FSInfo#getJarClassPath does not comply with the JAR specification

[Jonathan Gibbons]

Any changes/exceptions should be done in conjunction with updates to 
specification.

-- Jon

On 10/17/19 6:04 AM, David Lloyd wrote:
> It seems reasonable to include the special exception for `file:` absolute URLs.
>
> I did file a bug at bugreport but I haven't yet received a
> notification that the bug was created. If I do, I will post the JIRA #
> here.
>
> On Wed, Oct 16, 2019 at 9:33 PM Jaikiran Pai <jai.forums2013 at gmail.com> wrote:
>> One of the reasonsI hadn't done anything related to this in my proposed
>> change to FSInfo#getJarClassPath patch[1] was because I wasn't sure what
>> the actual expected semantics of the Class-Path attribute are.
>>
>> The jar Manifest documentation (which David pointed to) does state the
>> URI is to be relative, but I remember seeing a recent change discussed
>> in one of these mailing lists where absolute (file: scheme based) URIs
>> were supported. I finally found time to look through the JBS and here's
>> that issue https://bugs.openjdk.java.net/browse/JDK-8216401. So I think
>> whatever change we do here will then have to allow for absolute URI (for
>> file: scheme of local jars too).
>>
>> [1]
>> http://mail.openjdk.java.net/pipermail/compiler-dev/2019-October/013760.html
>>
>> -Jaikiran
>>
>> On 14/10/19 10:13 PM, David Lloyd wrote:
>>> The JAR specification specifies that the `Class-Path` attribute is a
>>> space-separated sequence of relative URLs.  A relative URL is defined
>>> ([2], [3]) as a hierarchical URI with no scheme component.
>>>
>>> Relative URLs resemble file paths.  However they differ in some
>>> important ways: for example, a relative URL is URL-encoded, whereas a
>>> file path is not, causing problems when dealing with paths that have
>>> embedded spaces (among other things).  Relative URLs representing
>>> absolute paths on Windows have a form like `/C:/Foo/Bar`, whereas the
>>> corresponding file path would be `C:/Foo/Bar` or `C:\Foo\Bar`.
>>>
>>> Note (since this is a point of frequent confusion) that a relative URL
>>> can have an absolute path.
>>>
>>> AFAIK neither of these cases work correctly when javac interacts with
>>> a JAR that contains a `Class-Path` attribute.
>>>
>>> The current FSInfo code, as noted in the recent thread entitled
>>> `FSInfo#getJarClassPath throws an exception not declared in its throws
>>> clause`, reads the class path attribute value with code that uses
>>> FileSystems.getDefault().getPath(xxx) on each class path element [4].
>>>
>>> The correct behavior would be to wrap each item in a `java.net.URI`.
>>> If the syntax is invalid, report an error or skip the element.  Then
>>> determine if the URI is absolute; if it is, report an error or skip
>>> the element.  Finally, query the Path API to look up the file by URI
>>> using Path.of(uri) or similar, reporting an error or skipping the
>>> element if there's a problem.
>>>
>>> The less-elegant solution would be to manually URL-decode the string,
>>> and (on windows) manually check to see if there's a drive letter,
>>> removing the leading slash if there is one.  However I would consider
>>> this to be more likely to be bug-prone.
>>>
>>> This problem is the underlying cause of at least one Quarkus bug [5],
>>> where the issue was discussed in depth.
>>>
>>> [1] https://docs.oracle.com/javase/10/docs/specs/jar/jar.html#class-path-attribute
>>> [2] RFC 3986 § 4.2 - https://tools.ietf.org/html/rfc3986#section-4.2
>>> [3] https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/URI.html
>>> [4] https://github.com/openjdk/jdk/blob/4ad3d82c76936a8927ed8a505689a3683144ad98/src/jdk.compiler/share/classes/com/sun/tools/javac/file/FSInfo.java#L112
>>> [5] https://github.com/quarkusio/quarkus/issues/3592
>>>
>