Harden web search context prop parsing

conversations/web_search_context.go

@@ -60,6 +60,12 @@ func (c *Conversations) unmarshalWebSearchContext(webSearchContextJSON string, p
 		return nil
 	}
 
+	// A "null" or absent JSON value unmarshals into a nil map, so ensure the
+	// map is initialized before writing tracking keys below.
+	if params == nil {
+		params = make(map[string]interface{})
+	}
+
 	// Reconstruct proper types for web search context values
 	if raw, ok := params[mmtools.WebSearchContextKey]; ok {
 		// Re-marshal and unmarshal to get proper types

conversations/web_search_context_test.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2023-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package conversations
+
+import (
+	"testing"
+
+	"github.com/mattermost/mattermost-plugin-agents/v2/mmapi/mocks"
+	"github.com/mattermost/mattermost-plugin-agents/v2/mmtools"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUnmarshalWebSearchContext(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		wantNil bool
+	}{
+		{
+			// A user-controlled post prop can carry the literal JSON string
+			// "null", which unmarshals into a nil map without error. The
+			// function must still return a usable, non-nil map rather than
+			// panicking on the tracking-key writes.
+			name:    "null literal returns usable map without panicking",
+			input:   "null",
+			wantNil: false,
+		},
+		{
+			name:    "valid object returns map with reset tracking keys",
+			input:   `{"some_existing_key":"some_value"}`,
+			wantNil: false,
+		},
+		{
+			name:    "malformed json returns nil",
+			input:   `{not valid json`,
+			wantNil: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			mmClient := mocks.NewMockClient(t)
+			mmClient.On("LogDebug", mock.Anything, mock.Anything).Maybe().Return()
+			mmClient.On("LogError", mock.Anything, mock.Anything).Maybe().Return()
+			mmClient.On("LogWarn", mock.Anything, mock.Anything).Maybe().Return()
+
+			c := &Conversations{mmClient: mmClient}
+
+			var result map[string]interface{}
+			require.NotPanics(t, func() {
+				result = c.unmarshalWebSearchContext(tc.input, "post-id")
+			}, "unmarshalWebSearchContext must not panic on user-controlled input")
+
+			if tc.wantNil {
+				assert.Nil(t, result)
+				return
+			}
+
+			require.NotNil(t, result, "expected a usable, non-nil map")
+
+			count, hasCount := result[mmtools.WebSearchCountKey]
+			require.True(t, hasCount, "expected reset search count key to be present")
+			assert.Equal(t, 0, count)
+
+			queries, hasQueries := result[mmtools.WebSearchExecutedQueriesKey]
+			require.True(t, hasQueries, "expected reset executed queries key to be present")
+			assert.Equal(t, []string{}, queries)
+		})
+	}
+}