jwambugu / crawler

Web Crawler built using go.

Task

Implement a recursive, mirroring web crawler . The crawler should be a command-line tool that accepts a starting URL and a destination directory. The crawler will then download the page at the URL, save it in the destination directory, and then recursively proceed to any valid links in this page.

A valid link is the value of an href attribute in an <a> tag the resolves to urls that are children of the initial URL.

For example, given initial URL https://start.url/abc , URLs that resolve to https://start.url/abc/foo and https://start.url/abc/foo/bar are valid URLs, but ones that resolve to https://another.domain/ or to https://start.url/baz are not valid URLs, and should be skipped.

Additionally, the crawler should:

• Correctly handle being interrupted by Ctrl-C
• Perform work in parallel where reasonable
• Support resume functionality by checking the destination directory for downloaded pages and skip downloading and processing where not necessary
• Provide “happy-path” test coverage

Some tips:

• If you’re not familiar with this kind of software, see wget --mirror for very similar functionality
• Document missing features and any other changes you would make if you had more time for the assignment implementation.

Usage

Install crawler using the command below:

go install

To view available options and usage, run

crawler --help

To crawl a website, run

crawler -s https://example.com -d downloads

Running tests and benchmarks

The project by default uses github actions to run tests and benchmarks. To run tests locally, please run the commands below.

Tests:

  go test -cover -race ./... -v

Benchmarks:

  go test -bench=.  ./...  

Benchmark Results on Apple M1 Pro:

goos: darwin
goarch: arm64
pkg: github.com/jwambugu/crawler/cmd/crawler
BenchmarkCrawler_Crawl-8                           25808             44546 ns/op
BenchmarkCrawler_CrawlWithoutConcurrency-8         34762             34582 ns/op
PASS
ok      github.com/jwambugu/crawler/cmd/crawler 3.955s

Benchmark Results on Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz:

goos: linux
goarch: amd64
pkg: github.com/jwambugu/crawler/cmd/crawler
cpu: Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz
BenchmarkCrawler_Crawl-2                     	   15939	     75629 ns/op
BenchmarkCrawler_CrawlWithoutConcurrency-2   	   23270	     50507 ns/op
PASS
ok  	github.com/jwambugu/crawler/cmd/crawler	3.680s

Missing features

• The crawler should not exit if a link returns a 404. It should attempt to go back to the previous link and skip the missing link's URL.
• Keep track of the last crawled link and resume from it instead of starting afresh.