ckanext-iiif

IIIF for CKAN

Overview

This extension enables IIIF functionality for CKAN by implementing the Presentation API. Currently, this includes a single manifest builder for records, but through the IIIIF interface you can extend the builders to include other IIIF resources.

Installation

Path variables used below:

• $INSTALL_FOLDER (i.e. where CKAN is installed), e.g. /usr/lib/ckan/default
• $CONFIG_FILE, e.g. /etc/ckan/default/development.ini

Installing from PyPI

pip install ckanext-iiif

Installing from source

1. Clone the repository into the src folder:

   cd $INSTALL_FOLDER/src
   git clone https://github.com/NaturalHistoryMuseum/ckanext-iiif.git

2. Activate the virtual env:

   . $INSTALL_FOLDER/bin/activate

3. Install via pip:

   pip install $INSTALL_FOLDER/src/ckanext-iiif

Installing in editable mode

Installing from a pyproject.toml in editable mode (i.e. pip install -e) requires setuptools>=64; however, CKAN 2.9 requires setuptools==44.1.0. See our CKAN fork for a version of v2.9 that uses an updated setuptools if this functionality is something you need.

Post-install setup

1. Add 'iiif' to the list of plugins in your $CONFIG_FILE:

   ckan.plugins = ... iiif

Configuration

There are no configuration options for this extension.

Usage

This extension's main function is provide a standard endpoint and action to create IIIF resources. These IIIF resources could be based on whatever you like - a record, a resource, a whole dataset etc.

Presentation API IIIF resources can be accessed via either the /iiif/<identifier> endpoint or the build_iiif_resource action where the identifier is passed in the data dict in the key "identifier". When this occurs the identifier is matched against any of the registered IIIF resource builders and if a match is found, the resource is returned. Identifiers can be built if the builder ID is known along with the necessary parameters by using the build_iiif_identifier action.

Record Manifest Builder

By default, the only IIIF resource this extension can build is record manifests. This requires the record_show action to be available from the ckanext-nhm extension (there is an open issue to move this action to a different extension, most likely ckanext-versioned-datastore) .

To build a record manifest you must provide the appropriate identifier, which must be of the format resource/<resource_id>/record/<record_id>, for example: resource/afea211d-1b3d-49ad-9d15-17f0de368967/record/429. This example identifies the record with ID 429 from the resource with ID afea211d-1b3d-49ad-9d15-17f0de368967. If the record and the resource can be found, and images can be found on the record, then a manifest is returned. If any of these conditions fail, the action returns None and the endpoint returns 404.

The images are detected in the record by looking for the _image_field extra on the resource. This should define the field name in the record where images can be found. The value associated with this image field in the record can be:

• a string (should be a URL)
• a list of strings (each element should be a URL)
• a string containing several URLs separated by a delimiter (this should be defined on the resource using the _image_delimiter extra)
• a list of dicts (the URL is extracted by looking for an identifier field within each dict)

To fill out the values in the manifest, the builder pulls out fields as specified by more resource level extras or by falling back to a default value. These are:

• "label" - attempts to use _title_field extra but falls back to record ID
• "rights" - attempts to use _image_licence extra but falls back to cc-by

The "metadata" field in the manifest is populated using the fields and values in the record data itself.

Adding a Custom Builder

To add a custom builder all you have to do is implement the IIIIF interface in your extension plugin. For example:

import ckan.plugins as plugins
from typing import Optional, Callable
from typing import OrderedDict

from ckanext.iiif.builders.abc import IIIFResourceBuilder
from ckanext.iiif.interfaces import IIIIF


class MyBuilder(IIIFResourceBuilder):

    def match_and_build(self, identifier: str) -> Optional[dict]:
        ...

    def build_identifier(self, *args, **kwargs) -> str:
        ...


class MyExtension(plugins.SingletonPlugin):
    plugins.implements(IIIIF)

    def register_iiif_builders(self, builders: OrderedDict[str, IIIFResourceBuilder]):
        builders["my_builder"]: MyBuilder()

When a request is made to build a IIIF resource, each of the registered builders is called in turn with the identifier. This means that the builders need to both match the identifier to confirm it matches its pattern or meets its criteria, and generate the manifest.

The builders should:

• Return None if the identifier doesn't match the builders requirements. When this happens, the logic continues and tries the next registered builder function.
• Raise a ckanext.iiif.builders.utils.IIIFBuildError if the identifier matched but the manifest couldn't be generated for any reason. This will stop the logic from checking any other builders for matches and return None to the caller.
• Raise any other type of Exception if an unexpected error occurred during matching or processing. This will be propagated to the caller.

Testing

There is a Docker compose configuration available in this repository to make it easier to run tests. The ckan image uses the Dockerfile in the docker/ folder.

To run the tests against ckan 2.9.x on Python3:

1. Build the required images:

   docker compose build

2. Then run the tests. The root of the repository is mounted into the ckan container as a volume by the Docker compose configuration, so you should only need to rebuild the ckan image if you change the extension's dependencies.

   docker compose run ckan