Visual Basic

27-Feb-06 4:07

I'm attempting to convert a .zip file to a string in order to pass as a parameter to a network service (see below code). The streamreader works except that it seems to ignore "non-text" characters and therefore the .zip file is then corrupt/invalid once received by the service.

Dim outstring As String = ""
Try
Dim sr As StreamReader = New StreamReader(INPATH, True)
outstring = sr.ReadToEnd()
sr.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Application.Exit()
End Try
return outstring

Should I be using a different method to convert the source to a string?

Guffa27-Feb-06 4:17

27-Feb-06 4:17

You are instructing the stream reader to detect the encoding of the file, but as the file is not a text file, there is no encoding. It will probably revert to ASCII encoding, resulting in ignoring all non-ASCII values, e.g. every byte with a value higher than 127.

Read the file as a binary file, returning the result as an array of bytes.

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pbaggett27-Feb-06 4:34

27-Feb-06 4:34

Thanks - I can't see a way to read the file into an array using the binary reader though (see below snippet). Any assistance you could provide (code snippets) would be greatly appreciated.

thanks again.

fs = New FileStream(inputfilename, _
FileMode.Open, FileAccess.Read)

Dim r As New BinaryReader(fs)
For i = 0 To r.BaseStream.Length
'outstring = outstring + r.ReadString()
Next i

-- modified at 12:03 Monday 27th February, 2006

Guffa27-Feb-06 6:27

27-Feb-06 6:27

Just read the bytes from the BinaryReader:

byte[] byffer = r.ReadBytes(int.MaxValue);

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pbaggett27-Feb-06 7:59

27-Feb-06 7:59

again , thanks for the assistance. Please excuse my lack of understanding here, but I am a novice with vb.net. I still don't know how to convert this array into a data string (to send as a parameter). I would need to send the string as it appears when you open it with notepad.exe.

Thanks again.

Guffa27-Feb-06 9:29

27-Feb-06 9:29

That depends on how you are sending the data.

If you want to convert the data into a string, you will have to know how the string is converted when it's sent. You will have to use the same encoding to convert the data into a string, as the encoding that is used when the string is converted to bytes when sending it.

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pbaggett27-Feb-06 10:30

27-Feb-06 10:30

Thanks a million! FYI, the encoding of a PKZIP file is apparently UTF8

Here's my code:

Dim ra As Array
fs = New FileStream(inputfilename, FileMode.Open, FileAccess.Read)
Dim r As New System.IO.BinaryReader(fs, Encoding.ASCII)
ra = r.ReadBytes(r.BaseStream.Length)
Dim [ASCII] As Encoding = Encoding.ASCII
Dim [UTF8] As Encoding = Encoding.UTF8
Dim asciiBytes As Byte() = Encoding.Convert([ASCII], [UTF8], ra)
Dim asciiChars(ascii.GetCharCount(asciiBytes, 0, asciiBytes.Length)) As Char
ascii.GetChars(asciiBytes, 0, asciiBytes.Length, asciiChars, 0)
Dim asciiString As New String(asciiChars)

Return asciistring

Guffa27-Feb-06 13:00

27-Feb-06 13:00

pbaggett wrote:
FYI, the encoding of a PKZIP file is apparently UTF8

No, it's definitely not. The PKZIP format is a binary format, not a text format, so it doesn't have any encoding. Also, the PKZIP format (1989) predates the Uncode standard (1991).

What you have done is to interpret the binary data as ASCII (which it isn't) and converted it to Unicode. The ASCII encoding only support character codes 0-127, so if you successfully decoded the file, you were just lucky to have a file where all the bytes happened to be in that range. You must have used a very small file, for this is not normal for compressed files.

The bytes that you handled as ASCII and converted to Unicode is in the asciiBytes array (so it's not at all ASCII bytes, but Unicode bytes). Then you decode the Uncode data as if it was ASCII and place it in the asciiChars array. The only reason this doesn't turn the data into total garbage, is that you were lucky again, and none of the "characters" did become a multi-byte code in Unicode.

Sorry to say it, but your code does at best virtually nothing at all. When used with most compressed files it will totally mangle the data, though.

Back to the drawing board. You still have to find out how the string that you send will be decoded.

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pbaggett28-Feb-06 3:14

28-Feb-06 3:14

I have now tested this code with 30 different zip files ranging in size from 1kb to 1gb and containing 1 to 100 compressed files. Each test run produced successful results for what I am attempting to accomplish - which is to convert the zip file contents into a single text string to be passed as a parameter to another process. I don't think this can be attributed to "luck".

That being said, this process is only designed to handle zip files with simple compressed ascii text files. Perhaps this is why the code does not produce total garbage.

Again, I appreciate your assistance.

Guffa28-Feb-06 8:52

28-Feb-06 8:52

I tested your method with one zip file, and it fails.

I examined the data in asciiBytes, and all character values above 127 turns into question marks.

Are you sure that you really use the code that you showed? Have you verified that the zip files are intact after you sent them?

I reduced the code substantially by skipping the BinaryReader and the double conversion. Closing the file might be a good idea, also. It's in C#, but I think you can see the changes:

FileStream fs = File.OpenRead(filename);<br />
byte[] ra = new byte[fs.Length];<br />
fs.Read(ra, 0, ra.Length);<br />
fs.Close();<br />
string asciiString = new string(Encoding.ASCII.GetChars(ra, 0, ra.Length));

Still doesn't work, though.

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pbaggett1-Mar-06 4:39