Fix memory leak (#36)

Fixes #35

Author: brudaswen

library/src/commonMain/kotlin/kotlinx/serialization/csv/decode/CsvReader.kt

@@ -190,15 +190,15 @@ internal class CsvReader(
      */
     fun unmark() {
         source.unmark()
-        marks.removeAt(marks.size - 1)
+        marks.removeLast()
     }
 
     /**
      * Reset the stream to the last [mark]ed position (and remove the mark).
      */
     fun reset() {
         source.reset()
-        recordNo = marks.removeAt(marks.size - 1)
+        recordNo = marks.removeLast()
     }
 
     /**

library/src/commonMain/kotlin/kotlinx/serialization/csv/source/CharStreamSource.kt

@@ -72,11 +72,13 @@ internal class CharStreamSource(
     }
 
     override fun unmark() {
-        marks.removeAt(marks.lastIndex)
+        marks.removeLast()
+
+        if (marks.isEmpty()) queue.clear()
     }
 
     override fun reset() {
-        offset = marks[marks.lastIndex]
-        marks.removeAt(marks.lastIndex)
+        offset = marks.last()
+        marks.removeLast()
     }
 }

library/src/commonMain/kotlin/kotlinx/serialization/csv/source/StringSource.kt

@@ -35,11 +35,11 @@ internal class StringSource(
     }
 
     override fun unmark() {
-        marks.removeAt(marks.size - 1)
+        marks.removeLast()
     }
 
     override fun reset() {
-        position = marks.removeAt(marks.size - 1)
+        position = marks.removeLast()
     }
 
     override fun toString(): String =

library/src/jvmTest/kotlin/kotlinx/serialization/csv/example/SteamingTest.kt

@@ -5,6 +5,7 @@ import kotlinx.coroutines.async
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
 import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.Serializable
 import kotlinx.serialization.csv.Csv
 import kotlinx.serialization.csv.example.Tire.Axis.FRONT
 import kotlinx.serialization.csv.example.Tire.Axis.REAR
@@ -13,13 +14,17 @@ import kotlinx.serialization.csv.example.Tire.Side.RIGHT
 import kotlinx.serialization.csv.recordReader
 import kotlinx.serialization.csv.recordWriter
 import kotlinx.serialization.modules.SerializersModule
+import java.io.File
+import java.io.FileInputStream
+import java.io.FileOutputStream
 import java.io.PipedReader
 import java.io.PipedWriter
 import kotlin.io.buffered
 import kotlin.io.println
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.time.Duration.Companion.milliseconds
+import kotlin.time.Duration.Companion.minutes
 import kotlin.use
 import kotlin.uuid.Uuid
 
@@ -129,4 +134,45 @@ class SteamingTest {
 
         assertEquals(testData, result)
     }
+
+    @Test
+    fun testLargeFile() = runTest(timeout = 10.minutes) {
+        @Serializable
+        data class Entry(
+            val id: Int,
+            val value: String,
+        )
+
+        val csv = Csv {
+            hasHeaderRecord = true
+        }
+
+        val file = File("file.csv")
+
+        println("Writing...")
+        FileOutputStream(file).buffered().use { output ->
+            val writer = csv.recordWriter(Entry.serializer(), output)
+            repeat(10_000_000) {
+                val entry = Entry(it, "Value $it")
+                writer.write(entry)
+
+                if (entry.id % 100_000 == 0) {
+                    println("$entry written.")
+                }
+            }
+        }
+
+        println("Reading...")
+        FileInputStream(file).buffered().use { input ->
+            val reader = csv.recordReader(Entry.serializer(), input)
+
+            reader.asSequence().forEach { entry ->
+                if (entry.id % 100_000 == 0) {
+                    println("$entry read.")
+                }
+            }
+        }
+
+        file.delete()
+    }
 }