S3Path: relativize can return an absolute path

[thsandu]

We are relying in a part of our implementation on the behavior of the Path.relativize() to return a relative path. I discovered that the S3Path gives an absolute path back, if the relativize is executed on the root path. I checked again against windows and jimfs implementation:

@Test
public void relativizeAbsolutePathOnRoot() {
    Path path = Paths.get("C:\\");
    Path path2 = Paths.get("C:\\foo\\bar\\");
    assertFalse(path.relativize(path2).isAbsolute());
    
    FileSystem linux = Jimfs.newFileSystem("testme", Configuration.unix());
    Path pathJim = linux.getPath("/");
    Path pathJim2 = linux.getPath("/foo/bar/");
    assertFalse(pathJim.relativize(pathJim2).isAbsolute());
}

Here again a matching unit test: https://github.com/thsandu/aws-java-nio-spi-for-s3-issues-with-s3x/blob/2cbb6d27b8adde8499f49a146eedce870dec1ec6/src/test/java/software/amazon/nio/spi/s3/S3PathTest.java#L293

[markjschreiber]

So does

    Path pathJim = linux.getPath("/");
    Path pathJim2 = linux.getPath("/foo/bar/");

    pathJim.relativize(pathJim2).isAbsolute();

result in a path equivalent to "./foo/bar/"?

[thsandu]

No, it results in a path equivalent to "foo/bar/". This I interpret as the relative path from "/foo/bar/" to "/".

[markjschreiber]

Can you check if PR #394 has fixed this?

[markjschreiber]

This test seems to pass with PR #394.

    @Test
    void testRelativizeAgainstRoot() {
        var s3Path = S3Path.getPath(fileSystem, "/");
        var relativePath = s3Path.relativize(S3Path.getPath(fileSystem, "/a/b/c/d"));
        assertEquals("a/b/c/d", relativePath.toString());
        assertFalse(relativePath.isAbsolute());

        var emptyS3Path = S3Path.getPath(fileSystem, "");
        relativePath = emptyS3Path.relativize(S3Path.getPath(fileSystem, "a/b/c/d"));
        assertEquals("a/b/c/d", relativePath.toString());
        assertFalse(relativePath.isAbsolute());
    }

[markjschreiber]

I have added some additional tests to prevent a regression. Feel free to open a new issue if this is still a problem.