dart:io library

File, socket, HTTP, and other I/O support for non-web applications.

Important: Browser-based apps can't use this library. Only the following can import and use the dart:io library:

• Servers
• Command-line scripts
• Flutter mobile apps
• Flutter desktop apps

This library allows you to work with files, directories, sockets, processes, HTTP servers and clients, and more. Many operations related to input and output are asynchronous and are handled using Futures or Streams, both of which are defined in the dart:async library.

To use the dart:io library in your code:

import 'dart:io';

For an introduction to I/O in Dart, see the dart:io library tour.

File, Directory, and Link

An instance of File, Directory, or Link represents a file, directory, or link, respectively, in the native file system.

You can manipulate the file system through objects of these types. For example, you can rename a file or directory:

File myFile = File('myFile.txt');
myFile.rename('yourFile.txt').then((_) => print('file renamed'));

Many methods provided by the File, Directory, and Link classes run asynchronously and return a Future.

FileSystemEntity

File, Directory, and Link all extend FileSystemEntity. In addition to being the superclass for these classes, FileSystemEntity has a number of static methods for working with paths.

To get information about a path, you can use the FileSystemEntity static methods such as FileSystemEntitiy.isDirectory, FileSystemEntitiy.isFile, and FileSystemEntitiy.exists. Because file system access involves I/O, these methods are asynchronous and return a Future.

FileSystemEntity.isDirectory(myPath).then((isDir) {
  if (isDir) {
    print('$myPath is a directory');
  } else {
    print('$myPath is not a directory');
  }
});

HttpServer and HttpClient

The classes HttpServer and HttpClient provide HTTP server and HTTP client functionality.

The HttpServer class provides the basic functionality for implementing an HTTP server. For some higher-level building-blocks, we recommend that you try the shelf pub package, which contains a set of high-level classes that, together with the HttpServer class in this library, make it easier to implement HTTP servers.

Process

The Process class provides a way to run a process on the native machine. For example, the following code spawns a process that recursively lists the files under web.

Process.start('ls', ['-R', 'web']).then((process) {
  stdout.addStream(process.stdout);
  stderr.addStream(process.stderr);
  process.exitCode.then(print);
});

Using Process.start returns a Future, which completes with a Process object when the process has started. This Process object allows you to interact with the process while it is running. Using Process.run returns a Future, which completes with a ProcessResult object when the spawned process has terminated. This ProcessResult object collects the output and exit code from the process.

When using Process.start, you need to read all data coming on the Process.stdout and Process.stderr streams, otherwise the system resources will not be freed.

WebSocket

The WebSocket class provides support for the web socket protocol. This allows full-duplex communications between client and server applications.

A web socket server uses a normal HTTP server for accepting web socket connections. The initial handshake is a HTTP request which is then upgraded to a web socket connection. The server upgrades the request using WebSocketTransformer and listens for the data on the returned web socket. For example, here's a mini server that listens for 'ws' data on a WebSocket:

runZoned(() async {
  var server = await HttpServer.bind('127.0.0.1', 4040);
  server.listen((HttpRequest req) async {
    if (req.uri.path == '/ws') {
      var socket = await WebSocketTransformer.upgrade(req);
      socket.listen(handleMsg);
    }
  });
}, onError: (e) => print("An error occurred."));

The client connects to the WebSocket using the WebSocket.connect method and a URI that uses the Web Socket protocol. The client can write to the WebSocket with the Websocket.add method. For example,

var socket = await WebSocket.connect('ws://127.0.0.1:4040/ws');
socket.add('Hello, World!');

Check out the websocket_sample app, which uses WebSockets to communicate with a server.

Socket and ServerSocket

Clients and servers use Sockets to communicate using the TCP protocol. Use ServerSocket on the server side and Socket on the client. The server creates a listening socket using the bind() method and then listens for incoming connections on the socket. For example:

ServerSocket.bind('127.0.0.1', 4041)
  .then((serverSocket) {
    serverSocket.listen((socket) {
      socket.transform(utf8.decoder).listen(print);
    });
  });

A client connects a Socket using the connect() method, which returns a Future. Using write(), writeln(), or writeAll() are the easiest ways to send data over the socket. For example:

Socket.connect('127.0.0.1', 4041).then((socket) {
  socket.write('Hello, World!');
});

Besides Socket and ServerSocket, the RawSocket and RawServerSocket classes are available for lower-level access to async socket IO.

Standard output, error, and input streams

This library provides the standard output, error, and input streams, named stdout, stderr, and stdin, respectively.

The stdout and stderr streams are both IOSinks and have the same set of methods and properties.

To write a string to stdout:

stdout.writeln('Hello, World!');

To write a list of objects to stderr:

stderr.writeAll([ 'That ', 'is ', 'an ', 'error.', '\n']);

The standard input stream is a true Stream, so it inherits properties and methods from the Stream class.

To read text synchronously from the command line (the program blocks waiting for user to type information):

String inputText = stdin.readLineSync();

Classes

BytesBuilder

Builds a list of bytes, allowing bytes and lists of bytes to be added at the end. [...]

CompressionOptions

Options controlling compression in a WebSocket. [...]

ConnectionTask<S>

A cancelable connection attempt. [...]

ContentType

A MIME/IANA media type used as the value of the HttpHeaders.contentTypeHeader header. [...]

Cookie

Representation of a cookie. For cookies received by the server as Cookie header values only name and value properties will be set. When building a cookie for the 'set-cookie' header in the server and when receiving cookies in the client as 'set-cookie' headers all fields can be used.

Datagram

A data packet received by a RawDatagramSocket.

DetachedSocket

When detaching a socket from either the HttpServer or the HttpClient due to a HTTP connection upgrade there might be unparsed data already read from the socket. This unparsed data together with the detached socket is returned in an instance of this class.

Directory

A reference to a directory (or folder) on the file system. [...]

File

A reference to a file on the file system. [...]

FileLock

Type of lock when requesting a lock on a file.

FileMode

The modes in which a File can be opened.

FileStat

The result of calling the POSIX stat() function on a file system object. [...]

FileSystemCreateEvent

File system event for newly created file system objects.

FileSystemDeleteEvent

File system event for deletion of file system objects.

FileSystemEntity

The common superclass of File, Directory, and Link. [...]

FileSystemEntityType

The type of an entity on the file system, such as a file, directory, or link. [...]

FileSystemEvent

Base event class emitted by FileSystemEntity.watch.

FileSystemModifyEvent

File system event for modifications of file system objects.

FileSystemMoveEvent

File system event for moving of file system objects.

GZipCodec

The GZipCodec encodes raw bytes to GZip compressed bytes and decodes GZip compressed bytes to raw bytes. [...]

HeaderValue

Representation of a header value in the form: [...]

HttpClient

A client that receives content, such as web pages, from a server using the HTTP protocol. [...]

HttpClientBasicCredentials

Represents credentials for basic authentication.

HttpClientCredentials

HttpClientDigestCredentials

Represents credentials for digest authentication. Digest authentication is only supported for servers using the MD5 algorithm and quality of protection (qop) of either "none" or "auth".

HttpClientRequest

HTTP request for a client connection. [...]

HttpClientResponse

HTTP response for a client connection. [...]

HttpConnectionInfo

Information about an HttpRequest, HttpResponse, HttpClientRequest, or HttpClientResponse connection.

HttpConnectionsInfo

Summary statistics about an HttpServers current socket connections.

HttpDate

Utility functions for working with dates with HTTP specific date formats.

HttpHeaders

Headers for HTTP requests and responses. [...]

HttpOverrides

This class facilitates overriding HttpClient with a mock implementation. It should be extended by another class in client code with overrides that construct a mock implementation. The implementation in this base class defaults to the actual HttpClient implementation. For example: [...]

HttpRequest

A server-side object that contains the content of and information about an HTTP request. [...]

HttpResponse

An HTTP response, which returns the headers and data from the server to the client in response to an HTTP request. [...]

HttpServer

A server that delivers content, such as web pages, using the HTTP protocol. [...]

HttpSession

HttpStatus

HTTP status codes. Exported in dart:io and dart:html.

InternetAddress

An internet address or a Unix domain address. [...]

InternetAddressType

The type, or address family, of an InternetAddress. [...]

IOOverrides

Facilities for overriding various APIs of dart:io with mock implementations. [...]

IOSink

A combined byte and text output. [...]

Link

References to filesystem links.

NetworkInterface

A NetworkInterface represents an active network interface on the current system. It contains a list of InternetAddresses that are bound to the interface.

Platform

Information about the environment in which the current program is running. [...]

Process

The means to execute a program. [...]

ProcessInfo

Methods for retrieving information about the current process.

ProcessResult

The result of running a non-interactive process started with Process.run or Process.runSync.

ProcessSignal

On Posix systems, ProcessSignal is used to send a specific signal to a child process, see Process.kill. [...]

ProcessStartMode

Modes for running a new process.

RandomAccessFile

Random access to the data in a file. [...]

RawDatagramSocket

An unbuffered interface to a UDP socket. [...]

RawSecureServerSocket

A server socket providing a stream of low-level RawSecureSockets. [...]

RawSecureSocket

RawSecureSocket provides a secure (SSL or TLS) network connection. [...]

RawServerSocket

A listening socket. [...]

RawSocket

A TCP connection. [...]

RawSocketEvent

Events for the RawSocket. [...]

RawSocketOption

The RawSocketOption is used as a parameter to Socket.setRawOption and RawSocket.setRawOption to customize the behaviour of the underlying socket. [...]

RawSynchronousSocket

A low-level class for communicating synchronously over a TCP socket. [...]

RawZLibFilter

The RawZLibFilter class provides a low-level interface to zlib.

RedirectInfo

Redirect information.

SecureServerSocket

A server socket, providing a stream of high-level Sockets. [...]

SecureSocket

A TCP socket using TLS and SSL. [...]

SecurityContext

The object containing the certificates to trust when making a secure client connection, and the certificate chain and private key to serve from a secure server. [...]

ServerSocket

A listening socket. [...]

Socket

A TCP connection between two sockets. [...]

SocketDirection

The SocketDirection is used as a parameter to Socket.close and RawSocket.close to close a socket in the specified direction(s).

SocketOption

An option for a socket which is configured using Socket.setOption. [...]

Stdin

The standard input stream of the process. [...]

StdioType

The type of object a standard IO stream can be attached to.

Stdout

An IOSink connected to either the standard out or error of the process. [...]

SystemEncoding

The system encoding is the current code page on Windows and UTF-8 on Linux and Mac.

WebSocket

A two-way HTTP communication object for client or server applications. [...]

WebSocketStatus

WebSocket status codes used when closing a WebSocket connection.

WebSocketTransformer

The WebSocketTransformer provides the ability to upgrade a HttpRequest to a WebSocket connection. It supports both upgrading a single HttpRequest and upgrading a stream of HttpRequests. [...]

X509Certificate

X509Certificate represents an SSL certificate, with accessors to get the fields of the certificate.

ZLibCodec

The ZLibCodec encodes raw bytes to ZLib compressed bytes and decodes ZLib compressed bytes to raw bytes.

ZLibDecoder

The ZLibDecoder is used by ZLibCodec and GZipCodec to decompress data.

ZLibEncoder

The ZLibEncoder encoder is used by ZLibCodec and GZipCodec to compress data.

ZLibOption

Exposes ZLib options for input parameters. [...]

Constants

APPEND → const FileMode

@Deprecated("Use FileMode.append instead")

The mode for opening a file for reading and writing to the end of it. The file is created if it does not already exist.

FileMode.append

GZIP → const GZipCodec

@Deprecated("Use gzip instead")

gzip

gzip → const GZipCodec

An instance of the default implementation of the GZipCodec.

const GZipCodec._default()

READ → const FileMode

@Deprecated("Use FileMode.read instead")

The mode for opening a file only for reading.

FileMode.read

SYSTEM_ENCODING → const SystemEncoding

@Deprecated("Use systemEncoding instead")

const SystemEncoding()

systemEncoding → const SystemEncoding

The current system encoding. [...]

const SystemEncoding()

WRITE → const FileMode

@Deprecated("Use FileMode.write instead")

The mode for opening a file for reading and writing. The file is overwritten if it already exists. The file is created if it does not already exist.

FileMode.write

WRITE_ONLY → const FileMode

@Deprecated("Use FileMode.writeOnly instead")

Mode for opening a file for writing only. The file is overwritten if it already exists. The file is created if it does not already exist.

FileMode.writeOnly

WRITE_ONLY_APPEND → const FileMode

@Deprecated("Use FileMode.writeOnlyAppend instead")

Mode for opening a file for writing only to the end of it. The file is created if it does not already exist.

FileMode.writeOnlyAppend

ZLIB → const ZLibCodec

@Deprecated("Use zlib instead")

zlib

zlib → const ZLibCodec

An instance of the default implementation of the ZLibCodec.

const ZLibCodec._default()

Properties

exitCode ↔ int

read / write

Get the global exit code for the Dart VM. [...]

pid → int

read-only

Returns the PID of the current process.

stderr → Stdout

read-only

The standard output stream of errors written by this program. [...]

stdin → Stdin

read-only

The standard input stream of data read by this program.

stdout → Stdout

read-only

The standard output stream of data written by this program. [...]

Functions

exit(int code) → Never

Exit the Dart VM process immediately with the given exit code. [...]

isInsecureConnectionAllowed(dynamic host) → bool

Whether insecure connections to host are allowed. [...]

sleep(Duration duration) → void

Sleep for the duration specified in duration. [...]

stdioType(dynamic object) → StdioType

Whether a stream is attached to a file, pipe, terminal, or something else.

Enums

HttpClientResponseCompressionState

Enum that specifies the compression state of the byte stream of an HttpClientResponse. [...]

Typedefs

BadCertificateCallback(X509Certificate cr, String host, int port) → bool

Exceptions / Errors

CertificateException

An exception that happens in the handshake phase of establishing a secure network connection, when looking up or verifying a certificate.

FileSystemException

Exception thrown when a file operation fails.

HandshakeException

An exception that happens in the handshake phase of establishing a secure network connection.

HttpException

IOException

Base class for all IO related exceptions.

OSError

An Exception holding information about an error from the operating system.

ProcessException

RedirectException

SignalException

SocketException

Exception thrown when a socket operation fails.

StdinException

Exception thrown by some operations of Stdin

StdoutException

Exception thrown by some operations of Stdout

TlsException

A secure networking exception caused by a failure in the TLS/SSL protocol.

WebSocketException