Create CACHING.md

architecture/CACHING.md

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+## Caching Middleware Architecture
+
+Package `cachemdw` is responsible for caching EVM requests and provides corresponding middleware
+
+package can work with any underlying storage which implements simple `cache.Cache` interface
+
+package provides two different middlewares:
+- `IsCachedMiddleware` (should be run before proxy middleware)
+- `CachingMiddleware`  (should be run after proxy middleware)
+
+`IsCachedMiddleware` is responsible for setting response in the context if it's in the cache
+
+`CachingMiddleware` is responsible for caching response by taking a value from context (should be set by `ProxyMiddleware`) and setting in the cache
+
+## CachingMiddleware
+
+`CachingMiddleware` returns kava-proxy-service compatible middleware which works in the following way:
+- tries to get decoded request from context (previous middleware should set it)
+- checks few conditions:
+  - if request isn't already cached
+  - if request is cacheable
+  - if response is present in context
+- if all above is true - caches the response
+- calls next middleware
+
+## IsCachedMiddleware
+
+`IsCachedMiddleware` returns kava-proxy-service compatible middleware which works in the following way:
+- tries to get decoded request from context (previous middleware should set it)
+- tries to get response from the cache
+  - if present sets cached response in context, marks as cached in context and forwards to next middleware
+  - if not present marks as uncached in context and forwards to next middleware
+- next middleware should check whether request was cached and act accordingly: