Fix confusion between buffer size and variable field size#702
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Enet4 merged 1 commit intoEnet4:masterfrom Oct 11, 2025
Merged
Fix confusion between buffer size and variable field size#702Enet4 merged 1 commit intoEnet4:masterfrom
Enet4 merged 1 commit intoEnet4:masterfrom
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According to the standard PS3.8 Annex D tables D.1-1 and D.1-2 <https://dicom.nema.org/medical/dicom/2025c/output/chtml/part08/chapter_D.html>, the maximum PDU length that the peers communicate to each other during association establishment, applies to "the variable field of the P-DATA-TF PDUs". The "variable field" refers to the bytes starting on the 7th, according to PS3.8 section 9.3.5 <https://dicom.nema.org/medical/dicom/2025c/output/chtml/part08/sect_9.3.5.html>, and thus does not include the header. The code was interpreting it as a mix of the correct length (especially in reader.rs and writer.rs), the length including the PDU header (especially in server.rs and client.rs) and the length including the PDU and the PDV header (especially in pdata.rs). This attempts to sort out the mess and uniformly use the same interpretation as the one the standard uses. A lot of it has to do with buffer size allocation: the buffers need room for maximum PDU size + the header.
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Sounds great! Thank you again for tracking down these issues with dicom_ul!
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The code is using max_pdu_size as both a limit for the variable field of the PDU (i.e. excluding the PDU header) and as a limit for the PDU as a whole (i.e. including the PDU header). The latter is wrong and affects send() and receive() in both server and client (see the commit message for full citations). As a consequence:
In the belief that the std library might allocate more than necessary when crossing a size that is a power of 2, I've reduced the constants
DEFAULT_MAX_PDU,MINIMUM_PDU_SIZEandLARGE_PDU_SIZEby 6 (the size of the PDU header) so that the full PDU fits within a buffer with a length that is a power of two.