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Scraping

2sb18 edited this page · 21 revisions

Node.io includes a robust framework for scraping data from the web. The primary methods for scraping data are get and getHtml, although there are methods for making any type of request, modifying headers, etc. See the API for a full list of methods.

A note before you start scraping

The --debug switch is your friend - use it to see the request and response headers, and whether there was an error with the request. If your scraping job is behaving unexpectedly, --debug will show you what's going on under the hood.

node.io --debug my_scraping_job

Example 1: Save a web page to disk

save.js

var nodeio = require('node.io');
exports.job = new nodeio.Job({
    input: false,
    run: function () {
        var self = this, url = this.options.args[0];
        this.get(url, function(err, data) {
            if (err) {
                self.exit(err);
            } else {
                self.emit(data);
            }
        });
    }
});

save.coffee

nodeio = require 'node.io'
class SavePage extends nodeio.JobClass
    input: false 
    run: () -> 
        url = @options.args[0]
        @get url, (err, data) =>
            if err? then @exit err else @emit data

To save a page to disk, run

$ node.io -s save "http://www.google.com/" > google.html

Which is equivalent to

$ curl "http://www.google.com/" > google.html

Example 2: Get the number of Google results for a list of keywords

To use node.io effectively, try and encapsulate common scraping code in run() so that the resulting job is as generic and versatile as possible. Each thread should contain only one request where possible.

keywords.js

var nodeio = require('node.io');
var options = {timeout: 10};

exports.job = new nodeio.Job(options, {
    input: ['hello', 'foobar','weather'],
    run: function (keyword) {
        var self = this, results;
        this.getHtml('http://www.google.com/search?q=' + encodeURIComponent(keyword), function (err, $) {
            results = $('#resultStats').text.toLowerCase();
            self.emit(keyword + ' has ' + results);
        });
    }
});

keywords.coffee

nodeio = require 'node.io'
class SavePage extends nodeio.JobClass
  input: false
  run: () ->
    url = @options.args[0]
    @get url, (err, data, headers) =>
      if err?
        @exit err
      else
        @emit data

@class = SavePage
@job = new SavePage()

Note: you can also override the input at the command line using the -i switch, e.g.

$ node.io -i list_of_words.txt keywords

Example 3: Scraping a page using CSS selector / traversal methods

When using getHtml(url, callback), the second argument of callback is $, an object similar to jQuery's. For advanced usage of $, see the API

reddit.js - scrape the front page stories from reddit.com

var nodeio = require('node.io');
var methods = {
    input: false,
    run: function() {
        var self = this;

        this.getHtml('http://www.reddit.com/', function(err, $) {

            //Handle any request / parsing errors
            if (err) self.exit(err);

            var titles = [], scores = [], output = [];

            //Select all titles on the page
            $('a.title').each(function(a) {
                titles.push(a.text); 
            });

            //Select all scores on the page
            $('div.score.unvoted').each(function(div) {
                scores.push(div.rawtext); //rawtext doesn't decode entities or trim the text
            });

            //Mismatch? page probably didn't load properly
            if (scores.length != titles.length) {
                self.exit('Title / score mismatch');
            }

            for (var i = 0, len = scores.length; i < len; i++) {
                //Ignore upcoming stories
                if (scores[i] == '&bull;') continue;

                //Check the data is ok
                self.assert(scores[i]).isInt();

                //Output = [score] title
                output.push('['+scores[i]+'] '+titles[i]);
            }

            self.emit(output);
        });
    }
}

exports.job = new nodeio.Job({timeout:10}, methods);

reddit.coffee

nodeio = require 'node.io'
titles = []
scores = []
output = []

class Reddit extends nodeio.JobClass
    input: false
    run: -> 
        @getHtml 'http://www.reddit.com/', (err, $, data) =>
            @exit err if err?

            $('a.title').each (a) -> titles.push a.text
            $('div.score.unvoted').each (div) -> scores.push div.rawtext

            @exit 'Title / score mismatch' if scores.length isnt titles.length

            for score, i in scores
                if score is '&bull;' then continue
                @assert(score).isInt()
                output.push '[' + score + '] ' + titles[i]

            @emit output

@class = Reddit
@job = new Reddit({timeout:10})

Goto part 4: Data validation and sanitization

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