Add `#verified` and `#valid_message?` to MessageVerifier

This commit adds a `#verified` method to
`ActiveSupport::MessageVerifier` which will return either `false` when
it encounters an error or the message. `#verify` continues to raise an
`InvalidSignature` exception on error.

This commit also adds a convenience boolean method on `MessageVerifier`
as a way to check if a message is valid without performing the
decoding.

3 files changed, 47 insertions, 22 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 810fc22cf5..72bdd0c509 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1 +1,9 @@
+*   Added `#verified` and `#valid_message?` methods to `ActiveSupport::MessageVerifier`
+    
+    Previously, the only way to decode a message with `ActiveSupport::MessageVerifier` was to use `#verify`, which would raise an exception on invalid messages. Now, `#verified` will return either `false` when it encounters an error or the message.
+    
+    Previously, there was no way to check if a message's format was valid without attempting to decode it. `#valid_message?` is a boolean convenience method that checks whether the message is valid without actually decoding it.
+    
+    *Logan Leger*
+
 Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/activesupport/CHANGELOG.md) for previous changes.
diff --git a/activesupport/lib/active_support/message_verifier.rb b/activesupport/lib/active_support/message_verifier.rb
index a8a8de5672..8e5d050540 100644
--- a/activesupport/lib/active_support/message_verifier.rb
+++ b/activesupport/lib/active_support/message_verifier.rb
@@ -34,21 +34,30 @@ module ActiveSupport
       @serializer = options[:serializer] || Marshal
     end
 
-    def verify(signed_message)
-      raise InvalidSignature if signed_message.blank?
-
+    def valid_message?(signed_message)
+      return false if signed_message.blank?
+      
       data, digest = signed_message.split("--")
-      if data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
+      data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
+    end
+
+    def verified(signed_message)
+      if valid_message?(signed_message)
         begin
+          data = signed_message.split("--")[0]
           @serializer.load(decode(data))
         rescue ArgumentError => argument_error
-          raise InvalidSignature if argument_error.message =~ %r{invalid base64}
+          return false if argument_error.message =~ %r{invalid base64}
           raise
         end
       else
-        raise InvalidSignature
+        false
       end
     end
+    
+    def verify(signed_message)
+      verified(signed_message) || raise(InvalidSignature)
+    end
 
     def generate(value)
       data = encode(@serializer.dump(value))
diff --git a/activesupport/test/message_verifier_test.rb b/activesupport/test/message_verifier_test.rb
index 28035bc428..68f40fbb28 100644
--- a/activesupport/test/message_verifier_test.rb
+++ b/activesupport/test/message_verifier_test.rb
@@ -27,21 +27,29 @@ class MessageVerifierTest < ActiveSupport::TestCase
     @data = { :some => "data", :now => Time.local(2010) }
   end
 
+  def test_valid_message
+    data, hash = @verifier.generate(@data).split("--")
+    assert !@verifier.valid_message?(nil)
+    assert !@verifier.valid_message?("")
+    assert !@verifier.valid_message?("#{data.reverse}--#{hash}")
+    assert !@verifier.valid_message?("#{data}--#{hash.reverse}")
+    assert !@verifier.valid_message?("purejunk")
+  end
+
   def test_simple_round_tripping
     message = @verifier.generate(@data)
+    assert_equal @data, @verifier.verified(message)
     assert_equal @data, @verifier.verify(message)
   end
-
-  def test_missing_signature_raises
-    assert_not_verified(nil)
-    assert_not_verified("")
+  
+  def test_verified_returns_false_on_invalid_message
+    assert !@verifier.verified("purejunk")
   end
-
-  def test_tampered_data_raises
-    data, hash = @verifier.generate(@data).split("--")
-    assert_not_verified("#{data.reverse}--#{hash}")
-    assert_not_verified("#{data}--#{hash.reverse}")
-    assert_not_verified("purejunk")
+  
+  def test_verify_exception_on_invalid_message
+    assert_raise(ActiveSupport::MessageVerifier::InvalidSignature) do
+      @verifier.verify("purejunk")
+    end
   end
 
   def test_alternative_serialization_method
@@ -50,6 +58,7 @@ class MessageVerifierTest < ActiveSupport::TestCase
     verifier = ActiveSupport::MessageVerifier.new("Hey, I'm a secret!", :serializer => JSONSerializer.new)
     message = verifier.generate({ :foo => 123, 'bar' => Time.utc(2010) })
     exp = { "foo" => 123, "bar" => "2010-01-01T00:00:00.000Z" }
+    assert_equal exp, verifier.verified(message)
     assert_equal exp, verifier.verify(message)
   ensure
     ActiveSupport.use_standard_json_time_format = prev
@@ -63,6 +72,11 @@ class MessageVerifierTest < ActiveSupport::TestCase
     #
     valid_message = "BAh7BjoIZm9vbzonTWVzc2FnZVZlcmlmaWVyVGVzdDo6QXV0b2xvYWRDbGFzcwY6CUBmb29JIghmb28GOgZFVA==--f3ef39a5241c365083770566dc7a9eb5d6ace914"
     exception = assert_raise(ArgumentError, NameError) do
+      @verifier.verified(valid_message)
+    end
+    assert_includes ["uninitialized constant MessageVerifierTest::AutoloadClass",
+                    "undefined class/module MessageVerifierTest::AutoloadClass"], exception.message
+    exception = assert_raise(ArgumentError, NameError) do
       @verifier.verify(valid_message)
     end
     assert_includes ["uninitialized constant MessageVerifierTest::AutoloadClass",
@@ -75,12 +89,6 @@ class MessageVerifierTest < ActiveSupport::TestCase
     end
     assert_equal exception.message, 'Secret should not be nil.'
   end
-
-  def assert_not_verified(message)
-    assert_raise(ActiveSupport::MessageVerifier::InvalidSignature) do
-      @verifier.verify(message)
-    end
-  end
 end
 
 end