README.md

Seamlessly fetch paginated data from any source!

walker

Walker simplifies the process of fetching paginated data from any data source. With Walker, you can easily configure the start position and count of documents to fetch, depending on your needs. Additionally, Walker supports parallel processing, allowing you to fetch data more efficiently and at a faster rate.

The real purpose of the library is to provide a solution for walking through the pagination of API endpoints. With the NewApiWalker, you can easily fetch data from any paginated API endpoint and process the data concurrently. You can also create your own custom walker to fit your specific use case.

Features

• Provides a walker to paginate through the pagination of API endpoint. This is for scraping an API, if such a term exists.
• cursor and offset pagination strategies.
• Fetching and processing data concurrently without any effort.
• Total fetch count limiting
• Rate limiting

Examples

Basic Usage

func source(start, fetchCount int) ([]int, error) {
	return []int{start, fetchCount}, nil
}

func sink(result []int, stop func()) error {
	fmt.Println(result)
	return nil
}

func main() {
	walker.New(source, sink).Walk()
}

Output:

[0 10]
[1 10]
[4 10]
[2 10]
[3 10]
[5 10]
[8 10]
[9 10]
[7 10]
[6 10]
...
to Infinity

• source function will receive start as the page number and count as the number of documents. Use this values to fetch data from your source.
• sink function will receive the result you returned from source and a stop function. You can save the results in this function and decide to stop sourcing any further pages depending on your results by calling stop function, otherwise it will continue to forever unless a limit provided.
• Beware of order is not ensured since source and sink functions called concurrently.

Walking through the pagination of API endpoints

Fetching all the breweries from Open Brewery DB:

func buildRequest(start, fetchCount int) (*http.Request, error) {
	url := fmt.Sprintf("https://api.openbrewerydb.org/breweries?page=%d&per_page=%d", start, fetchCount)
	return http.NewRequest(http.MethodGet, url, http.NoBody)
}

func sink(res *http.Response, stop func()) error {
	var payload []map[string]any
	json.NewDecoder(res.Body).Decode(&payload)

	if len(payload) == 0 {
		stop()
		return nil
	}

	return saveBreweries(payload)
}

func main() {
	walker.NewApiWalker(http.DefaultClient, buildRequest, sink).Walk()
}

To create API walker you just need to provide:

• RequestBuilder function to create http request using provided values
• sink function to process the http response

Check examples for more usecases.

Configuration

Option	Description	Default	Available Values
WithPagination	Defines the pagination strategy	walker.OffsetPagination{}	walker.OffsetPagination{}, walker.CursorPagination{}
WithMaxBatchSize	Defines limit for document count to stop after reached	10	int
WithParallelism	Defines number of workers to run provided source	runtime.NumCPU()	int
WithLimiter	Defines limit for document count to stop after reached	walker.InfiniteLimiter()	walker.InfiniteLimiter(), walker.ConstantLimiter(int)
WithRateLimit	Defines rate limit by count and per duration	unlimited	(int, time.Duration)
WithContext	Defines context	context.Background()	context.Context

Contribution

I would like to accept any contributions to make walker better and feature rich. Feel free to contribute with your usecase!