Support file size retrieval

Author: fzhinkin

core/api/kotlinx-io-core.api

@@ -197,8 +197,9 @@ public final class kotlinx/io/Utf8Kt {
 
 public final class kotlinx/io/files/FileMetadata {
 	public fun <init> ()V
-	public fun <init> (ZZ)V
-	public synthetic fun <init> (ZZILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public fun <init> (ZZJ)V
+	public synthetic fun <init> (ZZJILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public final fun getSize ()J
 	public final fun isDirectory ()Z
 	public final fun isRegularFile ()Z
 }

core/common/src/files/FileSystem.kt

@@ -130,8 +130,18 @@ internal abstract class SystemFileSystemImpl : FileSystem {
 internal expect val SystemFileSystem: FileSystem
 
 public class FileMetadata(
+    /**
+     * Flag indicating that the metadata was retrieved for a regular file.
+     */
     public val isRegularFile: Boolean = false,
-    public val isDirectory: Boolean = false
+    /**
+     * Flag indicating that the metadata was retrieved for a directory.
+     */
+    public val isDirectory: Boolean = false,
+    /**
+     * File size. Defined only for regular files, for other filesystem entities it will be `-1`.
+     */
+    public val size: Long = 0L
 )
 
 public expect class FileNotFoundException(message: String?) : IOException

core/common/test/files/SmokeFileTest.kt

@@ -235,6 +235,21 @@ class SmokeFileTest {
         }
     }
 
+    @OptIn(ExperimentalStdlibApi::class)
+    @Test
+    fun testFileSize() {
+        val path = createTempPath()
+        val expectedSize = 123
+        FileSystem.System.write(path).buffered().use {
+            it.write(ByteArray(expectedSize))
+        }
+        val metadata = FileSystem.System.metadataOrNull(path)
+        assertNotNull(metadata)
+        assertEquals(expectedSize.toLong(), metadata.size)
+
+        assertEquals(-1L, FileSystem.System.metadataOrNull(path.parent!!)!!.size)
+    }
+
     private fun constructAbsolutePath(vararg parts: String): String {
         return Path.separator.toString() + parts.joinToString(Path.separator.toString())
     }

core/js/src/files/FileSystemJs.kt

@@ -97,9 +97,11 @@ private class JsFileSystem : SystemFileSystemImpl() {
         return try {
             val stat = fs.statSync(path.path)
             val mode = stat.mode as Int
+            val isFile =  (mode and fs.constants.S_IFMT as Int) == fs.constants.S_IFREG
             FileMetadata(
-                isRegularFile = (mode and fs.constants.S_IFMT as Int) == fs.constants.S_IFREG,
-                isDirectory = (mode and fs.constants.S_IFMT as Int) == fs.constants.S_IFDIR
+                isRegularFile = isFile,
+                isDirectory = (mode and fs.constants.S_IFMT as Int) == fs.constants.S_IFDIR,
+                if (isFile) (stat.size as Int).toLong() else -1L
             )
         } catch (t: Throwable) {
             if (exists(path)) throw IOException("Stat failed for $path", t)

core/jvm/src/files/FileSystemJvm.kt

@@ -77,7 +77,8 @@ private class JvmFileSystem : SystemFileSystemImpl() {
 
     override fun metadataOrNull(path: Path): FileMetadata? {
         if (!path.file.exists()) return null
-        return FileMetadata(path.file.isFile, path.file.isDirectory)
+        return FileMetadata(path.file.isFile, path.file.isDirectory,
+            if (path.file.isFile) path.file.length() else -1L)
     }
 }
 

core/native/src/files/FileSystemNative.kt

@@ -73,9 +73,11 @@ private class NativeFileSystem : SystemFileSystemImpl() {
                 throw IOException("stat failed to ${path.path}: ${strerror(errno)?.toKString()}")
             }
             val mode = struct_stat.st_mode.toInt()
+            val isFile = (mode and S_IFMT) == S_IFREG
             return FileMetadata(
-                isRegularFile = (mode and S_IFMT) == S_IFREG,
-                isDirectory = (mode and S_IFMT) == S_IFDIR
+                isRegularFile = isFile,
+                isDirectory = (mode and S_IFMT) == S_IFDIR,
+                if (isFile) struct_stat.st_size.toLong() else -1L
             )
         }
     }