supercrawler

Supercrawler - Node.js Web Crawler

Supercrawler is a Node.js web crawler. It is designed to be highly configurable and easy to use.

Supercrawler can store state information in a database, so you an can start and stop crawls easily. It will automatically retry failed URLs in an exponential backoff style (starting at 1 hour and doubling thereafter).

When Supercrawler successfully crawls a page (which could be a image, text, etc), it will fire your custom content-type handlers. Define your own custom handlers to parse pages, save data and do anything else you need.

Step 1. Create a New Crawler

var crawler = new supercrawler.Crawler({
  interval: 100
});

Step 2. Add Content handlers

You can specify your own content handlers for all types of content or groups of content. You can target text or text/html documents easily.

The htmlLinkParser handler is included with Supercrawler. It automatically parses a HTML document, discovers links and adds them to the crawl queue. You can specify an array of allowed hostnames with the hostnames option, allowing you to easily control the scope of your crawl.

You can also specify your own handlers. Use these handlers to parse content, save files or identify links. Just return an array of links (absolute paths) from your handler, and Supercrawler will add them to the queue.

crawler.addHandler("text/html", supercrawler.handlers.htmlLinkParser({
  hostnames: ["example.com"]
}));
crawler.addHandler("text/html", function (body, url) {
  console.log("Got page", url);
});

Step 3. Start the Crawl

Insert a starting URL into the queue, and call crawler.start().

crawler.getUrlList()
  .insertIfNotExists(new supercrawler.Url("https://example.com/"))
  .then(function () {
    return crawler.start();
  });

Crawler

Each Crawler instance represents a web crawler. You can configure your crawler with the following options:

Option	Description
urlList	Custom instance of UrlList type queue. Defaults to FifoUrlList, which processes URLs in the order that they were added to the queue; once they are removed from the queue, they cannot be recrawled.
interval	Number of milliseconds between requests. Defaults to 1000.
concurrentRequestsLimit	Maximum number of concurrent requests. Defaults to 5.
robotsCacheTime	Number of milliseconds that robots.txt should be cached for. Defaults to 3600000 (1 hour).
userAgent	User agent to use for requests. Defaults to Mozilla/5.0 (compatible; supercrawler/1.0; +https://github.com/brendonboshell/supercrawler)

Example usage:

var crawler = new supercrawler.Crawler({
  interval: 1000,
  concurrentRequestsLimit: 1
});

The following methods are available:

Method	Description
getUrlList	Get the UrlList type instance.
getInterval	Get the interval setting.
getConcurrentRequestsLimit	Get the maximum number of concurrent requests.
getUserAgent	Get the user agent.
start	Start crawling.
stop	Stop crawling.
addHandler(handler)	Add a handler for all content types.
addHandler(contentType, handler)	Add a handler for a specific content type.

DbUrlList

DbUrlList is a queue backed with a database, such as MySQL, Postgres or SQLite. You can use any database engine supported by Sequelize.

If a request fails, this queue will ensure the request gets retried at some point in the future. The next request is schedule 1 hour into the future. After that, the period of delay doubles for each failure.

Options:

Option	Description
opts.db.database	Database name.
opts.db.username	Database username.
opts.db.password	Database password.
opts.db.sequelizeOpts	Options to pass to sequelize.

Example usage:

new supercrawler.DbUrlList({
  db: {
    database: "crawler",
    username: "root",
    password: "password",
    sequelizeOpts: {
      dialect: "mysql",
      host: "localhost"
    }
  }
})

The following methods are available:

Method	Description
insertIfNotExists(url)	Insert a Url object.
upsert(url)	Upsert Url object.
getNextUrl()	Get the next Url to be crawled.

FifoUrlList

The FifoUrlList is the default URL queue powering the crawler. You can add URLs to the queue, and they will be crawled in the same order (FIFO).

Note that, with this queue, URLs are only crawled once, even if the request fails. If you need retry functionality, you must use DbUrlList.

The following methods are available:

Method	Description
insertIfNotExists(url)	Insert a Url object.
upsert(url)	Upsert Url object.
getNextUrl()	Get the next Url to be crawled.

Url

A Url represents a URL to be crawled, or a URL that has already been crawled. It is uniquely identified by an absolute-path URL, but also contains information about errors and status codes.

Option	Description
url	Absolute-path string url
statusCode	HTTP status code or null.
errorCode	String error code or null.

Example usage:

var url = new supercrawler.Url({
  url: "https://example.com"
});

You can also call it just a string URL:

var url = new supercrawler.Url("https://example.com");

The following methods are available:

Method	Description
getUniqueId	Get the unique identifier for this object.
getUrl	Get the absolute-path string URL.
getErrorCode	Get the error code, or null if it is empty.
getStatusCode	Get the status code, or null if it is empty.

handlers.htmlLinkParser

A function that returns a handler which parses a HTML page and identifies any links.

Option	Description
hostnames	Array of hostnames that are allowed to be crawled.

Example usage:

var hlp = supercrawler.handlers.htmlLinkParser({
  hostnames: ["example.com"]
});

Features

• Pluggable priority queues. Supercrawler ships with a simple first-in, first-out style queue. But you can easily plug your own queue in, allowing you to retry failed crawls, prioritize specific pages or save crawl data in a database, for example.
• Concurrency limiting. You can set a maximum number of requests that can execute at the same time.
• Rate limiting. You can set a rate limit to prevent crawling too quickly.
• Robots adherence. Supercrawler automatically downloads, checks and caches the results of robots.txt exclusions.