Convert shelf to use the string_scanner package.

pkg/shelf/lib/src/util.dart

Index: pkg/shelf/lib/src/util.dart
diff --git a/pkg/shelf/lib/src/util.dart b/pkg/shelf/lib/src/util.dart
index 09b8cb4dd878f00e99ea087b864a90ec2f64aa8b..bf8e370804ddd81dbbdbe3f453ca760ad2372e26 100644
--- a/pkg/shelf/lib/src/util.dart
+++ b/pkg/shelf/lib/src/util.dart
@@ -7,8 +7,7 @@ library shelf.util;
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
-
-import 'string_scanner.dart';
+import 'package:string_scanner/string_scanner.dart';
 
 /// Like [Future.sync], but wraps the Future in [Chain.track] as well.
 Future syncFuture(callback()) => Chain.track(new Future.sync(callback));
@@ -56,88 +55,90 @@ String formatHttpDate(DateTime date) {
 /// 2616](http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.3). It will
 /// throw a [FormatException] if [date] is invalid.
 DateTime parseHttpDate(String date) {
-  var errorMessage = 'Invalid HTTP date "$date".';
-  var scanner = new StringScanner(date);
-
-  if (scanner.scan(_longWeekdayRegExp)) {
-    // RFC 850 starts with a long weekday.
-    scanner.expect(", ", errorMessage);
-    var day = _parseInt(scanner, errorMessage, 2);
-    scanner.expect("-", errorMessage);
-    var month = _parseMonth(scanner, errorMessage);
-    scanner.expect("-", errorMessage);
-    var year = 1900 + _parseInt(scanner, errorMessage, 2);
-    scanner.expect(" ", errorMessage);
-    var time = _parseTime(scanner, errorMessage);
-    scanner.expect(" GMT", errorMessage);
-    if (!scanner.isDone) throw new FormatException(errorMessage);
-
-    return _makeDateTime(year, month, day, time, errorMessage);
-  }
-
-  // RFC 1123 and asctime both start with a short weekday.
-  scanner.expect(_shortWeekdayRegExp, errorMessage);
-  if (scanner.scan(", ")) {
-    // RFC 1123 follows the weekday with a comma.
-    var day = _parseInt(scanner, errorMessage, 2);
-    scanner.expect(" ", errorMessage);
-    var month = _parseMonth(scanner, errorMessage);
-    scanner.expect(" ", errorMessage);
-    var year = _parseInt(scanner, errorMessage, 4);
-    scanner.expect(" ", errorMessage);
-    var time = _parseTime(scanner, errorMessage);
-    scanner.expect(" GMT", errorMessage);
-    if (!scanner.isDone) throw new FormatException(errorMessage);
-
-    return _makeDateTime(year, month, day, time, errorMessage);
+  try {
+    var scanner = new StringScanner(date);
+
+    if (scanner.scan(_longWeekdayRegExp)) {
+      // RFC 850 starts with a long weekday.
+      scanner.expect(", ");
+      var day = _parseInt(scanner, 2);
+      scanner.expect("-");
+      var month = _parseMonth(scanner);
+      scanner.expect("-");
+      var year = 1900 + _parseInt(scanner, 2);
+      scanner.expect(" ");
+      var time = _parseTime(scanner);
+      scanner.expect(" GMT");
+      scanner.expectDone();
+
+      return _makeDateTime(year, month, day, time);
+    }
+
+    // RFC 1123 and asctime both start with a short weekday.
+    scanner.expect(_shortWeekdayRegExp);
+    if (scanner.scan(", ")) {
+      // RFC 1123 follows the weekday with a comma.
+      var day = _parseInt(scanner, 2);
+      scanner.expect(" ");
+      var month = _parseMonth(scanner);
+      scanner.expect(" ");
+      var year = _parseInt(scanner, 4);
+      scanner.expect(" ");
+      var time = _parseTime(scanner);
+      scanner.expect(" GMT");
+      scanner.expectDone();
+
+      return _makeDateTime(year, month, day, time);
+    }
+
+    // asctime follows the weekday with a space.
+    scanner.expect(" ");
+    var month = _parseMonth(scanner);
+    scanner.expect(" ");
+    var day = scanner.scan(" ") ?
+        _parseInt(scanner, 1) :
+        _parseInt(scanner, 2);
+    scanner.expect(" ");
+    var time = _parseTime(scanner);
+    scanner.expect(" ");
+    var year = _parseInt(scanner, 4);
+    scanner.expectDone();
+
+    return _makeDateTime(year, month, day, time);
+  } on FormatException catch (error) {
+    throw new FormatException('Invalid HTTP date "$date": ${error.message}');
   }
-
-  // asctime follows the weekday with a space.
-  scanner.expect(" ", errorMessage);
-  var month = _parseMonth(scanner, errorMessage);
-  scanner.expect(" ", errorMessage);
-  var day = scanner.scan(" ") ?
-      _parseInt(scanner, errorMessage, 1) :
-      _parseInt(scanner, errorMessage, 2);
-  scanner.expect(" ", errorMessage);
-  var time = _parseTime(scanner, errorMessage);
-  scanner.expect(" ", errorMessage);
-  var year = _parseInt(scanner, errorMessage, 4);
-  if (!scanner.isDone) throw new FormatException(errorMessage);
-
-  return _makeDateTime(year, month, day, time, errorMessage);
 }
 
 /// Parses a short-form month name to a form accepted by [DateTime].
-int _parseMonth(StringScanner scanner, String errorMessage) {
-  scanner.expect(_monthRegExp, errorMessage);
+int _parseMonth(StringScanner scanner) {
+  scanner.expect(_monthRegExp);
   // DateTime uses 1-indexed months.
   return _MONTHS.indexOf(scanner.lastMatch[0]) + 1;
 }
 
 /// Parses an int an enforces that it has exactly [digits] digits.
-int _parseInt(StringScanner scanner, String errorMessage, int digits) {
-  scanner.expect(_digitRegExp, errorMessage);
+int _parseInt(StringScanner scanner, int digits) {
+  scanner.expect(_digitRegExp);
   if (scanner.lastMatch[0].length != digits) {
-    throw new FormatException(errorMessage);
+    scanner.error("expected a $digits-digit number.");
   } else {
     return int.parse(scanner.lastMatch[0]);
   }
 }
 
 /// Parses an timestamp of the form "HH:MM:SS" on a 24-hour clock.
-DateTime _parseTime(StringScanner scanner, String errorMessage) {
-  var hours = _parseInt(scanner, errorMessage, 2);
-  scanner.expect(':', errorMessage);
+DateTime _parseTime(StringScanner scanner) {
+  var hours = _parseInt(scanner, 2);
+  if (hours >= 24) scanner.error("hours may not be greater than 24.");
+  scanner.expect(':');
 
-  var minutes = _parseInt(scanner, errorMessage, 2);
-  scanner.expect(':', errorMessage);
+  var minutes = _parseInt(scanner, 2);
+  if (minutes >= 60) scanner.error("minutes may not be greater than 60.");
+  scanner.expect(':');
 
-  var seconds = _parseInt(scanner, errorMessage, 2);
-
-  if (hours >= 24 || minutes >= 60 || seconds >= 60) {
-    throw new FormatException(errorMessage);
-  }
+  var seconds = _parseInt(scanner, 2);
+  if (seconds >= 60) scanner.error("seconds may not be greater than 60.");
 
   return new DateTime(1, 1, 1, hours, minutes, seconds);
 }
@@ -145,14 +146,14 @@ DateTime _parseTime(StringScanner scanner, String errorMessage) {
 /// Returns a UTC [DateTime] from the given components.
 ///
 /// Validates that [day] is a valid day for [month]. If it's not, throws a
-/// [FormatException] with [errorMessage].
-DateTime _makeDateTime(int year, int month, int day, DateTime time,
-    String errorMessage) {
-  if (day < 1) throw new FormatException(errorMessage);
+/// [FormatException].
+DateTime _makeDateTime(int year, int month, int day, DateTime time) {
   var dateTime = new DateTime.utc(
       year, month, day, time.hour, time.minute, time.second);
 
   // If [day] was too large, it will cause [month] to overflow.
-  if (dateTime.month != month) throw new FormatException(errorMessage);
+  if (dateTime.month != month) {
+    throw new FormatException("invalid day '$day' for month '$month'.");
+  }
   return dateTime;
 }