问题
I am new to System.IO.Compression
I am trying to compress and decompress some information.
For compression I used code project and it seems to work. I am compressing string at the moment.
For decompressing I would like to docompress a Stream
This is what I have at the moment
var zipString = _compressor.Compress(request);
using (var sw = new StreamWriter(req.GetRequestStream()))
{
sw.Write(zipString);
sw.Close();
}
WebResponse respStream = req.GetResponse();
Stream resp = respStream.GetResponseStream();
resp = _compressor.UnCompress(resp);
Here is the code for compressing
public string Compress(string s)
{
//Transforming string into byte
var byteArray = new byte[s.Length];
var indexBa = 0;
foreach (var item in s.ToCharArray())
{
byteArray[indexBa++] = (byte) item;
}
//prepare for compress
var ms = new MemoryStream();
var sw = new GZipStream(ms, CompressionMode.Compress);
//compress
sw.Write(byteArray,0,byteArray.Length);
//close sw, DO NOT FLUSH because byes will go missing...
sw.Close();
//transform byte[] zip data to string
byteArray = ms.ToArray();
var sb = new StringBuilder(byteArray.Length);
foreach (var item in byteArray)
{
sb.Append((char) item);
}
ms.Close();
sw.Dispose();
ms.Dispose();
return sb.ToString();
}
And here is the code for decompressing
public Stream UnCompress(Stream s)
{
int readCount;
MemoryStream mem = new MemoryStream();
byte[] tmp = new byte[128];
while ((readCount = s.Read(tmp, 0, 128)) != 0)
{
mem.Write(tmp, 0, readCount);
}
StreamReader reader = new StreamReader(mem);
char[] buffer = new char[mem.Length];
mem.Position = 0;
reader.ReadBlock(buffer, 0, (int)mem.Length);
byte[] zip = Encoding.UTF8.GetBytes(buffer, 0, (int)mem.Length);
Stream wr = new MemoryStream();
wr.Write(zip, 0, zip.Length);
wr.Position = 0;
using (var stream = new GZipStream(wr, CompressionMode.Decompress))
{
mem = new MemoryStream();
while ((readCount = stream.Read(tmp, 0, 128)) != 0)
{
mem.Write(tmp, 0, readCount);
}
mem.Position = 0;
return mem;
}
}
At this point I get error while decompressing in following line:
while ((readCount = stream.Read(tmp, 0, 128)) != 0)
{
mem.Write(tmp, 0, readCount);
}
It just does not enter while loop and says:
The magic number in GZip header is not correct. Make sure you are passing in a GZip stream
My decompress method is based on following stackoverflow post
Try 2:
public Stream UnCompress(Stream s)
{
byte[] byteArray = null;
using (var m = new MemoryStream())
{
int count;
do
{
byte[] buf = new byte[1024];
count = s.Read(buf, 0, 1024);
m.Write(buf, 0, count);
} while (s.CanRead && count > 0);
byteArray = m.ToArray();
}
var indexBa = 0;
foreach (var item in s.ToString().ToCharArray())
{
byteArray[indexBa++] = (byte) item;
}
//Prepare for decompress
var ms = new MemoryStream(byteArray);
var sr = new GZipStream(ms,
CompressionMode.Decompress);
//Reset variable to collect uncompressed result
byteArray = new byte[byteArray.Length];
//Decompress
var rByte = sr.Read(byteArray, 0, byteArray.Length);
//Transform byte[] unzip data to string
var sB = new MemoryStream(rByte);
for (var i = 0; i < rByte; i++)
{
sB.Write(byteArray,0,rByte);
}
sr.Close();
ms.Close();
sr.Dispose();
ms.Dispose();
return sB;
}
Result : same error in line var rByte = sr.Read(byteArray, 0, byteArray.Length);
Update 1:
As given in code project decompressing string perfectly works.
public static string UnZip(string value)
{
//Transform string into byte[]
byte[] byteArray = new byte[value.Length];
int indexBA = 0;
foreach (char item in value.ToCharArray())
{
byteArray[indexBA++] = (byte)item;
}
//Prepare for decompress
System.IO.MemoryStream ms = new System.IO.MemoryStream(byteArray);
System.IO.Compression.GZipStream sr = new System.IO.Compression.GZipStream(ms,
System.IO.Compression.CompressionMode.Decompress);
//Reset variable to collect uncompressed result
byteArray = new byte[byteArray.Length];
//Decompress
int rByte = sr.Read(byteArray, 0, byteArray.Length);
//Transform byte[] unzip data to string
System.Text.StringBuilder sB = new System.Text.StringBuilder(rByte);
//Read the number of bytes GZipStream red and do not a for each bytes in
//resultByteArray;
for (int i = 0; i < rByte; i++)
{
sB.Append((char)byteArray[i]);
}
sr.Close();
ms.Close();
sr.Dispose();
ms.Dispose();
return sB.ToString();
}
回答1:
Your code has many issues, so it's easier to just write another version from scratch. Note that doing this:
var byteArray = new byte[s.Length];
var indexBa = 0;
foreach (var item in s.ToCharArray())
{
byteArray[indexBa++] = (byte) item;
}
to convert string to byte array is not a good idea. Instead choose some encoding and convert with it. Also, returning result of compression as string is also not a good idea - return that a byte array instead, because that byte array does not really represent any string - it's just arbitrary binary data.
Sample code:
static byte[] Compress(byte[] data) {
// `compressed` will contain result of compression
using (var compressed = new MemoryStream()) {
// source is our original uncompressed data
using (var source = new MemoryStream(data)) {
using (var gzip = new GZipStream(compressed, CompressionMode.Compress)) {
// just write whole source into gzip stream with CopyTo
source.CopyTo(gzip);
}
}
return compressed.ToArray();
}
}
static byte[] CompressString(string s, Encoding encoding) {
return Compress(encoding.GetBytes(s));
}
static string CompressStringToBase64(string s, Encoding encoding) {
return Convert.ToBase64String(CompressString(s, encoding));
}
static byte[] Decompress(Stream source) {
using (var gzip = new GZipStream(source, CompressionMode.Decompress)) {
using (var decompressed = new MemoryStream()) {
gzip.CopyTo(decompressed);
return decompressed.ToArray();
}
}
}
static byte[] Decompress(byte[] data) {
using (var ms = new MemoryStream(data)) {
return Decompress(ms);
}
}
static string DecompressString(Stream source, Encoding encoding) {
return encoding.GetString(Decompress(source));
}
Test
var source = "Some string";
var compressed = CompressString(source, Encoding.UTF8);
var decompressed = DecompressString(new MemoryStream(compressed), Encoding.UTF8);
Debug.Assert(source == decompressed);
来源：https://stackoverflow.com/questions/47513219/decompression-error-the-magic-number-in-gzip-header-is-not-correct