Screen scraping with Colly in Go

goquery: jQuery for Go

But oops, if you look closer, the span element contains not one but three lines. The first one, "8-12", shows the wave height I was searching for, and the second one contains <sup>FT</sup> to add feet as the unit of length next to it in the browser. The third line contains a "+", which indicates that the waves could be a bit higher than indicated.

How can the query processor separate these three lines? I didn't find anything helpful on this topic in the Colly documentation, but luckily Colly uses the goquery language internally, which is very similar to jQuery. Starting with a structure of HTMLElement type found in Colly, you can quickly extract to the corresponding goquery structure via its DOM attribute.

The corresponding goquery documentation [4] states that the Contents() function splits the text from the discovered element into its three components, and a subsequent call to Slice(0,1) then extracts the first bit.

As usual in Go, the index numbers for a slice always refer to the first (inclusive) and the last elements (exclusive). The following Each() in line 15 grabs the one and only result and calls the provided callback function with the selection at hand. The callback then uses s.Text() to extract the wave height in feet as a string, and we're in business.

High Waves

The following call to the compiled binary

$ ./surfline
8-12

thus reveals that the waves are 8 to 12 feet tall (or 2.4 to 3.6 meters if you prefer). That is a little beyond my capabilities, forcing me to leave my surfboard at home today for safety reasons and ensuring timely production of future columns. But tomorrow is another day!

Infos

  1. "Programming Snapshot: Protectli" by Mike Schilli, Linux Magazine, issue 208, March 2018, pp. 46-49, http://www.linux-magazine.com/Issues/2018/208/Servile-Guardian/(language)/eng-US
  2. Listings for this article: ftp://ftp.linux-magazine.com/pub/listings/linux-magazine.com/208/
  3. Colly documentation:http://go-colly.org/docs/
  4. goquery documentation: https://godoc.org/github.com/PuerkitoBio/goquery

The Author

Mike Schilli works as a software engineer in the San Francisco Bay area, California. Each month in his column, which has been running since 1997, he researches practical applications of various programming languages. If you email him at mailto:mschilli@perlmeister.com he will gladly answer any questions.

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