eSCL parsing fails on ADF‑only scanners: missing <scan:Platen> causes exception

[rw-django-fan-2020]

Describe the bug
When connecting to an ADF-only eSCL/AirScan scanner, ScanBridge fails to fetch scanner capabilities and throws an exception:

IllegalArgumentException: Required element not found: scan:Platen

This happens because the parser expects a <scan:Platen> element, which is absent on ADF-only devices. According to the eSCL specification, a scanner may expose only <scan:Adf> if it has no flatbed/platen.

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To Reproduce
Steps to reproduce the behavior:

1. Open ScanBridge
2. Connect to an ADF-only eSCL/AirScan scanner (e.g., Brother DS‑940DW)
3. Attempt to fetch scanner capabilities
4. Observe the exception during parsing

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Expected behavior
ScanBridge should:

• Accept scanners that expose only <scan:Adf>
• Handle the absence of <scan:Platen> gracefully
• Allow scanning via the ADF

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Screenshots
Not applicable (the failure occurs during capability fetch, no UI screenshot available)

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Smartphone (please complete the following information):

• Device: [Redacted / Your device, e.g., Pixel 7]
• Android version: [e.g., 14]
• ScanBridge version: [e.g., 22]

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Additional context
Redacted eSCL ScannerCapabilities XML (identifiers anonymized):

<?xml version="1.0" encoding="UTF-8"?>
<scan:ScannerCapabilities
  xmlns:scan="http://schemas.hp.com/imaging/escl/2011/05/03"
  xmlns:pwg="http://www.pwg.org/schemas/2010/12/sm"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <pwg:Version>2.63</pwg:Version>
  <pwg:MakeAndModel>DS-940DW</pwg:MakeAndModel>
  <pwg:SerialNumber>REDACTED</pwg:SerialNumber>
  <scan:UUID>REDACTED</scan:UUID>
  <scan:AdminURI>http://scanner.local/</scan:AdminURI>

  <scan:Adf>
    <scan:AdfSimplexInputCaps>
      <!-- capabilities omitted for brevity -->
    </scan:AdfSimplexInputCaps>

    <scan:AdfDuplexInputCaps>
      <!-- capabilities omitted for brevity -->
    </scan:AdfDuplexInputCaps>
  </scan:Adf>

  <!-- Note: No <scan:Platen> element is present, as this is an ADF-only device -->

</scan:ScannerCapabilities>

Suggested fix:

• Treat <scan:Platen> as optional
• Accept scanners that expose only <scan:Adf>
• Avoid failing capability parsing when platen support is absent

[Chrisimx]

Thank you for the bug report! I hope this is fixed in the newest release v1.6.1 of ScanBridge. This release is not yet on F-Droid, but can be downloaded here on GitHub..

If the issue persists, just write a comment over here.

Fixed in e696325 (upstream in Chrisimx/eSCLKt@9c5a4b3).

[rw-django-fan-2020]

Although it was mentioned that this issue has already been fixed, there is still another independent problem visible in the provided ScannerCapabilities XML.

In addition to the previously discussed AutoColorDetection enum handling, the XML shows that this device is an ADF-only scanner. It does not provide a <scan:Platen> element at all, which is fully valid according to the eSCL specification. A scanner is not required to expose a platen if the hardware does not have one.

However, ScanBridge currently appears to treat <scan:Platen> as a required element. When it is missing, capability parsing fails entirely, even though <scan:Adf> (including simplex and duplex capabilities) is present and complete. This causes the scanner to be rejected although the eSCL response itself is valid.

In other words, even if the AutoColorDetection enum issue is resolved, ScanBridge will still fail on ADF-only devices unless:

• <scan:Platen> is treated as optional, and
• capability parsing continues successfully when only <scan:Adf> is present.

This affects scanners such as the Brother DS-940DW and likely other portable or document-only scanners. From a specification and interoperability point of view, the absence of <scan:Platen> should not be considered an error.

It would therefore be necessary to relax the parser logic so that ScanBridge supports ADF-only scanners correctly, instead of aborting capability parsing when no platen is advertised.

[Chrisimx]

Please mark your comment as AI-generated, if you obtained it from a LLM.

Adf-only scanners (scanners without Platen element) are definitely accepted with the newest version 1.6.1 of ScanBridge. I tested this. This version is now also available on F-Droid in addition to GitHub. It is plausible, however, that there is another issue with parsing your scanner capabilities.

If there is another issue with the parsing of the scanner capabilities of your scanner, please send the full scanner caps file, so I can test against it, until I can assure it is working. The only personally identifiable data in the XML should be within the scan:UUID, pwg:SerialNumber, scan:AdminURI and scan:IconURI elements, so you can redact those and send this modified version over to me.

[rw-django-fan-2020]

Im sorry. I forgot to send you the error message.

ScannerCapabilitiesMalformed(content=<?xml version="1.0" encoding="UTF-8"?> <scan:ScannerCapabilities xmlns:scan="http://schemas.hp.com/imaging/escl/2011/05/03" xmlns:pwg="http://www.pwg.org/schemas/2010/12/sm" xmlns:dest="http://schemas.hp.com/imaging/destination/2011/06/06" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://schemas.hp.com/imaging/escl/2011/05/03 ../../schemas/eSCL.xsd"> <pwg:Version>2.63</pwg:Version> <pwg:MakeAndModel>DS-940DW</pwg:MakeAndModel> <pwg:SerialNumber>XXXXX</pwg:SerialNumber> <scan:UUID>XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX</scan:UUID> <scan:IconURI>none</scan:IconURI> <scan:AdminURI>http://HOSTNAME.local./</scan:AdminURI> <scan:Adf> <scan:AdfSimplexInputCaps> <scan:MinWidth>32</scan:MinWidth> <scan:MaxWidth>2550</scan:MaxWidth> <scan:MinHeight>32</scan:MinHeight> <scan:MaxHeight>36600</scan:MaxHeight> <scan:MinPageWidth>600</scan:MinPageWidth> <scan:MinPageHeight>870</scan:MinPageHeight> <scan:MaxScanRegions>1</scan:MaxScanRegions> <scan:SettingProfiles> <scan:SettingProfile> <scan:ColorModes> <scan:ColorMode>Grayscale8</scan:ColorMode> <scan:ColorMode>RGB24</scan:ColorMode> <scan:ColorMode>BlackAndWhite1</scan:ColorMode> <scan:ColorMode>scan:AutoColorDetection</scan:ColorMode> </scan:ColorModes> <scan:ContentTypes> <pwg:ContentType>Photo</pwg:ContentType> <pwg:ContentType>Text</pwg:ContentType> <pwg:ContentType>TextAndPhoto</pwg:ContentType> </scan:ContentTypes> <scan:DocumentFormats> <pwg:DocumentFormat>image/jpeg</pwg:DocumentFormat> <pwg:DocumentFormat>application/octet-stream</pwg:DocumentFormat> <pwg:DocumentFormat>application/pdf</pwg:DocumentFormat> <scan:DocumentFormatExt>image/jpeg</scan:DocumentFormatExt> <scan:DocumentFormatExt>application/octet-stream</scan:DocumentFormatExt> <scan:DocumentFormatExt>application/pdf</scan:DocumentFormatExt> </scan:DocumentFormats> <scan:SupportedResolutions> <scan:DiscreteResolutions> <scan:DiscreteResolution><scan:XResolution>100</scan:XResolution><scan:YResolution>100</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>150</scan:XResolution><scan:YResolution>150</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>200</scan:XResolution><scan:YResolution>200</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>300</scan:XResolution><scan:YResolution>300</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>400</scan:XResolution><scan:YResolution>400</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>600</scan:XResolution><scan:YResolution>600</scan:YResolution></scan:DiscreteResolution> </scan:DiscreteResolutions> </scan:SupportedResolutions> <scan:ColorSpaces> <scan:ColorSpace>YCC</scan:ColorSpace> <scan:ColorSpace>RGB</scan:ColorSpace> <scan:ColorSpace scan:default="true">sRGB</scan:ColorSpace> </scan:ColorSpaces> <scan:CcdChannels> <scan:CcdChannel>NTSC</scan:CcdChannel> <scan:CcdChannel>GrayCcd</scan:CcdChannel> <scan:CcdChannel scan:default="true">GrayCcdEmulated</scan:CcdChannel> <scan:CcdChannel>Red</scan:CcdChannel> <scan:CcdChannel>Green</scan:CcdChannel> </scan:CcdChannels> <scan:BinaryRenderings> <scan:BinaryRendering>Threshold</scan:BinaryRendering> </scan:BinaryRenderings> </scan:SettingProfile> </scan:SettingProfiles> <scan:SupportedIntents> <scan:Intent>Document</scan:Intent> <scan:Intent>Photo</scan:Intent> <scan:Intent>Preview</scan:Intent> <scan:Intent>TextAndGraphic</scan:Intent> </scan:SupportedIntents> <scan:BlackBackgroundSelectable>true</scan:BlackBackgroundSelectable> <scan:SupportedBackgroundLabColor> <scan:L><scan:Min>0.0</scan:Min><scan:Max>100.0</scan:Max><scan:Normal>25.0</scan:Normal><scan:Step>1.0</scan:Step></scan:L> <scan:a><scan:Min>0.0</scan:Min><scan:Max>255.0</scan:Max><scan:Normal>63.0</scan:Normal><scan:Step>1.0</scan:Step></scan:a> <scan:b><scan:Min>0.0</scan:Min><scan:Max>255.0</scan:Max><scan:Normal>63.0</scan:Normal><scan:Step>1.0</scan:Step></scan:b> </scan:SupportedBackgroundLabColor> <scan:MaxOpticalXResolution>600</scan:MaxOpticalXResolution> <scan:MaxOpticalYResolution>600</scan:MaxOpticalYResolution> </scan:AdfSimplexInputCaps> <scan:AdfDuplexInputCaps> <scan:MinWidth>32</scan:MinWidth> <scan:MaxWidth>2550</scan:MaxWidth> <scan:MinHeight>32</scan:MinHeight> <scan:MaxHeight>4200</scan:MaxHeight> <scan:MinPageWidth>600</scan:MinPageWidth> <scan:MinPageHeight>870</scan:MinPageHeight> <scan:MaxScanRegions>1</scan:MaxScanRegions> <scan:SettingProfiles> <scan:SettingProfile> <scan:ColorModes> <scan:ColorMode>Grayscale8</scan:ColorMode> <scan:ColorMode>RGB24</scan:ColorMode> <scan:ColorMode>BlackAndWhite1</scan:ColorMode> <scan:ColorMode>scan:AutoColorDetection</scan:ColorMode> </scan:ColorModes> <scan:ContentTypes> <pwg:ContentType>Photo</pwg:ContentType> <pwg:ContentType>Text</pwg:ContentType> <pwg:ContentType>TextAndPhoto</pwg:ContentType> </scan:ContentTypes> <scan:DocumentFormats> <pwg:DocumentFormat>image/jpeg</pwg:DocumentFormat> <pwg:DocumentFormat>application/octet-stream</pwg:DocumentFormat> <pwg:DocumentFormat>application/pdf</pwg:DocumentFormat> <scan:DocumentFormatExt>image/jpeg</scan:DocumentFormatExt> <scan:DocumentFormatExt>application/octet-stream</scan:DocumentFormatExt> <scan:DocumentFormatExt>application/pdf</scan:DocumentFormatExt> </scan:DocumentFormats> <scan:SupportedResolutions> <scan:DiscreteResolutions> <scan:DiscreteResolution><scan:XResolution>100</scan:XResolution><scan:YResolution>100</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>150</scan:XResolution><scan:YResolution>150</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>200</scan:XResolution><scan:YResolution>200</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>300</scan:XResolution><scan:YResolution>300</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>400</scan:XResolution><scan:YResolution>400</scan:YResolution></scan:DiscreteResolution> <scan:DiscreteResolution><scan:XResolution>600</scan:XResolution><scan:YResolution>600</scan:YResolution></scan:DiscreteResolution> </scan:DiscreteResolutions> </scan:SupportedResolutions> <scan:ColorSpaces> <scan:ColorSpace>YCC</scan:ColorSpace> <scan:ColorSpace>RGB</scan:ColorSpace> <scan:ColorSpace scan:default="true">sRGB</scan:ColorSpace> </scan:ColorSpaces> <scan:CcdChannels> <scan:CcdChannel>NTSC</scan:CcdChannel> <scan:CcdChannel>GrayCcd</scan:CcdChannel> <scan:CcdChannel scan:default="true">GrayCcdEmulated</scan:CcdChannel> <scan:CcdChannel>Red</scan:CcdChannel> <scan:CcdChannel>Green</scan:CcdChannel> </scan:CcdChannels> <scan:BinaryRenderings> <scan:BinaryRendering>Threshold</scan:BinaryRendering> </scan:BinaryRenderings> </scan:SettingProfile> </scan:SettingProfiles> <scan:SupportedIntents> <scan:Intent>Document</scan:Intent> <scan:Intent>Photo</scan:Intent> <scan:Intent>Preview</scan:Intent> <scan:Intent>TextAndGraphic</scan:Intent> </scan:SupportedIntents> <scan:BlackBackgroundSelectable>true</scan:BlackBackgroundSelectable> <scan:SupportedBackgroundLabColor> <scan:L><scan:Min>0.0</scan:Min><scan:Max>100.0</scan:Max><scan:Normal>25.0</scan:Normal><scan:Step>1.0</scan:Step></scan:L> <scan:a><scan:Min>0.0</scan:Min><scan:Max>255.0</scan:Max><scan:Normal>63.0</scan:Normal><scan:Step>1.0</scan:Step></scan:a> <scan:b><scan:Min>0.0</scan:Min><scan:Max>255.0</scan:Max><scan:Normal>63.0</scan:Normal><scan:Step>1.0</scan:Step></scan:b> </scan:SupportedBackgroundLabColor> <scan:MaxOpticalXResolution>600</scan:MaxOpticalXResolution> <scan:MaxOpticalYResolution>600</scan:MaxOpticalYResolution> </scan:AdfDuplexInputCaps> <scan:FeederCapacity>1</scan:FeederCapacity> <scan:Justification> <pwg:XImagePosition>Left</pwg:XImagePosition> <pwg:YImagePosition>None</pwg:YImagePosition> </scan:Justification> <scan:AdfOptions> <scan:AdfOption>DetectPaperLoaded</scan:AdfOption> <scan:AdfOption>Duplex</scan:AdfOption> <scan:AdfOption>MultipickDetection</scan:AdfOption> <scan:AdfOption>SelectSinglePage</scan:AdfOption> </scan:AdfOptions> </scan:Adf> <scan:AutoCrop>true</scan:AutoCrop> <scan:AutoExposure>true</scan:AutoExposure> <scan:BlankPageDetection>true</scan:BlankPageDetection> <scan:ThresholdSupport> <scan:Min>0</scan:Min> <scan:Max>255</scan:Max> <scan:Normal>128</scan:Normal> <scan:Step>1</scan:Step> </scan:ThresholdSupport> <scan:BlankPageSensitivitySupport> <scan:Min>0</scan:Min> <scan:Max>255</scan:Max> <scan:Normal>128</scan:Normal> <scan:Step>1</scan:Step> </scan:BlankPageSensitivitySupport> <scan:ColorSensitivitySupport> <scan:Min>0</scan:Min> <scan:Max>255</scan:Max> <scan:Normal>128</scan:Normal> <scan:Step>1</scan:Step> </scan:ColorSensitivitySupport> <scan:ColorRangeSupport> <scan:Min>0</scan:Min> <scan:Max>255</scan:Max> <scan:Normal>128</scan:Normal> <scan:Step>1</scan:Step> </scan:ColorRangeSupport> <scan:OverscanLengthSupport> <scan:Min>0</scan:Min> <scan:Max>60</scan:Max> <scan:Normal>60</scan:Normal> <scan:Step>1</scan:Step> </scan:OverscanLengthSupport> </scan:ScannerCapabilities> , exception=java.lang.IllegalArgumentException: No enum constant io.github.chrisimx.esclkt.ColorMode.scan:AutoColorDetection)

[Chrisimx]

Thank you! That is something I can work with. I've made some changes, trying to make it work (downstream ab064bc, upstream in Chrisimx/eSCLKt@1cfb5d4).

Please test if your issue is fixed with release v1.6.2 of ScanBridge.