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C# flushing StreamWriter and a MemoryStream

I use the following snippet of code, and I'm unsure whether I need to call the Flush methods (once on StreamWriter, once on MemoryStream):
//converts an xsd object to the corresponding xml string, using the UTF8 encoding
public string Serialize(T t)
{
using (var memoryStream = new MemoryStream())
{
var encoding = new UTF8Encoding(false);
using (var writer = new StreamWriter(memoryStream, encoding))
{
var serializer = new XmlSerializer(typeof (T));
serializer.Serialize(writer, t);
writer.Flush();
}
memoryStream.Flush();
return encoding.GetString(memoryStream.ToArray());
}
}
First of all, because the code is inside the using block, I think the automatically called dispose method might do this for me. Is this true, or is flushing an entirely different concept?
According to stackoverflow itself:
Flush meaning clears all buffers for a stream and causes any buffered data to be written to the underlying device.
What does that mean in the context of the code above?
Secondly, the flush method of the MemoryStream does nothing according to the api, so what's up with that? why do we call a method that does nothing?

You don't need to use Flush on the StreamWriter, as you are disposing it (by having it in a using block). When it's disposed, it's automatically flushed and closed.
You don't need to use Flush on the MemoryStream, as it's not buffering anything that is written to any other source. There is simply nothing to flush anywhere.
The Flush method is only present in the MemoryStream object because it inherits from the Stream class. You can see in the source code for the MemoryStream class that the flush method actually does nothing.

In general Streams will buffer data as it's written (periodically flushing the buffer to the associated device if there is one) because writing to a device, usually a file, is expensive. A MemoryStream writes to RAM so the whole concept of buffering and flushing is redundant. The data is always in RAM already.
And yes, disposing the stream will cause it to be flushed.

Commenting flush method returning empty byte[], Though I am Using Using block
byte[] filecontent = null;
using var ms = new MemoryStream();
using var sw = new StreamWriter(fs);
sw.WriteCSVLine(new[] { "A", "B" });//This is extension to write as CSV
//tx.Flush();
//fs.Flush();
fs.Position = 0;
filecontent = fs.ToArray();

Copy data from MemoryStream directly to BinaryWriter.BaseStream?

I have a bunch of data in a MemoryStream and I want to write all of it to a BinaryWriter.
Lucky for me all streams now have a Stream.CopyTo(Stream) method, and I can get the target stream from the BinaryWriter.BaseStream property.
public void WriteTo(BinaryWriter writer)
{
this.memoryStream.CopyTo(writer.BaseStream);
}
Can I safely bypass the writer like this and copy it directly to the base stream, or will this mess up the writer's buffer, position, or something else? Or, how would you propose copying a Stream to a BinaryWriter?

If you don't want to mess with the data you have in the initial stream would not something like this work:
var myStreamInitially = new MemoryStream();
var myStreamClone = new MemoryStream();
myStreamInitially.CopyTo(myStreamClone);
var binaryWriteb = new BinaryWriter(myStreamClone);
If you're using .NET 4+ the CopyTo method is very handy.
UPDATE
Isn't this then safer than changing the binaryStream underlying baseStream:
void WriteToStreamInUnknownStatus(BinaryWriter binaryWriter)
{
var myStream = new MemoryStream();
try
{
binaryWriter.Write(myStream.ToArray());
}
catch
{ }
}
UPDATE 2
If you try this you get an exception: "memory stream is not explandable"
static void Main(string[] args)
{
var binaryWrite = new BinaryWriter(new MemoryStream(new byte[] {1, 2, 3, 4}));
binaryWrite.Seek(3, SeekOrigin.Begin);
var position = binaryWrite.BaseStream.Position;
new MemoryStream(new byte[] {1, 2, 3, 4}).CopyTo(binaryWrite.BaseStream);
position = binaryWrite.BaseStream.Position;
}
So in top of having to be sure that the property is thread safe you also need to know the type of the inner stream. To risk IMO.

What you propose is safe, provided:
That you're using this in a single-threaded context. Either there are no other threads, or you have an exclusive lock on the writer at the time you call this. ... AND
You call Flush on the writer before writing directly to the BaseStream. The writer could have some data buffered that it hasn't yet written to the stream.
So your modified code is:
public void WriteTo(BinaryWriter writer)
{
writer.Flush();
this.memoryStream.CopyTo(writer.BaseStream);
}

Can't create MemoryStream

Is there any reason why this code shouldn't produce a memory stream with the word Slappy in it?
private MemoryStream StringBuilderToMemoryStream(StringBuilder source)
{
MemoryStream memoryStream = new MemoryStream();
StreamWriter streamWriter = new StreamWriter(memoryStream);
streamWriter.Write("slappy");
return memoryStream;
}
Even if I say streamWriter.Write(source.toString()); it fails.
Funny thing is, that it works on one of the methods that calls this routine but not on any of the others.
And the order I call them in makes no difference either.
But regardless, even when I call the above, from the method that works, the output is still an empty MemoryStream.
Any thoughts?

You don't flush the stream writer so the word never gets written to the memory stream.
Add the following after the call to streamWriter.Write:
streamWriter.Flush();
Furthermore, if you want to read that word later from the memory stream, make sure to reset its position, because after the Write it is located after the word slappy:
memoryStream.Position = 0;

If you don't want to call streamWriter.Flush(); you can set the AutoFlush-Property of the StreamWriter, at the moment you create it.
MemoryStream memoryStream = new MemoryStream();
StreamWriter streamWriter = new StreamWriter(memoryStream)
{
AutoFlush = true
}

Cannot access a closed Stream while creating a downloadable text file in ASP MVC 3

Im trying to prompt a downloadable text file (.txt), but I get this error:
Cannot access a closed Stream.
I have looked at simular questions in here:
Cannot Access Closed Stream
But it was not very useful.
Here is my code:
private FileStreamResult Export()
{
string name = "filename.txt";
MemoryStream stream = new MemoryStream();
using (StreamWriter writer = new StreamWriter(stream))
{
StringBuilder sb = new StringBuilder();
sb.Append("A text...");
writer.WriteLine(sb.ToString());
}
return File(stream, "text/plain", name);
}
UPDATE (working copy):
This gives me an blank text file.
private FileResult Export()
{
string name = "filename.txt";
MemoryStream stream = new MemoryStream();
StreamWriter writer = new StreamWriter(stream);
StringBuilder sb = new StringBuilder();
sb.Append("A text...");
writer.WriteLine(sb.ToString());
writer.Flush();
stream.Seek(0, SeekOrigin.Begin);
return File(stream, "text/plain", name);
}

That is correct, when you wrap a stream in another stream, calling .Close() or .Dispose() on any of them will dispose the whole stream. In this case, wrapping the MemoryStream in a StreamWriter means that when the using statement completes the StreamWriter and MemoryStream are both disposed.
My guess is since you are returning a FileStreamResult the encapsulating File will close the stream for you after the stream is no longer used. In this case, you do not want to use the using statement and will want to leave the stream open when returning it.
UPDATE
Since a stream is forward access you'll need to see the stream back to the beginning to allow the data to be read back out.
stream.Seek(0, SeekOrigin.Begin);

Just remove that using statement - you are passing disposed object reference to File method and you that's the reason why you get exception. From MSDN,
The StreamWriter object calls Dispose on the provided Stream object
when StreamWriter.Dispose is called.
I believe File will dispose stream by itself after usage (not verified by looking at source code).
UPDATE:
writer.Flush(); before return statement should help you

You have to set the position of the memorystream to 0 before using it in your FileStreamResult, otherwise it will be read from current position (IE the end of the stream).
stream.Position = 0;
return File(stream, "text/plain", name);
Just had the same thing.
I know this thread is ancient, just hoping to aid others having the same issue.

Replace the FileStreamResult type on your action with FileResult.

Writing to then reading from a MemoryStream

I'm using DataContractJsonSerializer, which likes to output to a Stream. I want to top-and-tail the outputs of the serializer so I was using a StreamWriter to alternately write in the extra bits I needed.
var ser = new DataContractJsonSerializer(typeof (TValue));
using (var stream = new MemoryStream())
{
using (var sw = new StreamWriter(stream))
{
sw.Write("{");
foreach (var kvp in keysAndValues)
{
sw.Write("'{0}':", kvp.Key);
ser.WriteObject(stream, kvp.Value);
}
sw.Write("}");
}
using (var streamReader = new StreamReader(stream))
{
return streamReader.ReadToEnd();
}
}
When I do this I get an ArgumentException "Stream was not readable".
I'm probably doing all sorts wrong here so all answers welcome. Thanks.

Three things:
Don't close the StreamWriter. That will close the MemoryStream. You do need to flush the writer though.
Reset the position of the stream before reading.
If you're going to write directly to the stream, you need to flush the writer first.
So:
using (var stream = new MemoryStream())
{
var sw = new StreamWriter(stream);
sw.Write("{");
foreach (var kvp in keysAndValues)
{
sw.Write("'{0}':", kvp.Key);
sw.Flush();
ser.WriteObject(stream, kvp.Value);
}
sw.Write("}");
sw.Flush();
stream.Position = 0;
using (var streamReader = new StreamReader(stream))
{
return streamReader.ReadToEnd();
}
}
There's another simpler alternative though. All you're doing with the stream when reading is converting it into a string. You can do that more simply:
return Encoding.UTF8.GetString(stream.GetBuffer(), 0, (int) stream.Length);
Unfortunately MemoryStream.Length will throw if the stream has been closed, so you'd probably want to call the StreamWriter constructor that doesn't close the underlying stream, or just don't close the StreamWriter.
I'm concerned by you writing directly to the the stream - what is ser? Is it an XML serializer, or a binary one? If it's binary, your model is somewhat flawed - you shouldn't mix binary and text data without being very careful about it. If it's XML, you may find that you end up with byte-order marks in the middle of your string, which could be problematic.

setting the memory streams position to the beginning might help.
stream.Position = 0;
But the core problem is that the StreamWriter is closing your memory stream when it is closed.
Simply flushing that stream where you end the using block for it and only disposing of it fter you have read the data out of the memory stream will solve this for you.
You may also want to consider using a StringWriter instead...
using (var writer = new StringWriter())
{
using (var sw = new StreamWriter(stream))
{
sw.Write("{");
foreach (var kvp in keysAndValues)
{
sw.Write("'{0}':", kvp.Key);
ser.WriteObject(writer, kvp.Value);
}
sw.Write("}");
}
return writer.ToString();
}
This would require your serialization WriteObject call can accept a TextWriter instead of a Stream.

To access the content of a MemoryStream after it has been closed use the ToArray() or GetBuffer() methods. The following code demonstrates how to get the content of the memory buffer as a UTF8 encoded string.
byte[] buff = stream.ToArray();
return Encoding.UTF8.GetString(buff,0,buff.Length);
Note: ToArray() is simpler to use than GetBuffer() because ToArray() returns the exact length of the stream, rather than the buffer size (which might be larger than the stream content). ToArray() makes a copy of the bytes.
Note: GetBuffer() is more performant than ToArray(), as it doesn't make a copy of the bytes. You do need to take care about possible undefined trailing bytes at the end of the buffer by considering the stream length rather than the buffer size. Using GetBuffer() is strongly advised if stream size is larger than 80000 bytes because the ToArray copy would be allocated on the Large Object Heap where it's lifetime can become problematic.
It is also possible to clone the original MemoryStream as follows, to facilitate accessing it via a StreamReader e.g.
using (MemoryStream readStream = new MemoryStream(stream.ToArray()))
{
...
}
The ideal solution is to access the original MemoryStream before it has been closed, if possible.

Just a wild guess: maybe you need to flush the streamwriter? Possibly the system sees that there are writes "pending". By flushing you know for sure that the stream contains all written characters and is readable.