URLCache

UrlCache, often encountered as a programming term or in reference to software libraries, is a mechanism for storing responses retrieved via URLs to speed up subsequent requests. It is used by web browsers, mobile applications, and server frameworks to reduce latency, conserve bandwidth, and improve responsiveness. Caches can be in-memory, on-disk, or a combination, and are typically governed by size limits and eviction policies.

How it works: When a client requests a URL, the cache is consulted. If a valid cached response exists, it can be served without a new network fetch. Validity is determined by HTTP caching headers such as Cache-Control, Expires, ETag, and Last-Modified. The cache may revalidate with the origin server to ensure freshness. Entries include the stored response plus metadata and may vary based on request headers. Caches are subject to expiration, user settings, and eviction policies like least recently used.

Implementation examples: In the Apple ecosystem, the Foundation framework provides NSURLCache, representing a cache of URL requests and responses. Applications can configure memory and disk capacity, store and remove cached responses, and integrate with the URL loading system. Web browsers implement their own HTTP caches that persist across navigations and sessions, and most offer separate caches for private or incognito modes to isolate browsing data.

Security and privacy considerations: Caching improves performance but can expose data if not managed carefully. Sensitive information should not be cached or should be restricted, especially on shared devices or over non-secure connections. Proper cache invalidation and respecting expiration headers are important for data freshness and correctness.