fetchers

A fetcher is a software component whose primary function is to retrieve data from remote or local sources for use by an application. Fetchers are common in data integration, web applications, and ETL pipelines, where they act as the first step in acquiring inputs for processing, storage, or display.

There are several categories of fetchers. Web fetchers retrieve data over networks using HTTP(S) or other protocols, and may handle REST or GraphQL endpoints, web pages, or feeds. File fetchers obtain data from local disks or network shares, including plain files, archives, or streamed files. Database fetchers execute queries against relational or NoSQL databases to obtain records. API fetchers combine authentication, request construction, and response parsing for structured interfaces, and streaming fetchers consume data from continuous feeds.

Core responsibilities of a fetcher include locating the data source, constructing requests, handling authentication and authorization, managing rate limits and retries, and parsing or transforming the received payload into internal data structures. They often support pagination, incremental or delta fetching, and data format negotiation (JSON, CSV, XML, etc.).

Design considerations include idempotence and retry strategies, caching to improve latency and reduce load on sources, observability through logging and metrics, and robust error handling. Security concerns include safeguarding credentials, encryption in transit, and least-privilege access. Ethical and legal considerations may apply for scraping or accessing restricted data.

Common use cases are data synchronization, content aggregation, dashboard data feeds, and integration between microservices. Effective fetchers are configurable, testable, and resilient to source variability.