File scan API

Availability

[SINCE Orbeon Forms 2017.2]

This is an Orbeon Forms PE feature.

Rationale

When a user uploads files via one of the Form Runner attachment controls, a virus scanner can verify the file before it gets attached to the current form.

Orbeon Forms provides a simple Java API which allows integrating with virus scanning solutions.

NOTE: At this time Orbeon doesn't provide integrations with specific virus scanning solutions.

API

Orbeon Forms provide the following FileScanProvider abstract class as a base for concrete providers:

package org.orbeon.oxf.xforms.upload.api.java;

public abstract class FileScanProvider {

    public void init();
    public void destroy();

    public FileScan startStream(String fileName, Map<String, String[]> headers);
}

When Orbeon Forms initializes the provider, it:

  • creates an instance of the class
  • calls the init() method

When Orbeon Forms is starting to receive an upload file, it calls the startStream() method. The method receives a file name as provided by the web browser (which means that it must not be trusted), and HTTP header name/values as they are received by Orbeon Forms.

The provider implementation must return an implementation of a FileScan.

The FileScan interface is as follows :

package org.orbeon.oxf.xforms.upload.api.java;

interface FileScan {
    public FileScanStatus bytesReceived(byte[] bytes, int offset, int length);
    public FileScanStatus complete(File file);
    public void abort();
}

As bytes are received, the bytesReceived() method is called. A provider may or may not make use of this method. If it is unused, the provider must return an ACCEPT FileScanStatus (see below). This method allows incremental scanning of a file.

When the file is completely uploaded and stored into a temporary file, but not yet attached to the user's form, the complete() method is called with a pointer to the temporary file. The scanner can use this method to perform the entirety of the scan in case bytesReceived() is not used.

Upon processing the complete() method, resources associated with the file scan must be cleared by the provider, whether REJECT or ERROR is returned, or if any exception is thrown as part of the processing of complete().

Both bytesReceived() and complete() must return a value from the FileScanStatus enumeration:

package org.orbeon.oxf.xforms.upload.api.java;

public enum FileScanStatus { ACCEPT, REJECT, ERROR }
  • ACCEPT: accept the uploaded content
  • REJECT: reject the uploaded content (for example because it is suspected to contain a virus)
  • ERROR: any other error happened

If REJECT or ERROR is returned, or if any exception is thrown as part of startStream(), bytesReceived(), or complete(), the uploaded file is rejected and an error is shown to the user.

File scan error

If the user cancels the upload, or if any other error occurs on the Orbeon Forms side, the abort() method is called. In this case, the file scan for the given file must be stopped and associated resources must be cleared, if any.

The abort() method may be called after the complete() method.

Registering a provider

The file scanning API uses the standard Java ServiceLoader API with a provider name of org.orbeon.oxf.xforms.upload.api.FileScanProvider.

The provider must:

  • be a public class
  • have a public no-arguments constructor
  • implement the FileScanProvider Java interface

To enable a provider with Orbeon Forms:

  • create your provider as per the standard Java ServiceLoader
  • create a JAR file containing the code or your provider
  • place your JAR file under the Orbeon Forms WEB-INF/lib directory

The Orbeon Forms log files will log errors if any when starting if the provider was found but could not be instantiated.

Example

AcmeFileScanProvider is a Java example of a provider which does nothing but:

  • log method calls
  • reject files which contain in their name the string "virus"

NOTE: This obviously is not the right way to determine whether a file contains a virus or not.

The service provider is described with this META-INF/services/org.orbeon.oxf.xforms.upload.api.FileScanProvider file.

The example project is provided here.

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