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EPSV implementation not compliant with some FTP servers (AS/400)


EPSV is not working when trying to connect to some FTP Server (sorry, we don't know any details about this server).
Here is the error:
"System.Net.FtpClient.FtpException : Failed to get the EPSV port from: Entering Extended Passive Mode (!!!51603!). at System.Net.FtpClient.FtpClient.OpenPassiveDataStream(" [...]

I think that the line 1087 of the function "OpenPassiveDataStream" from the file "FtpClient.cs" is incorrect :
 m = Regex.Match(reply.Message, @"\(\|\|\|(?<port>\d+)\|\)");
So the client is expecting the "|" character, and the server we are facing is responding with the "!" character.
This "!" seems to be allowed by the RFC 2428, which indeed recommands the "|", but allows any ASCII separator from 33 to 126.

Reference: RFC 2428, search for "The EPSV Command" and also "delimiter"

I don't know much about Regex, but going to modify it to accept 33 to 126 delimiters.
Please correct me if i'm wrong somewhere.

Modified 1087 line to accept 33-126 delimiters in passive mode :
m = Regex.Match(reply.Message, @"\([\x21-\x7E][\x21-\x7E][\x21-\x7E](?<port>\d+)[\x21-\x7E]\)");


manuellb wrote Mar 23, 2016 at 4:52 PM

Got the FTP server details. It is IBM AS/400.
See the correction at the end of the description.