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  1. JDK
  2. JDK-8172711

toRealPath fails?with volumes in Windows Docker containers

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    • Subcomponent:
    • CPU:
      x86
    • OS:
      windows_10

      Description

      FULL PRODUCT VERSION :
      openjdk version "1.8.0_111-3-ojdkbuild"
      OpenJDK Runtime Environment (build 1.8.0_111-3-ojdkbuild-b15)
      OpenJDK 64-Bit Server VM (build 25.111-b15, mixed mode)

      ADDITIONAL OS VERSION INFORMATION :
      Microsoft Windows [Version 10.0.14986]

      EXTRA RELEVANT SYSTEM CONFIGURATION :
      Docker version 1.13.0-rc4

      A DESCRIPTION OF THE PROBLEM :
      Method toRealPath in java.nio.file.Path resolves the underlying path for a symlink directory in Windows. It works correctly in Windows 10 and Windows Server 2016, but not for the symlinks used in Docker containers.

      With Docker you can create a volume in a container which uses a symlink directory to store data outside of the container. The format of the mapping causes toRealPath to fail.

      This means you can't run Java apps in Windows Docker containers and store the data persistently outside of the container. It will affect all Java apps that access a path which is a volume in a container.

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      I have pushed a Docker image to the hub with a basic Java app that uses toRealPath(). You can test on Windows 10 or 2016 with Docker installed:

      >docker run -it --rm sixeyed/openjdk-symlinktest
      >java -cp . SymLinkTest c:\volume-directory
      Path: c:\volume-directory
      Exception in thread "main" java.nio.file.NoSuchFileException: c:\volume-directory
              at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:79)
              at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
              at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
              at sun.nio.fs.WindowsLinkSupport.getFinalPath(WindowsLinkSupport.java:82)
              at sun.nio.fs.WindowsLinkSupport.getRealPath(WindowsLinkSupport.java:242)
              at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:836)
              at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:44)
              at SymLinkTest.main(symlinkd-test.java:9)

      The error is NoSuchFileException, but the path does exist:

      >dir c:\
      ...
      01/09/2017 08:02 AM <SYMLINKD> volume-directory [\\?\ContainerMappedDirectories\01BA2580-95DA-48B9-94F2-B397D00CD0A1]

      And it is a valid reparse point:

      >fsutil reparsepoint query c:\volume-directory
      Reparse Tag Value : 0xa000000c
      Tag value: Microsoft
      Tag value: Name Surrogate
      Tag value: Symbolic Link

      Reparse Data Length: 0x00000116
      Reparse Data:
      0000: 00 00 80 00 82 00 86 00 00 00 00 00 5c 00 43 00 ............\.C.
      0010: 6f 00 6e 00 74 00 61 00 69 00 6e 00 65 00 72 00 o.n.t.a.i.n.e.r.
      0020: 4d 00 61 00 70 00 70 00 65 00 64 00 44 00 69 00 M.a.p.p.e.d.D.i.
      0030: 72 00 65 00 63 00 74 00 6f 00 72 00 69 00 65 00 r.e.c.t.o.r.i.e.
      0040: 73 00 5c 00 30 00 31 00 42 00 41 00 32 00 35 00 s.\.0.1.B.A.2.5.
      0050: 38 00 30 00 2d 00 39 00 35 00 44 00 41 00 2d 00 8.0.-.9.5.D.A.-.
      0060: 34 00 38 00 42 00 39 00 2d 00 39 00 34 00 46 00 4.8.B.9.-.9.4.F.
      0070: 32 00 2d 00 42 00 33 00 39 00 37 00 44 00 30 00 2.-.B.3.9.7.D.0.
      0080: 30 00 43 00 44 00 30 00 41 00 31 00 00 00 5c 00 0.C.D.0.A.1...\.
      0090: 5c 00 3f 00 5c 00 43 00 6f 00 6e 00 74 00 61 00 \.?.\.C.o.n.t.a.
      00a0: 69 00 6e 00 65 00 72 00 4d 00 61 00 70 00 70 00 i.n.e.r.M.a.p.p.
      00b0: 65 00 64 00 44 00 69 00 72 00 65 00 63 00 74 00 e.d.D.i.r.e.c.t.
      00c0: 6f 00 72 00 69 00 65 00 73 00 5c 00 30 00 31 00 o.r.i.e.s.\.0.1.
      00d0: 42 00 41 00 32 00 35 00 38 00 30 00 2d 00 39 00 B.A.2.5.8.0.-.9.
      00e0: 35 00 44 00 41 00 2d 00 34 00 38 00 42 00 39 00 5.D.A.-.4.8.B.9.
      00f0: 2d 00 39 00 34 00 46 00 32 00 2d 00 42 00 33 00 -.9.4.F.2.-.B.3.
      0100: 39 00 37 00 44 00 30 00 30 00 43 00 44 00 30 00 9.7.D.0.0.C.D.0.
      0110: 41 00 31 00 00 00 A.1...

      More details and source for the repo on GitHub- https://github.com/sixeyed/dockers-windows/tree/master/openjdk/symlink-test

      The issue looks to be with WindowsLinkSupport.java. There was a similar problem in Go, which was down to how Windows Server 2016 display reparse data - https://github.com/golang/go/issues/15978#issuecomment-224387894


      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      The call to toRealPath should resolve the underlying path to the Docker volume, which is a valid symlink.
      ACTUAL -
      The call raises NoSuchFileException.

      ERROR MESSAGES/STACK TRACES THAT OCCUR :
      Exception in thread "main" java.nio.file.NoSuchFileException: c:\volume-directory
              at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:79)
              at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
              at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
              at sun.nio.fs.WindowsLinkSupport.getFinalPath(WindowsLinkSupport.java:82)
              at sun.nio.fs.WindowsLinkSupport.getRealPath(WindowsLinkSupport.java:242)
              at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:836)
              at sun.nio.fs.WindowsPath.toRealPath(WindowsPath.java:44)
              at SymLinkTest.main(symlinkd-test.java:9)

      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      import java.nio.file.Path;
      import java.nio.file.Paths;

      class SymLinkTest {

          public static void main(String[] args) throws Exception {
              Path path = Paths.get(args[0]);
              System.out.println("Path: " + args[0]);
              System.out.println("toRealPath: " + path.toRealPath());
          }
      }
      ---------- END SOURCE ----------

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            Assignee:
            alanb Alan Bateman
            Reporter:
            webbuggrp Webbug Group
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              Created:
              Updated: