How do I delete all blobs in app engine on Go?

The blobstore API has no function to list all blobs. How can I get this list and then delete all blobs?

The blobstore API on appengine for go has no way to do this. Instead, use the datastore to fetch __BlobInfo__ entities as appengine.BlobInfo. Although the API claims to have a BlobKey field, it is not populated. Instead, use the string ID of the returned key and cast it to an appengine.BlobKey, which you can then pass to blobstore.Delete.

Here's a handler at "/tasks/delete-blobs" to delete 20k blobs at a time in a loop until they are all deleted. Also note that cursors are not used here. I suspect that __BlobInfo__ is special and doesn't support cursors. (When I attempted to use them, they did nothing.)

func DeleteBlobs(w http.ResponseWriter, r *http.Request) {
    c := appengine.NewContext(r)
	c = appengine.Timeout(c, time.Minute)
	q := datastore.NewQuery("__BlobInfo__").KeysOnly()
	it := q.Run(ctx)
	wg := sync.WaitGroup{}
	something := false
	for _i := 0; _i < 20; _i++ {
		var bk []appengine.BlobKey
		for i := 0; i < 1000; i++ {
			k, err := it.Next(nil)
			if err == datastore.Done {
				break
			} else if err != nil {
				c.Errorf("err: %v", err)
				continue
			}
			bk = append(bk, appengine.BlobKey(k.StringID()))
		}
		if len(bk) == 0 {
			break
		}
		go func(bk []appengine.BlobKey) {
			something = true
			c.Errorf("deleteing %v blobs", len(bk))
			err := blobstore.DeleteMulti(ctx, bk)
			if err != nil {
				c.Errorf("blobstore delete err: %v", err)
			}
			wg.Done()
		}(bk)
		wg.Add(1)
	}
	wg.Wait()
	if something {
		taskqueue.Add(c, taskqueue.NewPOSTTask("/tasks/delete-blobs", nil), "")
	}
}