api: Various fixes.

- limit list buckets to limit only 100 buckets, all uppercase buckets
  are now lowercase and work transparently with all calls.
- Change disk.Stat to disk.GetInfo and return back disk.Info{} struct.
- Introduce new ioutils package which implements ReadDirN(path, n),
  ReadDirNamesN(path, n)

pkg/ioutils/ioutils.go

@@ -0,0 +1,45 @@
+package ioutils
+
+import (
+	"os"
+	"sort"
+)
+
+// byName implements sort.Interface for sorting os.FileInfo list.
+type byName []os.FileInfo
+
+func (f byName) Len() int           { return len(f) }
+func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
+func (f byName) Swap(i, j int)      { f[i], f[j] = f[j], f[i] }
+
+// ReadDirN reads the directory named by dirname and returns
+// a list of sorted directory entries of size 'n'.
+func ReadDirN(dirname string, n int) ([]os.FileInfo, error) {
+	f, err := os.Open(dirname)
+	if err != nil {
+		return nil, err
+	}
+	list, err := f.Readdir(n)
+	f.Close()
+	if err != nil {
+		return nil, err
+	}
+	sort.Sort(byName(list))
+	return list, nil
+}
+
+// ReadDirNamesN reads the directory named by dirname and returns
+// a list of sorted directory names of size 'n'.
+func ReadDirNamesN(dirname string, n int) ([]string, error) {
+	f, err := os.Open(dirname)
+	if err != nil {
+		return nil, err
+	}
+	names, err := f.Readdirnames(n)
+	f.Close()
+	if err != nil {
+		return nil, err
+	}
+	sort.Strings(names)
+	return names, nil
+}