RFR: 8287843: File::getCanonicalFile doesn't work for \?\C:\ style paths DOS device paths

[Brian Burkhalter]

On Thu, 7 Sep 2023 08:33:39 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> Would it be possible to summarise how this behaves when File just represents a prefix?

Baseline:

jshell> File f = new File("\\\?\")
f ==> \?

jshell> f.getCanonicalPath()
|  Exception java.io.IOException: Bad pathname
|        at WinNTFileSystem.canonicalize0 (Native Method)
|        at WinNTFileSystem.canonicalize (WinNTFileSystem.java:463)
|        at File.getCanonicalPath (File.java:626)
|        at (#2:1)

jshell> f = new File("\\\?\\UNC\")
f ==> \?\UNC

jshell> f.getCanonicalPath()
|  Exception java.io.IOException: Bad pathname
|        at WinNTFileSystem.canonicalize0 (Native Method)
|        at WinNTFileSystem.canonicalize (WinNTFileSystem.java:463)
|        at File.getCanonicalPath (File.java:626)
|        at (#4:1)


Proposed patch:

jshell> File f = new File("\\\?\")
f ==> \?

jshell> f.getCanonicalPath()
|  Exception java.io.IOException: Bad pathname
|        at WinNTFileSystem.canonicalize0 (Native Method)
|        at WinNTFileSystem.canonicalize (WinNTFileSystem.java:472)
|        at File.getCanonicalPath (File.java:626)
|        at (#2:1)

jshell> f = new File("\\\?\\UNC\")
f ==> \?\UNC

jshell> f.getCanonicalPath()
$4 ==> "C:\\Users\\bpb\\dev\\jdk\\jdk\\UNC"

Presumably the constructor removes the trailing `\`, hence I suppose the special case of `\?\UNC` should be checked in the code right after the proposed change.

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PR Comment: https://git.openjdk.org/jdk/pull/15603#issuecomment-1710409880