Max Shenfield created NET-663:
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Summary: NullPointerException when FTPClient remote verification
fails
Key: NET-663
URL: https://issues.apache.org/jira/browse/NET-663
Project: Commons Net
Issue Type: Bug
Components: FTP
Affects Versions: 3.6
Environment: OS: Linux
Reporter: Max Shenfield
At L934 of the {{FTPClient}} code, Apache does a check to see whether the data
and control connections are at the same IP address ({{verifyRemote}}). If they
differ, the data connection socket is closed and an exception is raised. This
can be disabled, but is the default behavior ({{__remoteVerificationEnabled =
true}}).
The L934-939 code path where {{verifyRemote}} returns false always raises a
{{java.lang.NullPointerException}}. {{socket.getInetAddress()}} seems to
return {{null}} after {{socket.close}} is called, leading to
{{socket.getInetAdress().getHostAddress()}} to raise the
{{java.lang.NullPointerException}} at L938. This obfuscates a really useful
error message ("Host attempting data connection is not the same as server")
with a difficult to debug {{NullPointerException}}.
Example State:
{code}
this.__remoteVerificationEnabled -> true
this.getRemoteAddress().toString() -> "ftp.example.com/987.654.321.000"
socket.getInetAddress.toString() -> "/123.456.789.000"
{code}
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