Use the cached pubspec if possible for describing hosted packages.

utils/pub/hosted_source.dart

Index: utils/pub/hosted_source.dart
diff --git a/utils/pub/hosted_source.dart b/utils/pub/hosted_source.dart
index bd017e667a61f48e912f40600dcbede85071d10a..103ea5eb7363a07076cfd72e709c7c24095309c5 100644
--- a/utils/pub/hosted_source.dart
+++ b/utils/pub/hosted_source.dart
@@ -49,15 +49,23 @@ class HostedSource extends Source {
   /// Downloads and parses the pubspec for a specific version of a package that
   /// is available from the site.
   Future<Pubspec> describe(PackageId id) {
-    var url = _makeVersionUrl(id, (server, package, version) =>
-        "$server/packages/$package/versions/$version.yaml");
+    return systemCacheDirectory(id).then((cacheDir) {
+      // See if we already have it in the cache. If so, just load it locally.
+      if (fileExists(path.join(cacheDir, "pubspec.yaml"))) {
+        return new Pubspec.load(id.name, cacheDir, systemCache.sources);

[nweiz, 2013/04/18 22:50:03]

We should catch format/IO errors, print a warning, and fall back to requesting
the pubspec from the server if something goes wrong with loading it. We don't
want a corrupted cache to break "pub install".

[Bob Nystrom, 2013/04/18 23:07:10]

Done.

+      }
 
-    log.io("Describe package at $url.");
-    return httpClient.read(url).then((yaml) {
-      return new Pubspec.parse(null, yaml, systemCache.sources);
-    }).catchError((ex) {
-      var parsed = _parseDescription(id.description);
-      _throwFriendlyError(ex, id, parsed.last);
+      // Request it from the server.
+      var url = _makeVersionUrl(id, (server, package, version) =>
+          "$server/packages/$package/versions/$version.yaml");
+
+      log.io("Describe package at $url.");
+      return httpClient.read(url).then((yaml) {

[nweiz, 2013/04/18 22:50:03]

Add a TODO to cache these pubspecs as well. We probably don't want to put them
in the actual system cache directories, but we could have a secondary
pubspec-only cache for packages we haven't downloaded.

[Bob Nystrom, 2013/04/18 23:07:10]

Done.

+        return new Pubspec.parse(null, yaml, systemCache.sources);
+      }).catchError((ex) {
+        var parsed = _parseDescription(id.description);
+        _throwFriendlyError(ex, id, parsed.last);
+      });
     });
   }
 
@@ -122,11 +130,11 @@ class HostedSource extends Source {
     var cacheDir = path.join(systemCacheRoot,
                              _getSourceDirectory(_defaultUrl));
     if (!dirExists(cacheDir)) return [];
-  
+
     return listDir(path.join(cacheDir)).map((entry) =>
         new Package.load(null, entry, systemCache.sources)).toList();
   }
-  
+
   /// When an error occurs trying to read something about [package] from [url],
   /// this tries to translate into a more user friendly error message. Always
   /// throws an error, either the original one or a better one.