Allow password to be a callable.

Fix: redis/redis-rb#1299

Makes it easy to implement short lived password authentication strategies.

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+- Allow `password` to be a callable. Makes it easy to implement short lived password authentication strategies.
 - Fix a thread safety issue in `hiredis-client` when using the `pubsub` client concurrently.
 
 # 0.22.2

README.md

@@ -78,7 +78,7 @@ redis.call("GET", "mykey")
 - `db`: The database to select after connecting, defaults to `0`.
 - `id` ID for the client connection, assigns name to current connection by sending `CLIENT SETNAME`.
 - `username` Username to authenticate against server, defaults to `"default"`.
-- `password` Password to authenticate against server.
+- `password` Password to authenticate against server. Can either be a String or a callable that recieve `username` as argument and return a passowrd as a String.
 - `timeout`: The general timeout in seconds, default to `1.0`.
 - `connect_timeout`: The connection timeout, takes precedence over the general timeout when connecting to the server.
 - `read_timeout`: The read timeout, takes precedence over the general timeout when reading responses from the server.

lib/redis_client/config.rb

@@ -12,8 +12,8 @@ class Config
     DEFAULT_DB = 0
 
     module Common
-      attr_reader :db, :password, :id, :ssl, :ssl_params, :command_builder, :inherit_socket,
-        :connect_timeout, :read_timeout, :write_timeout, :driver, :connection_prelude, :protocol,
+      attr_reader :db, :id, :ssl, :ssl_params, :command_builder, :inherit_socket,
+        :connect_timeout, :read_timeout, :write_timeout, :driver, :protocol,
         :middlewares_stack, :custom, :circuit_breaker
 
       alias_method :ssl?, :ssl
@@ -70,7 +70,7 @@ def initialize(
 
         reconnect_attempts = Array.new(reconnect_attempts, 0).freeze if reconnect_attempts.is_a?(Integer)
         @reconnect_attempts = reconnect_attempts
-        @connection_prelude = build_connection_prelude
+        @connection_prelude = (build_connection_prelude unless @password&.respond_to?(:call))
 
         circuit_breaker = CircuitBreaker.new(**circuit_breaker) if circuit_breaker.is_a?(Hash)
         if @circuit_breaker = circuit_breaker
@@ -87,6 +87,22 @@ def initialize(
         @middlewares_stack = middlewares_stack
       end
 
+      def connection_prelude
+        if @password&.respond_to?(:call)
+          build_connection_prelude
+        else
+          @connection_prelude
+        end
+      end
+
+      def password
+        if @password&.respond_to?(:call)
+          @password.call(username)
+        else
+          @password
+        end
+      end
+
       def username
         @username || DEFAULT_USERNAME
       end
@@ -151,17 +167,18 @@ def server_url
 
       def build_connection_prelude
         prelude = []
+        pass = password
         if protocol == 3
-          prelude << if @password
-            ["HELLO", "3", "AUTH", @username || DEFAULT_USERNAME, @password]
+          prelude << if pass
+            ["HELLO", "3", "AUTH", username, pass]
           else
             ["HELLO", "3"]
           end
-        elsif @password
+        elsif pass
           prelude << if @username && !@username.empty?
-            ["AUTH", @username, @password]
+            ["AUTH", @username, pass]
           else
-            ["AUTH", @password]
+            ["AUTH", pass]
           end
         end
 

test/redis_client/config_test.rb

@@ -218,5 +218,23 @@ def test_custom_field
       config = Config.new(custom: { foo: "bar" })
       assert_equal({ foo: "bar" }, config.custom)
     end
+
+    def test_callable_password
+      called = 0
+      argument = nil
+      password_callable = ->(username) do
+        called += 1
+        argument = username
+        username.upcase.reverse
+      end
+      config = Config.new(
+        username: "george",
+        password: password_callable,
+      )
+
+      assert_equal [%w(HELLO 3 AUTH george EGROEG)], config.connection_prelude
+      assert_equal 1, called
+      assert_equal "george", argument
+    end
   end
 end