open-consul/agent/cache/request.go

package cache

import (
	"time"
)

// Request is a cacheable request.
//
// This interface is typically implemented by request structures in
// the agent/structs package.
type Request interface {
	// CacheInfo returns information used for caching this request.
	CacheInfo() RequestInfo
}

// RequestInfo represents cache information for a request. The caching
// framework uses this to control the behavior of caching and to determine
// cacheability.
type RequestInfo struct {
	// Key is a unique cache key for this request. This key should
	// be globally unique to identify this request, since any conflicting
	// cache keys could result in invalid data being returned from the cache.
	// The Key does not need to include ACL or DC information, since the
	// cache already partitions by these values prior to using this key.
	Key string

	// Token is the ACL token associated with this request.
	//
	// Datacenter is the datacenter that the request is targeting.
	//
	// Both of these values are used to partition the cache. The cache framework
	// today partitions data on these values to simplify behavior: by
	// partitioning ACL tokens, the cache doesn't need to be smart about
	// filtering results. By filtering datacenter results, the cache can
	// service the multi-DC nature of Consul. This comes at the expense of
	// working set size, but in general the effect is minimal.
	Token      string
	Datacenter string

	// MinIndex is the minimum index being queried. This is used to
	// determine if we already have data satisfying the query or if we need
	// to block until new data is available. If no index is available, the
	// default value (zero) is acceptable.
	MinIndex uint64

	// Timeout is the timeout for waiting on a blocking query. When the
	// timeout is reached, the last known value is returned (or maybe nil
	// if there was no prior value). This "last known value" behavior matches
	// normal Consul blocking queries.
	Timeout time.Duration

	// MaxAge if set limits how stale a cache entry can be. If it is non-zero and
	// there is an entry in cache that is older than specified, it is treated as a
	// cache miss and re-fetched. It is ignored for cachetypes with Refresh =
	// true.
	MaxAge time.Duration

	// MustRevalidate forces a new lookup of the cache even if there is an
	// existing one that has not expired. It is implied by HTTP requests with
	// `Cache-Control: max-age=0` but we can't distinguish that case from the
	// unset case for MaxAge. Later we may support revalidating the index without
	// a full re-fetch but for now the only option is to refetch. It is ignored
	// for cachetypes with Refresh = true.
	MustRevalidate bool
}