Sevenzipsharp CompressStream throws Exception: Value cannot be null

Question

I am trying out following code in order to compress and save a bitmap of a screenshot but get this error. I haven't tried using CompressFiles as I have to do it using memory stream.

        public void CompressAndSaveBitmap(Bitmap bitmap)
        {
            using (MemoryStream memStream = new MemoryStream())
            {
                using (FileStream file = new FileStream("XYZ", FileMode.Create, System.IO.FileAccess.Write))
                {
                    bitmap.Save(memStream, System.Drawing.Imaging.ImageFormat.Bmp);
                    // tried these but they don't work.
                    //memStream.Seek(0, 0);
                    //memStream.Position = 0; 
                    this.compressor.CompressStream(memStream, file); // throws error here

                // also tried the following to see if Bitmap contains the problem
                //UnicodeEncoding uniEncoding = new UnicodeEncoding();
                //byte[] firstString = uniEncoding.GetBytes("Invalid file path characters are: ");

                //int count = 0;
                //while (count < firstString.Length)

                //memStream.WriteByte(firstString[count++]);
                //memStream.Flush();
                ////memStream.Seek(0, 0);
                //memStream.Position = 0;
                //this.compressor.CompressStream(memStream, file);
                }
           }
        }

Compressor initialization code:

public Compressor()
{
    SevenZipCompressor.SetLibraryPath(@"D:\7z.dll");

    this.compressor = new SevenZip.SevenZipCompressor();
    compressor.CompressionLevel = CompressionLevel.Ultra;
    compressor.CompressionMethod = CompressionMethod.Ppmd;
}

It's crashes on this line in the library:

    var lockObject = (object) _files ?? _streams;
    lock (lockObject) // here in ArchiveUpdateCallback.cs

I see that the file is created but it's corrupt.

What line throws the error? We can't see your screen, remember. — , Feb 12 '18 at 16:43
@Amy Edited the code. Though it already says in the title CompressStream is throwing the error. — AbbasFaisal, Feb 12 '18 at 16:45
Try flushing the stream before seeking to the beginning of the stream. — , Feb 12 '18 at 16:47
@FaizanRabbani Yes, it's not. It shows memorystream.length is 16xxxxx something. — AbbasFaisal, Feb 12 '18 at 16:54
@AbbasFaisal see my answer below, additionally I think the only problem with your code is this.compressor is not initialized. — FaizanHussainRabbani, Feb 13 '18 at 08:34
@AbbasFaisal Why was library path set? SetLibraryPath(@"D:\7z.dll"); I didn't have to set path anywhere, just provided 7z.dll in the executable folder. — FaizanHussainRabbani, Feb 13 '18 at 09:43
@FaizanRabbani I tried without it. Doesn't make a difference. At the moment I can't get a handle of why this is happening so trying out random stuff. — AbbasFaisal, Feb 13 '18 at 09:46
I downloaded 7z.dll file from https://archive.codeplex.com/?p=sevenzipsharp — FaizanHussainRabbani, Feb 13 '18 at 09:47
I have the one from Github (https://github.com/tomap/SevenZipSharp/blob/master/SevenZip/7z.dll). It works for other things I tried out. Not just compressing the memory stream. So I don't thing the dll shouldn't be an issue. — AbbasFaisal, Feb 13 '18 at 09:50

FaizanHussainRabbani · Answer 1 · 2018-02-13T08:35:33.823

2

I was able to successfully compress file using following code:

public void CompressAndSaveBitmap(Bitmap bitmap)
        {
            using (MemoryStream memStream = new MemoryStream())
            {
                using (FileStream file = new FileStream("XYZ", FileMode.Create, System.IO.FileAccess.Write))
                {
                    bitmap.Save(memStream, System.Drawing.Imaging.ImageFormat.Bmp);
                    // tried these but they don't work.
                    //memStream.Seek(0, 0);
                    //memStream.Position = 0; 

                    SevenZipCompressor compressor =
                        new SevenZipCompressor
                        {
                            CompressionLevel = CompressionLevel.Ultra,
                            CompressionMethod = CompressionMethod.Lzma
                        };

                    compressor.CompressStream(memStream, file); // throws error here
                }
            }
        }

Following was the bitmap file:

Executed code:

            Bitmap bmp = new Bitmap("Test.bmp");
            res.CompressAndSaveBitmap(bmp);

After execution got following output:

Opened the file with WinRar and extracted file:

In folder found the extracted image:

UPDATE: I think the only problem with OP's code is this.compressor is not initialized.

edited Feb 13 '18 at 08:35

answered Feb 12 '18 at 18:43

FaizanHussainRabbani

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Excellent answer. +1 – Ignacio Soler Garcia Feb 13 '18 at 08:38
@FaizanRabbani Thanks for trying it out. I have tried your code but still the same results. I have updated the question to add more details. – AbbasFaisal Feb 13 '18 at 09:31
@AbbasFaisal will it possible to upload original bitmap file as well that you are trying to compress? – FaizanHussainRabbani Feb 13 '18 at 09:44
@FaizanRabbani Not sure if I can do that. Updated the question. – AbbasFaisal Feb 13 '18 at 10:00
@AbbasFaisal Can you share it's size? I should try compressing an image of same size. – FaizanHussainRabbani Feb 13 '18 at 10:01
@FaizanRabbani Checked. It's working fine with 7z application. Size is 106 KB. – AbbasFaisal Feb 13 '18 at 10:06
@AbbasFaisal I tried using an image of same size and CompressionMethod as Ppmd and works fine. – FaizanHussainRabbani Feb 13 '18 at 16:58
@FaizanRabbani I made it work. I deleted the sevenzipsharp.dll and 7z.dll that was downloaded from Github repo. Then used sevenzipsharp and SevenZipSharp.interop (for 7z dll) from Nuget and attempted again. It worked. Not sure if I should put this in an answer. Thank you so much for all your help. – AbbasFaisal Feb 14 '18 at 09:58
@AbbasFaisal glad to hear that, yes I also followed same steps initially and it worked. – FaizanHussainRabbani Feb 14 '18 at 10:33

Sevenzipsharp CompressStream throws Exception: Value cannot be null

1 Answers1