open-consul/agent/cache/type.go

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package cache
import (
"time"
)
// Type implements the logic to fetch certain types of data.
type Type interface {
// Fetch fetches a single unique item.
//
// The FetchOptions contain the index and timeouts for blocking queries.
// The MinIndex value on the Request itself should NOT be used
// as the blocking index since a request may be reused multiple times
// as part of Refresh behavior.
//
// The return value is a FetchResult which contains information about
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// the fetch. If an error is given, the FetchResult is ignored. The
// cache does not support backends that return partial values.
//
// On timeout, FetchResult can behave one of two ways. First, it can
// return the last known value. This is the default behavior of blocking
// RPC calls in Consul so this allows cache types to be implemented with
// no extra logic. Second, FetchResult can return an unset value and index.
// In this case, the cache will reuse the last value automatically.
Fetch(FetchOptions, Request) (FetchResult, error)
}
// FetchOptions are various settable options when a Fetch is called.
type FetchOptions struct {
// MinIndex is the minimum index to be used for blocking queries.
// If blocking queries aren't supported for data being returned,
// this value can be ignored.
MinIndex uint64
// Timeout is the maximum time for the query. This must be implemented
// in the Fetch itself.
Timeout time.Duration
}
// FetchResult is the result of a Type Fetch operation and contains the
// data along with metadata gathered from that operation.
type FetchResult struct {
// Value is the result of the fetch.
Value interface{}
// Index is the corresponding index value for this data.
Index uint64
}