Digest-Based Caching for Idempotent HTTP POST Requests
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Solution Overview
Problem
HTTP caching is limited to idempotent requests, such as GET requests, and cannot effectively handle non-idempotent POST requests due to their variable nature, leading to inefficiencies in bandwidth usage and round trip delays.
Innovation Solution
Implementing a cache system with a forward and reverse proxy that digests the POST request body, using the digest as a cache key, and employing cache handshaking to send only the digest across the network, allowing for caching of POST requests and responses while maintaining HTTP compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HTTP caching is applied to GET requests (idempotent requests), then caching performance is improved, but POST requests (non-idempotent requests) cannot be cached leading to increased bandwidth consumption and response time
Solution Approach 1:
The patent changes the fundamental parameter of request categorization by introducing digest-based identification for POST requests. Instead of treating all POST requests as non-cacheable, the system computes a digest (hash) of the request body and uses this digest as a cache key, transforming POST requests into cacheable entities while maintaining their non-idempotent nature.
Solution Approach 2:
The patent introduces a cache intermediary layer that sits between the client and server. This intermediary computes digests of POST request bodies, stores them in the cache with appropriate metadata, and handles cache hits/misses for POST requests. The intermediary acts as a mediator that enables caching without violating HTTP semantics.
2Loss of energy
If POST requests are cached using digest as cache key, then bandwidth consumption is reduced, but system complexity increases due to digest computation and cache handshaking
Solution Approach 1:
The patent applies preliminary action by pre-computing the digest of the POST request body before making the actual request. The digest is computed once and stored, and this pre-computed digest is then used as the cache key. This preliminary computation avoids the need to compute digests repeatedly for cache lookups.
Solution Approach 2:
The patent uses copying by creating a simplified representation (digest) of the original POST request body. Instead of storing or transmitting the entire request body for caching purposes, the system creates a compact digest copy that serves as the cache key, reducing the complexity of cache management while maintaining effectiveness.
3Reliability
If only GET requests are cached, then HTTP specification compliance is maintained, but performance improvement is limited due to inability to cache POST requests
Solution Approach 1:
The patent introduces dynamics by making the caching behavior adaptive rather than static. The system dynamically determines whether a POST request can be cached based on digest computation and cache handshaking. This dynamic approach allows the system to cache POST requests when appropriate while maintaining HTTP specification compliance, thereby improving performance without sacrificing reliability.
Data Source
AI summary
With an idempotent POST request, the URL (and headers) cannot be used as an HTTP cache key. To cache idempotent POST requests, the POST body is digested and appended the URL with the digest and used as the cache key. Subsequent requests with the same payload will end up hitting the cache rather than the origin server. A forward cache proxy at the client end and reverse cache proxy at the server end are deployed. The client sends the request to the forward proxy that looks up the cache. If there is a cache miss, the forward cache proxy digests the body and sends only the digest to the reverse proxy. The reverse cache proxy looks up request cache to find if there is a match for the request and send that request to the server.