Scraping Google with Golang

I have previously written a post on scraping Google with Python. As I am starting to write more Golang, I thought I should write the same tutorial using Golang to scrape Google. Why not scrape Google search results using Google’s home grown programming language.

Imports & Setup

This example will only being using one external dependency. While it is possible to parse HTML using Go’s standard library, this involves writing a lot of code. So instead we are going to be using the very popular Golang library, Goquery which supports JQuery style selection of HTML elements.

Defining What To Return

We can get a variety of different information from Google, but we typically want to return a result’s position, URL, title and description. In Golang it makes sense to create a struct representing the data we want to be gathered by our scraper.

We can build a simple struct which will hold an individual search result, when writing our final function we can then set the return value to be a slice of our GoogleResult struct. This will make it very easy for us to manipulate our search results once we have scraped them from Google.

Making A Request To Google

To scrape Google results we have to make a request to Google using a URL containing our search parameters. For instance Google allows you to pass a number of different parameters to a search query. In this particular example we are going to write a function that will generate us a search URL with our desired parameters.

But first we are going to define a “map” of supported Google geo locations. In this post we are only going to support a few major geographical locations, but Google operates in over 100 different geographical locations.

This will allow pass a two letter country code to our scraping function and scrape results from that particular version of Google. Using the different base domains in combination with a language code allows us to scrape results as they appear in the country in question.

We then write a function that allows us to build a Google search URL. The function takes in three arguments, all of the string type and returns a URL also a string. We first trim the search term to remove any trailing or proceeding white-space.  We then replace any of the remaining spaces with ‘+’, the -1 in this line of code means that we replace every-single remaining instance of white-space with a plus.

We then look up the country code passed as an argument against the map we defined earlier. If the countryCode is found in our map, we use the respective URL from the map, otherwise we use the default ‘.com’ Google site. We then use the format packages “Sprintf” function to format a string made up of our base URL, our search term and language code. We don’t check the validity of the language code, which is something we might want to do if we were writing a more fully featured scraper.

We can now write a function to make a request. Go has a very easy to use and power “net/http” library which makes it relatively easy to make HTTP requests. We first get a client to make our request with. We then start building a new HTTP request which will be eventually executed using our client. This allows us to set custom headers to be sent with our request. In this instance we our replicating the User-Agent header of a real browser.

We then execute this request, with the client’s Do method returning us a response and error. If something went wrong with the request we return a nil value and the error. Otherwise we simply return the response object and a nil value to show that we did not encounter an error.

Parsing the Result

Google results are divided up to ‘div’ elements with the class ‘g’.

Now we move onto parsing the result of request. Compared with Python the options when it comes to HTML parsing libraries is not as robust, with nothing coming close to the ease of use of BeautifulSoup. In this example, we are going to use the very popular Goquery package which uses JQuery style selectors to allow users to extract data from HTML documents.

We generate a goquery document from our response, and if we encounter any errors we simply return the error and a nil value object. We then create an empty slice of Google results which we will eventually append results to. On a Google results page, each organic result can be found in ‘div’ block with the class of ‘g’. So we can simply use the JQuery selector “div.g” to pick out all of the organic links.

We then loop through each of these found ‘div’ tags finding the link and it’s href attribute, as well as extracting the title and meta description information. Providing the link isn’t an empty string or a navigational reference, we then create an GoogleResult struct holding our information. This can then be appended to the slice of structs which we defined earlier. Finally, we increment the rank so we can tell the order in which the results appeared on the page.

Wrapping It All Up

We can then simply write a function which encompasses all the previous functions. Note when writing this function we capitalise the function name to ensure that it is exported. This will allow us to use this function in other Go programs. We don’t do much in the way of error handling, if anything goes wrong we simply return nil and the error, without any logging along the way. Ideally, we would want some sort of logging to alert us exactly what went wrong with a particular scrape.

Example Usage

The above program makes use of our GoogleScraper function by working through a list of keywords and scraping search results. After each scrape we are waiting a total of 30 seconds, this should help us avoid being banned. Should we want to scrape a larger set of keywords, we would want to randomise our User-Agent and change up the proxy we were using in each request. Otherwise we are very likely to run into a Google captcha which would prevent us from gathering any results.

The full Google scraping script can be found here. Feel free to play with it and think about some of the additional functionality that could be added. You might for instance want to scrape the first few pages of Google, or pass in a custom number of results to be returned by the script.

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