Bug fix for issue 745 : Fix string duplication on escaped chunk boundaries

json/src/main/scala/fs2/data/json/internal/JsonTokenParser.scala

@@ -55,6 +55,7 @@ private[json] class JsonTokenParser[F[_], T, Res](
         case '\\' =>
           T.appendMarked(context, acc)
           T.advance(context)
+          T.mark(context)
           slowString_(key, StringState.SeenBackslash, 0, acc)
         case c =>
           if (c >= 0x20 && c <= 0x10ffff) {

json/src/test/scala/fs2/data/json/Issue745Spec.scala

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2024 fs2-data Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package fs2
+package data.json
+
+import cats.effect.IO
+import weaver.SimpleIOSuite
+
+object Issue745Spec extends SimpleIOSuite {
+
+  // Tests the fix for https://github.com/gnieh/fs2-data/issues/745
+  // Same root cause as #515, but for the String chunk path.
+  // The fast-path string_ method was missing T.mark(context) after seeing a backslash,
+  // so when a chunk boundary fell right after the backslash, appendMarked in slowString_
+  // would re-append already-consumed content, duplicating part of the string.
+
+  test("not duplicate tokens for escaped quotes on String chunk boundaries") {
+    val input = """{"message":"said \"hello\""}"""
+    // Try every possible 2-chunk split position
+    (1 until input.length).toList.foldLeft(IO.pure(expect(true))) { (acc, splitAt) =>
+      acc.flatMap { prev =>
+        val (a, b) = input.splitAt(splitAt)
+        (Stream.emit(a) ++ Stream.emit(b))
+          .through(tokens[IO, String])
+          .through(render.compact)
+          .compile
+          .foldMonoid
+          .map(out => prev and expect.eql(input, out))
+      }
+    }
+  }
+
+  test("not duplicate tokens for backslash-backslash on String chunk boundaries") {
+    val input =
+      """{"FilePaths":["\\\\path\\to\\some\\file.txt","\\\\path\\to\\some\\other\\file.txt","\\\\path\\to\\another\\file.txt"]}"""
+    (1 until input.length).toList.foldLeft(IO.pure(expect(true))) { (acc, splitAt) =>
+      acc.flatMap { prev =>
+        val (a, b) = input.splitAt(splitAt)
+        (Stream.emit(a) ++ Stream.emit(b))
+          .through(tokens[IO, String])
+          .through(render.compact)
+          .compile
+          .foldMonoid
+          .map(out => prev and expect.eql(input, out))
+      }
+    }
+  }
+
+}