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#![no_std]
use core::str;
use byteorder::{ByteOrder, BigEndian};
#[cfg(feature = "postcard-values")]
use serde::{Deserialize, Serialize};
mod error;
pub use error::{Error, ReadError, WriteError};
mod iter;
use iter::Iter;
pub mod no_flash;
mod test;
pub trait StoreBackend {
type Data: ?Sized + AsRef<[u8]>;
fn data(&self) -> &Self::Data;
fn len(&self) -> usize {
self.data().as_ref().len()
}
type Error;
fn erase(&mut self) -> Result<(), Self::Error>;
fn program(&mut self, offset: usize, payload: &[u8]) -> Result<(), Self::Error>;
fn program_done(&mut self) {}
fn backup_space(&self) -> &'static mut [u8];
}
pub struct Store<B: StoreBackend> {
backend: B,
}
impl<B: StoreBackend> Store<B> {
pub fn new(backend: B) -> Self {
Store { backend }
}
pub fn read(&self, key: &str) -> Result<Option<&[u8]>, ReadError> {
let mut iter = Iter::new(self.backend.data().as_ref());
let mut value = None;
while let Some(result) = iter.next() {
let (record_key, record_value) = result?;
if key.as_bytes() == record_key {
value = Some(record_value)
}
}
Ok(value)
}
pub fn read_str(&self, key: &str) -> Result<Option<&str>, ReadError> {
self.read(key)
.and_then(|value| value
.map(|value| str::from_utf8(value)
.map_err(ReadError::Utf8Error)
)
.transpose()
)
}
#[cfg(feature = "postcard-values")]
pub fn read_value<'a, T: Deserialize<'a>>(&'a self, key: &str) -> Result<Option<T>, Error<B::Error>> {
self.read(key)?
.map(
|data| postcard::from_bytes(data)
.map_err(Error::Decode)
).transpose()
}
pub fn get_bytes_used(&self) -> Result<usize, ReadError> {
let mut iter = Iter::new(self.backend.data().as_ref());
while let Some(result) = iter.next() {
let _ = result?;
}
Ok(iter.offset)
}
unsafe fn append_at(&mut self, mut offset: usize,
key: &[u8], value: &[u8]) -> Result<usize, WriteError<B::Error>> {
let record_size = 4 + key.len() + 1 + value.len();
if offset + record_size > self.backend.len() {
return Err(WriteError::SpaceExhausted)
}
let mut record_size_bytes = [0u8; 4];
BigEndian::write_u32(&mut record_size_bytes[..], record_size as u32);
{
let mut write = |payload| -> Result<(), WriteError<B::Error>> {
self.backend.program(offset, payload)
.map_err(WriteError::Backend)?;
offset += payload.len();
Ok(())
};
write(&record_size_bytes[..])?;
write(key)?;
write(&[0])?;
write(value)?;
}
self.backend.program_done();
Ok(offset)
}
fn compact(&mut self) -> Result<(), Error<B::Error>> {
let old_data = self.backend.backup_space();
old_data.copy_from_slice(self.backend.data().as_ref());
self.erase()?;
let mut offset = 0;
let mut iter = Iter::new(old_data.as_ref());
'iter: while let Some(result) = iter.next() {
let (key, value) = result?;
if value.is_empty() {
continue
}
let mut next_iter = iter.clone();
while let Some(next_result) = next_iter.next() {
let (next_key, _) = next_result?;
if key == next_key {
continue 'iter
}
}
offset = unsafe { self.append_at(offset, key, value)? };
}
Ok(())
}
fn append(&mut self, key: &str, value: &[u8]) -> Result<(), Error<B::Error>> {
let free_offset = {
let mut iter = Iter::new(self.backend.data().as_ref());
let mut not_modified = false;
while let Some(result) = iter.next() {
let (record_key, record_value) = result?;
if key.as_bytes() == record_key {
not_modified = value == record_value;
}
}
if not_modified {
return Ok(())
}
iter.offset
};
unsafe { self.append_at(free_offset, key.as_bytes(), value)? };
Ok(())
}
pub fn write<V: AsRef<[u8]>>(&mut self, key: &str, value: V) -> Result<(), Error<B::Error>> {
let value = value.as_ref();
match self.append(key, value) {
Err(Error::Write(WriteError::SpaceExhausted)) => {
self.compact()?;
self.append(key, value)
}
res => res
}
}
#[cfg(feature = "postcard-values")]
pub fn write_value<T, V>(&mut self, key: &str, value: &T, mut value_buf: V) -> Result<(), Error<B::Error>>
where
T: Serialize,
V: AsMut<[u8]>,
{
let data = postcard::to_slice(value, value_buf.as_mut())
.map_err(Error::Encode)?;
self.write(key, data)
}
pub fn remove(&mut self, key: &str) -> Result<(), Error<B::Error>> {
self.write(key, &[])
}
pub fn erase(&mut self) -> Result<(), WriteError<B::Error>> {
self.backend.erase()
.map_err(WriteError::Backend)?;
Ok(())
}
}