Fixes reading CSV files with BOM characters

core/build.gradle.kts

@@ -66,6 +66,7 @@ dependencies {
     implementation(libs.kotlin.stdlib.jdk8)
 
     api(libs.commonsCsv)
+    implementation(libs.commonsIo)
     implementation(libs.serialization.core)
     implementation(libs.serialization.json)
 

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/io/csv.kt

@@ -2,6 +2,7 @@ package org.jetbrains.kotlinx.dataframe.io
 
 import org.apache.commons.csv.CSVFormat
 import org.apache.commons.csv.CSVRecord
+import org.apache.commons.io.input.BOMInputStream
 import org.jetbrains.kotlinx.dataframe.AnyFrame
 import org.jetbrains.kotlinx.dataframe.AnyRow
 import org.jetbrains.kotlinx.dataframe.DataColumn
@@ -19,6 +20,7 @@ import org.jetbrains.kotlinx.dataframe.impl.ColumnNameGenerator
 import org.jetbrains.kotlinx.dataframe.impl.api.Parsers
 import org.jetbrains.kotlinx.dataframe.impl.api.parse
 import org.jetbrains.kotlinx.dataframe.values
+import java.io.BufferedInputStream
 import java.io.BufferedReader
 import java.io.File
 import java.io.FileInputStream
@@ -272,21 +274,20 @@ public fun DataFrame.Companion.readDelim(
     duplicate: Boolean = true,
     charset: Charset = defaultCharset,
     parserOptions: ParserOptions? = null,
-): AnyFrame =
-    if (isCompressed) {
-        InputStreamReader(GZIPInputStream(inStream), charset)
-    } else {
-        BufferedReader(InputStreamReader(inStream, charset))
-    }.run {
-        readDelim(
-            this,
-            getFormat(csvType, delimiter, header, duplicate),
-            colTypes,
-            skipLines,
-            readLines,
-            parserOptions,
-        )
-    }
+): AnyFrame {
+    val bufferedInStream = BufferedInputStream(if (isCompressed) GZIPInputStream(inStream) else inStream)
+    val bomIn = BOMInputStream.builder().setInputStream(bufferedInStream).get()
+    val bufferedReader = BufferedReader(InputStreamReader(bomIn, charset))
+
+    return readDelim(
+        reader = bufferedReader,
+        format = getFormat(csvType, delimiter, header, duplicate),
+        colTypes = colTypes,
+        skipLines = skipLines,
+        readLines = readLines,
+        parserOptions = parserOptions,
+    )
+}
 
 public enum class ColType {
     Int,

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/io/CsvTests.kt

@@ -276,10 +276,17 @@ class CsvTests {
         df shouldBe dataFrameOf("a", "b", "c")(1, 2, 3)
     }
 
+    @Test
+    fun `file with BOM`() {
+        val df = DataFrame.readCSV(withBomCsv, delimiter = ';')
+        df.columnNames() shouldBe listOf("Column1", "Column2")
+    }
+
     companion object {
         private val simpleCsv = testCsv("testCSV")
         private val csvWithFrenchLocale = testCsv("testCSVwithFrenchLocale")
         private val wineCsv = testCsv("wine")
         private val durationCsv = testCsv("duration")
+        private val withBomCsv = testCsv("with-bom")
     }
 }

core/src/test/resources/with-bom.csv

@@ -0,0 +1,3 @@
+Column1;Column2
+0,25;18
+1,24;19

gradle/libs.versions.toml

@@ -24,6 +24,7 @@ kover = "0.6.1"
 
 commonsCsv = "1.10.0"
 commonsCompress = "1.26.0"
+commonsIo = "2.16.1"
 serialization = "1.7.0"
 fuel = "2.3.1"
 poi = "5.2.5"
@@ -71,6 +72,7 @@ kotlin-reflect = { group = "org.jetbrains.kotlin", name = "kotlin-reflect", vers
 kotlin-scriptingJvm = { group = "org.jetbrains.kotlin", name = "kotlin-scripting-jvm", version.ref = "kotlin" }
 commonsCsv = { group = "org.apache.commons", name = "commons-csv", version.ref = "commonsCsv" }
 commonsCompress = { group = "org.apache.commons", name = "commons-compress", version.ref = "commonsCompress" }
+commonsIo = { group = "commons-io", name = "commons-io", version.ref = "commonsIo" }
 # Serialization
 serialization-core = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-core", version.ref = "serialization" }
 serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "serialization" }