Add flash functionality to session

Author: sdogruyol

spec/flash_spec.cr

@@ -0,0 +1,116 @@
+require "./spec_helper"
+
+describe "Flash" do
+  before_each do
+    Kemal::Session.config.engine = Kemal::Session::MemoryEngine.new
+    Kemal::Session.config.secret = "kemal_rocks"
+  end
+
+  describe "#[]=" do
+    it "can set a flash value" do
+      context = create_context(SESSION_ID)
+      session = context.session
+      flash = context.flash
+      flash["notice"] = "welcome"
+      session.string?("#{Kemal::Session::Flash::FLASH_PREFIX}notice").should eq("welcome")
+    end
+  end
+
+  describe "#[]?" do
+    it "returns nil when flash key does not exist" do
+      context = create_context(SESSION_ID)
+      flash = context.flash
+      flash["notice"]?.should be_nil
+    end
+
+    it "returns the value and deletes it" do
+      context = create_context(SESSION_ID)
+      session = context.session
+      flash = context.flash
+      flash["notice"] = "welcome"
+      flash["notice"]?.should eq("welcome")
+      # Second access should return nil (deleted after first read)
+      flash["notice"]?.should be_nil
+    end
+
+    it "removes the flash from session storage after reading" do
+      context = create_context(SESSION_ID)
+      session = context.session
+      flash = context.flash
+      flash["notice"] = "welcome"
+      flash["notice"]?
+      session.string?("#{Kemal::Session::Flash::FLASH_PREFIX}notice").should be_nil
+    end
+  end
+
+  describe "#[]" do
+    it "returns the value when it exists" do
+      context = create_context(SESSION_ID)
+      flash = context.flash
+      flash["notice"] = "welcome"
+      flash["notice"].should eq("welcome")
+    end
+
+    it "raises KeyError when flash key does not exist" do
+      context = create_context(SESSION_ID)
+      flash = context.flash
+      expect_raises(KeyError, /Flash key not found: notice/) do
+        flash["notice"]
+      end
+    end
+
+    it "raises KeyError on second access (already consumed)" do
+      context = create_context(SESSION_ID)
+      flash = context.flash
+      flash["notice"] = "welcome"
+      flash["notice"].should eq("welcome")
+      expect_raises(KeyError, /Flash key not found: notice/) do
+        flash["notice"]
+      end
+    end
+  end
+
+  describe "multiple flash values" do
+    it "can handle multiple flash keys" do
+      context = create_context(SESSION_ID)
+      flash = context.flash
+      flash["notice"] = "Success!"
+      flash["error"] = "Something went wrong"
+      flash["warning"] = "Be careful"
+
+      flash["notice"]?.should eq("Success!")
+      flash["error"]?.should eq("Something went wrong")
+      flash["warning"]?.should eq("Be careful")
+
+      # All should be consumed now
+      flash["notice"]?.should be_nil
+      flash["error"]?.should be_nil
+      flash["warning"]?.should be_nil
+    end
+  end
+
+  describe "flash across requests" do
+    it "persists flash to next request via session" do
+      # First request: set flash
+      context1 = create_context(SESSION_ID)
+      flash1 = context1.flash
+      flash1["notice"] = "Welcome!"
+
+      # Second request: read flash (same session - using Session.get to avoid re-creating)
+      session2 = Kemal::Session.get(SESSION_ID)
+      session2.should_not be_nil
+      if session2
+        flash2 = Kemal::Session::Flash.new(session2)
+        flash2["notice"]?.should eq("Welcome!")
+
+        # Third request: flash should be gone (already consumed)
+        session3 = Kemal::Session.get(SESSION_ID)
+        session3.should_not be_nil
+        if session3
+          flash3 = Kemal::Session::Flash.new(session3)
+          flash3["notice"]?.should be_nil
+        end
+      end
+    end
+  end
+end

src/kemal-session/ext/context.cr

@@ -5,9 +5,15 @@
 # end
 class HTTP::Server::Context
   property! session : Kemal::Session
+  property! flash : Kemal::Session::Flash
 
   def session
     @session ||= Kemal::Session.new(self)
     @session.not_nil!
   end
+
+  def flash
+    @flash ||= Kemal::Session::Flash.new(session)
+    @flash.not_nil!
+  end
 end

src/kemal-session/flash.cr

@@ -0,0 +1,28 @@
+module Kemal
+  class Session
+    class Flash
+      FLASH_PREFIX = "_flash_"
+
+      def initialize(@session : Session)
+      end
+
+      # env.flash["notice"] = "welcome"
+      def []=(key : String, value : String)
+        @session.string("#{FLASH_PREFIX}#{key}", value)
+      end
+
+      # env.flash["notice"]? - returns value and marks for deletion
+      def []?(key : String) : String?
+        full_key = "#{FLASH_PREFIX}#{key}"
+        value = @session.string?(full_key)
+        @session.delete_string(full_key) if value
+        value
+      end
+
+      # env.flash["notice"] - raises if not found
+      def [](key : String) : String
+        self[key]? || raise KeyError.new("Flash key not found: #{key}")
+      end
+    end
+  end
+end