filters/keys: duplicate hashes while filtering

Fixes #592 (Session deep values are modified if it contains filtered (blocklist)
keys)

CHANGELOG.md

@@ -3,6 +3,9 @@ Airbrake Ruby Changelog
 
 ### master
 
+* Fixed unwanted mutation of nested hashes passed through `Notice#[]=`
+  ([#597](https://github.com/airbrake/airbrake-ruby/pull/597))
+
 ### [v5.0.0.rc.2][v5.0.0.rc.2] (July 29, 2020)
 
 * Started sending information about notifier name & version, operating system &

lib/airbrake-ruby/filters/keys_filter.rb

@@ -64,7 +64,10 @@ def call(notice)
           validate_patterns
         end
 
-        FILTERABLE_KEYS.each { |key| filter_hash(notice[key]) }
+        FILTERABLE_KEYS.each do |key|
+          notice[key] = filter_hash(notice[key])
+        end
+
         FILTERABLE_CONTEXT_KEYS.each { |key| filter_context_key(notice, key) }
 
         return unless notice[:context][:url]
@@ -81,15 +84,21 @@ def should_filter?(_key)
       def filter_hash(hash)
         return hash unless hash.is_a?(Hash)
 
+        hash_copy = hash.dup
+
         hash.each_key do |key|
           if should_filter?(key.to_s)
-            hash[key] = FILTERED
-          elsif hash[key].is_a?(Hash)
-            filter_hash(hash[key])
+            hash_copy[key] = FILTERED
+          elsif hash_copy[key].is_a?(Hash)
+            hash_copy[key] = filter_hash(hash_copy[key])
           elsif hash[key].is_a?(Array)
-            hash[key].each { |h| filter_hash(h) }
+            hash_copy[key].each_with_index do |h, i|
+              hash_copy[key][i] = filter_hash(h)
+            end
           end
         end
+
+        hash_copy
       end
 
       def filter_url_params(url)
@@ -142,7 +151,9 @@ def validate_patterns
       def filter_context_key(notice, key)
         return unless notice[:context][key]
         return if notice[:context][key] == FILTERED
-        return filter_hash(notice[:context][key]) unless should_filter?(key)
+        unless should_filter?(key)
+          return notice[:context][key] = filter_hash(notice[:context][key])
+        end
 
         notice[:context][key] = FILTERED
       end

spec/filters/keys_blocklist_spec.rb

@@ -150,6 +150,17 @@
           { bongo: { bish: '[Filtered]' } },
         ],
       )
+
+      it "doesn't mutate the original hash" do
+        blocklist = described_class.new([:bish])
+
+        params = { bongo: { bish: 'bash' } }
+        notice[:params] = params
+
+        blocklist.call(notice)
+
+        expect(params[:bongo][:bish]).to eq('bash')
+      end
     end
 
     context "and it is recursive" do

spec/notice_spec.rb

@@ -268,7 +268,7 @@ def to_json(*)
     it "sets a payload value" do
       hash = { bingo: 'bango' }
       notice[:params] = hash
-      expect(notice[:params]).to equal(hash)
+      expect(notice[:params]).to eq(hash)
     end
 
     it "raises error if notice is ignored" do