filters: make it possible to filter out user

A user reported that it's not possible to filter context/user. It's a
reasonable request given that the user information has been moved to
context recently.

Here we special-case context/user because we do want to be able to
filter it, but we don't want to filter out other payload in `context`.

CHANGELOG.md

@@ -3,6 +3,8 @@ Airbrake Ruby Changelog
 
 ### master
 
+* Started filtering the context payload
+  ([#55](https://github.com/airbrake/airbrake-ruby/pull/55))
 * Fixed bug when similar keys would be filtered out using non-regexp values for
   `Airbrake.blacklist/whitelist_keys`
   ([#54](https://github.com/airbrake/airbrake-ruby/pull/54))

lib/airbrake-ruby/filters/keys_filter.rb

@@ -9,6 +9,8 @@ module Filters
     # @see KeysWhitelist
     # @see KeysBlacklist
     module KeysFilter
+      FILTERED = '[Filtered]'.freeze
+
       ##
       # Creates a new KeysBlacklist or KeysWhitelist filter that uses the given
       # +patterns+ for filtering a notice's payload.
@@ -28,6 +30,10 @@ def initialize(*patterns)
       def call(notice)
         FILTERABLE_KEYS.each { |key| filter_hash(notice[key]) }
 
+        if notice[:context][:user] && should_filter?(:user)
+          notice[:context][:user] = FILTERED
+        end
+
         return unless notice[:context][:url]
         url = URI(notice[:context][:url])
         return if url.nil? || url.query.nil?

spec/notifier_spec.rb

@@ -553,6 +553,17 @@ def to_json(*)
         with(body: expected_body)
       ).to have_been_made.once
     end
+
+    it "filters out user" do
+      @airbrake.blacklist_keys('user')
+
+      notice = @airbrake.build_notice(ex)
+      notice[:context][:user] = { id: 1337, name: 'Bingo Bango' }
+
+      @airbrake.notify_sync(notice)
+
+      expect_a_request_with_body(/"user":"\[Filtered\]"/)
+    end
   end
 
   describe "#whitelist_keys" do