clonebundles: filter on bundle specification Not all clients are capable of reading every bundle. Currently, content negotiation to ensure a server sends a client a compatible bundle format is performed at request time. The response bundle is dynamically generated at request time, so this works fine. Clone bundles are statically generated *before* the request. This means that a modern server could produce bundles that a legacy client isn't capable of reading. Without some kind of "type hint" in the clone bundles manifest, a client may attempt to download an incompatible bundle. Furthermore, a client may not realize a bundle is incompatible until it has processed part of the bundle (imagine consuming a 1 GB changegroup bundle2 part only to discover the bundle2 part afterwards is incompatibl). This would waste time and resources. And it isn't very user friendly. Clone bundle manifests thus need to advertise the *exact* format of the hosted bundles so clients may filter out entries that they don't know how to read. This patch introduces that mechanism. We introduce the BUNDLESPEC attribute to declare the "bundle specification" of the entry. Bundle specifications are parsed using exchange.parsebundlespecification, which uses the same strings as the "--type" argument to `hg bundle`. The supported bundle specifications are well defined and backwards compatible. When a client encounters a BUNDLESPEC that is invalid or unsupported, it silently ignores the entry.

--- a/hgext/clonebundles.py	Tue Oct 13 10:41:54 2015 -0700
+++ b/hgext/clonebundles.py	Tue Oct 13 11:45:30 2015 -0700
@@ -32,7 +32,23 @@
 
 Metadata Attributes:
 
-TBD
+BUNDLESPEC
+   A "bundle specification" string that describes the type of the bundle.
+
+   These are string values that are accepted by the "--type" argument of
+   `hg bundle`.
+
+   The values are parsed in strict mode, which means they must be of the
+   "<compression>-<type>" form. See
+   mercurial.exchange.parsebundlespec() for more details.
+
+   Clients will automatically filter out specifications that are unknown or
+   unsupported so they won't attempt to download something that likely won't
+   apply.
+
+   The actual value doesn't impact client behavior beyond filtering:
+   clients will still sniff the bundle type from the header of downloaded
+   files.
 """
 
 from mercurial import (