Getting data from host, convert to string and then to bytes

Maurizio

Hi.

I want to make a program to download files from a remote host.

So what i do is to send throw sockets all the binary information + a string used as end "mystyring".

To check if i have to continue writing the buffer to the file i first convert all to string, so if i find "mystring" it will finish, if not, i reconvert all to bytes and i copy data.

The problem im having is that, .txt files are writed well, but binaris not, it always show error at opening. I ve tried copying a pdf, and when i open it show all the pages, but in blank :S. Also if i check the size of the original file is always some bytes bigger than the copy.

[CODE]FileStream fs = new FileStream("C:\\Users\\Mauri\\Desktop\\" + item.Name, FileMode.Append, FileAccess.Write);

BinaryWriter writer = new BinaryWriter(fs);

bool continua = true;

while (continua)

{

recibido = getSocket(numsock).socketRecv(); // This return the data converted to string.

words = recibido.Split('|'); //We split "|mystring" to find the end of file.

foreach (string s in words)

{

if ((String.Compare(s, "mystring") != 0))

writer.Write(StringToBytes(s)); // Write converted data.

else

continua = false; // if we find "mystring", end the action.

}

writer.Close();

fs.Close();

// Convert string to bytes

public byte[] StringToBytes(String cadena)

{

System.Text.ASCIIEncoding codificador = new System.Text.ASCIIEncoding();

return codificador.GetBytes(cadena);

}

[/CODE]

The strange thing is that .txt files are writed correctly.

Thanks

10 Replies

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Maurizio15y ago
Yes, i think i would send first the length is the best solution.
Thanks
Sam Hobbs15y ago
You can use System.Text.Encoding.ASCII.GetBytes to convert a string to a byte array but I don't know an easy way to search a byte array.

So I suggest that you read the data as a byte array and then convert that to a string just for the purpose of searching for the string. Use the string only for searching for "|mystring". The string would be useless for use as binary data because about half the data (all bytes with a value in the range 128-255) will be incorrect due to the conversion from binary to string. You can use the offset of "|mystring" in the string to determine the location in the byte array.

A much better solution would be to send a count of the number of bytes (the size of the file) at the beginning of every file instead of putting "|mystring" at the end. Nearly thirty years ago I wrote a program (in COBOL) to send files from an unclassified environment to a classified environment using magnetic tape. At the time I was a contractor and they were so impressed that I was able to do it so quickly that they hired me as a permanent employee at a rate higher than I first asked for. I think that sending a file size preceding every file will work better.
Sam Hobbs15y ago
That looks like C/C++ code. The strlen function is not Unicode. Also, Unicode strings in C/C++ are preceded with "L" so if the string was Unicode then it would be L"|mystring" or maybe T("|mystring") for programs written to work both ways. Anyway, the string is not Unicode (it is ASCII). So I will look to see how to convert a ASCII string to binary and then search for that.
Maurizio15y ago
How can i know if it is unicode?
I send "mystring" throw c++ function send.
len = send(sock,"|mystring",(int)strlen("|mystring"),0);

Thanks
Sam Hobbs15y ago
Do you know if "mystring" is Unicode or not? I need to look in my code to find where I search for a string in binary data but I think I did to at least once, but it matters whether the string is Unicode because if it looks for "mystring" as a Unicode string but it is not Unicode then of course it won't find it.
Maurizio15y ago
Searching in msdn i find something, i have this code:

NetworkStream nStream = new NetworkStream(getSocket(numsock).getSocket(),true);
byte[] myReadBuffer = new byte[1024];
FileStream fs = new FileStream("C:\\Users\\Mauri\\Desktop\\" + item.Name, FileMode.Append, FileAccess.Write);
BinaryWriter writer = new BinaryWriter(fs);
do
{
nStream.Read(myReadBuffer, 0, myReadBuffer.Length);

writer.Write(myReadBuffer);

}
while (nStream.DataAvailable);

writer.Close();
fs.Close();

When the program makes the first archive, it is make ok, rar, zip, pdf, any extension works well, but when i try to download a second file, it is corrupted.
Any idea what is going wrong ?
Maurizio15y ago
socketrecv is a method i ve maked, that receive the data and change to string, i can modify that and keep it in bytes. But the problem is... i convert the data to string to look for the end of file ("mystring"). If you know any other way to read data without searching for an end of file mark i will read about. Im now trying with networkstream, but it isnt working well :/
Sam Hobbs15y ago
Well I don't see a declaration of recibido and I don't know what getSocket is nor do I know what socketRecv does. I searched MSDN for socketRecv and it does not seem to exist there. Is it possible to use something else that reads the data as binary? That would be the next best choice. You can convert binary to a string but it is best to not convert a string to binary. We can try to help you converting string to binary if necessary but it is better to not do that.
Maurizio15y ago
Thanks for your answer.
I can't use webclient class, beacuse im not downloading the data from an http or ftp server, is for a connection between 2 computers, like a remote access program.
Thank you.
Sam Hobbs15y ago
There was a similar question a few weeks ago that was discussed for a couple of weeks. In the end we were able to make it clear to do not do that! That is, do not download to a string. After the person finally understood that, he discovered that there was a way to use the downloaded data as binary that was easier than doing it the way he was trying to do it.

Can you use the WebClient class to download the files? If not then why not; if you can explain what you need to do then hopefully someone can help you with it.