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// Copyright © 2022 siddharth ravikumar <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
// A simple in-memory cache store.
package cache
import "time"
// An item in the key-value cache store.
type item struct {
value []byte
expires time.Time // Time when the key-value expires
}
// A key-value cache store.
type Cache struct {
sema chan int // Semaphore for read/write access to cache.
store map[string]item
}
// Returns a new empty cache store.
func NewCache() *Cache {
c := new(Cache)
c.sema = make(chan int, 1)
c.store = make(map[string]item)
return c
}
// Set the (key,value) item to the cache store. This item will be
// considered expired after time `expires`.
//
// Cache.Get will return an empty string once `expires` is past the
// current time.
func (c *Cache) Set(key string, value []byte, expires time.Time) {
// Get sema token before accessing the cache.
c.sema <- 1
defer func() {
// Give up sema token.
<-c.sema
}()
c.store[key] = item{
value: value,
expires: expires,
}
}
// Get an (key,value) item from the cache store by key.
//
// An empty []byte will be returned when if the key does not exist or
// if the item corresponding to the key has expired.
func (c *Cache) Get(key string) []byte {
// Get sema token before accessing the cache.
c.sema <- 1
defer func() {
// Give up sema token.
<-c.sema
}()
if _, ok := c.store[key]; !ok {
return []byte{}
}
// Check if the item expired.
if time.Until(c.store[key].expires).Seconds() < 0 {
return []byte{}
}
return c.store[key].value
}
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