Accessing CDS API from a WASM/JupyterLite context

[MMesch]

What happened?

Hi all,

I'm trying to access ECMWF data from JupyterLite in a WASM context (xpython kernel not pyodide but I don't think that matters). Being able to do so would enable lots of use cases, greatly lowering barriers to access and analyze that data. We are particularly interested in demonstrating how to display that data in JupyterGIS.

I didn't manage to do so for now because

client.retrieve(
    "reanalysis-era5-single-levels",
    {
        "product_type": "reanalysis",
        "variable": "2m_temperature",
        "year": "2023",
        "month": "07",
        "day": "15",
        "time": "12:00",
        "area": [60, -15, 35, 25],  # Europe: N, W, S, E
        "format": "netcdf",
    },
    str(nc_file)
)

on url="https://cds.climate.copernicus.eu/api",

fails with

Access to XMLHttpRequest at '' from origin '' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status

It seems that it is mostly due to the CORS policy although I am not fully sure. If this is indeed the case, is it possible to relax that policy and allow cross-origin requests?

What are the steps to reproduce the bug?

Deploy JupyterLite with cdsapi (you can use notebook.link if you don't want to do it yourself, or locally). Then run:

client = cdsapi.Client(
    url="https://cds.climate.copernicus.eu/api",
    key="xxx",
    verify=True
)

nc_file = output_dir / "temperature.nc"
tif_file = output_dir / "temperature.tif"

client.retrieve(
    "reanalysis-era5-single-levels",
    {
        "product_type": "reanalysis",
        "variable": "2m_temperature",
        "year": "2023",
        "month": "07",
        "day": "15",
        "time": "12:00",
        "area": [60, -15, 35, 25],  # Europe: N, W, S, E
        "format": "netcdf",
    },
    str(nc_file)
)

Version

see below

Platform (OS and architecture)

emscription / WASM (xpython)

Relevant log output

"cdsapi-0.7.7-py2.py3-none-any.whl": {
      "url": "https://files.pythonhosted.org/packages/4f/f4/4a65460d5cb6784128019fd707a87993f378db25e796eba01400a0903f62/cdsapi-0.7.7-py2.py3-none-any.whl",
      "hash": {
        "md5": "46183ae020940acdcb7a985b102c8dcb",
        "sha256": "384c1658572d6dc53f4111f6dd46fcdfe6fea54a688af9756d71f6fe9118b66d"
      },
      "name": "cdsapi",
      "size": 12293,
      "version": "0.7.7",
      "registry": "PyPi"
    },
    "ecmwf_datastores_client-0.4.1-py3-none-any.whl": {
      "url": "https://files.pythonhosted.org/packages/a3/cf/7feb3222d770566ca9eaf0bf6922745fadd1ed7ab11832520063a515c240/ecmwf_datastores_client-0.4.1-py3-none-any.whl",
      "hash": {
        "md5": "291634c20afffb2cb303aeb37925e9ca",
        "sha256": "a14515a892889a602ec2c81b15ec81d048932ca05480f12c778136028b6230a3"
      },
      "name": "ecmwf-datastores-client",
      "size": 29094,
      "version": "0.4.1",
      "registry": "PyPi"
    }

Accompanying data

No response

Organisation

No response