add mime, use simple insert and update filer store API

1. add mime type to file in filer
2. purge old chunks if overwrite during insert

weed/filesys/filehandle.go

@@ -11,6 +11,7 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"strings"
 	"sync"
+	"net/http"
 )
 
 type FileHandle struct {
@@ -18,10 +19,6 @@ type FileHandle struct {
 	dirtyPages    *ContinuousDirtyPages
 	dirtyMetadata bool
 
-	cachePath string
-
-	handle uint64
-
 	f         *File
 	RequestId fuse.RequestID // unique ID for request
 	NodeId    fuse.NodeID    // file or directory the request is about
@@ -135,6 +132,11 @@ func (fh *FileHandle) Write(ctx context.Context, req *fuse.WriteRequest, resp *f
 
 	resp.Size = len(req.Data)
 
+	if req.Offset == 0 {
+		fh.f.attributes.Mime = http.DetectContentType(req.Data)
+		fh.dirtyMetadata = true
+	}
+
 	if chunk != nil {
 		fh.f.Chunks = append(fh.f.Chunks, chunk)
 		glog.V(1).Infof("uploaded %s/%s to %s [%d,%d)", fh.f.dir.Path, fh.f.Name, chunk.FileId, chunk.Offset, chunk.Offset+int64(chunk.Size))