Cannot append value to string C#

Question

I've got two methods in my Windows Forms application for parsing some gzip encoded strings.

Here are my two methods, which both return the same value.

public static async Task<string> DecodeGzipAsync(string str)
{
    var values = new Dictionary<string, string>
    {
        { "data", str }
    };

    var content = new FormUrlEncodedContent(values);

    var client = new HttpClient();

    var response = await client.PostAsync("http://www.txtwizard.net/compression/decompress/gz", content);

    var json = await response.Content.ReadAsStringAsync();

    var result = JsonConvert.DeserializeObject<GzipData>(json);

    return result.DecompressedData;
}

public static string DecodeGzip(string str)
{
    byte[] gzBuffer = Convert.FromBase64String(str);

    using (MemoryStream ms = new MemoryStream())
    {
        int msgLength = BitConverter.ToInt32(gzBuffer, 0);
        ms.Write(gzBuffer, 0, gzBuffer.Length);

        byte[] buffer = new byte[msgLength];

        ms.Position = 0;

        using (GZipStream zip = new GZipStream(ms, CompressionMode.Decompress))
        {
            zip.Read(buffer, 0, buffer.Length);
        }

        return Encoding.UTF8.GetString(buffer);

    }

And then I call these two methods from my main form.

var string1 = await Utilities.DecodeGzipAsync(xml.InnerText);
var string1Concat = string.Concat("<Connotes>", string1, "</Connotes>");

var string2 = Utilities.DecodeGzip(xml.InnerText);
var string2Concat = string.Concat("<Connotes>", string2, "</Connotes>");

Where xml.InnerText is

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

The results I get are really frustrating (and weird!)

string1 and string2 both return the same string, however string1Concat and string2Concat return different results.

string1Concat = "<Connotes>" + string1 + "</Connotes>"

string2Concat = "<Connotes>" + string2  // Notice how it is missing the concatenation on the end     

What might be causing this behaviour? I have tried changing the encoding to ASCII and UTF8 but both give the same results.

Any help is much appreciated!

Answer 1

This was a little tricky, but I found the problem/solution:
You convert the array of the size of the compressed data to a string at Encoding.UTF8.GetString(buffer) . This will create a string which a length of 559903 instead of the correct 9209. If you create a new byte-array with the actually read bytes it is working:

public static string DecodeGzip(string str)
{
    byte[] gzBuffer = Convert.FromBase64String(str);

    using (MemoryStream ms = new MemoryStream())
    {
        int msgLength = BitConverter.ToInt32(gzBuffer, 0);
        ms.Write(gzBuffer, 0, gzBuffer.Length);

        byte[] buffer = new byte[msgLength];

        ms.Position = 0;
        int length;
        using (GZipStream zip = new GZipStream(ms, CompressionMode.Decompress))
        {
            length = zip.Read(buffer, 0, buffer.Length);
        }

        var data = new byte[length];
        Array.Copy(buffer, data, length);
        return Encoding.UTF8.GetString(data);   
    }
}