sdk/pkg/http/lib/src/utils.dart

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library utils;

import 'dart:async';
import 'dart:crypto';
import 'dart:io';
import 'dart:scalarlist';
import 'dart:uri';
import 'dart:utf';

import 'byte_stream.dart';

/// Converts a URL query string (or `application/x-www-form-urlencoded` body)
/// into a [Map] from parameter names to values.
///
///     queryToMap("foo=bar&baz=bang&qux");
///     //=> {"foo": "bar", "baz": "bang", "qux": ""}
Map<String, String> queryToMap(String queryList) {
  var map = {};
  for (var pair in queryList.split("&")) {
    var split = split1(pair, "=");
    if (split.isEmpty) continue;
    var key = urlDecode(split[0]);
    var value = urlDecode(split.length > 1 ? split[1] : "");
    map[key] = value;
  }
  return map;
}

/// Converts a [Map] from parameter names to values to a URL query string.
///
///     mapToQuery({"foo": "bar", "baz": "bang"});
///     //=> "foo=bar&baz=bang"
String mapToQuery(Map<String, String> map) {
  var pairs = <List<String>>[];
  map.forEach((key, value) =>
      pairs.add([encodeUriComponent(key), encodeUriComponent(value)]));
  return Strings.join(pairs.map((pair) => "${pair[0]}=${pair[1]}"), "&");
}

/// Adds all key/value pairs from [source] to [destination], overwriting any
/// pre-existing values.
///
///     var a = {"foo": "bar", "baz": "bang"};
///     mapAddAll(a, {"baz": "zap", "qux": "quux"});
///     a; //=> {"foo": "bar", "baz": "zap", "qux": "quux"}
void mapAddAll(Map destination, Map source) =>
  source.forEach((key, value) => destination[key] = value);

/// Decodes a URL-encoded string. Unlike [decodeUriComponent], this includes
/// replacing `+` with ` `.
String urlDecode(String encoded) =>
  decodeUriComponent(encoded.replaceAll("+", " "));

/// Like [String.split], but only splits on the first occurrence of the pattern.
/// This will always return an array of two elements or fewer.
///
///     split1("foo,bar,baz", ","); //=> ["foo", "bar,baz"]
///     split1("foo", ","); //=> ["foo"]
///     split1("", ","); //=> []
List<String> split1(String toSplit, String pattern) {
  if (toSplit.isEmpty) return <String>[];

  var index = toSplit.indexOf(pattern);
  if (index == -1) return [toSplit];
  return [
    toSplit.substring(0, index),
    toSplit.substring(index + pattern.length)
  ];
}

/// Returns the [Encoding] that corresponds to [charset]. Returns [fallback] if
/// [charset] is null or if no [Encoding] was found that corresponds to
/// [charset].
Encoding encodingForCharset(
    String charset, [Encoding fallback = Encoding.ISO_8859_1]) {
  if (charset == null) return fallback;
  var encoding = _encodingForCharset(charset);
  return encoding == null ? fallback : encoding;
}

/// Returns the [Encoding] that corresponds to [charset]. Throws a
/// [FormatException] if no [Encoding] was found that corresponds to [charset].
/// [charset] may not be null.
Encoding requiredEncodingForCharset(String charset) {
  var encoding = _encodingForCharset(charset);
  if (encoding != null) return encoding;
  throw new FormatException('Unsupported encoding "$charset".');
}

/// Returns the [Encoding] that corresponds to [charset]. Returns null if no
/// [Encoding] was found that corresponds to [charset]. [charset] may not be
/// null.
Encoding _encodingForCharset(String charset) {
  charset = charset.toLowerCase();
  if (charset == 'ascii' || charset == 'us-ascii') return Encoding.ASCII;
  if (charset == 'utf-8') return Encoding.UTF_8;
  if (charset == 'iso-8859-1') return Encoding.ISO_8859_1;
  return null;
}

/// Converts [bytes] into a [String] according to [encoding].
String decodeString(List<int> bytes, Encoding encoding) {
  // TODO(nweiz): implement this once issue 6284 is fixed.
  return new String.fromCharCodes(bytes);
}

/// Converts [string] into a byte array according to [encoding].
List<int> encodeString(String string, Encoding encoding) {
  // TODO(nweiz): implement this once issue 6284 is fixed.
  return string.charCodes;
}

/// A regular expression that matches strings that are composed entirely of
/// ASCII-compatible characters.
final RegExp _ASCII_ONLY = new RegExp(r"^[\x00-\x7F]+$");

/// Returns whether [string] is composed entirely of ASCII-compatible
/// characters.
bool isPlainAscii(String string) => _ASCII_ONLY.hasMatch(string);

/// Converts [input] into a [Uint8List]. If [input] is a [ByteArray] or
/// [ByteArrayViewable], this just returns a view on [input].
Uint8List toUint8List(List<int> input) {
  if (input is Uint8List) return input;
  if (input is ByteArrayViewable) input = input.asByteArray();
  if (input is ByteArray) return new Uint8List.view(input);
  var output = new Uint8List(input.length);
  output.setRange(0, input.length, input);
  return output;
}

/// If [stream] is already a [ByteStream], returns it. Otherwise, wraps it in a
/// [ByteStream].
ByteStream toByteStream(Stream<List<int>> stream) {
  if (stream is ByteStream) return stream;
  return new ByteStream(stream);
}

/// Calls [onDone] once [stream] (a single-subscription [Stream]) is finished.
/// The return value, also a single-subscription [Stream] should be used in
/// place of [stream] after calling this method.
Stream onDone(Stream stream, void onDone()) {
  var pair = tee(stream);
  pair.first.listen((_) {}, onError: (_) {}, onDone: onDone);
  return pair.last;
}

// TODO(nweiz): remove this once issue 7785 is fixed.
/// Wraps [stream] in a single-subscription [ByteStream] that emits the same
/// data.
ByteStream wrapInputStream(InputStream stream) {
  if (stream.closed) return emptyStream;

  var controller = new StreamController();
  stream.onClosed = controller.close;
  stream.onData = () => controller.add(stream.read());
  stream.onError = (e) => controller.signalError(new AsyncError(e));
  return new ByteStream(controller.stream);
}

// TODO(nweiz): remove this once issue 7785 is fixed.
/// Wraps [stream] in a [StreamConsumer] so that [Stream]s can by piped into it
/// using [Stream.pipe].
StreamConsumer<List<int>, dynamic> wrapOutputStream(OutputStream stream) =>
  new _OutputStreamConsumer(stream);

/// A [StreamConsumer] that pipes data into an [OutputStream].
class _OutputStreamConsumer implements StreamConsumer<List<int>, dynamic> {
  final OutputStream _outputStream;

  _OutputStreamConsumer(this._outputStream);

  Future consume(Stream<List<int>> stream) {
    // TODO(nweiz): we have to manually keep track of whether or not the
    // completer has completed since the output stream could signal an error
    // after close() has been called but before it has shut down internally. See
    // the following TODO.
    var completed = false;
    var completer = new Completer();
    stream.listen((data) {
      // Writing empty data to a closed stream can cause errors.
      if (data.isEmpty) return;

      // TODO(nweiz): remove this try/catch when issue 7836 is fixed.
      try {
        _outputStream.write(data);
      } catch (e, stack) {
        if (!completed) completer.completeError(e, stack);
        completed = true;
      }
    }, onDone: () => _outputStream.close());

    _outputStream.onError = (e) {
      if (!completed) completer.completeError(e);
      completed = true;
    };

    _outputStream.onClosed = () {
      if (!completed) completer.complete();
      completed = true;
    };

    return completer.future;
  }
}

// TODO(nweiz): remove this when issue 7786 is fixed.
/// Pipes all data and errors from [stream] into [sink]. When [stream] is done,
/// [sink] is closed and the returned [Future] is completed.
Future store(Stream stream, StreamSink sink) {
  var completer = new Completer();
  stream.listen(sink.add,
      onError: sink.signalError,
      onDone: () {
        sink.close();
        completer.complete();
      });
  return completer.future;
}

/// Pipes all data and errors from [stream] into [sink]. Completes [Future] once
/// [stream] is done. Unlike [store], [sink] remains open after [stream] is
/// done.
Future writeStreamToSink(Stream stream, StreamSink sink) {
  var completer = new Completer();
  stream.listen(sink.add,
      onError: sink.signalError,
      onDone: () => completer.complete());
  return completer.future;
}

/// Returns a [Future] that asynchronously completes to `null`.
Future get async => new Future.immediate(null);

/// Returns a closed [Stream] with no elements.
Stream get emptyStream => streamFromIterable([]);

/// Creates a single-subscription stream that emits the items in [iter] and then
/// ends.
Stream streamFromIterable(Iterable iter) {
  var controller = new StreamController();
  iter.forEach(controller.add);
  controller.close();
  return controller.stream;
}

// TODO(nweiz): remove this when issue 7787 is fixed.
/// Creates two single-subscription [Stream]s that each emit all values and
/// errors from [stream]. This is useful if [stream] is single-subscription but
/// multiple subscribers are necessary.
Pair<Stream, Stream> tee(Stream stream) {
  var controller1 = new StreamController();
  var controller2 = new StreamController();
  stream.listen((value) {
    controller1.add(value);
    controller2.add(value);
  }, onError: (error) {
    controller1.signalError(error);
    controller2.signalError(error);
  }, onDone: () {
    controller1.close();
    controller2.close();
  });
  return new Pair<Stream, Stream>(controller1.stream, controller2.stream);
}

/// A pair of values.
class Pair<E, F> {
  E first;
  F last;

  Pair(this.first, this.last);

  String toString() => '($first, $last)';

  bool operator==(other) {
    if (other is! Pair) return false;
    return other.first == first && other.last == last;
  }

  int get hashCode => first.hashCode ^ last.hashCode;
}

/// Configures [future] so that its result (success or exception) is passed on
/// to [completer].
void chainToCompleter(Future future, Completer completer) {
  future.then((v) => completer.complete(v)).catchError((e) {
    completer.completeError(e.error, e.stackTrace);
  });
}

// TOOD(nweiz): Get rid of this once https://codereview.chromium.org/11293132/
// is in.
/// Runs [fn] for each element in [input] in order, moving to the next element
/// only when the [Future] returned by [fn] completes. Returns a [Future] that
/// completes when all elements have been processed.
///
/// The return values of all [Future]s are discarded. Any errors will cause the
/// iteration to stop and will be piped through the return value.
Future forEachFuture(Iterable input, Future fn(element)) {
  var iterator = input.iterator;
  Future nextElement(_) {
    if (!iterator.moveNext()) return new Future.immediate(null);
    return fn(iterator.current).then(nextElement);
  }
  return nextElement(null);
}

// TODO(nweiz): remove this when issue 8310 is fixed.
/// Returns a [Stream] identical to [stream], but piped through a new
/// [StreamController]. This exists to work around issue 8310.
Stream wrapStream(Stream stream) {
  var controller = stream.isBroadcast
      ? new StreamController.broadcast()
      : new StreamController();
  stream.listen(controller.add,
      onError: (e) => controller.signalError(e),
      onDone: controller.close);
  return controller.stream;
}