Introduce the StrStrU8 heed codec

src/heed_codec/mod.rs

@@ -2,8 +2,10 @@ mod beu32_str_codec;
 mod byteorder_x_roaring_bitmap_codec;
 mod csv_string_record_codec;
 mod roaring_bitmap_codec;
+mod str_str_u8_codec;
 
 pub use self::beu32_str_codec::BEU32StrCodec;
 pub use self::byteorder_x_roaring_bitmap_codec::ByteorderXRoaringBitmapCodec;
 pub use self::csv_string_record_codec::CsvStringRecordCodec;
 pub use self::roaring_bitmap_codec::RoaringBitmapCodec;
+pub use self::str_str_u8_codec::StrStrU8Codec;

src/heed_codec/str_str_u8_codec.rs

@@ -0,0 +1,30 @@
+use std::borrow::Cow;
+use std::str;
+
+pub struct StrStrU8Codec;
+
+impl<'a> heed::BytesDecode<'a> for StrStrU8Codec {
+    type DItem = (&'a str, &'a str, u8);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let (n, bytes) = bytes.split_last()?;
+        let s1_end = bytes.iter().position(|b| *b == 0)?;
+        let (s1_bytes, s2_bytes) = bytes.split_at(s1_end);
+        let s1 = str::from_utf8(s1_bytes).ok()?;
+        let s2 = str::from_utf8(&s2_bytes[1..]).ok()?;
+        Some((s1, s2, *n))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for StrStrU8Codec {
+    type EItem = (&'a str, &'a str, u8);
+
+    fn bytes_encode((s1, s2, n): &Self::EItem) -> Option<Cow<[u8]>> {
+        let mut bytes = Vec::with_capacity(s1.len() + s2.len() + 1 + 1);
+        bytes.extend_from_slice(s1.as_bytes());
+        bytes.push(0);
+        bytes.extend_from_slice(s2.as_bytes());
+        bytes.push(*n);
+        Some(Cow::Owned(bytes))
+    }
+}