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require 'nokogiri'
require 'date'
module Agents
class WebsiteAgent < Agent
include WebRequestConcern
default_schedule "every_12h"
UNIQUENESS_LOOK_BACK = 200
UNIQUENESS_FACTOR = 3
description <<-MD
The WebsiteAgent scrapes a website, XML document, or JSON feed and creates Events based on the results.
Specify a `url` and select a `mode` for when to create Events based on the scraped data, either `all` or `on_change`.
`url` can be a single url, or an array of urls (for example, for multiple pages with the exact same structure but different content to scrape)
The `type` value can be `xml`, `html`, `json`, or `text`.
To tell the Agent how to parse the content, specify `extract` as a hash with keys naming the extractions and values of hashes.
When parsing HTML or XML, these sub-hashes specify how each extraction should be done. The Agent first selects a node set from the document for each extraction key by evaluating either a CSS selector in `css` or an XPath expression in `xpath`. It then evaluates an XPath expression in `value` on each node in the node set, converting the result into string. Here's an example:
"extract": {
"url": { "css": "#comic img", "value": "@src" },
"title": { "css": "#comic img", "value": "@title" },
"body_text": { "css": "div.main", "value": ".//text()" }
}
"@_attr_" is the XPath expression to extract the value of an attribute named _attr_ from a node, and ".//text()" is to extract all the enclosed texts. You can also use [XPath functions](http://www.w3.org/TR/xpath/#section-String-Functions) like `normalize-space` to strip and squeeze whitespace, `substring-after` to extract part of a text, and `translate` to remove comma from a formatted number, etc. Note that these functions take a string, not a node set, so what you may think would be written as `normalize-space(.//text())` should actually be `normalize-space(.)`.
When parsing JSON, these sub-hashes specify [JSONPaths](http://goessner.net/articles/JsonPath/) to the values that you care about. For example:
"extract": {
"title": { "path": "results.data[*].title" },
"description": { "path": "results.data[*].description" }
}
When parsing text, each sub-hash should contain a `regexp` and `index`. Output text is matched against the regular expression repeatedly from the beginning through to the end, collecting a captured group specified by `index` in each match. Each index should be either an integer or a string name which corresponds to <code>(?<<em>name</em>>...)</code>. For example, to parse lines of <code><em>word</em>: <em>definition</em></code>, the following should work:
"extract": {
"word": { "regexp": "^(.+?): (.+)$", index: 1 },
"definition": { "regexp": "^(.+?): (.+)$", index: 2 }
}
Or if you prefer names to numbers for index:
"extract": {
"word": { "regexp": "^(?<word>.+?): (?<definition>.+)$", index: 'word' },
"definition": { "regexp": "^(?<word>.+?): (?<definition>.+)$", index: 'definition' }
}
To extract the whole content as one event:
"extract": {
"content": { "regexp": "\A(?m:.)*\z", index: 0 }
}
Beware that `.` does not match the newline character (LF) unless the `m` flag is in effect, and `^`/`$` basically match every line beginning/end. See [this document](http://ruby-doc.org/core-#{RUBY_VERSION}/doc/regexp_rdoc.html) to learn the regular expression variant used in this service.
Note that for all of the formats, whatever you extract MUST have the same number of matches for each extractor. E.g., if you're extracting rows, all extractors must match all rows. For generating CSS selectors, something like [SelectorGadget](http://selectorgadget.com) may be helpful.
Can be configured to use HTTP basic auth by including the `basic_auth` parameter with `"username:password"`, or `["username", "password"]`.
Set `expected_update_period_in_days` to the maximum amount of time that you'd expect to pass between Events being created by this Agent. This is only used to set the "working" status.
Set `uniqueness_look_back` to limit the number of events checked for uniqueness (typically for performance). This defaults to the larger of #{UNIQUENESS_LOOK_BACK} or #{UNIQUENESS_FACTOR}x the number of detected received results.
Set `force_encoding` to an encoding name if the website does not return a Content-Type header with a proper charset.
Set `user_agent` to a custom User-Agent name if the website does not like the default value (`#{default_user_agent}`).
The `headers` field is optional. When present, it should be a hash of headers to send with the request.
Set `disable_ssl_verification` to `true` to disable ssl verification.
The WebsiteAgent can also scrape based on incoming events. It will scrape the url contained in the `url` key of the incoming event payload. If you specify `merge` as the mode, it will retain the old payload and update it with the new values.
In Liquid templating, the following variable is available:
* `_response_`: A response object with the following keys:
* `status`: HTTP status as integer. (Almost always 200)
* `headers`: Reponse headers; for example, `{{ _response_.headers.Content-Type }}` expands to the value of the Content-Type header. Keys are insentitive to cases and -/_.
MD
event_description do
"Events will have the following fields:\n\n %s" % [
Utils.pretty_print(Hash[options['extract'].keys.map { |key|
[key, "..."]
}])
]
end
def working?
event_created_within?(interpolated['expected_update_period_in_days']) && !recent_error_logs?
end
def default_options
{
'expected_update_period_in_days' => "2",
'url' => "http://xkcd.com",
'type' => "html",
'mode' => "on_change",
'extract' => {
'url' => { 'css' => "#comic img", 'value' => "@src" },
'title' => { 'css' => "#comic img", 'value' => "@alt" },
'hovertext' => { 'css' => "#comic img", 'value' => "@title" }
}
}
end
def validate_options
# Check for required fields
errors.add(:base, "url and expected_update_period_in_days are required") unless options['expected_update_period_in_days'].present? && options['url'].present?
if !options['extract'].present? && extraction_type != "json"
errors.add(:base, "extract is required for all types except json")
end
# Check for optional fields
if options['mode'].present?
errors.add(:base, "mode must be set to on_change, all or merge") unless %w[on_change all merge].include?(options['mode'])
end
if options['expected_update_period_in_days'].present?
errors.add(:base, "Invalid expected_update_period_in_days format") unless is_positive_integer?(options['expected_update_period_in_days'])
end
if options['uniqueness_look_back'].present?
errors.add(:base, "Invalid uniqueness_look_back format") unless is_positive_integer?(options['uniqueness_look_back'])
end
if (encoding = options['force_encoding']).present?
case encoding
when String
begin
Encoding.find(encoding)
rescue ArgumentError
errors.add(:base, "Unknown encoding: #{encoding.inspect}")
end
else
errors.add(:base, "force_encoding must be a string")
end
end
validate_web_request_options!
end
def check
check_urls(interpolated['url'])
end
def check_urls(in_url)
return unless in_url.present?
Array(in_url).each do |url|
check_url(url)
end
end
def check_url(url, payload = {})
log "Fetching #{url}"
response = faraday.get(url)
raise "Failed: #{response.inspect}" unless response.success?
interpolation_context.stack {
interpolation_context['_response_'] = ResponseDrop.new(response)
body = response.body
if (encoding = interpolated['force_encoding']).present?
body = body.encode(Encoding::UTF_8, encoding)
end
doc = parse(body)
if extract_full_json?
if store_payload!(previous_payloads(1), doc)
log "Storing new result for '#{name}': #{doc.inspect}"
create_event payload: payload.merge(doc)
end
return
end
output =
case extraction_type
when 'json'
extract_json(doc)
when 'text'
extract_text(doc)
else
extract_xml(doc)
end
num_unique_lengths = interpolated['extract'].keys.map { |name| output[name].length }.uniq
if num_unique_lengths.length != 1
raise "Got an uneven number of matches for #{interpolated['name']}: #{interpolated['extract'].inspect}"
end
old_events = previous_payloads num_unique_lengths.first
num_unique_lengths.first.times do |index|
result = {}
interpolated['extract'].keys.each do |name|
result[name] = output[name][index]
if name.to_s == 'url'
result[name] = (response.env[:url] + result[name]).to_s
end
end
if store_payload!(old_events, result)
log "Storing new parsed result for '#{name}': #{result.inspect}"
create_event payload: payload.merge(result)
end
end
}
rescue => e
error "Error when fetching url: #{e.message}\n#{e.backtrace.join("\n")}"
end
def receive(incoming_events)
incoming_events.each do |event|
interpolate_with(event) do
url_to_scrape = event.payload['url']
next unless url_to_scrape =~ /^https?:\/\//i
check_url(url_to_scrape,
interpolated['mode'].to_s == "merge" ? event.payload : {})
end
end
end
private
# This method returns true if the result should be stored as a new event.
# If mode is set to 'on_change', this method may return false and update an existing
# event to expire further in the future.
def store_payload!(old_events, result)
case interpolated['mode'].presence
when 'on_change'
result_json = result.to_json
old_events.each do |old_event|
if old_event.payload.to_json == result_json
old_event.expires_at = new_event_expiration_date
old_event.save!
return false
end
end
true
when 'all', 'merge', ''
true
else
raise "Illegal options[mode]: #{interpolated['mode']}"
end
end
def previous_payloads(num_events)
if interpolated['uniqueness_look_back'].present?
look_back = interpolated['uniqueness_look_back'].to_i
else
# Larger of UNIQUENESS_FACTOR * num_events and UNIQUENESS_LOOK_BACK
look_back = UNIQUENESS_FACTOR * num_events
if look_back < UNIQUENESS_LOOK_BACK
look_back = UNIQUENESS_LOOK_BACK
end
end
events.order("id desc").limit(look_back) if interpolated['mode'] == "on_change"
end
def extract_full_json?
!interpolated['extract'].present? && extraction_type == "json"
end
def extraction_type
(interpolated['type'] || begin
case interpolated['url']
when /\.(rss|xml)$/i
"xml"
when /\.json$/i
"json"
when /\.(txt|text)$/i
"text"
else
"html"
end
end).to_s
end
def extract_each(doc, &block)
interpolated['extract'].each_with_object({}) { |(name, extraction_details), output|
output[name] = block.call(extraction_details)
}
end
def extract_json(doc)
extract_each(doc) { |extraction_details|
result = Utils.values_at(doc, extraction_details['path'])
log "Extracting #{extraction_type} at #{extraction_details['path']}: #{result}"
result
}
end
def extract_text(doc)
extract_each(doc) { |extraction_details|
regexp = Regexp.new(extraction_details['regexp'])
result = []
doc.scan(regexp) {
result << Regexp.last_match[extraction_details['index']]
}
log "Extracting #{extraction_type} at #{regexp}: #{result}"
result
}
end
def extract_xml(doc)
extract_each(doc) { |extraction_details|
case
when css = extraction_details['css']
nodes = doc.css(css)
when xpath = extraction_details['xpath']
doc.remove_namespaces! # ignore xmlns, useful when parsing atom feeds
nodes = doc.xpath(xpath)
else
raise '"css" or "xpath" is required for HTML or XML extraction'
end
case nodes
when Nokogiri::XML::NodeSet
result = nodes.map { |node|
case value = node.xpath(extraction_details['value'])
when Float
# Node#xpath() returns any numeric value as float;
# convert it to integer as appropriate.
value = value.to_i if value.to_i == value
end
value.to_s
}
else
raise "The result of HTML/XML extraction was not a NodeSet"
end
log "Extracting #{extraction_type} at #{xpath || css}: #{result}"
result
}
end
def parse(data)
case extraction_type
when "xml"
Nokogiri::XML(data)
when "json"
JSON.parse(data)
when "html"
Nokogiri::HTML(data)
when "text"
data
else
raise "Unknown extraction type #{extraction_type}"
end
end
def is_positive_integer?(value)
Integer(value) >= 0
rescue
false
end
# Wraps Faraday::Response
class ResponseDrop < LiquidDroppable::Drop
def headers
HeaderDrop.new(@object.headers)
end
# Integer value of HTTP status
def status
@object.status
end
end
# Wraps Faraday::Utilsa::Headers
class HeaderDrop < LiquidDroppable::Drop
def before_method(name)
@object[name.tr('_', '-')]
end
end
end
end
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