C-Find doesn't return private tag value if value is too long

[fehermate]

Hi all,
I've been struggling with receiving Private Tag Data when the value of that private tag is too long.
I have the following function (simplified for this discussion):

def c_find_func():
    ae = AE(ae_title=MY_AET)

    ae.add_requested_context(StudyRootQueryRetrieveInformationModelFind, transfer_syntax=ExplicitVRLittleEndian)

    assoc = ae.associate(TARGET_IP, TARGET_PORT, ae_title=TARGET_AET)
    
    dataset = Dataset()
    dataset.QueryRetrieveLevel = "IMAGE"
    dataset.SeriesInstanceUID = "UID"
    block = dataset.private_block(PRIVATE_GROUP, PRIVATE_CREATOR, create=True)
    block.add_new(PRIVATE_TAG_OFFSET_1, "UT", "")
    block.add_new(PRIVATE_TAG_OFFSET_2, "LT", "")

    responses = assoc.send_c_find(dataset, query_model=StudyRootQueryRetrieveInformationModelFind)
    
    datasets = [ds for (status, ds) in responses if f"{status.Status:04X}" != "0000"]

    assoc.release()
    return datasets

The response contains all the tags you'd expect it to contain:

(0008, 0005) Specific Character Set              CS: 'ISO_IR 100'
(0008, 0052) Query/Retrieve Level                CS: 'IMAGE'
(0008, 0054) Retrieve AE Title                   AE: 'ORTHANC'
(0020, 000e) Series Instance UID                 UI: MY_UID
(gggg, eexx) Private Creator                     LO: 'PRIVATE_CREATOR'
(gggg, xxyy) Private tag data                    UN: None
(gggg, xxzz) Private tag data                    UN: b'D2'

But as you can see, the first private tag doesn't contain any value (and the VR is also not known in the response, even though it's available in the DICOM file), the second one has the correct value, but again without the proper VR.

When creating the DICOM file that contains these private tags, it's done like this:

...
block = dataset.private_block(PRIVATE_TAG_GROUP, PRIVATE_TAG_CREATOR, create=True)
dataset.add_new(Tag(gggg, xxyy), "UT", json.dumps(MY_DICT))
dataset.add_new(Tag(gggg, xxzz), "LT", "D2")
...

(The tag's are defined properly, I'm just anonymizing the actual values.)

The transfer syntax is set correctly on the "creation" side, and if I intercept the Dataset in some other DICOM server when sending C-Store, all the data is available correctly there, so it seem that there's an issue on the C-Find side.

Any ideas?
Thanks in advance for any responses/ideas.

[scaramallion]

What transfer syntax are you using?

[fehermate]

Explicit VR Little Endian, both when creating and when reading (as detailed above):

...
ae.add_requested_context(StudyRootQueryRetrieveInformationModelFind, transfer_syntax=ExplicitVRLittleEndian)
...

But I'm facing the same issue when trying to do the same with a file not created by me but it follows same format.

[scaramallion]

Have you tried writing the query result dataset directly to file (i.e. without first decoding it) and checking it in a hex editor (or even just using DCMTK's dcmdump as a sanity check) to see if the value is correct? I'm not really sure where the problem is occurring: the peer, pynetdicom or pydicom's decoding.