Allow to set cache expiry as an absolute timestamp

Sometime it can be useful to set a cache entry expiry
not relative to current time, but as an absolute timestamps,
e.g.:

  - If you want to cache an API token that was provided to
    you with a precise expiry time.
  - If you want to cache something until a precise cutoff
    time, e.g. `expires_at: Time.now.at_end_of_hour`

This leaves the `@created_at` variable in a weird state,
but this is to avoid breaking the binary format.

activesupport/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Add `expires_at` argument to `ActiveSupport::Cache` `write` and `fetch` to set a cache entry TTL as an absolute time.
+
+    ```ruby
+    Rails.cache.write(key, value, expires_at: Time.now.at_end_of_hour)
+    ```
+
+    *Jean Boussier*
+
 *   Deprecate `ActiveSupport::TimeWithZone.name` so that from Rails 7.1 it will use the default implementation.
 
     *Andrew White*

activesupport/lib/active_support/cache.rb

@@ -267,6 +267,14 @@ module ActiveSupport
       #   cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)
       #   cache.write(key, value, expires_in: 1.minute) # Set a lower value for one entry
       #
+      # Setting <tt>:expires_at</tt> will set an absolute expiration time on the cache.
+      # All caches support auto-expiring content after a specified number of
+      # seconds. This value can only be supplied to the +fetch+ or +write+ method to
+      # affect just one entry.
+      #
+      #   cache = ActiveSupport::Cache::MemoryStore.new
+      #   cache.write(key, value, expires_at: Time.now.at_end_of_hour)
+      #
       # Setting <tt>:version</tt> verifies the cache stored under <tt>name</tt>
       # is of the same version. nil is returned on mismatches despite contents.
       # This feature is used to support recyclable cache keys.
@@ -751,7 +759,7 @@ module ActiveSupport
             if (race_ttl > 0) && (Time.now.to_f - entry.expires_at <= race_ttl)
               # When an entry has a positive :race_condition_ttl defined, put the stale entry back into the cache
               # for a brief period while the entry is being recalculated.
-              entry.expires_at = Time.now + race_ttl
+              entry.expires_at = Time.now.to_f + race_ttl
               write_entry(key, entry, expires_in: race_ttl * 2)
             else
               delete_entry(key, **options)
@@ -801,12 +809,12 @@ module ActiveSupport
       DEFAULT_COMPRESS_LIMIT = 1.kilobyte
 
       # Creates a new cache entry for the specified value. Options supported are
-      # +:compress+, +:compress_threshold+, +:version+ and +:expires_in+.
-      def initialize(value, compress: true, compress_threshold: DEFAULT_COMPRESS_LIMIT, version: nil, expires_in: nil, **)
+      # +:compress+, +:compress_threshold+, +:version+, +:expires_at+ and +:expires_in+.
+      def initialize(value, compress: true, compress_threshold: DEFAULT_COMPRESS_LIMIT, version: nil, expires_in: nil, expires_at: nil, **)
         @value      = value
         @version    = version
-        @created_at = Time.now.to_f
-        @expires_in = expires_in && expires_in.to_f
+        @created_at = 0.0
+        @expires_in = expires_at&.to_f || expires_in && (expires_in.to_f + Time.now.to_f)
 
         compress!(compress_threshold) if compress
       end

activesupport/test/cache/behaviors/cache_store_behavior.rb

@@ -393,16 +393,42 @@ module CacheStoreBehavior
     time = Time.local(2008, 4, 24)
 
     Time.stub(:now, time) do
-      @cache.write("foo", "bar")
+      @cache.write("foo", "bar", expires_in: 1.minute)
+      @cache.write("egg", "spam", expires_in: 2.minute)
       assert_equal "bar", @cache.read("foo")
+      assert_equal "spam", @cache.read("egg")
     end
 
     Time.stub(:now, time + 30) do
       assert_equal "bar", @cache.read("foo")
+      assert_equal "spam", @cache.read("egg")
     end
 
     Time.stub(:now, time + 61) do
       assert_nil @cache.read("foo")
+      assert_equal "spam", @cache.read("egg")
+    end
+
+    Time.stub(:now, time + 121) do
+      assert_nil @cache.read("foo")
+      assert_nil @cache.read("egg")
+    end
+  end
+
+  def test_expires_at
+    time = Time.local(2008, 4, 24)
+
+    Time.stub(:now, time) do
+      @cache.write("foo", "bar", expires_at: time + 15.seconds)
+      assert_equal "bar", @cache.read("foo")
+    end
+
+    Time.stub(:now, time + 10) do
+      assert_equal "bar", @cache.read("foo")
+    end
+
+    Time.stub(:now, time + 30) do
+      assert_nil @cache.read("foo")
     end
   end
 

activesupport/test/cache/cache_entry_test.rb

@@ -9,8 +9,14 @@ class CacheEntryTest < ActiveSupport::TestCase
     assert_not entry.expired?, "entry not expired"
     entry = ActiveSupport::Cache::Entry.new("value", expires_in: 60)
     assert_not entry.expired?, "entry not expired"
-    Time.stub(:now, Time.now + 61) do
+    Time.stub(:now, Time.at(entry.expires_at + 1)) do
       assert entry.expired?, "entry is expired"
     end
   end
+
+  def test_initialize_with_expires_at
+    entry = ActiveSupport::Cache::Entry.new("value", expires_in: 60)
+    clone = ActiveSupport::Cache::Entry.new("value", expires_at: entry.expires_at)
+    assert_equal entry.expires_at, clone.expires_at
+  end
 end