directory structure change to work with glide

glide has its own requirements. My previous workaround caused me some
code checkin errors. Need to fix this.

weed/command/download.go

@@ -0,0 +1,130 @@
+package command
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/chrislusf/seaweedfs/weed/operation"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+var (
+	d DownloadOptions
+)
+
+type DownloadOptions struct {
+	server *string
+	dir    *string
+}
+
+func init() {
+	cmdDownload.Run = runDownload // break init cycle
+	d.server = cmdDownload.Flag.String("server", "localhost:9333", "SeaweedFS master location")
+	d.dir = cmdDownload.Flag.String("dir", ".", "Download the whole folder recursively if specified.")
+}
+
+var cmdDownload = &Command{
+	UsageLine: "download -server=localhost:9333 -dir=one_directory fid1 [fid2 fid3 ...]",
+	Short:     "download files by file id",
+	Long: `download files by file id.
+
+  Usually you just need to use curl to lookup the file's volume server, and then download them directly.
+  This download tool combine the two steps into one.
+
+  What's more, if you use "weed upload -maxMB=..." option to upload a big file divided into chunks, you can
+  use this tool to download the chunks and merge them automatically.
+
+  `,
+}
+
+func runDownload(cmd *Command, args []string) bool {
+	for _, fid := range args {
+		if e := downloadToFile(*d.server, fid, *d.dir); e != nil {
+			fmt.Println("Download Error: ", fid, e)
+		}
+	}
+	return true
+}
+
+func downloadToFile(server, fileId, saveDir string) error {
+	fileUrl, lookupError := operation.LookupFileId(server, fileId)
+	if lookupError != nil {
+		return lookupError
+	}
+	filename, rc, err := util.DownloadUrl(fileUrl)
+	if err != nil {
+		return err
+	}
+	defer rc.Close()
+	if filename == "" {
+		filename = fileId
+	}
+	isFileList := false
+	if strings.HasSuffix(filename, "-list") {
+		// old command compatible
+		isFileList = true
+		filename = filename[0 : len(filename)-len("-list")]
+	}
+	f, err := os.OpenFile(path.Join(saveDir, filename), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, os.ModePerm)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	if isFileList {
+		content, err := ioutil.ReadAll(rc)
+		if err != nil {
+			return err
+		}
+		fids := strings.Split(string(content), "\n")
+		for _, partId := range fids {
+			var n int
+			_, part, err := fetchContent(*d.server, partId)
+			if err == nil {
+				n, err = f.Write(part)
+			}
+			if err == nil && n < len(part) {
+				err = io.ErrShortWrite
+			}
+			if err != nil {
+				return err
+			}
+		}
+	} else {
+		if _, err = io.Copy(f, rc); err != nil {
+			return err
+		}
+
+	}
+	return nil
+}
+
+func fetchContent(server string, fileId string) (filename string, content []byte, e error) {
+	fileUrl, lookupError := operation.LookupFileId(server, fileId)
+	if lookupError != nil {
+		return "", nil, lookupError
+	}
+	var rc io.ReadCloser
+	if filename, rc, e = util.DownloadUrl(fileUrl); e != nil {
+		return "", nil, e
+	}
+	content, e = ioutil.ReadAll(rc)
+	rc.Close()
+	return
+}
+
+func WriteFile(filename string, data []byte, perm os.FileMode) error {
+	f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
+	if err != nil {
+		return err
+	}
+	n, err := f.Write(data)
+	f.Close()
+	if err == nil && n < len(data) {
+		err = io.ErrShortWrite
+	}
+	return err
+}