First Party Data: Updates OpenRTB Field Merging (prebid#2825)

Co-authored-by: VeronikaSolovei9 <kalypsonika@gmail.com>

firstpartydata/extmerger.go

@@ -0,0 +1,60 @@
+package firstpartydata
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/prebid/prebid-server/util/sliceutil"
+	jsonpatch "gopkg.in/evanphx/json-patch.v4"
+)
+
+var (
+	ErrBadRequest = fmt.Errorf("invalid request ext")
+	ErrBadFPD     = fmt.Errorf("invalid first party data ext")
+)
+
+// extMerger tracks a JSON `ext` field within an OpenRTB request. The value of the
+// `ext` field is expected to be modified when calling unmarshal on the same object
+// and will later be updated when invoking Merge.
+type extMerger struct {
+	ext      *json.RawMessage // Pointer to the JSON `ext` field.
+	snapshot json.RawMessage  // Copy of the original state of the JSON `ext` field.
+}
+
+// Track saves a copy of the JSON `ext` field and stores a reference to the extension
+// object for comparison later in the Merge call.
+func (e *extMerger) Track(ext *json.RawMessage) {
+	e.ext = ext
+	e.snapshot = sliceutil.Clone(*ext)
+}
+
+// Merge applies a JSON merge of the stored extension snapshot on top of the current
+// JSON of the tracked extension object.
+func (e extMerger) Merge() error {
+	if e.ext == nil {
+		return nil
+	}
+
+	if len(e.snapshot) == 0 {
+		return nil
+	}
+
+	if len(*e.ext) == 0 {
+		*e.ext = e.snapshot
+		return nil
+	}
+
+	merged, err := jsonpatch.MergePatch(e.snapshot, *e.ext)
+	if err != nil {
+		if errors.Is(err, jsonpatch.ErrBadJSONDoc) {
+			return ErrBadRequest
+		} else if errors.Is(err, jsonpatch.ErrBadJSONPatch) {
+			return ErrBadFPD
+		}
+		return err
+	}
+
+	*e.ext = merged
+	return nil
+}

firstpartydata/extmerger_test.go

@@ -0,0 +1,109 @@
+package firstpartydata
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/prebid/prebid-server/util/sliceutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestExtMerger(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		merger := extMerger{ext: nil, snapshot: json.RawMessage(`{"a":1}`)}
+		assert.NoError(t, merger.Merge())
+		assert.Nil(t, merger.ext)
+	})
+
+	testCases := []struct {
+		name          string
+		givenOriginal json.RawMessage
+		givenFPD      json.RawMessage
+		expectedExt   json.RawMessage
+		expectedErr   string
+	}{
+		{
+			name:          "both-populated",
+			givenOriginal: json.RawMessage(`{"a":1,"b":2}`),
+			givenFPD:      json.RawMessage(`{"b":200,"c":3}`),
+			expectedExt:   json.RawMessage(`{"a":1,"b":200,"c":3}`),
+		},
+		{
+			name:          "both-nil",
+			givenFPD:      nil,
+			givenOriginal: nil,
+			expectedExt:   nil,
+		},
+		{
+			name:          "both-empty",
+			givenOriginal: json.RawMessage(`{}`),
+			givenFPD:      json.RawMessage(`{}`),
+			expectedExt:   json.RawMessage(`{}`),
+		},
+		{
+			name:          "ext-nil",
+			givenOriginal: json.RawMessage(`{"b":2}`),
+			givenFPD:      nil,
+			expectedExt:   json.RawMessage(`{"b":2}`),
+		},
+		{
+			name:          "ext-empty",
+			givenOriginal: json.RawMessage(`{"b":2}`),
+			givenFPD:      json.RawMessage(`{}`),
+			expectedExt:   json.RawMessage(`{"b":2}`),
+		},
+		{
+			name:          "ext-malformed",
+			givenOriginal: json.RawMessage(`{"b":2}`),
+			givenFPD:      json.RawMessage(`malformed`),
+			expectedErr:   "invalid first party data ext",
+		},
+		{
+			name:          "snapshot-nil",
+			givenOriginal: nil,
+			givenFPD:      json.RawMessage(`{"a":1}`),
+			expectedExt:   json.RawMessage(`{"a":1}`),
+		},
+		{
+			name:          "snapshot-empty",
+			givenOriginal: json.RawMessage(`{}`),
+			givenFPD:      json.RawMessage(`{"a":1}`),
+			expectedExt:   json.RawMessage(`{"a":1}`),
+		},
+		{
+			name:          "snapshot-malformed",
+			givenOriginal: json.RawMessage(`malformed`),
+			givenFPD:      json.RawMessage(`{"a":1}`),
+			expectedErr:   "invalid request ext",
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.name, func(t *testing.T) {
+			// Initialize A Ext Raw Message For Testing
+			simulatedExt := json.RawMessage(sliceutil.Clone(test.givenOriginal))
+
+			// Begin Tracking
+			var merger extMerger
+			merger.Track(&simulatedExt)
+
+			// Unmarshal
+			simulatedExt.UnmarshalJSON(test.givenFPD)
+
+			// Merge
+			actualErr := merger.Merge()
+
+			if test.expectedErr == "" {
+				assert.NoError(t, actualErr, "error")
+
+				if test.expectedExt == nil {
+					assert.Nil(t, simulatedExt, "json")
+				} else {
+					assert.JSONEq(t, string(test.expectedExt), string(simulatedExt), "json")
+				}
+			} else {
+				assert.EqualError(t, actualErr, test.expectedErr, "error")
+			}
+		})
+	}
+}