Add the new tasks with most of the job done

crates/milli/src/heed_codec/mod.rs

@@ -10,6 +10,7 @@ mod roaring_bitmap_length;
 mod str_beu32_codec;
 mod str_ref;
 mod str_str_u8_codec;
+pub mod version;
 
 pub use byte_slice_ref::BytesRefCodec;
 use heed::BoxedError;

crates/milli/src/heed_codec/version.rs

@@ -0,0 +1,44 @@
+use std::mem::size_of;
+use std::{borrow::Cow, mem::size_of_val};
+
+use byteorder::{BigEndian, ByteOrder};
+use heed::{BoxedError, BytesDecode, BytesEncode};
+
+const VERSION_SIZE: usize = std::mem::size_of::<u32>() * 3;
+
+#[derive(thiserror::Error, Debug)]
+#[error(
+    "Could not decode the version: Expected {} bytes but instead received {0} bytes",
+    VERSION_SIZE
+)]
+pub struct DecodeVersionError(usize);
+
+pub struct VersionCodec;
+impl<'a> BytesEncode<'a> for VersionCodec {
+    type EItem = (u32, u32, u32);
+
+    fn bytes_encode(item: &'a Self::EItem) -> Result<Cow<'a, [u8]>, BoxedError> {
+        let mut ret = Vec::with_capacity(size_of::<u32>() * 3);
+        ret.extend(&item.0.to_be_bytes());
+        ret.extend(&item.1.to_be_bytes());
+        ret.extend(&item.2.to_be_bytes());
+        Ok(Cow::Owned(ret))
+    }
+}
+impl<'a> BytesDecode<'a> for VersionCodec {
+    type DItem = (u32, u32, u32);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        if bytes.len() != VERSION_SIZE {
+            Err(Box::new(DecodeVersionError(bytes.len())))
+        } else {
+            let major = BigEndian::read_u32(bytes);
+            let bytes = &bytes[size_of_val(&major)..];
+            let minor = BigEndian::read_u32(bytes);
+            let bytes = &bytes[size_of_val(&major)..];
+            let patch = BigEndian::read_u32(bytes);
+
+            Ok((major, minor, patch))
+        }
+    }
+}