WAF timestamp extract optimization

[rshewitt]

User Story

In order to efficiently compare waf records, datagov wants to incorporate the timestamp of the record(s).

Acceptance Criteria

[ACs should be clearly demoable/verifiable whenever possible. Try specifying them using BDD.]

• [ ] GIVEN harvest.py
  AND a waf source url WHEN the waf traversal occurs
  THEN the timestamp of the record should be included in the Record instance
  AND used in the comparison function

Background

• we are responsible for harvesting records from a waf
• in order to be more efficient with our comparison we want to consider the timestamp of the files. the idea is to reduce the work required for a given waf source by only downloading what we need which means fewer network calls and fewer opportunities for something wrong to happen.
• this ticket assumes a date/time stamp is included on DB harvest record read

Security Considerations (required)

[Any security concerns that might be implicated in the change. "None" is OK, just be explicit here!]

Sketch

• update traverse_waf to get the timestamp of the files
• update compare to use the waf record timestamp instead of the hash
• update order of functions in extract and compare
  • traverse_waf
    • get all record urls
  • compare
    • if the source is a waf then we want to compare the timestamp of the records not the hash
    • label the file url to indicate if it needs to be downloaded
  • download_waf
    • skip if file url doesn't need to be downloaded

[FuhuXia]

It could be a challenge to scrap timestamp out of a WAF list since different web servers (or version) have different ways to show timestamps. Here is how ckanext-spatial does it.