Move pub over to using the pub.dartlang.org API v2.

sdk/lib/_internal/pub/lib/src/http.dart

Index: sdk/lib/_internal/pub/lib/src/http.dart
diff --git a/sdk/lib/_internal/pub/lib/src/http.dart b/sdk/lib/_internal/pub/lib/src/http.dart
index 00fa9522faac49dd50bc3565c09caf60d097ce72..e7da34c6c6189989e31d0d17d637bf2770ff3487 100644
--- a/sdk/lib/_internal/pub/lib/src/http.dart
+++ b/sdk/lib/_internal/pub/lib/src/http.dart
@@ -14,6 +14,7 @@ import 'package:http/http.dart' as http;
 import 'io.dart';
 import 'log.dart' as log;
 import 'oauth2.dart' as oauth2;
+import 'sdk.dart' as sdk;
 import 'utils.dart';
 
 // TODO(nweiz): make this configurable
@@ -24,6 +25,13 @@ final HTTP_TIMEOUT = 30 * 1000;
 /// Headers and field names that should be censored in the log output.
 final _CENSORED_FIELDS = const ['refresh_token', 'authorization'];
 
+/// Headers required for pub.dartlang.org API requests.
+///
+/// The Accept header tells pub.dartlang.org which version of the API we're
+/// expecting, so it can either serve that version or give us a 406 error if
+/// it's not supported.
+final PUB_API_HEADERS = const {'Accept': 'application/vnd.pub.v2+json'};
+
 /// Whether dart:io's SecureSocket has been initialized with pub's resources
 /// yet.
 bool _initializedSecureSocket = false;
@@ -54,8 +62,6 @@ class PubHttpClient extends http.BaseClient {
       stackTrace = localStackTrace;
     }
 
-    // TODO(nweiz): Ideally the timeout would extend to reading from the
-    // response input stream, but until issue 3657 is fixed that's not feasible.
     return timeout(inner.send(request).then((streamedResponse) {
       _logResponse(streamedResponse);
 
@@ -69,6 +75,13 @@ class PubHttpClient extends http.BaseClient {
         return streamedResponse;
       }
 
+      if (status == 406 &&
+          request.headers['Accept'] == PUB_API_HEADERS['Accept']) {
+        fail("Pub ${sdk.version} is incompatible with the current version of "
+                 "${request.url.host}.\n"
+             "Upgrade pub to the latest version and try again.");
+      }
+
       return http.Response.fromStream(streamedResponse).then((response) {
         throw new PubHttpException(response);
       });