Split and then combine byte[]

Question

So what I'm trying to do is to save a byte[] into my database. If the byte is to long to be send to the database I whould like to split it into two bytes of half the size. However I'm doing something wrong, because when I check that the splittet bytes combined is equal to the original byte is ain't.

My code looks like this:

    public File Add(File item)
    {
        try
        {
            if (item == null)
            {
                throw new ArgumentNullException("item");
            }

            db.Entry(item).State = EntityState.Added;
            db.SaveChanges();
        }
        catch
        {
            File firstHalf = item;
            File lastHalf = item;
            firstHalf.@byte = item.@byte.Take(item.@byte.Length / 2).ToArray();
            lastHalf.@byte = item.@byte.Skip(item.@byte.Length / 2).ToArray();

            byte[] rv = new byte[firstHalf.@byte.Length + firstHalf.@byte.Length];
            System.Buffer.BlockCopy(firstHalf.@byte, 0, rv, 0, firstHalf.@byte.Length);
            System.Buffer.BlockCopy(lastHalf.@byte, 0, rv, firstHalf.@byte.Length, lastHalf.@byte.Length);

            if(rv == item.@byte)
            {
                Add(firstHalf);
                Add(lastHalf);
            }
        }

        return item;
    }

Edit

public partial class File
{
    public int C_id { get; set; }
    public string name { get; set; }
    public byte[] @byte { get; set; }
    public int file_id { get; set; }
    public int fk_folder { get; set; }
    public int fk_profile { get; set; }
}

What is it with those `@byte` members? Is that really correct syntax? — Thorsten Dittmar, Jan 13 '15 at 15:15
@AndyKorneyev: `File` is a class. I will update the question to include a diffinition of that ^^ — Michael Tot Korsgaard, Jan 13 '15 at 15:15
@ThorstenDittmar: Using the `@` prefix before a variable in C# lets you name a variable with a reserved word. ([see this](http://stackoverflow.com/questions/429529/what-does-the-symbol-before-a-variable-name-mean-in-c)) — abelenky, Jan 13 '15 at 15:17
@AlexK. Thanks. You learn something new every day. Though I'd presume it's easier to come up with a different name. It should be capitalized anyway. — Thorsten Dittmar, Jan 13 '15 at 15:17

score 3 · Answer 1 · answered Jan 13 '15 at 15:16

3

To compare use rv.SequenceEqual(item.@byte) (or a loop) as currently you look to see if they are equal references (which they are not).

Also don't use an Exception for control-of-flow!

answered Jan 13 '15 at 15:16

Alex K.

171,639
30
264
288

How would you set up a way to control it? – Michael Tot Korsgaard Jan 13 '15 at 15:22
1

Just an `else` for the `if (item == null)` ? – Alex K. Jan 13 '15 at 15:28
Ah I see. The try-catch was for the `SaveChange` the `if(item == null)` should be before the try-catch ^^ my bad – Michael Tot Korsgaard Jan 13 '15 at 15:31

Andrey Korneyev · Accepted Answer · 2015-01-13T15:26:47.907

2

Problem starts here:

File firstHalf = item;
File lastHalf = item;
firstHalf.@byte = item.@byte.Take(item.@byte.Length / 2).ToArray();

You just creating new reference to item in first line, so then in third line you're corrupting original @byte.

You need to use deep copy of item instead.

One of possible approaches - create Clone method in File class which will be return new instance of File with copied fiedls, and instead of File firstHalf = item; it will be File firstHalf = item.Clone();

It is first approach came into my mind, probably not the best one. In fact, I can't estimate right now - do you really need two exact copies of your item - probably this logic should be refactored.

edited Jan 13 '15 at 15:26

answered Jan 13 '15 at 15:17

Andrey Korneyev

26,353
15
70
71

1

This is just the first of a dozen mistakes :( – Ben Voigt Jan 13 '15 at 15:18
1

@BenVoigt, yes and most obvious one. In fact only this is enough to corrupt source data. – Andrey Korneyev Jan 13 '15 at 15:20
@BenVoigt: I would love if you could elaborate ;-) I know I'm not the best and would like to learn – Michael Tot Korsgaard Jan 13 '15 at 15:21
2

@MichaelTotKorsgaard: Well, the line immediately following does not skip the same number of items taken in the first set. And then it throws away half the remaining items. Size of `rv` is not computed correctly. Comparison is done incorrectly as Alex mentioned. – Ben Voigt Jan 13 '15 at 15:24

Split and then combine byte[]

2 Answers2