leveldb 0.8.6

An interface for leveldb
Documentation 
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//! Module providing write batches

use leveldb_sys::*;
use libc::{c_char, size_t, c_void};
use std::marker::PhantomData;
use database::key::Key;
use database::key::from_u8;
use std::slice;
use options::{WriteOptions, c_writeoptions};
use super::error::Error;
use std::ptr;
use super::Database;

#[allow(missing_docs)]
struct RawWritebatch {
    ptr: *mut leveldb_writebatch_t,
}

impl Drop for RawWritebatch {
    fn drop(&mut self) {
        unsafe {
            leveldb_writebatch_destroy(self.ptr);
        }
    }
}

#[allow(missing_docs)]
pub struct Writebatch<K: Key> {
    #[allow(dead_code)]
    writebatch: RawWritebatch,
    marker: PhantomData<K>,
}

/// Batch access to the database
pub trait Batch<K: Key> {
    /// Write a batch to the database, ensuring success for all items or an error
    fn write(&self, options: WriteOptions, batch: &Writebatch<K>) -> Result<(), Error>;
}

impl<K: Key> Batch<K> for Database<K> {
    fn write(&self, options: WriteOptions, batch: &Writebatch<K>) -> Result<(), Error> {
        unsafe {
            let mut error = ptr::null_mut();
            let c_writeoptions = c_writeoptions(options);

            leveldb_write(self.database.ptr,
                          c_writeoptions,
                          batch.writebatch.ptr,
                          &mut error);
            leveldb_writeoptions_destroy(c_writeoptions);

            if error == ptr::null_mut() {
                Ok(())
            } else {
                Err(Error::new_from_char(error))
            }
        }
    }
}

impl<K: Key> Writebatch<K> {
    /// Create a new writebatch
    pub fn new() -> Writebatch<K> {
        let ptr = unsafe { leveldb_writebatch_create() };
        let raw = RawWritebatch { ptr: ptr };
        Writebatch {
            writebatch: raw,
            marker: PhantomData,
        }
    }

    /// Clear the writebatch
    pub fn clear(&mut self) {
        unsafe { leveldb_writebatch_clear(self.writebatch.ptr) };
    }

    /// Batch a put operation
    pub fn put(&mut self, key: K, value: &[u8]) {
        unsafe {
            key.as_slice(|k| {
                leveldb_writebatch_put(self.writebatch.ptr,
                                       k.as_ptr() as *mut c_char,
                                       k.len() as size_t,
                                       value.as_ptr() as *mut c_char,
                                       value.len() as size_t);
            })
        }
    }

    /// Batch a delete operation
    pub fn delete(&mut self, key: K) {
        unsafe {
            key.as_slice(|k| {
                leveldb_writebatch_delete(self.writebatch.ptr,
                                          k.as_ptr() as *mut c_char,
                                          k.len() as size_t);
            })
        }
    }

    /// Iterate over the writebatch, returning the resulting iterator
    pub fn iterate<T: WritebatchIterator<K = K>>(&mut self, iterator: Box<T>) -> Box<T> {
        unsafe {
            let iter = Box::into_raw(iterator);
            leveldb_writebatch_iterate(self.writebatch.ptr,
                                       iter as *mut c_void,
                                       put_callback::<K, T>,
                                       deleted_callback::<K, T>);
            Box::from_raw(iter)
        }
    }
}

/// A trait for iterators to iterate over written batches and check their validity.
pub trait WritebatchIterator {
    /// The database key type this iterates over
    type K: Key;

    /// Callback for put items
    fn put(&mut self, key: Self::K, value: &[u8]);

    /// Callback for deleted items
    fn deleted(&mut self, key: Self::K);
}

extern "C" fn put_callback<K: Key, T: WritebatchIterator<K = K>>(state: *mut c_void,
                                                                 key: *const c_char,
                                                                 keylen: size_t,
                                                                 val: *const c_char,
                                                                 vallen: size_t) {
    unsafe {
        let iter: &mut T = &mut *(state as *mut T);
        let key_slice = slice::from_raw_parts::<u8>(key as *const u8, keylen as usize);
        let val_slice = slice::from_raw_parts::<u8>(val as *const u8, vallen as usize);
        let k = from_u8::<<T as WritebatchIterator>::K>(key_slice);
        iter.put(k, val_slice);
    }
}

extern "C" fn deleted_callback<K: Key, T: WritebatchIterator<K = K>>(state: *mut c_void,
                                                                     key: *const c_char,
                                                                     keylen: size_t) {
    unsafe {
        let iter: &mut T = &mut *(state as *mut T);
        let key_slice = slice::from_raw_parts::<u8>(key as *const u8, keylen as usize);
        let k = from_u8::<<T as WritebatchIterator>::K>(key_slice);
        iter.deleted(k);
    }
}