Customize subsecond digits when encoding DateWithTime

The subsecond fraction digits had been hardcoded to 3. This forced all
timestamps to include the subsecond digits with no way to customize the
value. While the subsecond format is part of the ISO8601 spec, it is not
adhered to by all parsers (notably mobile clients). This adds the
ability to customize the number of digits used, optionally setting them
to 0 in order to eliminate the subsecond fraction entirely:

ActiveSupport::JSON::Encoding.subsecond_fraction_digits = 0

3 files changed, 30 insertions, 9 deletions

diff --git a/activesupport/lib/active_support/json/encoding.rb b/activesupport/lib/active_support/json/encoding.rb
index 2859075e10..23896316e2 100644
--- a/activesupport/lib/active_support/json/encoding.rb
+++ b/activesupport/lib/active_support/json/encoding.rb
@@ -4,6 +4,7 @@ require 'active_support/core_ext/module/delegation'
 module ActiveSupport
   class << self
     delegate :use_standard_json_time_format, :use_standard_json_time_format=,
+      :subsecond_fraction_digits, :subsecond_fraction_digits=,
       :escape_html_entities_in_json, :escape_html_entities_in_json=,
       :encode_big_decimal_as_string, :encode_big_decimal_as_string=,
       :json_encoder, :json_encoder=,
@@ -60,7 +61,7 @@ module ActiveSupport
           end
 
           # Mark these as private so we don't leak encoding-specific constructs
-          private_constant :ESCAPED_CHARS, :ESCAPE_REGEX_WITH_HTML_ENTITIES, 
+          private_constant :ESCAPED_CHARS, :ESCAPE_REGEX_WITH_HTML_ENTITIES,
             :ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, :EscapedString
 
           # Convert an object into a "JSON-ready" representation composed of
@@ -105,6 +106,10 @@ module ActiveSupport
         # as a safety measure.
         attr_accessor :escape_html_entities_in_json
 
+        # Configures the inclusion of subsecond resolution when serializing instances
+        # of ActiveSupport::TimeWithZone.
+        attr_accessor :subsecond_fraction_digits
+
         # Sets the encoder used by Rails to encode Ruby objects into JSON strings
         # in +Object#to_json+ and +ActiveSupport::JSON.encode+.
         attr_accessor :json_encoder
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index d47aee00f4..26d4e686fd 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -154,7 +154,8 @@ module ActiveSupport
     #   # => "2005/02/01 05:15:10 -1000"
     def as_json(options = nil)
       if ActiveSupport::JSON::Encoding.use_standard_json_time_format
-        xmlschema(3)
+        digits = ActiveSupport::JSON::Encoding.subsecond_fraction_digits || 3
+        xmlschema(digits)
       else
         %(#{time.strftime("%Y/%m/%d %H:%M:%S")} #{formatted_offset(false)})
       end
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 43fe572bfc..4ea8d2bed6 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -67,17 +67,25 @@ class TimeWithZoneTest < ActiveSupport::TestCase
   end
 
   def test_to_json_with_use_standard_json_time_format_config_set_to_false
-    old, ActiveSupport.use_standard_json_time_format = ActiveSupport.use_standard_json_time_format, false
-    assert_equal "\"1999/12/31 19:00:00 -0500\"", ActiveSupport::JSON.encode(@twz)
-  ensure
-    ActiveSupport.use_standard_json_time_format = old
+    with_standard_json_time_format(false) do
+      assert_equal "\"1999/12/31 19:00:00 -0500\"", ActiveSupport::JSON.encode(@twz)
+    end
   end
 
   def test_to_json_with_use_standard_json_time_format_config_set_to_true
-    old, ActiveSupport.use_standard_json_time_format = ActiveSupport.use_standard_json_time_format, true
-    assert_equal "\"1999-12-31T19:00:00.000-05:00\"", ActiveSupport::JSON.encode(@twz)
+    with_standard_json_time_format(true) do
+      assert_equal "\"1999-12-31T19:00:00.000-05:00\"", ActiveSupport::JSON.encode(@twz)
+    end
+  end
+
+  def test_to_json_with_custom_subsecond_resolution
+    with_standard_json_time_format(true) do
+      ActiveSupport::JSON::Encoding.subsecond_fraction_digits = 0
+
+      assert_equal "\"1999-12-31T19:00:00-05:00\"", ActiveSupport::JSON.encode(@twz)
+    end
   ensure
-    ActiveSupport.use_standard_json_time_format = old
+    ActiveSupport::JSON::Encoding.subsecond_fraction_digits = nil
   end
 
   def test_to_json_when_wrapping_a_date_time
@@ -814,6 +822,13 @@ class TimeWithZoneTest < ActiveSupport::TestCase
     ensure
       old_tz ? ENV['TZ'] = old_tz : ENV.delete('TZ')
     end
+
+    def with_standard_json_time_format(boolean = true)
+      old, ActiveSupport.use_standard_json_time_format = ActiveSupport.use_standard_json_time_format, boolean
+      yield
+    ensure
+      ActiveSupport.use_standard_json_time_format = old
+    end
 end
 
 class TimeWithZoneMethodsForTimeAndDateTimeTest < ActiveSupport::TestCase