RFC7: add support for validator plugins

[tomkralidis]

Overview

This PR implements RFC7, adding support for validation plugin facilities in support of data validation on item transactions.

Related Issue / discussion

Additional information

RFC7: https://pygeoapi.io/development/rfc/7

Dependency policy (RFC2)

• I have ensured that this PR meets RFC2 requirements

Updates to public demo

• I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • https://github.com/geopython/demo.pygeoapi.io/blob/master/services/pygeoapi_master/local.config.yml

Contributions and licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi wilxl be compatible with the pygeoapi license guidelines at the time of contribution
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[justb4]

Very useful addition. What I don't understand: in the configuration example a Python Module path is specified like name: path.to.validator. But in plugin.py a name: Python path is defined like:

'validator': {
        'GeoJSON': 'pygeoapi.validator.geojson.GeoJSONValidator'

Maybe I did not understand, or is the idea one can also refer by name, like GeoJSON, to a pre-configured validator in plugin.py?

[tomkralidis]

Very useful addition. What I don't understand: in the configuration example a Python Module path is specified like name: path.to.validator. But in plugin.py a name: Python path is defined like:

'validator': {
        'GeoJSON': 'pygeoapi.validator.geojson.GeoJSONValidator'

Maybe I did not understand, or is the idea one can also refer by name, like GeoJSON, to a pre-configured validator in plugin.py?

Yes, validators that are shipped "on board" with pygeoapi can be referrred to by a shortname (i.e. GeoJSON), which evaluates to the dotted path, in configuration. Configuration can also explicitly point to a dotted path just the same; the result of both approaches is a dotted path/class that is instantiated accordingly.

[justb4]

Very useful addition. What I don't understand: in the configuration example a Python Module path is specified like name: path.to.validator. But in plugin.py a name: Python path is defined like:

'validator': {
        'GeoJSON': 'pygeoapi.validator.geojson.GeoJSONValidator'

Maybe I did not understand, or is the idea one can also refer by name, like GeoJSON, to a pre-configured validator in plugin.py?

Yes, validators that are shipped "on board" with pygeoapi can be referrred to by a shortname (i.e. GeoJSON), which evaluates to the dotted path, in configuration. Configuration can also explicitly point to a dotted path just the same; the result of both approaches is a dotted path/class that is instantiated accordingly.

Ok, suggestion to add this to the documentation, which only mentions/suggests "module path".

[tomkralidis]

Very useful addition. What I don't understand: in the configuration example a Python Module path is specified like name: path.to.validator. But in plugin.py a name: Python path is defined like:

'validator': {
        'GeoJSON': 'pygeoapi.validator.geojson.GeoJSONValidator'

Maybe I did not understand, or is the idea one can also refer by name, like GeoJSON, to a pre-configured validator in plugin.py?

Yes, validators that are shipped "on board" with pygeoapi can be referrred to by a shortname (i.e. GeoJSON), which evaluates to the dotted path, in configuration. Configuration can also explicitly point to a dotted path just the same; the result of both approaches is a dotted path/class that is instantiated accordingly.

Ok, suggestion to add this to the documentation, which only mentions/suggests "module path".

+1, docs updated.