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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.
 
 /// Generic utility functions. Stuff that should possibly be in core.
 library pub.utils;
 
 import 'dart:async';
 import "dart:convert";
 import 'dart:io';
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         onError: controller.addError,
         onDone: () {
       doneCount++;
       if (doneCount == 2) controller.close();
     });
   }
 
   return controller.stream;
 }
 
+/// Returns a [Stream] that will emit the same values as the stream returned by
+/// [callback].
+///
+/// [callback] will only be called when the returned [Stream] gets a subscriber.
+Stream callbackStream(Stream callback()) {
+  var subscription;
+  var controller;
+  controller = new StreamController(onListen: () {
+    subscription = callback().listen(controller.add,
+        onError: controller.addError,
+        onDone: controller.close);
+  },
+      onCancel: () => subscription.cancel(),
+      onPause: () => subscription.pause(),
+      onResume: () => subscription.resume(),
+      sync: true);
+  return controller.stream;
+}
+
 /// A regular expression matching a trailing CR character.
 final _trailingCR = new RegExp(r"\r$");
 
 // TODO(nweiz): Use `text.split(new RegExp("\r\n?|\n\r?"))` when issue 9360 is
 // fixed.
 /// Splits [text] on its line breaks in a Windows-line-break-friendly way.
 List<String> splitLines(String text) =>
   text.split("\n").map((line) => line.replaceFirst(_trailingCR, "")).toList();
 
 /// Converts a stream of arbitrarily chunked strings into a line-by-line stream.
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   } else {
     throw new ApplicationException(message);
   }
 }
 
 /// Throw a [DataException] with [message] to indicate that the command has
 /// failed because of invalid input data.
 ///
 /// This will report the error and cause pub to exit with [exit_codes.DATA].
 void dataError(String message) => throw new DataException(message);