How to open a export database file?

I exported the database from memory and save it on server.The next time,when i re-open the exported file via XMLHttpRequest,it said the file is not a database file.How can I re-use the saved data?
The code to export and post to server:

        var data = db.export();
 	
 	db.close();
 	$.post("saveDb.php",{
 		data:data
 	},function(result){
	    console.log(result);
	});

On the server,I used the http_put_contents() to save the data to file "sqlite.db".
The code to load the saved db file is as below:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'sqlite.db', true);
xhr.responseType = 'arraybuffer';
xhr.onload = function(e) {
	var uInt8Array = new Uint8Array(this.response);
	db = new SQL.Database(uInt8Array);
	//......
};
xhr.send();

Then it raise an error:Uncaught Error: file is not a database

Thank you.

Start with the JavaScript export and XMLHttpRequest loading snippets, then inspect how saveDb.php writes the posted data to sqlite.db. Verify that the fetched file contains the exported database bytes and that it can be passed to SQL.Database without the file error.