deleteIfExists() throws IOException if remote file does not exist

[wgtthompson]

Summary

java.nio.file.spi.FileSystemProvider.deleteIfExists(Path) implementation will catch a FileNotFoundException from it's call to delete(Path) and suppress it and return false.

    //snippet from java.nio.file.spi.FileSystemProvider
    public boolean deleteIfExists(Path path) throws IOException {
        try {
            delete(path);
            return true;
        } catch (NoSuchFileException ignore) {
            return false;
        }
    }

The problem is that UnixSshFileSystemProvider.delete(Path) throws an IOException instead of FileNotFoundException when the file does not exist. This means that UnixSshFileSystemProvider does not implement the documented behavior of FileSystemProvider. Specifically, "

     * @return  {@code true} if the file was deleted by this method; {@code
     *          false} if the file could not be deleted because it did not
     *          exist

Proposed Solution

Override deleteIfExists(Path) in UnixSshFileSystemProvider. Add check for file existing before propogating the exception.

    @Override
    public boolean deleteIfExists(Path path) throws IOException {
        try {
            delete(path);
            return true;
        } catch (NoSuchFileException ignore) {
            return false;
        } catch (IOException ioe) {
            try {
                //remote calls can result in cases where it is unclear why the remote command
                //failed (inconsistent exit codes, etc).  such events may be handled by
                //throwing IOException when the cause was the file not existing.  here, the
                //exception is suppressed if the file does not exist (to be consistent with
                //the overridden method documentation).
                if (!exists(path)) {
                    return false;
                }
            } catch (Exception e) {
                //suppress so original exception is thrown
            }
            throw ioe;
        }
    }

Cause

UnixSshFileSystem.delete(Path) creates a new BasicFileAttributesImpl which calls remote stat command in its initializer. Since the remote file does not exist, the stat command returns a non-zero error code which results in a thrown IOException instead of FileNotFoundException. The IOException propogates up the call-stack and is not detected as a non-existent file event.

    private Map<String, Object> readAttributes( Path path, SupportedAttribute[] attributes, LinkOption... linkOptions ) throws IOException {
        UnixSshPath unixPath = checkPath( path ).toAbsolutePath();

        String command = statCommand( unixPath, attributes ) + " " + unixPath.toString();
        ExecuteResult result = execute( unixPath, command );
        if ( result.getExitCode() == 0 ) {
            return statParse( result.getStdout(), attributes );
        }
        else {
            throw new IOException( "failed to list directory (" + result.getExitCode() + "): " +
                    "out='" + result.getStdout() + "', " +
                    "err='" + result.getStderr() + "'" );
        }
    }

Example code to generate the problem

        //delete file if it exists
        try {
            Files.deleteIfExists(p);
        } catch (Exception e) {
            e.printStackTrace();
        }

Stack trace

java.io.IOException: failed to list directory (1): out='', err='stat: cannot stat `/home/myname/testfile_jschnio_test.txt': No such file or directory
'
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider.readAttributes(UnixSshFileSystemProvider.java:540)
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider.access$600(UnixSshFileSystemProvider.java:61)
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider$BasicFileAttributesImpl.<init>(UnixSshFileSystemProvider.java:771)
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider$BasicFileAttributesImpl.<init>(UnixSshFileSystemProvider.java:758)
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider$BasicFileAttributesImpl.<init>(UnixSshFileSystemProvider.java:750)
    at com.pastdev.jsch.nio.file.UnixSshFileSystemProvider.delete(UnixSshFileSystemProvider.java:231)
    at java.nio.file.spi.FileSystemProvider.deleteIfExists(FileSystemProvider.java:735)
    at java.nio.file.Files.deleteIfExists(Files.java:1116)
    at com.mypackage.JschNio_Test.testJschNioFilesystem(JschNio_Test.java:109)


    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Remote host machine:

Linux homer 3.2.0-4-amd64 #1 SMP Debian 3.2.60-1+deb7u1 x86_64 GNU/Linux

[wgtthompson]

Occurs for both non-existent files and non-existent directories.

[Lucas Theisen]

@wgtthompson, I fixed this and released a new version for you: 0.1.3. It will take a few hours to propagate to maven central. Thanks for the bug report. On a side note, I wasn't sure anybody other than me was using this. Mind if I ask what you are using it for?

[wgtthompson]

@lucastheisen File storage/retrieval system across multiple machines. The abstraction to FileSystem provides a consistent interface and re-usable set of algorithms whether the file is local or remote.