Fix mcpe example

examples/mcpe/src/main.rs

@@ -1,12 +1,16 @@
-use miniz_oxide::deflate::{compress_to_vec, compress_to_vec_zlib};
+use miniz_oxide::deflate::{compress_to_vec, compress_to_vec_zlib, CompressionLevel};
 use miniz_oxide::inflate::{decompress_to_vec, decompress_to_vec_zlib};
+use rusty_leveldb::compressor::NoneCompressor;
 use rusty_leveldb::{Compressor, CompressorList, Options, DB};
 use std::rc::Rc;
 
+/// A zlib compressor that with zlib wrapper
+/// 
+/// This is use for old world format 
 struct ZlibCompressor(u8);
 
 impl ZlibCompressor {
-    /// level 0-10
+    /// compression level 0-10
     pub fn new(level: u8) -> Self {
         assert!(level <= 10);
         Self(level)
@@ -26,10 +30,19 @@ impl Compressor for ZlibCompressor {
     }
 }
 
+/// A zlib compressor that without zlib wrapper
+///
+/// > windowBits can also be –8..–15 for raw deflate. In this case, -windowBits determines the window size. deflate() will then generate raw deflate data with no zlib header or trailer, and will not compute a check value.
+/// >
+/// > From [zlib manual](https://zlib.net/manual.html)
+///
+/// It seems like Mojang use this for newer version
+///
+/// A copy of Mojang's implementation can be find [here](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/db/zlib_compressor.cc#L119).
 struct RawZlibCompressor(u8);
 
 impl RawZlibCompressor {
-    /// level 0-10
+    /// compression level 0-10
     pub fn new(level: u8) -> Self {
         assert!(level <= 10);
         Self(level)
@@ -51,19 +64,40 @@ impl Compressor for RawZlibCompressor {
 
 pub fn mcpe_options(compression_level: u8) -> Options {
     let mut opt = Options::default();
-    opt.compressor = 0;
+
+    // Mojang create a custom [compressor list](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/include/leveldb/options.h#L123)
+    // Sample config for compressor list can be find in [here](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/mcpe_sample_setup.cpp#L24-L28)
+    // 
+    // Their compression id can be find in [here](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/include/leveldb/zlib_compressor.h#L38)
+    // and [here](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/include/leveldb/zlib_compressor.h#L48)
+    // 
+    // Compression id will be use in [here](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/table/format.cc#L125-L150)
     let mut list = CompressorList::new();
-    list.set_with_id(0, RawZlibCompressor::new(compression_level));
-    list.set_with_id(1, ZlibCompressor::new(compression_level));
+    list.set_with_id(0, NoneCompressor::default());
+    list.set_with_id(2, ZlibCompressor::new(compression_level));
+    list.set_with_id(4, RawZlibCompressor::new(compression_level));
     opt.compressor_list = Rc::new(list);
+
+    // Set compressor
+    // Minecraft bedrock may use other id than 4 however default is 4. [Mojang's implementation](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/table/table_builder.cc#L152)
+    //
+    // There is a bug in this library that you have to open a database with the same compression type as it was written to.
+    // If raw data is smaller than compression, Mojang will use raw data. [Mojang's implementation](https://github.com/reedacartwright/rbedrock/blob/fb32a899da4e15c1aaa0d6de2b459e914e183516/src/leveldb-mcpe/table/table_builder.cc#L155-L165)
+    // There is a small chance that compression id 0 exists, you should use compression id 0 to write it.
+    opt.compressor = 4;
+
     opt
 }
 
+/// Path to world's db folder
+const PATH: &str = "mcpe_db";
+
+/// Mojang use `DefaultLevel` for world compression
+const COMPRESSION_LEVEL: u8 = CompressionLevel::DefaultLevel as u8;
+
 fn main() {
-    let path = "mcpe_db";
-    let compression_level = 10;
-    let opt = mcpe_options(compression_level);
-    let mut db = DB::open(path, opt).unwrap();
+    let opt = mcpe_options(COMPRESSION_LEVEL);
+    let mut db = DB::open(PATH, opt).unwrap();
     db.put(b"~local_player", b"NBT data goes here").unwrap();
     let value = db.get(b"~local_player").unwrap();
     assert_eq!(&value, b"NBT data goes here")