Feature issue #53 rest db

[grantmacken]

issue #53
enables rest interaction with xqerl db collections and XDM items

Uses cowboy rest handler in conjunction with xQuery main modules,
to allow CRUD ops on xqerl database collections and items.

• POST collection URI with request body and ''content-type' header and optional Slug creates a resource
• GET collection URI with accept header retrieves lists collection resources
• GET resource URI with accept header retrieves serialized XDM item
• PUT resource URI with content-type header and request body updates resource
• DELETE resource URI deletes resource
• HEAD resource URI, with accept header determines resource available status and provide content-length header
• HEAD collection URI, with accept header determine if collection available.and provide content-length header
• OPTIONS collection URI, allowable methods for collection.

checks: Curl is used to to check correct responses to HTTP requests
https://github.com/grantmacken/xqerl/runs/5169676947?check_suite_focus=true

Content negotiation
GET and HEAD request can return different resource representations depending on Accept Header
example: retrieving a list of collection items

curl -s  -H  'Accept: application/xml' http://localhost:8081/db/example.com/docs
# Returns  list as XML (serialised XDM document-node  )
curl -s  -H  'Accept: application/json' http://localhost:8081/db/example.com/docs
# Returns list as json (serialized XDM array)
curl -s  -H  'Accept: text/plain' http://localhost:8081/db/example.com/docs
# Returns list as text

HEAD request can be used to check for db collection or resource item availability.
HEAD request provides content-length header so you can determine resource size

DELETE requests only are available for items not collections as
deleting collections looks a bit dangerous but I can try to enable if requested

POSTS when posting requests MUST use a content-type header
at the moment only XML or JSON data types are accepted.
If there is a SLUG header then that will be used as the item name
otherwise the item name is generated as a uuid

curl -s  \
--header  'content-type: application/xml'  \
--header 'Slug: my-doc.xml'  \
-d '<data>test</data>'
http://localhost:8081/db/example.com/docs

The POST 'content-type' XML or JSON limitation is not set in stone and can be extended later.
e.g. when posting CSV, this can be stored as XDM array item.
then you might want to retrieve the resource using an Accept Header as text, JSON array or XML

[zadean]

Very cool!! Thank you for this @grantmacken!