CODEWITHSUNDEEP
c#compressiongzipstream
duckus
duckus

Reputation: 213

GZipStream only decompresses first line

My GZipStream will only decompress the first line of the file. Extracting the contents via 7-zip works as expected and gives me the entire file contents. It also extracts as expected using gunzip on cygwin and linux, so I expect this is O/S specific (Windows 7).

I'm not certain how to go about troubleshooting this, so any tips on that would help me a great deal. It sounds very similar to this, but using SharpZLib results in the same thing.

Here's what I'm doing: 

var inputFile = String.Format(@"{0}\{1}", inputDir, fileName);
var outputFile = String.Format(@"{0}\{1}.gz", inputDir, fileName);
var dcmpFile = String.Format(@"{0}\{1}", outputDir, fileName);

    using (var input = File.OpenRead(inputFile)) 
    using (var fileOutput = File.Open(outputFile, FileMode.Append))
    using (GZipStream gzOutput = new GZipStream(fileOutput, CompressionMode.Compress, true))
    {
        input.CopyTo(gzOutput);
    }

// Now, decompress
using (FileStream of = new FileStream(outputFile, FileMode.Open, FileAccess.Read))
using (GZipStream ogz = new GZipStream(of, CompressionMode.Decompress, false))
using (FileStream wf = new FileStream(dcmpFile, FileMode.Append, FileAccess.Write))
{
    ogz.CopyTo(wf); 
}

Upvotes: 1

Views: 1186

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1500903

Your output file only contains a single line (gzipped) - but it contains all of the text data other than the line breaks.

You're repeatedly calling ReadLine() which returns a line of text without the line break and converting that text to bytes. So if you had an input file which had:

abc
def
ghi

You'd end up with an output file which was the compressed version of

abcdefghi

If you don't want that behaviour, why even go through a StreamReader in the first place? Just copy from the input FileStream straight to the GZipStream a block at a time, or use Stream.CopyTo if you're using .NET 4:

// Note how much simpler the code is using File.*
using (var input = File.OpenRead(inputFile))
using (var fileOutput = File.Open(outputFile, FileMode.Append))
using (GZipStream gzOutput = new GZipStream(os, CompressionMode.Compress, true)) 
{
    input.CopyTo(gzOutput);
}

Also note that appending to a compressed file is rarely a good idea, unless you've got some sort of special handling for multiple "chunks" within a single file.

Upvotes: 4

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