Support long paths and getting/setting the current working directory (#236)

Author: brianquinlan

pkgs/io_file/constants.json

@@ -53,6 +53,9 @@
     "O_TRUNC",
     "O_WRONLY"
   ],
+  "<limits.h>": [
+    "PATH_MAX"
+  ],
   "<dirent.h>" : [
     "DT_BLK",
     "DT_CHR",

pkgs/io_file/dart_test.yaml

@@ -0,0 +1,3 @@
+concurrency: 1
+reporter: compact
+test-randomize-ordering-seed: random

pkgs/io_file/lib/src/constant_bindings.g.dart

@@ -132,7 +132,13 @@ class WriteMode {
 ///
 /// TODO(brianquinlan): Far now, this class is not meant to be implemented,
 /// extended outside of this package. Clarify somewhere that people implementing
-/// this class should reach out to be.
+/// this class should reach out to me.
+///
+/// On Windows, paths refering to objects in the
+/// [win32 device namespace](https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-device-namespaces),
+/// such as named pipes, physical disks, and serial comnmunications ports
+/// (e.g. 'COM1'), must be prefixed with `r'\\.\'`. For example, `'COM1'` would
+/// be refered to by the path `r'\\.\COM1'`.
 @sealed
 abstract class FileSystem {
   /// Create a directory at the given path.
@@ -186,6 +192,19 @@ abstract class FileSystem {
   /// written to is to attempt to open it.
   Metadata metadata(String path);
 
+  /// The current
+  /// [working directory](https://en.wikipedia.org/wiki/Working_directory) of
+  /// the Dart process.
+  ///
+  /// Setting the value of this field will change the working directory for
+  /// *all* isolates.
+  ///
+  /// On Windows, unless
+  /// [long paths are enabled](https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation),
+  /// the maximum length of the [currentDirectory] path is 260 characters.
+  String get currentDirectory;
+  set currentDirectory(String path);
+
   /// Deletes the directory at the given path.
   ///
   /// If `path` is a directory but the directory is not empty, then

pkgs/io_file/lib/src/constants.g.dart

@@ -26,7 +26,7 @@ const _nanosecondsPerSecond = 1000000000;
 bool _isDotOrDotDot(Pointer<Char> s) => // ord('.') == 46
     s[0] == 46 && ((s[1] == 0) || (s[1] == 46 && s[2] == 0));
 
-Exception _getError(int err, String message, String path) {
+Exception _getError(int err, String message, [String? path]) {
   // TODO(brianquinlan): In the long-term, do we need to avoid exceptions that
   // are part of `dart:io`? Can we move those exceptions into a different
   // namespace?
@@ -35,12 +35,16 @@ Exception _getError(int err, String message, String path) {
     err,
   );
 
-  if (err == libc.EPERM || err == libc.EACCES) {
-    return io.PathAccessException(path, osError, message);
-  } else if (err == libc.EEXIST) {
-    return io.PathExistsException(path, osError, message);
-  } else if (err == libc.ENOENT) {
-    return io.PathNotFoundException(path, osError, message);
+  if (path != null) {
+    if (err == libc.EPERM || err == libc.EACCES) {
+      return io.PathAccessException(path, osError, message);
+    } else if (err == libc.EEXIST) {
+      return io.PathExistsException(path, osError, message);
+    } else if (err == libc.ENOENT) {
+      return io.PathNotFoundException(path, osError, message);
+    } else {
+      return io.FileSystemException(message, path, osError);
+    }
   } else {
     return io.FileSystemException(message, path, osError);
   }
@@ -241,6 +245,24 @@ final class PosixFileSystem extends FileSystem {
     }
   });
 
+  @override
+  set currentDirectory(String path) => ffi.using((arena) {
+    if (libc.chdir(path.toNativeUtf8(allocator: arena).cast()) == -1) {
+      final errno = libc.errno;
+      throw _getError(errno, 'chdir failed', path);
+    }
+  });
+
+  @override
+  String get currentDirectory => ffi.using((arena) {
+    final buffer = arena<Char>(libc.PATH_MAX);
+    if (libc.getcwd(buffer, libc.PATH_MAX) == nullptr) {
+      final errno = libc.errno;
+      throw _getError(errno, 'getcwd failed', null);
+    }
+    return buffer.cast<ffi.Utf8>().toDartString();
+  });
+
   @override
   String createTemporaryDirectory({String? parent, String? prefix}) =>
       ffi.using((arena) {