Custom ONNX metadata unreadable for PaddlePaddle PIR-mode models

[Goldziher]

Summary

session.metadata().custom_keys() returns an empty list and session.metadata().custom("character") returns an empty string when loading PaddlePaddle PIR-mode exported ONNX models that contain custom metadata.

The same models loaded via Python's onnxruntime.InferenceSession correctly return the metadata through session.get_modelmeta().custom_metadata_map.

Reproduction

Model: en_PP-OCRv4_rec_infer.onnx (PaddleOCR v4 recognition model exported with PIR mode, ~7.7MB)

Rust (ort 2.0.0-rc.11, load-dynamic feature, onnxruntime 1.24.1):

let session = Session::builder()?.commit_from_file("en_PP-OCRv4_rec_infer.onnx")?;
let metadata = session.metadata()?;
println!("{:?}", metadata.custom_keys());   // prints: []
println!("{:?}", metadata.custom("character")); // prints: Some("")

Python (onnxruntime 1.21.0):

import onnxruntime as ort
session = ort.InferenceSession("en_PP-OCRv4_rec_infer.onnx")
meta = session.get_modelmeta().custom_metadata_map
print(len(meta["character"]))  # prints: 190 (correct)

Environment

• ort 2.0.0-rc.11 with load-dynamic feature
• Tested with onnxruntime 1.23.2 and 1.24.1 — same result
• macOS (aarch64) and Linux (x86_64)
• Model exported by PaddlePaddle in PIR mode (paddle2onnx)

Notes

The metadata is present in the ONNX protobuf — Python reads it fine. The issue appears to be in how ort surfaces custom metadata entries from the C API. Standard metadata fields (producer, description, etc.) read correctly; only the custom key-value map is affected.

Workaround: ship the dictionary as a separate file and load it outside the ONNX model.

[decahedron1]

Can't reproduce with this file (SHA256: 5CA59A096CF493D5FD5044B9CCC1BDEA9229FBCF656BD76040FF80A00201EE16). Could you provide the model file you're using, if it's different from that one?

[Goldziher]

Sure, here

[decahedron1]

Can't reproduce with that one either.

let session = Session::builder()?.commit_from_file(path)?;
let meta = session.metadata()?;
println!("{:?}", meta.custom_keys());
// Ok(["character"])
println!("{:?}", meta.custom("character"));
// Some("0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n:\n;\n<\n=\n>\n?\n@\nA\nB\nC\nD\nE\nF\nG\nH\nI\nJ\nK\nL\nM\nN\nO\nP\nQ\nR\nS\nT\nU\nV\nW\nX\nY\nZ\n[\n\\\n]\n^\n_\n`\na\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\no\np\nq\nr\ns\nt\nu\nv\nw\nx\ny\nz\n{\n|\n}\n~\n!\n\"\n#\n$\n%\n&\n'\n(\n)\n*\n+\n,\n-\n.\n/\n ")

[Goldziher]

Hmm. I'll check again on my end.