path).is_ok());
}

#[test]
fn snapshot_test() {
    let path = "_rust_rocksdb_snapshottest";
    {
        let db = DB::open_default(path).unwrap();
        let p = db.put(b"k1", b"v1111");
        assert!(p.is_ok());

        let snap = db.snapshot();
        let r: Result<Option<Vec<u8>>, Error> = snap.get(b"k1");
        assert_eq!(r.unwrap().unwrap(), b"v1111");

        let p = db.put(b"k2", b"v2222");
        assert!(p.is_ok());

        assert!(db.get(b"k2").unwrap().is_some());
        assert!(snap.get(b"k2").unwrap().is_none());
    }
    let opts = Options::default();
    assert!(DB::destroy(&opts, path).is_ok());
}

#[test]
fn set_option_test() {
    let path = "_rust_rocksdb_set_optionstest";
    {
        let db = DB::open_default(path).unwrap();
        // set an option to valid values
        assert!(db
            .set_options(&[("disable_auto_compactions", "true")])
            .is_ok());
        assert!(db
            .set_options(&[("disable_auto_compactions", "false")])
            .is_ok());
        // invalid names/values should result in an error
        assert!(db
            .set_options(&[("disable_auto_compactions", "INVALID_VALUE")])
            .is_err());
        assert!(db
            .set_options(&[("INVALID_NAME", "INVALID_VALUE")])
            .is_err());
        // option names/values must not contain NULLs
        assert!(db
            .set_options(&[("disable_auto_compactions", "true\0")])
            .is_err());
        assert!(db
            .set_options(&[("disable_auto_compactions\0", "true")])
            .is_err());
        // empty options are not allowed
        assert!(db.set_options(&[]).is_err());
        // multiple options can be set in a single API call
        let multiple_options = [
            ("paranoid_file_checks", "true"),
            ("report_bg_io_stats", "true"),
        ];
        db.set_options(&multiple_options).unwrap();
    }
    assert!(DB::destroy(&Options::default(), path).is_ok());
}