[Feature] Handle Accept header for JSON/XML response in WPS 2.0

[fmigneault]

Context

Given that WPS 2.0 supports JSON response, we should handle a provided Accept=application/json header on the WPS route (eg: /ows/wps by default). By default this route returns XML.
Some code to do the detection of WPS version/format was introduced in f0cd31e but is still unused.
This is now functional

GET /ows/wps?service=wps&request=describeprocess&identifier=jsonarray2netcdf
Accept: application/json

See returned response (proper OGCAPI - Processes content)

{
    "id": "jsonarray2netcdf",
    "title": "JSON array to NetCDF",
    "version": "1.1",
    "description": "Extracts and fetches NetCDF files from a JSON file containing an URL string array, and provides them on the output directory.",
    "keywords": [
        "builtin"
    ],
    "metadata": [],
    "inputs": {
        "input": {
            "title": "input",
            "minOccurs": 1,
            "maxOccurs": 1,
            "formats": [
                {
                    "default": true,
                    "mediaType": "application/json"
                }
            ]
        }
    },
    "outputs": {
        "output": {
            "title": "output",
            "formats": [
                {
                    "default": true,
                    "mediaType": "application/x-netcdf"
                }
            ]
        }
    },
    "visibility": "public",
    "jobControlOptions": [
        "async-execute"
    ],
    "outputTransmission": [
        "reference"
    ],
    "processDescriptionURL": "http://localhost:4002/processes/jsonarray2netcdf",
    "processEndpointWPS1": "http://localhost:4002/ows/wps",
    "executeEndpoint": "http://localhost:4002/processes/jsonarray2netcdf/jobs",
    "links": [
        {
            "type": "application/json",
            "title": "Current process description.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes/jsonarray2netcdf",
            "rel": "self"
        },
        {
            "type": "application/json",
            "title": "Process definition.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes/jsonarray2netcdf",
            "rel": "process-meta"
        },
        {
            "type": "application/json",
            "title": "Process execution endpoint for job submission.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes/jsonarray2netcdf/execution",
            "rel": "http://www.opengis.net/def/rel/ogc/1.0/execute"
        },
        {
            "type": "application/json",
            "title": "List of registered processes.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes",
            "rel": "http://www.opengis.net/def/rel/ogc/1.0/processes"
        },
        {
            "type": "application/json",
            "title": "List of job executions corresponding to this process.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes/jsonarray2netcdf/jobs",
            "rel": "http://www.opengis.net/def/rel/ogc/1.0/job-list"
        },
        {
            "type": "application/json",
            "title": "List of processes registered under the service.",
            "hreflang": "en-CA",
            "href": "http://localhost:4002/processes",
            "rel": "up"
        }
    ]
}

If version is WPS 1.x, the only supported format is XML. This should also be the default return on /ows/wps route if no version=... parameter was provided in the URL.
Default behaviour is to provide the corresponding XML into JSON format, regardless of version:

GET /ows/wps?service=wps&request=describeprocess&identifier=jsonarray2netcdf&f=json

See produced response (JSON PyWPS content)

{
  "pywps_version": "4.5.0",
  "processes": [
    {
      "class": "weaver.processes.wps_package:WpsPackage",
      "uuid": "None",
      "workdir": null,
      "version": "1.1",
      "identifier": "jsonarray2netcdf",
      "title": "JSON array to NetCDF",
      "abstract": "Extracts and fetches NetCDF files from a JSON file containing an URL string array, and provides them on the output directory.",
      "keywords": [
        "builtin"
      ],
      "metadata": [],
      "inputs": [
        {
          "identifier": "input",
          "title": "input",
          "abstract": "",
          "keywords": [],
          "metadata": [],
          "type": "complex",
          "data_format": {
            "mime_type": "application/json",
            "encoding": "",
            "schema": "",
            "extension": ".json"
          },
          "asreference": false,
          "supported_formats": [
            {
              "mime_type": "application/json",
              "encoding": "",
              "schema": "",
              "extension": ".json"
            }
          ],
          "workdir": null,
          "mode": 1,
          "min_occurs": 1,
          "max_occurs": 1,
          "translations": null,
          "mimetype": "application/json"
        }
      ],
      "outputs": [
        {
          "identifier": "output",
          "title": "output",
          "abstract": "",
          "keywords": [],
          "type": "complex",
          "supported_formats": [
            {
              "mime_type": "application/x-netcdf",
              "encoding": "",
              "schema": "",
              "extension": ".nc"
            }
          ],
          "asreference": false,
          "data_format": {
            "mime_type": "application/x-netcdf",
            "encoding": "",
            "schema": "",
            "extension": ".nc"
          },
          "file": null,
          "workdir": null,
          "mode": 1,
          "min_occurs": 1,
          "max_occurs": 1,
          "translations": null,
          "mimetype": "application/x-netcdf"
        }
      ],
      "store_supported": "true",
      "status_supported": "true",
      "profile": [],
      "translations": null
    }
  ],
  "language": "fr-CA"
}

TODO

• redirect a WPS-REST (3.0) call (eg: /processes, /processes/{id}, etc.) to their corresponding WPS 2.0 /ows/wps request if any from (Accept: application/xml, Accept: text/xml, f=xml, format=xml) is provided (inverse of what is currently functional).
  Use dict2xml (or similar) to provide an XML body corresponding to the original JSON.
• handle other variation format= as alias of f= on OWS endpoint.
• convert the PyWPS JSON to an actual (valid) OGC API - Processes representation rather than plain XML->JSON conversion.
• Employ this tween definition to detect Accept header / format query and raise HTTP 422 if not acceptable :
  https://github.com/Ouranosinc/Magpie/blob/f67a134d52ec8f3951cb1a08a07c1c5beb518882/magpie/api/generic.py#L106-L202