Downloader Middlewares

class kingfisher_scrapy.downloadermiddlewares.ParaguayAuthMiddleware(spider)

Downloader middleware that manages API authentication for Paraguay scrapers.

Both DNCP (procurement authority) and Hacienda (finance ministry) use an authentication protocol based on OAuth 2.

This middleware helps us to manage the protocol, which consists on acquiring an access token every x minutes (usually 15) and sending the token on each request. The acquisition method of the token is delegated to the spider, since each publisher has their own credentials and requirements.

Apparently, a Downloader Middleware is the best place to set HTTP Request Headers (see https://docs.scrapy.org/en/latest/topics/architecture.html), but it’s not enough for this case :(. Tokens should be generated and assigned just before sending a request, but Scrapy does not provide any way to do this, which in turn means that sometimes we accidentally send expired tokens. For now, the issue seems to be avoided by setting the number of concurrent requests to 1, at cost of download speed.

class Paraguay:
    name = 'paraguay'

    # ParaguayAuthMiddleware
    access_token = None
    access_token_scheduled_at = None
    # The maximum age is less than the API's limit, since we don't precisely control Scrapy's scheduler.
    access_token_maximum_age = 14 * 60
    access_token_request_failed = False
    requests_backlog = []

    def build_access_token_request(self):
        self.access_token_scheduled_at = datetime.now()

        return scrapy.Request("https://example.com")

classmethod from_crawler(crawler)

process_request(request, spider)

process_response(request, response, spider)

add_request_to_backlog_and_build_access_token_request(spider, request)

class kingfisher_scrapy.downloadermiddlewares.OpenOppsAuthMiddleware

Downloader middleware that intercepts requests and adds the token for OpenOpps scraper.

static process_request(request, spider)

class kingfisher_scrapy.downloadermiddlewares.DelayedRequestMiddleware

Downloader middleware that allows for delaying a request by a set ‘wait_time’ number of seconds.

A delayed request is useful when an API fails and works again after waiting a few minutes.

process_request(request, spider)