Download File chunks (wodFTPServer)
Hi,
I want to allow the download of file chunks by supporting special filenames. If I would request BigFile.dat:4096:8191 I want to send the 4K Block starting at offset 4096 of BigFile.dat to the client. Can this be done with your FTPServer component?
Bernd
Re: Download File chunks
Bernd,
hi. Unfortunatelly, FTP protocol doesn't support that, so no client nor the server will make it the way you need.
But.. In theory.. You could let your client send REST command to continue at specific position, and then after it receives enough data to send ABOR command - so you get part of the file you need. But it's up to your client to do that.
As for SFTP protocol - any client could do this for you.
Hope I helped.
Kreso
Re: Download File chunks
Kreso,
thank you for your answer.
hi. Unfortunatelly, FTP protocol doesn't support that, so no client nor the server will make it the way you need.But.. In theory.. You could let your client send REST command to continue at specific position, and then after it receives enough data to send ABOR command - so you get part of the file you need. But it's up to your client to do that.
Of course the standard FTP protcol does not support that. I would implement both the client and the server portion. The server should behave like any standard FTP server to regular FTP clients but should also allow sending data chunks to the client when a special request is received.
I think it could be easily done if you allow to redirect requests to some sort of virtual files. I read the doc's and realized that I can redirect to an arbitrary file but when using this mechanism I had to copy each chunk before transferring. So the main question is if there is a way to replace the file stream functions you use.
So what do you think?
Bernd
Re: Download File chunks
Bernd,
would FileTransferData help?
http://www.weonlydo.com/FTPServer/Help/wodFTPDLib~wodFTPD~FileTransferData_EV.html
I think you can feed it the way you need?
Kreso
Re: Download File chunks
Kreso,
would FileTransferData help?http://www.weonlydo.com/FTPServer/Help/wodFTPDLib~wodFTPD~FileTransferData_EV.html
I think you can feed it the way you need?
I don't think it will work since it FIRST reads the data and the allows me to modify the data. If you'd implement another callback to FEED the data, it should work. You may also think about some more generic support of virtual files. So one could get SHA-1 checksums from files by retrieving SHA1:filename.ext for example.
I am thinking of an alternate way to use your WebServer component since this component can feed any data as desired. At least as far as I unterstood.
Bernd
Re: Download File chunks
Bernd,
but I think you could have, for example, 1-byte file and then in the event change that 1-byte array to *anything* else - a bit strange approach but will work.
As for SHA1.. Hmm.. If we would implement something like that (which isn't any standard btw) which command exactly would you use to obtain it?
With little tweaks you cuold do it too btw - you could intercept DownloadFile event, check if SHA1 exists in the name and return different error?
Kreso
Re: Download File chunks
Kreso,
okay, this should work but is a little bit ugly . 
The SHA-1 was just an example. I thought of extending a standard protocol (FTP) to support some special behaviour. What I want to develop ist a file-sync application which works over FTP and/or HTTP to sync two directories. So to check if two files area identical I need to retrieve some information about them. This could be the time stamp or for example the SHA-1 checksum. I thought of handling all this with special filenames:
FTP request test.txt -> Get test.txt content
FTP request SHA1:test.txt -> Get SHA-1 string of test.txt
FTP request test.txt:2000:3000 -> Get byte 2000-3000 of test.txt
If you'd implement the possibility to replace the standard file stream this could be easily done. It my be sufficient to implement an IFtpFile interface with some member functions: GetFileSize(), ReadFile(nStartPos, nCountBytes), ... Any function could pass to the original function if no special functionality is required.
This way out FTP server would work as any standard FTP server but has an extension for or own client. There should not be any compatibilty issues here.
Bernd
Re: Download File chunks
Why not sending something like
SITE SHA1 /path/to/file
command? You can catch that easily in Site event and return reply back.
why don't you try that? This is regular mechanism.
Kreso
Re: Download File chunks
Kreso,
this may work for a SHA-1 checksum, but will probably not work with sending file data.
Is it so complicated to do the stream replacement stuff? We would for sure license FtpServer if this was implemented.
Right now we own HttpDlx and think about FtpServer, WebServer and later SSHpackage.
Bernd
