Frontier objects

Frontier uses 2 object types: Request and Response. They are used to represent crawling HTTP requests and responses respectively.

These classes are used by most Frontier API methods either as a parameter or as a return value depending on the method used.

Frontier also uses these objects to internally communicate between different components (middlewares and backend).

Request objects

class frontera.core.models.Request(url, method='GET', headers=None, cookies=None, meta=None)

A Request object represents an HTTP request, which is generated for seeds, extracted page links and next pages to crawl. Each one should be associated to a Response object when crawled.

Parameters:
  • url (string) – URL to send.
  • method (string) – HTTP method to use.
  • headers (dict) – dictionary of headers to send.
  • cookies (dict) – dictionary of cookies to attach to this request.
  • meta (dict) – dictionary that contains arbitrary metadata for this request.
cookies

Dictionary of cookies to attach to this request.

headers

A dictionary which contains the request headers.

meta

A dict that contains arbitrary metadata for this request. This dict is empty for new Requests, and is usually populated by different Frontera components (middlewares, etc). So the data contained in this dict depends on the components you have enabled.

method

A string representing the HTTP method in the request. This is guaranteed to be uppercase. Example: GET, POST, PUT, etc

url

A string containing the URL of this request.

Response objects

class frontera.core.models.Response(url, status_code=200, headers=None, body='', request=None)

A Response object represents an HTTP response, which is usually downloaded (by the crawler) and sent back to the frontier for processing.

Parameters:
  • url (string) – URL of this response.
  • status_code (int) – the HTTP status of the response. Defaults to 200.
  • headers (dict) – dictionary of headers to send.
  • body (dict) – the response body.
  • request (dict) – The Request object that generated this response.
body

A str containing the body of this Response.

headers

A dictionary object which contains the response headers.

meta

A shortcut to the Request.meta attribute of the Response.request object (ie. self.request.meta).

request

The Request object that generated this response.

status_code

An integer representing the HTTP status of the response. Example: 200, 404, 500.

url

A string containing the URL of the response.

Fields domain and fingerprint are added by built-in middlewares

Identifying unique objects

As frontier objects are shared between the crawler and the frontier, some mechanism to uniquely identify objects is needed. This method may vary depending on the frontier logic (in most cases due to the backend used).

By default, Frontera activates the fingerprint middleware to generate a unique fingerprint calculated from the Request.url and Response.url fields, which is added to the Request.meta and Response.meta fields respectively. You can use this middleware or implement your own method to manage frontier objects identification.

An example of a generated fingerprint for a Request object:

>>> request.url
'http://thehackernews.com'

>>> request.meta['fingerprint']
'198d99a8b2284701d6c147174cd69a37a7dea90f'

Adding additional data to objects

In most cases frontier objects can be used to represent the information needed to manage the frontier logic/policy.

Also, additional data can be stored by components using the Request.meta and Response.meta fields.

For instance the frontier domain middleware adds a domain info field for every Request.meta and Response.meta if is activated:

>>> request.url
'http://www.scrapinghub.com'

>>> request.meta['domain']
{
    "name": "scrapinghub.com",
    "netloc": "www.scrapinghub.com",
    "scheme": "http",
    "sld": "scrapinghub",
    "subdomain": "www",
    "tld": "com"
}