read_value()/write_value(): implement serialization via postcard crate

Cargo.toml

@@ -12,4 +12,6 @@ license = "GPL-3"
 edition = "2018"
 
 [dependencies]
-byteorder = { version = "1.0", default-features = false }
+byteorder = { version = "1", default-features = false }
+serde = { version = "1.0", default-features = false }
+postcard = "0.5"

src/error.rs

@@ -1,9 +1,11 @@
 use core::{fmt, str};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Error<B> {
     Read(ReadError),
     Write(WriteError<B>),
+    Encode(postcard::Error),
+    Decode(postcard::Error),
 }
 
 impl<B> From<ReadError> for Error<B> {

src/lib.rs

@@ -2,6 +2,7 @@
 
 use core::{fmt::Write, mem::size_of, str};
 use byteorder::{ByteOrder, BigEndian};
+use serde::{Deserialize, Serialize};
 
 mod error;
 pub use error::{Error, ReadError, WriteError};
@@ -14,7 +15,7 @@ mod test;
 
 pub trait StoreBackend {
     type Data: Sized + AsRef<[u8]> + Clone;
-    
+
     /// Memory-mapped
     fn data(&self) -> &Self::Data;
     fn len(&self) -> usize {
@@ -63,6 +64,15 @@ impl<B: StoreBackend> Store<B> {
                       .transpose())
     }
 
+    /// read from `key`, decode with `postcard`
+    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()
+    }
+
     /// how many bytes are currently used
     ///
     /// equally, offset of free space
@@ -157,11 +167,20 @@ impl<B: StoreBackend> Store<B> {
         self.write(key, wrapper.contents())
     }
 
+    /// encode with `postcard`, write at `key`
+    pub fn write_value<T: Serialize>(&mut self, key: &str, value: T) -> Result<(), Error<B::Error>> {
+        let mut buf = [0; 64];
+        let data = postcard::to_slice(&value, &mut buf)
+            .map_err(Error::Encode)?;
+        self.write(key, data)
+    }
+
     /// store a 0-byte tombstone value at `key`
     pub fn remove(&mut self, key: &str) -> Result<(), Error<B::Error>> {
         self.write(key, &[])
     }
 
+    /// invokes erase on the backend (this is no compaction!)
     pub fn erase(&mut self) -> Result<(), WriteError<B::Error>> {
         self.backend.erase()
             .map_err(WriteError::Backend)?;

src/test.rs

@@ -52,14 +52,48 @@ fn empty_read_not_found() {
     assert_eq!(store.read("foo").unwrap(), None)
 }
 
-    
 #[test]
 fn write_read() {
     let mut store = make_store();
     store.write("foo", b"bar").unwrap();
     assert_eq!(store.read("foo").unwrap().unwrap(), b"bar");
 }
-    
+
+#[test]
+fn write_read_value_str() {
+    let mut store = make_store();
+    store.write_value("foo", "bar").unwrap();
+    assert_eq!(store.read_value("foo"), Ok(Some("bar")));
+}
+
+#[test]
+fn write_read_value_u32() {
+    let mut store = make_store();
+    store.write_value("foo", 42005u32).unwrap();
+    assert_eq!(store.read_value("foo"), Ok(Some(42005u32)));
+}
+
+#[test]
+fn write_read_value_i64() {
+    let mut store = make_store();
+    store.write_value("foo", -99999999i64).unwrap();
+    assert_eq!(store.read_value("foo"), Ok(Some(-99999999i64)));
+}
+
+#[test]
+fn write_read_value_f32() {
+    let mut store = make_store();
+    store.write_value("foo", 3.75e17f32).unwrap();
+    assert_eq!(store.read_value("foo"), Ok(Some(3.75e17f32)));
+}
+
+#[test]
+fn write_read_value_f64() {
+    let mut store = make_store();
+    store.write_value("foo", -1.999e-13f64).unwrap();
+    assert_eq!(store.read_value("foo"), Ok(Some(-1.999e-13f64)));
+}
+
 #[test]
 fn write_int_read_str() {
     let mut store = make_store();