Smack 4.4.6: XML TransformerFactory does not support indent-number attribute

[cmeng]

During aTalk legacy File Transfer debugging, smack returns an IllegalArgumentException on receiving the remote Si-Transfer request.
What is the root cause of the problem?
No sure if there is something aTalk done incorrectly.

2022-07-16 04:57:35.568 22212-22631/org.atalk.android D/SMACK: RECV (0): 
    <iq xml:lang='en' to='peacock@atalk.sytes.net/atalk' from='swordfish@atalk.sytes.net/atalk' type='set' id='Z977M-92'>
      <si xmlns='http://jabber.org/protocol/si' id='jsi_1609371131' mime-type='image/png' profile='http://jabber.org/protocol/si/profile/file-transfer'>
        <file xmlns='http://jabber.org/protocol/si/profile/file-transfer' name='Prudential_JB.png' size='1191179'>
          <desc>
            Sending file
          </desc>
        </file>
        <feature xmlns='http://jabber.org/protocol/feature-neg'>
          <x xmlns='jabber:x:data' type='form'>
            <field var='stream-method' type='list-single'>
              <option>
                <value>
                  http://jabber.org/protocol/bytestreams
                </value>
              </option>
              <option>
                <value>
                  http://jabber.org/protocol/ibb
                </value>
              </option>
            </field>
          </x>
        </feature>
      </si>
    </iq>
2022-07-16 04:57:35.640 22212-22631/org.atalk.android I/aTalk: [65555] org.jivesoftware.smack.util.XmlUtil.<clinit>() XML TransformerFactory does not support indent-number attribute
    java.lang.IllegalArgumentException: Not supported: indent-number
        at org.apache.xalan.processor.TransformerFactoryImpl.setAttribute(TransformerFactoryImpl.java:580)
        at org.jivesoftware.smack.util.XmlUtil.<clinit>(XmlUtil.java:39)
        at org.jivesoftware.smack.util.XmlUtil.isClarkNotation(XmlUtil.java:69)
        at org.jivesoftware.smackx.formtypes.FormFieldRegistry.register(FormFieldRegistry.java:81)
        at org.jivesoftware.smackx.formtypes.FormFieldRegistry.register(FormFieldRegistry.java:66)
        at org.jivesoftware.smackx.xdata.packet.DataForm.<init>(DataForm.java:112)
        at org.jivesoftware.smackx.xdata.packet.DataForm.<init>(DataForm.java:54)
        at org.jivesoftware.smackx.xdata.packet.DataForm$Builder.build(DataForm.java:561)
        at org.jivesoftware.smackx.xdata.provider.DataFormProvider.parse(DataFormProvider.java:139)
        at org.jivesoftware.smackx.xdata.provider.DataFormProvider.parse(DataFormProvider.java:61)
        at org.jivesoftware.smack.provider.Provider.parse(Provider.java:53)
        at org.jivesoftware.smack.provider.Provider.parse(Provider.java:43)
        at org.jivesoftware.smackx.thumbnail.ThumbnailStreamInitiationProvider.parse(ThumbnailStreamInitiationProvider.java:91)
        at org.jivesoftware.smackx.thumbnail.ThumbnailStreamInitiationProvider.parse(ThumbnailStreamInitiationProvider.java:39)
        at org.jivesoftware.smack.provider.IQProvider.parse(IQProvider.java:64)
        at org.jivesoftware.smack.provider.IqProvider.parse(IqProvider.java:40)
        at org.jivesoftware.smack.util.PacketParserUtils.parseIQ(PacketParserUtils.java:555)
        at org.jivesoftware.smack.util.PacketParserUtils.parseStanza(PacketParserUtils.java:113)
        at org.jivesoftware.smack.AbstractXMPPConnection.parseAndProcessStanza(AbstractXMPPConnection.java:1450)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection.access$1000(XMPPTCPConnection.java:131)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets(XMPPTCPConnection.java:972)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.access$700(XMPPTCPConnection.java:916)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader$1.run(XMPPTCPConnection.java:939)
        at java.lang.Thread.run(Thread.java:764)
2022-07-16 04:57:35.646 22212-22629/org.atalk.android D/(OperationSetFileTransferJabberImpl.java:393)#fileTransferRequest: Received incoming Jabber file transfer request.

2022-07-16 04:59:09.857 22212-22630/org.atalk.android D/SMACK: SENT (0): 
    <iq to='swordfish@atalk.sytes.net/atalk' id='Z977M-92' type='result'>
      <si xmlns='http://jabber.org/protocol/si'>
        <feature xmlns="http://jabber.org/protocol/feature-neg">
          <x xmlns='jabber:x:data' type='submit'>
            <field var='stream-method'>
              <value>
                http://jabber.org/protocol/bytestreams
              </value>
            </field>
          </x>
        </feature>
      </si>
    </iq>

[Flow]

It is not visible from the log, but that is a exception logged using ‘info’ log level. Check the call site, i.e., the address of the second topmost entry of the stack trace, org.jivesoftware.smack.util.XmlUtil.(XmlUtil.java:39), to see the JUL log call.

Smack merely wants to tell you what a certain non-necessary functionality is not available.

[cmeng]

Below is the captured log that leads to the above problem; when smack is trying to register a form field (formType == null) i.e. <field var=‘stream-method’ type=‘list-single’>

at org.jivesoftware.smackx.formtypes.FormFieldRegistry.register(FormFieldRegistry.java:85)

and XmlUtil throws the exception; else everything is working OK.
No sure if smack team needs to take any action; aTalk will just ignore it for now.

    public static void register(String formType, String fieldName, FormField.Type fieldType) {
        StringUtils.requireNotNullNorEmpty(fieldName, "fieldName must be provided");
        Objects.requireNonNull(fieldType);

        Timber.d("formType: %s; fieldName: %s;  FormField.Type: %s", formType, fieldName, fieldType);
        if (formType == null) {
            if (XmlUtil.isClarkNotation(fieldName)) {
                CLARK_NOTATION_FIELD_REGISTRY.put(fieldName, fieldType);
            }
            return;
        }
    ...
 }

public class XmlUtil {

    private static final TransformerFactory transformerFactory = TransformerFactory.newInstance();

    static {
        try {
            transformerFactory.setAttribute("indent-number", 2);
        } catch (IllegalArgumentException e) {
            LOGGER.log(Level.INFO, "XML TransformerFactory does not support indent-number attribute", e);
        }
    }
...
}

2022-07-19 10:01:24.311 7282-8984/org.atalk.android D/(FormFieldRegistry.java:83)#register: formType: null; fieldName: stream-method;  FormField.Type: list-single
2022-07-19 10:01:24.403 7282-8984/org.atalk.android I/aTalk: [1525] org.jivesoftware.smack.util.XmlUtil.<clinit>() XML TransformerFactory does not support indent-number attribute
    java.lang.IllegalArgumentException: Not supported: indent-number
        at org.apache.xalan.processor.TransformerFactoryImpl.setAttribute(TransformerFactoryImpl.java:580)
        at org.jivesoftware.smack.util.XmlUtil.<clinit>(XmlUtil.java:39)
        at org.jivesoftware.smack.util.XmlUtil.isClarkNotation(XmlUtil.java:69)
        at org.jivesoftware.smackx.formtypes.FormFieldRegistry.register(FormFieldRegistry.java:85)
        at org.jivesoftware.smackx.formtypes.FormFieldRegistry.register(FormFieldRegistry.java:69)
        at org.jivesoftware.smackx.xdata.packet.DataForm.<init>(DataForm.java:112)
        at org.jivesoftware.smackx.xdata.packet.DataForm.<init>(DataForm.java:54)
        at org.jivesoftware.smackx.xdata.packet.DataForm$Builder.build(DataForm.java:561)
        at org.jivesoftware.smackx.filetransfer.FileTransferNegotiator.createDefaultInitiationForm(FileTransferNegotiator.java:375)
        at org.jivesoftware.smackx.filetransfer.FileTransferNegotiator.negotiateOutgoingTransfer(FileTransferNegotiator.java:315)
        at org.jivesoftware.smackx.filetransfer.OutgoingFileTransfer.negotiateStream(OutgoingFileTransfer.java:372)
        at org.jivesoftware.smackx.filetransfer.OutgoingFileTransfer.access$100(OutgoingFileTransfer.java:44)
        at org.jivesoftware.smackx.filetransfer.OutgoingFileTransfer$2.run(OutgoingFileTransfer.java:232)
        at java.lang.Thread.run(Thread.java:920)

[Flow]

@cmeng

Below is the captured log that leads to the above problem

Just to be clear, there is no problem. Smack is just telling you that a library used by Smack does not provide all functionality. But the missing functionality is also not essential.

@cmeng

and XmlUtil throws the exception

That is also not accurate, as XmlUtil does not throw an exception, it merely catches one and logs it.

I hope this clarifies the significance of the situation.