Bug 27086 - Writing in asynchronous FileStream adds 0 bytes at the beginning of the file
Summary: Writing in asynchronous FileStream adds 0 bytes at the beginning of the file
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: master
Hardware: PC Linux
: --- normal
Target Milestone: Untriaged
Assignee: Marek Safar
Depends on:
Reported: 2015-02-16 03:35 UTC by guillaume.turri
Modified: 2015-02-18 07:34 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

Test case (1.05 KB, text/x-csharp)
2015-02-16 03:35 UTC, guillaume.turri

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Description guillaume.turri 2015-02-16 03:35:31 UTC
Created attachment 9843 [details]
Test case


I just tested this on a version of Mono build from source, from the current HEAD (bc57fda921d7c35dd7f52f71bdbdff9e831f328e) on Ubuntu.

* How to reproduce: Run the code attached with this bug report (and copy/pasted below)
* Expected behavior: We can read the DateTime we just wrote (ie: 03/04/1985)
* Behavior with .Net: same as the expected one
* Actual behavior: The DateTime read is "01/01/0001 12:00 AM"

Some more details:
* When we remove the FileOptions.Asynchronous flag, it works fine
* If we don't write the Guid (ie: if we only write the TimeStamp), it works fine
* When we open the file with an hexadecimal editor, it seems the file starts with several 0 bytes, and then we have the expected content (and "01/01/0001 12:00 AM" is the result of DateTime.FromBinary(0), so the issue if likely when we write, not when we read).



    using System;
    using System.IO;
    using System.Linq;
    public class Program
    	public static void Main(String[] args)
    		string filename = "myfilename";
    		File.Delete (filename);
    		using (var file = new FileStream (filename, FileMode.Append, FileAccess.Write, FileShare.Read, 4096, FileOptions.Asynchronous))
    		using (var writer = new BinaryWriter (file)){
    			WriteTimeStamp (writer);
    			WriteGuid (writer);
    			writer.Flush ();
    			file.Close ();
    			writer.Close ();
    		ReadFile (filename);
    	private static void WriteTimeStamp(BinaryWriter writer){
    		var timeStamp = new DateTime (1985, 04, 03);
    		writer.Write (timeStamp.ToBinary ());
    	private static void WriteGuid(BinaryWriter writer){
    		var id = new Guid (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
    		writer.Write (id.ToByteArray ());
    	private static void ReadFile(string filename){
    		using (var inputStream = new FileStream (filename, FileMode.Open))
    		using (var reader = new BinaryReader (inputStream)) {
    			var timeStamp = DateTime.FromBinary (reader.ReadInt64 ());
    			Console.WriteLine (timeStamp);
Comment 1 Marek Safar 2015-02-18 06:57:02 UTC
Fixed in master
Comment 2 guillaume.turri 2015-02-18 07:34:56 UTC