Add torrent.Mmap and MmapSpan, types that abstract memory-mapped torrent data

mmap_span.go

@@ -0,0 +1,56 @@
+package torrent
+
+import (
+	"io"
+	"launchpad.net/gommap"
+)
+
+type Mmap struct {
+	gommap.MMap
+}
+
+func (me Mmap) Size() int64 {
+	return int64(len(me.MMap))
+}
+
+type MmapSpan []Mmap
+
+func (me MmapSpan) span() (s span) {
+	for _, mmap := range me {
+		s = append(s, mmap)
+	}
+	return
+}
+
+func (me MmapSpan) Size() (ret int64) {
+	for _, mmap := range me {
+		ret += mmap.Size()
+	}
+	return
+}
+
+func (me MmapSpan) ReadAt(p []byte, off int64) (n int, err error) {
+	me.span().ApplyTo(off, func(intervalOffset int64, interval sizer) (stop bool) {
+		_n := copy(p, interval.(Mmap).MMap[intervalOffset:])
+		p = p[_n:]
+		n += _n
+		return len(p) == 0
+	})
+	if len(p) != 0 {
+		err = io.EOF
+	}
+	return
+}
+
+func (me MmapSpan) WriteAt(p []byte, off int64) (n int, err error) {
+	me.span().ApplyTo(off, func(iOff int64, i sizer) (stop bool) {
+		_n := copy(i.(Mmap).MMap[iOff:], p)
+		p = p[_n:]
+		n += _n
+		return len(p) == 0
+	})
+	if len(p) != 0 {
+		err = io.EOF
+	}
+	return
+}

span.go

@@ -0,0 +1,23 @@
+package torrent
+
+type sizer interface {
+	Size() int64
+}
+
+type (
+	span []sizer
+)
+
+func (me span) ApplyTo(off int64, f func(int64, sizer) (stop bool)) {
+	for _, interval := range me {
+		iSize := interval.Size()
+		if off >= iSize {
+			off -= iSize
+		} else {
+			if f(off, interval) {
+				return
+			}
+			off = 0
+		}
+	}
+}