Verify FSEntry name

src/main/kotlin/filesystem/FSCreator.kt

@@ -2,8 +2,10 @@ package filesystem
 
 import java.nio.file.FileAlreadyExistsException
 import java.nio.file.FileSystemException
-import java.nio.file.Files
 import java.nio.file.Path
+import kotlin.io.path.createDirectory
+import kotlin.io.path.createFile
+import kotlin.io.path.writeText
 
 class FSCreator {
     /**
@@ -22,13 +24,13 @@ class FSCreator {
             val path = dest.resolve(entry.name)
             try {
                 when (entry) {
-                    is FSFile -> Files.createFile(path)
-                    is FSFolder -> Files.createDirectory(path)
+                    is FSFile -> path.createFile()
+                    is FSFolder -> path.createDirectory()
                 }
             } catch (_: FileAlreadyExistsException) {
             } // Allow files/folders to already exist.
             when (entry) {
-                is FSFile -> Files.write(path, entry.content.toByteArray())
+                is FSFile -> path.writeText(entry.content)
                 is FSFolder -> queue.addAll(entry.entries.map { it to path })
             }
         }

src/main/kotlin/filesystem/FSEntry.kt

@@ -1,9 +1,21 @@
 package filesystem
 
+import kotlin.io.path.Path
+
 // Note sealed allows for simpler logic in FSCreator by guaranteeing FSFile and FSFolder are the only possible FSEntries
 // (as we expect), and it also implicitly makes the class abstract as required.
-sealed class FSEntry(val name: String)
+sealed class FSEntry(val name: String) {
+    init {
+        val p = Path(name)
+        // Only allow single filenames (no paths or relative references (e.g. ".."))
+        if (p.toList().size != 1 || p.fileName != p.toFile().canonicalFile.toPath().fileName) {
+            throw InvalidEntryNameException(name)
+        }
+    }
+}
 
 class FSFile(name: String, val content: String) : FSEntry(name)
 
 class FSFolder(name: String, val entries: List<FSEntry>) : FSEntry(name)
+
+class InvalidEntryNameException(name: String) : Exception("Invalid FSEntry name: '$name'")

src/test/kotlin/filesystem/FSCreatorTest.kt

@@ -1,10 +1,11 @@
 package filesystem
 
 import org.junit.jupiter.api.*
+import java.io.File
 import java.nio.file.FileSystemException
-import java.nio.file.Files
-import java.nio.file.Path
 import java.util.concurrent.TimeUnit
+import kotlin.io.path.Path
+import kotlin.io.path.createDirectory
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -14,17 +15,26 @@ class FSCreatorTest {
     @BeforeEach
     fun `before each`() {
         assertDoesNotThrow("should create _tmp directory") {
-            Files.createDirectory(Path.of("_tmp"))
+            Path("_tmp").createDirectory()
         }
     }
 
     @AfterEach
     fun `after each`() {
         assertDoesNotThrow("should delete _tmp directory") {
-            deleteRecursive(Path.of("_tmp"))
+            File("_tmp").deleteRecursively()
         }
     }
 
+    @Test
+    fun `create file`() {
+        val file = FSFile("test.txt", "This is a file")
+        assertDoesNotThrow("should create file") {
+            creator.create(file, "_tmp")
+        }
+        assertEquals(file.content, File("_tmp/", file.name).readText())
+    }
+
     @Test
     fun `create entries`() {
         val readme = FSFile("README", "Hello World!")
@@ -62,10 +72,10 @@ class FSCreatorTest {
         }
         // If objects don't exist, these functions will throw anyway, so don't explicitly check for existence.
         // Similarly, don't explicitly check if an object is a directory.
-        assertEquals(readme.content, Files.readString(Path.of("_tmp/folder", readme.name)))
-        assertEquals(gomod.content, Files.readString(Path.of("_tmp/folder", gomod.name)))
-        assertEquals(maingo.content, Files.readString(Path.of("_tmp/folder", maingo.name)))
-        assertEquals(helloworldgo.content, Files.readString(Path.of("_tmp/folder/utils", helloworldgo.name)))
+        assertEquals(readme.content, File("_tmp/folder", readme.name).readText())
+        assertEquals(gomod.content, File("_tmp/folder", gomod.name).readText())
+        assertEquals(maingo.content, File("_tmp/folder", maingo.name).readText())
+        assertEquals(helloworldgo.content, File("_tmp/folder/utils", helloworldgo.name).readText())
     }
 
     @Test
@@ -112,11 +122,11 @@ class FSCreatorTest {
                 "_tmp",
             )
         }
-        assertEquals("hi", Files.readString(Path.of("_tmp/folder/sub-folder/hi")))
-        assertEquals("P4ssW0rd", Files.readString(Path.of("_tmp/folder/another-folder/secrets/secret")))
-        assertEquals("One is a good number", Files.readString(Path.of("_tmp/folder/1.txt")))
-        assertEquals("Two!", Files.readString(Path.of("_tmp/folder/2.txt")))
-        assertEquals("Three!", Files.readString(Path.of("_tmp/folder/3.txt")))
+        assertEquals("hi", File("_tmp/folder/sub-folder/hi").readText())
+        assertEquals("P4ssW0rd", File("_tmp/folder/another-folder/secrets/secret").readText())
+        assertEquals("One is a good number", File("_tmp/folder/1.txt").readText())
+        assertEquals("Two!", File("_tmp/folder/2.txt").readText())
+        assertEquals("Three!", File("_tmp/folder/3.txt").readText())
     }
 
     @Test
@@ -130,12 +140,3 @@ class FSCreatorTest {
         }
     }
 }
-
-fun deleteRecursive(path: Path) {
-    if (Files.isDirectory(path)) {
-        for (child in Files.list(path)) {
-            deleteRecursive(child)
-        }
-    }
-    Files.delete(path)
-}