initial import

core/filex/rangereader.go

@@ -0,0 +1,43 @@
+package filex
+
+import (
+	"errors"
+	"os"
+)
+
+type RangeReader struct {
+	file  *os.File
+	start int64
+	stop  int64
+}
+
+func NewRangeReader(file *os.File, start, stop int64) *RangeReader {
+	return &RangeReader{
+		file:  file,
+		start: start,
+		stop:  stop,
+	}
+}
+
+func (rr *RangeReader) Read(p []byte) (n int, err error) {
+	stat, err := rr.file.Stat()
+	if err != nil {
+		return 0, err
+	}
+
+	if rr.stop < rr.start || rr.start >= stat.Size() {
+		return 0, errors.New("exceed file size")
+	}
+
+	if rr.stop-rr.start < int64(len(p)) {
+		p = p[:rr.stop-rr.start]
+	}
+
+	n, err = rr.file.ReadAt(p, rr.start)
+	if err != nil {
+		return n, err
+	}
+
+	rr.start += int64(n)
+	return
+}