I've worked a lot with DICOM which has plenty of warts (as expected with a 30 year old living standard), but HL7 is a bit much for me. At least FHIR and DICOMweb are considerably saner.
You haven't lived until you've tried to debug it.
The array isn't zero based. The line breaks have different characters for breaking the lines, and you get to guess which ones are doing it.
Certain characters are ok (ASKII) but when a Mac gets a nice ' into the field, all hell breaks loose. Things like "lesion at 9 o'clock" then break the system, as does Mr O'Leary. The hours spent chasing down how some failure happened are countless. Pity those working with HL7.
Healthcare is the perfect storm of layered, ossified systems created across decades + input data that's normal just often enough... that everyone thinks bounds are actually handled.
And then Mr. O'Leary checks in.
Fuzz testing tools would be great, but I haven't seen many institutions that have functional 1:1 lower environments (i.e. including all system-system integrations working in test).
Add to that the fun bits like "let's attach a whole base64 encoded PDF as a field of the hl7 message". Which honestly is not a terrible solution given you want to keep it all together, but still... It would be nice if you could attach binaries after the ASCII content.
Certain characters are ok (ASKII) but when a Mac gets a nice ' into the field, all hell breaks loose. Things like "lesion at 9 o'clock" then break the system, as does Mr O'Leary. The hours spent chasing down how some failure happened are countless. Pity those working with HL7.