starrify / scrapy-hcf

Scrapy spider middleware to use Scrapinghub's Hub Crawl Frontier as a backend for URLs

scrapy-hcf

This Scrapy spider middleware uses the HCF backend from Scrapinghub's Scrapy Cloud service to retrieve the new urls to crawl and store back the links extracted.

Installation

Install scrapy-hcf using pip:

$ pip install scrapy-hcf

Configuration

To activate this middleware it needs to be added to the SPIDER_MIDDLEWARES dict, i.e:

SPIDER_MIDDLEWARES = {
    'scrapy_hcf.HcfMiddleware': 543,
}

And the following settings need to be defined:

HS_AUTH

Scrapy Cloud API key

HS_PROJECTID

Scrapy Cloud project ID (not needed if the spider is ran on dash)

HS_FRONTIER

Frontier name.

HS_CONSUME_FROM_SLOT

Slot from where the spider will read new URLs.

Note that HS_FRONTIER and HS_CONSUME_FROM_SLOT can be overriden from inside a spider using the spider attributes hs_frontier and hs_consume_from_slot respectively.

The following optional Scrapy settings can be defined:

HS_ENDPOINT

URL to the API endpoint, i.e: http://localhost:8003. The default value is provided by the python-hubstorage package.

HS_MAX_LINKS

Number of links to be read from the HCF, the default is 1000.

HS_START_JOB_ENABLED

Enable whether to start a new job when the spider finishes. The default is False

HS_START_JOB_ON_REASON

This is a list of closing reasons, if the spider ends with any of these reasons a new job will be started for the same slot. The default is ['finished']

HS_NUMBER_OF_SLOTS

This is the number of slots that the middleware will use to store the new links. The default is 8.

Usage

The following keys can be defined in a Scrapy Request meta in order to control the behavior of the HCF middleware:

'use_hcf'

If set to True the request will be stored in the HCF.

'hcf_params'

Dictionary of parameters to be stored in the HCF with the request fingerprint

'qdata'

data to be stored along with the fingerprint in the request queue

'fdata'

data to be stored along with the fingerprint in the fingerprint set

'p'

Priority - lower priority numbers are returned first. The default is 0

The value of 'qdata' parameter could be retrieved later using response.meta['hcf_params']['qdata'].

The spider can override the default slot assignation function by setting the spider slot_callback method to a function with the following signature:

def slot_callback(request):
    ...
    return slot