Fix blocking initialization of readers

brudaswen · Dec 13, 2024 · fb4152f · fb4152f
1 parent ea7f0c1
commit fb4152f
Show file tree

Hide file tree

Showing 2 changed files with 28 additions and 13 deletions.
diff --git a/library/src/main/kotlin/kotlinx/serialization/csv/decode/CsvReader.kt b/library/src/main/kotlin/kotlinx/serialization/csv/decode/CsvReader.kt
@@ -5,7 +5,17 @@ import kotlinx.serialization.csv.config.CsvConfig
 /**
  * Reader that parses CSV input.
  */
-internal class CsvReader(private val source: Source, private val config: CsvConfig) {
+internal class CsvReader(source: Source, private val config: CsvConfig) {
+
+    private val source: Source by lazy {
+        source.also {
+            // Skip Microsoft Excel's byte order marker, should it appear.
+            // This has to happen lazily to avoid blocking read calls during the initialization of the CsvReader.
+            if (source.peek() == '\uFEFF') {
+                source.read()
+            }
+        }
+    }
 
     val offset
         get() = source.offset
@@ -21,11 +31,6 @@ internal class CsvReader(private val source: Source, private val config: CsvConf
 
     private var marks = arrayListOf<Int>()
 
-    init {
-        // Skip Microsoft Excel's byte order marker, should it appear:
-        read("\uFEFF")
-    }
-
     /**
      * Read value in the next column.
      */

diff --git a/library/src/main/kotlin/kotlinx/serialization/csv/decode/FetchSource.kt b/library/src/main/kotlin/kotlinx/serialization/csv/decode/FetchSource.kt
@@ -1,5 +1,6 @@
 package kotlinx.serialization.csv.decode
 
+import java.io.EOFException
 import java.io.Reader
 
 internal class FetchSource(
@@ -20,18 +21,27 @@ internal class FetchSource(
     override var offset: Int = 0
         private set
 
-    private var next: Char? = getChar()
+    private var queue = ArrayList<Char>(2048)
+    private var marks = ArrayList<Int>(2048)
+    private var queueOffset = 0
+
+    private var next: Char? = null
+        get() {
+            if (field == null && nextPosition == 0) {
+                // Reading first char has to happen lazily to avoid blocking read calls
+                // during the initialization of the FetchSource.
+                field = getChar()
+            }
+            return field
+        }
+
     private fun nextChar(): Char {
-        val n = next ?: throw IllegalStateException("Out of characters")
+        val nextChar = next ?: throw EOFException("No more characters to read.")
         next = getChar()
         nextPosition++
-        return n
+        return nextChar
     }
 
-    private var queue = ArrayList<Char>(2048)
-    private var marks = ArrayList<Int>(2048)
-    private var queueOffset = 0
-
     override fun canRead(): Boolean = offset <= nextPosition
 
     override fun read(): Char? {