add `cache` package

A simple key-value store.

2 files changed, 126 insertions, 0 deletions

diff --git a/cache/cache.go b/cache/cache.go
new file mode 100644
index 0000000..fbc763e
--- /dev/null
+++ b/cache/cache.go
@@ -0,0 +1,54 @@
+// 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   string
+	expires time.Time // Time when the key-value expires
+}
+
+// A key-value cache store.
+type Cache struct {
+	store map[string]item
+}
+
+// Returns a new empty cache store.
+func NewCache() *Cache {
+	c := new(Cache)
+	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, value string, expires time.Time) {
+	c.store[key] = item{
+		value:   value,
+		expires: expires,
+	}
+}
+
+// Get an (key,value) item from the cache store by key.
+//
+// An empty string will be returned when if the key does not exist or
+// if the item corresponding to the key has expired. An expired
+// (key,value) item will be removed from the cache store.
+func (c *Cache) Get(key string) string {
+	if _, ok := c.store[key]; !ok {
+		return ""
+	}
+	// Check if the item expired.
+	if time.Until(c.store[key].expires).Seconds() < 0 {
+		delete(c.store, key)
+		return ""
+	}
+	return c.store[key].value
+}
diff --git a/cache/cache_test.go b/cache/cache_test.go
new file mode 100644
index 0000000..41e0d25
--- /dev/null
+++ b/cache/cache_test.go
@@ -0,0 +1,72 @@
+// Copyright © 2022 siddharth ravikumar <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package cache
+
+import (
+	"testing"
+	"time"
+)
+
+func TestNewCache(t *testing.T) {
+	c := NewCache()
+	if c == nil {
+		t.Errorf("cache is nil")
+		return
+	}
+	if c.store == nil {
+		t.Errorf("cache.store is nil")
+		return
+	}
+	// Try manually adding an item.
+	c.store["foo"] = item{
+		value:   "bar",
+		expires: time.Now().Add(time.Second * 10),
+	}
+	if c.store["foo"].value != "bar" {
+		t.Errorf("cache.store['foo'] is not bar")
+		return
+	}
+}
+
+func TestCacheSet(t *testing.T) {
+	c := NewCache()
+	if c == nil {
+		t.Errorf("cache is nil")
+		return
+	}
+	exp := time.Now().Add(time.Second * 10)
+	c.Set("foo", "bar", exp)
+	if c.store["foo"].value != "bar" {
+		t.Errorf("cache.store['foo'] is not bar")
+		return
+	}
+	if c.store["foo"].expires.Unix() != exp.Unix() {
+		t.Errorf("cache.store['foo'].expires no set correctly")
+		return
+	}
+}
+
+func TestCacheGet(t *testing.T) {
+	c := NewCache()
+	if c == nil {
+		t.Errorf("cache is nil")
+		return
+	}
+
+	// Test 1
+	exp := time.Now().Add(time.Second * 10)
+	c.Set("foo", "bar", exp)
+	if c.Get("foo") != "bar" {
+		t.Errorf("cache.Get(foo) is not bar")
+		return
+	}
+
+	// Test 2
+	exp = time.Now().Add(time.Second * -10)
+	c.Set("sna", "fu", exp)
+	if c.Get("sna") != "" {
+		t.Errorf("cache.Get(sna) is not empty: %s", c.Get("sna"))
+		return
+	}
+}