Web crawler for Node.js
npm install js-crawlerjs-crawler
==========
Web crawler for Node.JS, both HTTP and HTTPS are supported.
``
npm install js-crawler
The crawler provides intuitive interface to crawl links on web sites. Example:
`javascript
var Crawler = require("js-crawler");
new Crawler().configure({depth: 3})
.crawl("http://www.google.com", function onSuccess(page) {
console.log(page.url);
});
`
The call to configure is optional, if it is omitted the default option values will be used.
onSuccess callback will be called for each page that the crawler has crawled. page value passed to the callback will contain the following fields:
* url - URL of the pagecontent
* - body of the page (usually HTML)status
* - the HTTP status code
Extra information can be retrieved from the rest of the page fields: error, response, body which are identical to the ones passed to the callback of request invocation of the Request module.referer field will reference the url of the page that lead the crawler to the current page.
#### Options-based API
Alternative APIs for passing callbacks to the crawl function.
`javascript
var Crawler = require("js-crawler");
var crawler = new Crawler().configure({ignoreRelative: false, depth: 2});
crawler.crawl({
url: "https://github.com",
success: function(page) {
console.log(page.url);
},
failure: function(page) {
console.log(page.status);
},
finished: function(crawledUrls) {
console.log(crawledUrls);
}
});
`
#### Handling errors
It is possible to pass an extra callback to handle errors, consider the modified example above:
`javascript
var Crawler = require("js-crawler");
new Crawler().configure({depth: 3})
.crawl("http://www.google.com", function(page) {
console.log(page.url);
}, function(response) {
console.log("ERROR occurred:");
console.log(response.status);
console.log(response.url);
console.log(response.referer);
});
`
Here the second callback will be called for each page that could not be accessed (maybe because the corresponding site is down). status may be not defined.
#### Knowing when all crawling is finished
Extra callback can be passed that will be called when all the urls have been crawled and crawling has finished.
All crawled urls will be passed to that callback as an argument.
`javascript
var Crawler = require("js-crawler");
new Crawler().configure({depth: 2})
.crawl("http://www.google.com", function onSuccess(page) {
console.log(page.url);
}, null, function onAllFinished(crawledUrls) {
console.log('All crawling finished');
console.log(crawledUrls);
});
`
#### Limiting the rate at which requests are made
##### maxRequestsPerSecond option
By default the maximum number of HTTP requests made per second is 100, but this can be adjusted by using the option maxRequestsPerSecond if one wishes not to use too much of network or, opposite, wishes for yet faster crawling.
`javascript
var Crawler = require("js-crawler");
var crawler = new Crawler().configure({maxRequestsPerSecond: 2});
crawler.crawl({
url: "https://github.com",
success: function(page) {
console.log(page.url);
},
failure: function(page) {
console.log(page.status);
}
});
`
With this configuration only at most 2 requests per second will be issued. The actual request rate depends on the network speed as well, maxRequestsPerSecond configures just the upper boundary.
maxRequestsPerSecond can also be fractional, the value 0.1, for example, would mean maximum one request per 10 seconds.
##### maxConcurrentRequests option
Even more flexibility is possible when using maxConcurrentRequests option, it limits the number of HTTP requests that can be active simultaneously.maxConcurrentRequests
If the number of requests per second is too high for a given set of sites/network requests may start to pile up, then specifying
can help ensure that the network is not overloaded with piling up requests.
##### Specifying both options
It is possible to customize both options in case we are not sure how performant the network and sites are. Then maxRequestsPerSecond limits how many requests the crawler is allowed to make and maxConcurrentRequests allows to specify how should the crawler adjust its rate of requests depending on the real-time performance of the network/sites.
`javascript
var Crawler = require("js-crawler");
var crawler = new Crawler().configure({
maxRequestsPerSecond: 10,
maxConcurrentRequests: 5
});
crawler.crawl({
url: "https://github.com",
success: function(page) {
console.log(page.url);
},
failure: function(page) {
console.log(page.status);
}
});
`
##### Default option values
By default the values are as follows:
maxRequestsPerSecond 100
maxConcurrentRequests 10
That is, we expect on average that 100 requests will be made every second and only 10 will be running concurrently, and every request will take something like 100ms to complete.
#### Reusing the same crawler instance for repeated crawling: forgetting crawled urls
By default a crawler instance will remember all the urls it ever crawled and will not crawl them again. In order to make it forget all the crawled urls the method forgetCrawled can be used. There is another way to solve the same problem: create a new instance of a crawler. Example https://github.com/antivanov/js-crawler/blob/master/examples/github_forgetting_crawled_urls.js
#### Supported options
* depth - the depth to which the links from the original page will be crawled.site1.com
Example: if contains a link to site2.com which contains a link to site3.com, depth is 2 and we crawl from site1.com then we will crawl site2.com but will not crawl site3.com as it will be too deep.
The default value is 2.
* ignoreRelative - ignore the relative URLs, the relative URLs on the same page will be ignored when crawling, so /wiki/Quick-Start will not be crawled and https://github.com/explore will be crawled. This option can be useful when we are mainly interested in sites to which the current sites refers and not just different sections of the original site.
The default value is false.
* userAgent - User agent to send with crawler requests.
The default value is crawler/js-crawler
* maxRequestsPerSecond - the maximum number of HTTP requests per second that can be made by the crawler, default value is 100
* maxConcurrentRequests - the maximum number of concurrent requests that should not be exceeded by the crawler, the default value is 10
* shouldCrawl - function that specifies whether a url should be crawled/requested, returns true or false,url
argument is the current the crawler considers for crawling
* shouldCrawlLinksFrom - function that specifies whether the crawler should crawl links found at a given url, returns true or false, argument is the current url being crawled
Note: shouldCrawl determines if a given URL should be requested/visited at all, where as shouldCrawlLinksFrom determines if the links on a given URL should be harvested/added to the crawling queue. Many users may find that using shouldCrawl is sufficient, as links from a page cannot be crawled if the page is never visited/requested in the first place. A common use case for having these functions separated: if a user would like to check external links on a site for errors without crawling those external links, the user could create a shouldCrawlLinksFrom function that restricts crawling to the original url without visiting external links.
Examples:
The following will crawl the specified URL, but not allow external URLs to be visited/requested, and therefore not search for additional links to crawl on the external URLs:
`javascript
var Crawler = require("js-crawler");
var crawler = new Crawler().configure({
shouldCrawl: function(url) {
return url.indexOf("reddit.com") < 0;
}
});
crawler.crawl("http://www.reddit.com/r/javascript", function(page) {
console.log(page.url);
});
`
The following will crawl the specified URL, allow external URLs to be visited/requested, but will not search for additional links to crawl on the external URLs:
`javascript
var Crawler = require("js-crawler");
var crawler = new Crawler().configure({
shouldCrawlLinksFrom: function(url) {
return url.indexOf("reddit.com") < 0;
}
});
crawler.crawl("http://www.reddit.com/r/javascript", function(page) {
console.log(page.url);
});
`
The default value for each is a function that always returns true.
#### Development
Install dependencies
npm install
Running the build
grunt
##### Unit tests
grunt karma:unit
launches unit tests in the console mode
grunt karma:unit_browser
launches a browser in which unit tests can be debugged
##### End-to-end tests
jasmine-node and express are used to setup and run end-to-end tests
Install jasmine-node and express globablly
`
npm install -g jasmine-node
npm install -g express
Start the end-to-end target server
`
cd e2e
node server.js
Now the server runs on the port 3000.
Run the end-to-end specs:
`
jasmine-node e2e/
MIT License
(c) Anton Ivanov
Credits
---------------
The crawler depends on the following Node.JS modules:
* [Underscore.js]
* [Request]
[Underscore.js]: http://underscorejs.org/
[Request]: https://github.com/mikeal/request