Use the dart:async Stream API thoroughly in Pub.

utils/pub/utils.dart

Index: utils/pub/utils.dart
diff --git a/utils/pub/utils.dart b/utils/pub/utils.dart
index aac48fe0e305a7203f943955e5cd9619b3594c9e..d1cea825419a3f29e3014a3eb476eabc8a71733a 100644
--- a/utils/pub/utils.dart
+++ b/utils/pub/utils.dart
@@ -118,6 +118,83 @@ void chainToCompleter(Future future, Completer completer) {
       onError: (e) => completer.completeError(e.error, e.stackTrace));
 }
 
+// TODO(nweiz): remove this when issue 7964 is fixed.
+/// Returns a [Future] that will complete to the first element of [stream].
+/// Unlike [Stream.first], this is safe to use with single-subscription streams.
+Future streamFirst(Stream stream) {
+  var completer = new Completer();
+  var subscription;
+  subscription = stream.listen((value) {
+    subscription.cancel();
+    completer.complete(value);
+  },
+      onError: (e) => completer.completeError(e.error, e.stackTrace),
+      onDone: () => completer.completeError(new StateError("No elements")),
+      unsubscribeOnError: true);
+  return completer.future;
+}
+
+/// Returns a wrapped version of [stream] along with a [StreamSubscription] that
+/// can be used to control the wrapped stream.
+Pair<Stream, StreamSubscription> streamWithSubscription(Stream stream) {
+  var controller = stream.isSingleSubscription ?
+      new StreamController() :
+      new StreamController.multiSubscription();
+  var subscription = stream.listen(controller.add,
+      onError: controller.signalError,
+      onDone: controller.close);
+  return new Pair<Stream, StreamSubscription>(controller.stream, subscription);
+}
+
+// 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 regular expression matching a line termination character or character
+/// sequence.
+final RegExp _lineRegexp = new RegExp(r"\r\n|\r|\n");
+
+/// Converts a stream of arbitrarily chunked strings into a line-by-line stream.
+/// The lines don't include line termination characters. A single trailing
+/// newline is ignored.
+Stream<String> streamToLines(Stream<String> stream) {
+  var buffer = new StringBuffer();
+  return stream.transform(new StreamTransformer.from(
+      onData: (chunk, sink) {
+        var lines = chunk.split(_lineRegexp);
+        var leftover = lines.removeLast();
+        for (var line in lines) {
+          if (!buffer.isEmpty) {
+            buffer.add(line);
+            line = buffer.toString();
+            buffer.clear();
+          }
+
+          sink.add(line);
+        }
+        buffer.add(leftover);
+      }, onDone: (sink) {
+        if (!buffer.isEmpty) sink.add(buffer.toString());
+        sink.close();
+      }));
+}
+
 // TODO(nweiz): unify the following functions with the utility functions in
 // pkg/http.