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WebsiteAgent: Introduce per-node XPath evaluation in extraction.

The new extraction sub-hash key `value` holds an XPath expression which
should be applied to each node to get the result value.

The previous directives `"text": true` and `"attr": "src"` are now
written as `"value": "text()"` and `"value": "@src"`, respectively.

With this enhancement, it is now possible for this agent to perform some
basic text processing on its own by making use of XPath functions like
`normalize-space`, `substring-after` and `translate`.

Akinori MUSHA 10 years ago
parent
e746bee3dc
commit
4d623c5893
5 changed files with 50 additions and 29 deletions
Show Diff Stats
  1. 13 14
      app/models/agents/website_agent.rb
  2. 22 0
      db/migrate/20140723110551_adopt_xpath_in_website_agent.rb
  3. 4 4
      spec/fixtures/agents.yml
  4. 2 2
      spec/models/agent_spec.rb
  5. 9 9
      spec/models/agents/website_agent_spec.rb

+ 13 - 14
app/models/agents/website_agent.rb
View File 

@@ -23,14 +23,16 @@ module Agents
23 23
24 24 
       To tell the Agent how to parse the content, specify `extract` as a hash with keys naming the extractions and values of hashes.
25 25
26 
-      When parsing HTML or XML, these sub-hashes specify how to extract with either a `css` CSS selector or a `xpath` XPath expression and either `"text": true` or `attr` pointing to an attribute name to grab.  An example:
26 
+      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:
27 27
28 28 
           "extract": {
29 
-            "url": { "css": "#comic img", "attr": "src" },
30 
-            "title": { "css": "#comic img", "attr": "title" },
31 
-            "body_text": { "css": "div.main", "text": true }
29 
+            "url": { "css": "#comic img", "value": "@src" },
30 
+            "title": { "css": "#comic img", "value": "@title" },
31 
+            "body_text": { "css": "div.main", "value": "text()" }
32 32 
           }
33 33
34 
+      "@_attr_" is the XPath expression to extract the value of an attribute named _attr_ from a node, and "text()" is to extract the enclosed text.  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.
35 
+
34 36 
       When parsing JSON, these sub-hashes specify [JSONPaths](http://goessner.net/articles/JsonPath/) to the values that you care about.  For example:
35 37
36 38 
           "extract": {
 
@@ -70,9 +72,9 @@ module Agents
70 72 
           'type' => "html",
71 73 
           'mode' => "on_change",
72 74 
           'extract' => {
73 
-            'url' => { 'css' => "#comic img", 'attr' => "src" },
74 
-            'title' => { 'css' => "#comic img", 'attr' => "alt" },
75 
-            'hovertext' => { 'css' => "#comic img", 'attr' => "title" }
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+            'url' => { 'css' => "#comic img", 'value' => "@src" },
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+            'title' => { 'css' => "#comic img", 'value' => "@alt" },
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+            'hovertext' => { 'css' => "#comic img", 'value' => "@title" }
76 78 
           }
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       }
78 80 
     end
 
@@ -157,14 +159,11 @@ module Agents
157 159 
                   return
158 160 
                 end
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                 result = nodes.map { |node|
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-                  if extraction_details['attr']
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-                    node.attr(extraction_details['attr'])
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-                  elsif extraction_details['text']
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-                    node.text()
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-                  else
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-                    error '"attr" or "text" is required on HTML or XML extraction patterns'
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-                    return
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+                  value, = node.xpath(extraction_details['value'])
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+                  if value.is_a?(Float) && value.to_i == value
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+                    value = value.to_i
167 165 
                   end
166 
+                  value.to_s
168 167 
                 }
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                 log "Extracting #{extraction_type} at #{xpath || css}: #{result}"
170 169 
               end

+ 22 - 0
db/migrate/20140723110551_adopt_xpath_in_website_agent.rb
View File 

@@ -0,0 +1,22 @@
1 
+class AdoptXpathInWebsiteAgent < ActiveRecord::Migration
2 
+  def up
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+    Agent.where(type: 'Agents::WebsiteAgent').each do |agent|
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+      next if agent.extraction_type == 'json'
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+
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+      agent.options_will_change!
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+      agent.options['extract'].each { |name, extraction|
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+        case
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+        when extraction.delete('text')
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+          extraction['value'] = 'text()'
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+        when attr = extraction.delete('attr')
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+          extraction['value'] = "@#{attr}"
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+        end
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+      }
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+      agent.save!
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+    end
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+  end
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+
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+  def down
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+    raise ActiveRecord::IrreversibleMigration, "Cannot revert this migration"
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+  end
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+end

+ 4 - 4
spec/fixtures/agents.yml
View File 

@@ -10,8 +10,8 @@ jane_website_agent:
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                  :expected_update_period_in_days => 2,
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                  :mode => :on_change,
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                  :extract => {
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-                     :title => {:css => "item title", :text => true},
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-                     :url => {:css => "item link", :text => true}
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+                     :title => {:css => "item title", :value => 'text()'},
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+                     :url => {:css => "item link", :value => 'text()'}
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                  }
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                }.to_json.inspect %>
17 17 
 
@@ -27,8 +27,8 @@ bob_website_agent:
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                  :expected_update_period_in_days => 2,
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                  :mode => :on_change,
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                  :extract => {
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-                   :url => {:css => "#comic img", :attr => "src"},
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-                   :title => {:css => "#comic img", :attr => "title"}
30 
+                   :url => {:css => "#comic img", :value => "@src"},
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+                   :title => {:css => "#comic img", :value => "@title"}
32 32 
                  }
33 33 
                }.to_json.inspect %>
34 34

+ 2 - 2
spec/models/agent_spec.rb
View File 

@@ -768,8 +768,8 @@ describe AgentDrop do
768 768 
         url: 'http://dilbert.com/',
769 769 
         mode: 'on_change',
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         extract: {
771 
-          url: { css: '[id^=strip_enlarged_] img', attr: 'src' },
772 
-          title: { css: '.STR_DateStrip', text: true },
771 
+          url: { css: '[id^=strip_enlarged_] img', value: '@src' },
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+          title: { css: '.STR_DateStrip', value: 'text()' },
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         },
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       },
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       schedule: 'every_12h',

+ 9 - 9
spec/models/agents/website_agent_spec.rb
View File 

@@ -11,9 +11,9 @@ describe Agents::WebsiteAgent do
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         'url' => "http://xkcd.com",
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         'mode' => 'on_change',
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         'extract' => {
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-          'url' => { 'css' => "#comic img", 'attr' => "src" },
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-          'title' => { 'css' => "#comic img", 'attr' => "alt" },
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-          'hovertext' => { 'css' => "#comic img", 'attr' => "title" }
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+          'url' => { 'css' => "#comic img", 'value' => "@src" },
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+          'title' => { 'css' => "#comic img", 'value' => "@alt" },
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+          'hovertext' => { 'css' => "#comic img", 'value' => "@title" }
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         }
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       }
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       @checker = Agents::WebsiteAgent.new(:name => "xkcd", :options => @valid_options, :keep_events_for => 2)
 
@@ -256,8 +256,8 @@ describe Agents::WebsiteAgent do
256 256 
           'url' => "http://xkcd.com",
257 257 
           'mode' => "on_change",
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           'extract' => {
259 
-            'url' => {'css' => "#topLeft a", 'attr' => "href"},
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-            'title' => {'css' => "#topLeft a", 'text' => "true"}
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+            'url' => {'css' => "#topLeft a", 'value' => "@href"},
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+            'title' => {'css' => "#topLeft a", 'value' => "text()"}
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           }
262 262 
         }
263 263 
         rel = Agents::WebsiteAgent.new(:name => "xkcd", :options => rel_site)
 
@@ -389,9 +389,9 @@ describe Agents::WebsiteAgent do
389 389 
         'url' => "http://www.example.com",
390 390 
         'mode' => 'on_change',
391 391 
         'extract' => {
392 
-          'url' => { 'css' => "#comic img", 'attr' => "src" },
393 
-          'title' => { 'css' => "#comic img", 'attr' => "alt" },
394 
-          'hovertext' => { 'css' => "#comic img", 'attr' => "title" }
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+          'url' => { 'css' => "#comic img", 'value' => "@src" },
393 
+          'title' => { 'css' => "#comic img", 'value' => "@alt" },
394 
+          'hovertext' => { 'css' => "#comic img", 'value' => "@title" }
395 395 
         },
396 396 
         'basic_auth' => "user:pass"
397 397 
       }
 
@@ -421,7 +421,7 @@ describe Agents::WebsiteAgent do
421 421 
         'mode' => 'on_change',
422 422 
         'headers' => { 'foo' => 'bar' },
423 423 
         'extract' => {
424 
-          'url' => { 'css' => "#comic img", 'attr' => "src" },
424 
+          'url' => { 'css' => "#comic img", 'value' => "@src" },
425 425 
         }
426 426 
       }
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       @checker = Agents::WebsiteAgent.new(:name => "ua", :options => @valid_options)