A Symbolic Puzzler

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Here's a little Java puzzler I encountered back in August. Essentially, the test below creates a symlink to /testdir/file, and validates that the symlink is in fact pointing to it.

This test was run on a Mac Book Pro running OSX 10.5.8 using a 1.5.0 JVM, though I originally discovered this problem using Linux and a Java 1.6 VM. The path /testdir is not a symbolic link to another directory, and the user running the test also owns /testdir.

import java.io.*;
import junit.framework.TestCase;

public class ATest extends TestCase {
  public void testSymlink() throws Exception {
    // Setup
    run("/bin/rm", "/testdir/file", "/testdir/symlink");
    run("/usr/bin/touch", "/testdir/file");

    File TESTDIR_SYMLINK = new File("/testdir/symlink");

    // Symlink doesn't exist yet
    assertFalse(TESTDIR_SYMLINK.exists());

    // And so its canonical path points to itself.
    assertEquals("/testdir/symlink", TESTDIR_SYMLINK.getCanonicalPath());

    // Now point the symlink to the file.
    run("/bin/ln", "-s", "/testdir/file", "/testdir/symlink");

    // The symlink exists
    assertTrue(TESTDIR_SYMLINK.exists());

    // The canonical path should be up to date.
    assertEquals("/testdir/file", TESTDIR_SYMLINK.getCanonicalPath());
  }

  private static void run(String... args)
      throws IOException, InterruptedException {
    new ProcessBuilder(args).start().waitFor();
  }
}

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Voting is open until some time early Wednesday morning, Oct 21.