read mca region file

save/mca.go

@@ -1,4 +0,0 @@
-package save
-
-type Region struct {
-}

save/region/mca.go

@@ -0,0 +1,99 @@
+package region
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+	"os"
+)
+
+type Region struct {
+	f          *os.File
+	offsets    [32][32]int32
+	timestamps [32][32]int32
+
+	// sectors record if a sector is in used.
+	// contrary to mojang's, because false is the default value in Go.
+	sectors map[int32]bool
+}
+
+// In calculate chunk's coordinates relative to region
+func In(cx, cy int) (int, int) {
+	// c & (32-1)
+	// is equal to:
+	// (c %= 32) > 0 ? c : -c; //C language
+	return cx & 31, cy & 31
+}
+
+// OpenRegion open a .mca file and read the head.
+// Close the Region after used.
+func OpenRegion(name string) (r *Region, err error) {
+	r = new(Region)
+	r.sectors = make(map[int32]bool)
+
+	r.f, err = os.OpenFile(name, os.O_RDWR, 0666)
+	if err != nil {
+		return nil, err
+	}
+
+	// read the offsets
+	err = binary.Read(r.f, binary.BigEndian, &r.offsets)
+	if err != nil {
+		_ = r.f.Close()
+		return nil, err
+	}
+	r.sectors[0] = true
+
+	// read the timestamps
+	err = binary.Read(r.f, binary.BigEndian, &r.timestamps)
+	if err != nil {
+		_ = r.f.Close()
+		return nil, err
+	}
+	r.sectors[1] = true
+
+	// generate sectorFree table
+	for _, v := range r.offsets {
+		for _, v := range v {
+			if o, s := sectorLoc(v); o != 0 {
+				for i := int32(0); i < s; i++ {
+					r.sectors[o+i] = true
+				}
+			}
+		}
+	}
+
+	return r, nil
+}
+
+func (r *Region) Close() error {
+	return r.f.Close()
+}
+
+func sectorLoc(offset int32) (o, s int32) {
+	return offset >> 8, offset & 0xFF
+}
+
+func (r *Region) ReadSector(x, y int) (data []byte, err error) {
+	offset, _ := sectorLoc(r.offsets[x][y])
+
+	if offset == 0 {
+		return nil, errors.New("sector not exist")
+	}
+
+	_, err = r.f.Seek(4096*int64(offset), 0)
+	if err != nil {
+		return
+	}
+
+	var length int32
+	err = binary.Read(r.f, binary.BigEndian, &length)
+	if err != nil {
+		return
+	}
+
+	data = make([]byte, length)
+	_, err = io.ReadFull(r.f, data)
+
+	return
+}

save/region/mca_test.go

@@ -0,0 +1,46 @@
+package region
+
+import (
+	"bytes"
+	"compress/zlib"
+	"io/ioutil"
+	"testing"
+)
+
+func TestIn(t *testing.T) {
+	for i := -10000; i < 10000; i++ {
+		getX, _ := In(i, i)
+		want := i % 32
+		if want < 0 {
+			want += 32
+		}
+
+		if getX != want {
+			t.Errorf("fail when convert cord: get %d, want %d", getX, want)
+		}
+	}
+}
+
+func TestReadRegion(t *testing.T) {
+	r, err := OpenRegion("../testdata/region/r.0.-1.mca")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s, err := r.ReadSector(In(31, 0))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	reader, err := zlib.NewReader(bytes.NewReader(s[1:]))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s, err = ioutil.ReadAll(reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Log(s)
+}