Re: "memory stream is not expandable" - C# Discussion Boards

29-Aug-03 7:32

I've trouble getting this work, not sure why. Trying to write encrypted to a memory stream. Exception was thrown with everycall to MemoryStream.Close(): "System.NotSupportedException. Memory Stream is not expandable"

code looks like this:

ASCIIEncoding AE = new ASCIIEncoding ();
byte[] buffer = new byte [10];

buffer = ASCIIEncoding.GetBytes("ABCDE");

byte[] Key = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16};
byte[] IV = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16};

TcpClient TCP = new TcpClient("localhost",11000);
NetworkStream NetStream = TCP.GetStream();
RijndaelManaged RMCrypto = new RijndaelManaged();

MemoryStream mstream2 = new MemoryStream(buffer, 5, 5, true, true);
CryptoStream cstream2 = new CryptoStream(
mstream2,
RMCrypto.CreateEncryptor(Key, IV),
CryptoStreamMode.Write);

StreamWriter cswriter = new StreamWriter(cstream2);
cswriter.Write(AE.GetBytes("AA"));
cswriter.Flush();
cswriter.Close(); <---- EXCEPTION HERE! "memory stream is not expandable"???

Help! What happenned here?

norm

Daniel Turini29-Aug-03 7:52

29-Aug-03 7:52

Your code is a bit confuse:

norm wrote:
byte[] buffer = new byte [10];
buffer = ASCIIEncoding.GetBytes("ABCDE");

Why are you initializing if you are going to set it on the next line?

norm wrote:
MemoryStream mstream2 = new MemoryStream(buffer, 5, 5, true, true);
CryptoStream cstream2 = new CryptoStream(
mstream2,
RMCrypto.CreateEncryptor(Key, IV),
CryptoStreamMode.Write);

Doing this will write on the MemoryStream. This would be ok, but why don't you use the default constructor (which creates an expandable memorystream)? See what's on MSDN about the constructor you used:

Initializes a new non-resizable instance of the MemoryStream class based on the specified region of a byte array, with the CanWrite property set as specified.

This means you'll never be able to write more than the size of "ABCDE" in ASCII encoding, i.e., 5 bytes. This is very low, and some compression schemes add salt. If you eliminate the "buffer" variable, you probably will get the code working right.

You can do it on anything you choose - from .bat to .net - A customer

devvvy29-Aug-03 8:19

29-Aug-03 8:19

Thanks, first of all.

Quote: "byte[] buffer = new byte [10];
buffer = ASCIIEncoding.GetBytes("ABCDE");"
>> This is merely cut-&-paste mistakes. Forget it.

The following constructors allows me to specify that the stream is expandable.
MemoryStream mstream2 = new MemoryStream(buffer, 5, 5, true, true);

Using another overload, "Capacity" is NOT expandable and is set to length of input/specified "buffer".
MemoryStream mstream2 = new MemoryStream(buffer);

QUESTION: I tried both ways. Now, how do I work with default constructor that takes no argument? How can I associate a buffer to the stream after construction?

memoryStream.GetBuffer() retrives buffer. But there's no SetBuffer member for me to associate MemoryStream with a buffer.

Thanks.

norm

Daniel Turini29-Aug-03 8:26

29-Aug-03 8:26

norm wrote:
memoryStream.GetBuffer() retrives buffer. But there's no SetBuffer member for me to associate MemoryStream with a buffer.
Byte[]'s are not expandable, so any MemoryStream you create with them will make your stream fixed-size. Either pass a buffer bigger or use a memorystream-managed buffer.
This is what I don't get. Why do you need to set the memorystream buffer? After all, if I understood you correctly, what you need is a byte[] with the encrypted data, right?
Why can't you simply call memoryStream.GetBuffer() and create it with new MemoryStream() ?

You can do it on anything you choose - from .bat to .net - A customer

MeisterBiber29-Aug-03 8:02

MeisterBiber

29-Aug-03 8:02

hi !

maybe:
you defined your buffer with size 10.
your memorystream size is set to 5.

andi

devvvy29-Aug-03 8:23

29-Aug-03 8:23

Thanks, tried that. But the problem is that memorystream is not resizable - but even that shouldn't be the problem since Close() throw an exception complaining that memory stream is not resizable even if I'm just writing ONE character to it!? I didn't Seek() on the memory stream - so, should be writing from beginning - if so, i'd just be overwriting ONE character/byte. The buffer has 10 bytes in it. I don't see how why we need to 'expand' the memorystream in the first place.

norm

MeisterBiber29-Aug-03 8:32

MeisterBiber

29-Aug-03 8:32

>I didn't Seek() on the memory stream - so, should be writing from beginning

i thought you set the position to the end! (buffer, 5, 5!!!!!!!, true, true)

andi

devvvy29-Aug-03 14:22

29-Aug-03 14:22

I use:
MemoryStream(buffer);

when I Seeked(). By the way, not sure if the following overload make the stream expandable or not:

public MemoryStream(byte[], int, int, bool, bool);

MSDN didn't state explicitly that the memory stream is expandable or not as in other versions/overloads. But IF it is, it's the only overload that takes a byte array as argument AND expandable.

Anyway, how can you use default constructor:

MemoryStream mem = new MemoryStream();

and associate a buffer with it later on?

norm

Daniel Turini29-Aug-03 8:33

29-Aug-03 8:33

norm wrote:
The buffer has 10 bytes in it. I don't see how why we need to 'expand' the memorystream in the first place.
Because it seems that the stupid memorystream will try to trim the buffer for you (instead of leaving the rest of unneeded data untouched). And it can't, as byte[]'s are fixed size.
And yes, the error message is very misleading.

You can do it on anything you choose - from .bat to .net - A customer

devvvy29-Aug-03 14:16

29-Aug-03 14:16

Daniel Turini wrote:
You can do it on anything you choose - from .bat to .net - A customer

>> it's a lot more painful doing .bat

Daniel Turini wrote:
Because it seems that the stupid memorystream will try to trim the buffer for you (instead of leaving the rest of unneeded data untouched). And it can't, as byte[]'s are fixed size.

>> don't get it, can you elaborate a little more?

norm

David Stone29-Aug-03 10:19

David Stone

29-Aug-03 10:19

Jeez norm, what kind of application are you writing? First the crypto stuff, now this... Wink | ;)

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Bulldozer Rental - £100
Destroying the MS campus single handedly for not doing an Academic upgrade, PRICELESS!
-Jonny Newman

devvvy29-Aug-03 14:02

29-Aug-03 14:02

i'm workinng for dexter in his secret laboratory

norm

David Stone29-Aug-03 17:20

David Stone

29-Aug-03 17:20

Shweet. Now, does DeeDee bug you too? Roll eyes | :rolleyes:

Hawaian shirts and shorts work too in Summer.
People assume you're either a complete nut (in which case not a worthy target) or so damn good you don't need to worry about camouflage...
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devvvy29-Aug-03 17:55

How do I Prevent addition to collections returned by properties

29-Aug-03 17:55

don't have a sister. But my brother boo has gone back to Penn States, which makes it kind of nice if someone can bug me from time to time.

norm

C# and Outlook...

theJazzyBrain29-Aug-03 6:24

theJazzyBrain

29-Aug-03 6:24

Hello all,

Has anyone got any idea on how to use the Outlook database through my C# application?

I want to retrieve the Task entries from Outlook XP to my Access database and then use them on an ASP.NET application using C#.

Is there an API that MS provides?

Thank you.

theJazzyBrain
Wise is he who asks good questions, not he who gives good answers

Re: C# and Outlook...

apferreira29-Aug-03 6:52

apferreira

29-Aug-03 6:52

If you are using Outlook 2002 Why not use the Office 10 Primary Interop Assemblies provided by Microsoft.

You can download them here[^]

A good starting point for installing them and using them can be found here[^]

Rahul Singh29-Aug-03 6:21

Rahul Singh

29-Aug-03 6:21

Hi,

I have a class that has a get property, Edges that returns an ArrayList. Due to the internal organization of what the class does I want to disallow people getting the property and then adding stuff to it. I want them to use the Add method of the class instead. I could document it and say "dont do that" but I was wondering if there is a way to do it in C#. I can't think of one. Here is some code

public class foo
{
private ArrayList _edges;
public ArrayList Edges
{
get { return _edges; }
}
public void Add(string myString)
{
_edges.Add(myString);
}

}

//I want to prevent the following
foo myFoo = new foo();
//The next statement should throw an exception or something
myFoo.Edges.Add("Hello");
//the following instead should be used.

myFoo.Add("Hello2");

Thanks,

Rahul

Re: How do I Prevent addition to collections returned by properties

Frank Olorin Rizzi29-Aug-03 7:34

Frank Olorin Rizzi

29-Aug-03 7:34

..ehr... pass them deep copies in the returned ArrayList ?

<br />
//...<br />
public ArrayList Edges<br />
{<br />
  get<br />
  {<br />
    ArrayList r = new ArrayList();<br />
    foreach(Edge e in this._edges)<br />
      r.Add(e.DeepCopy());<br />
    return r;<br />
  }<br />
}<br />
//...<br />
<br />

Granted, your Edge class has to have a public method to provide a DeepCopy.
I usually use the Clone() method for that.

<br />
public Edge Clone()<br />
{ return new Edge(this); }<br />
<br />
public Edge(Edge rhs)<br />
{<br />
  //Set all of the interanls of the new Edge to be equal<br />
  //to the internals of rhs...<br />
}<br />

[shameless self plug]

I actually use this kind of thing in CFGLite:
http://www.codeproject.com/csharp/CFGLitepack.asp

[/shameless self plug]

HTH,
F.O.R.

Re: How do I Prevent addition to collections returned by properties

leppie29-Aug-03 7:43

leppie

29-Aug-03 7:43

Hmm didnt we cover this just a few days ago..... Sigh | :sigh:

leppie ::AllocCPArticle("Zee blog");

Re: How do I Prevent addition to collections returned by properties

Daniel Turini29-Aug-03 8:38