Verify FSEntry name

Contributes to #2 .

Handle cyclic folders explicitly, instead of relying on the filesystem.

Reviewed-on: #3

src/main/kotlin/filesystem/FSCreator.kt

@@ -1,36 +1,49 @@
 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 {
     /**
      * Create entry, leaving existing folders' contents, but overwriting existing files.
+     * @throws CyclicFolderException Cyclic folders cannot be created.
      */
-    @Throws(FileSystemException::class)
+    @Throws(CyclicFolderException::class)
     fun create(
         entryToCreate: FSEntry,
         destination: String,
     ) {
-        val queue = ArrayDeque<Pair<FSEntry, Path>>()
-        queue.add(entryToCreate to Path.of(destination))
+        // No point in running anything if we know the input is invalid.
+        if (entryToCreate is FSFolder && entryToCreate.isCyclic()) {
+            throw CyclicFolderException()
+        }
+
+        val queue =
+            ArrayDeque(
+                listOf(
+                    entryToCreate to Path.of(destination),
+                ),
+            )
 
         while (queue.isNotEmpty()) {
             val (entry, dest) = queue.removeFirst()
             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 })
             }
         }
     }
 }
+
+class CyclicFolderException : Exception("Cyclic FSFolders are not supported")

src/main/kotlin/filesystem/FSEntry.kt

@@ -1,9 +1,39 @@
 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 FSFolder(name: String, val entries: List<FSEntry>) : FSEntry(name) {
+    /**
+     * Check whether a folder is cyclic.
+     */
+    fun isCyclic(): Boolean {
+        val seen = listOf(this).toHashSet<FSEntry>()
+        val queue = ArrayDeque(entries)
+        while (queue.isNotEmpty()) {
+            val entry = queue.removeFirst()
+            if (!seen.add(entry)) {
+                return true
+            }
+            if (entry is FSFolder) {
+                queue.addAll(entry.entries)
+            }
+        }
+        return false
+    }
+}
+
+class InvalidEntryNameException(name: String) : Exception("Invalid FSEntry name: '$name'")

src/test/kotlin/filesystem/FSCreatorTest.kt

@@ -1,10 +1,10 @@
 package filesystem
 
 import org.junit.jupiter.api.*
-import java.nio.file.FileSystemException
-import java.nio.file.Files
-import java.nio.file.Path
+import java.io.File
 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 +14,26 @@ 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 +71,10 @@ 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
@@ -81,7 +90,7 @@ class FSCreatorTest {
                                 FSFile("hi", "hi"),
                             ),
                         ),
-                        FSFolder("another-folder", listOf()),
+                        FSFolder("folder", listOf()),
                         FSFile("1.txt", "One!"),
                         FSFile("2.txt", "Two!"),
                     ),
@@ -95,7 +104,7 @@ class FSCreatorTest {
                     "folder",
                     listOf(
                         FSFolder(
-                            "another-folder",
+                            "folder",
                             listOf(
                                 FSFolder(
                                     "secrets",
@@ -112,30 +121,35 @@ 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/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
-    @Timeout(500, unit = TimeUnit.MILLISECONDS) // in case implementation starts trying to handle recursion
-    fun `create throws on recursive folder`() {
+    @Timeout(500, unit = TimeUnit.MILLISECONDS) // in case implementation starts trying to handle cyclic folders
+    fun `create throws on cyclic folder`() {
         val files = mutableListOf<FSEntry>()
         val folder = FSFolder("folder", files)
         files.add(folder)
-        assertThrows<FileSystemException> {
+        assertThrows<CyclicFolderException> {
             creator.create(folder, "_tmp")
         }
     }
-}
 
-fun deleteRecursive(path: Path) {
-    if (Files.isDirectory(path)) {
-        for (child in Files.list(path)) {
-            deleteRecursive(child)
+    @Test
+    @Timeout(500, unit = TimeUnit.MILLISECONDS)
+    fun `create throws on long cyclic folder`() {
+        val files = mutableListOf<FSEntry>()
+        val folder1 = FSFolder("folder", files)
+        val folder2 = FSFolder("folder2", listOf(folder1))
+        val folder3 = FSFolder("folder3", listOf(folder2))
+        val folder4 = FSFolder("folder4", listOf(folder3))
+        files.add(folder4)
+        assertThrows<CyclicFolderException> {
+            creator.create(folder4, "_tmp")
         }
     }
-    Files.delete(path)
 }

src/test/kotlin/filesystem/FSEntryTest.kt

@@ -0,0 +1,42 @@
+package filesystem
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class FSEntryTest {
+    @Test
+    fun `non-cyclic folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFolder("folder", listOf()),
+                    FSFile("text.txt", "Hello!"),
+                ),
+            )
+        assertFalse(folder.isCyclic())
+    }
+
+    @Test
+    fun `cyclic folder`() {
+        val files = mutableListOf<FSEntry>()
+        val folder = FSFolder("folder", files)
+        files.add(folder)
+        assertTrue(folder.isCyclic())
+    }
+
+    @Test
+    fun `long cyclic folder`() {
+        val files = mutableListOf<FSEntry>()
+        val folder1 = FSFolder("folder", files)
+        val folder2 = FSFolder("folder2", listOf(folder1))
+        val folder3 = FSFolder("folder3", listOf(folder2))
+        val folder4 = FSFolder("folder4", listOf(folder3))
+        files.add(folder4)
+        assertTrue(folder1.isCyclic())
+        assertTrue(folder2.isCyclic())
+        assertTrue(folder3.isCyclic())
+        assertTrue(folder4.isCyclic())
+    }
+}