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diff mercurial/exchange.py @ 26648:c347d532bb56

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exchange: support sorting URLs by client-side preferences Not all bundles are appropriate for all clients. For example, someone with a slow Internet connection may want to prefer bz2 bundles over gzip bundles because they are smaller and don't take as long to transfer. This is information that a server cannot know on its own. So, we invent a mechanism for "preferring" server-advertised URLs based on their attributes. We could invent a negotiation between client and server where the client sends its preferences and the sorting/filtering is done server-side. However, this feels complex. We can avoid complicating the wire protocol and exposing ourselves to backwards compatible concerns by performing the sorting locally. This patch defines a new config option for expressing preferred attributes in server-advertised bundles. At Mozilla, we leverage this feature so clients in fast data centers prefer uncompressed bundles. (We advertise gzip bundles first because that is a reasonable default.) I consider this an advanced feature. I'm on the fence as to whether it should be documented in `hg help config`.
author Gregory Szorc <gregory.szorc@gmail.com>
date Tue, 13 Oct 2015 12:30:39 -0700
parents 62b0fa0d8787
children 90df14eb3d0e
line wrap: on
line diff
--- a/mercurial/exchange.py	Tue Oct 13 12:31:19 2015 -0700
+++ b/mercurial/exchange.py	Tue Oct 13 12:30:39 2015 -0700
@@ -1622,7 +1622,7 @@
                        'operator)\n'))
         return
 
-    # TODO sort entries by user preferences.
+    entries = sortclonebundleentries(repo.ui, entries)
 
     url = entries[0]['URL']
     repo.ui.status(_('applying clone bundle from %s\n') % url)
@@ -1700,6 +1700,51 @@
 
     return newentries
 
+def sortclonebundleentries(ui, entries):
+    # experimental config: experimental.clonebundleprefers
+    prefers = ui.configlist('experimental', 'clonebundleprefers', default=[])
+    if not prefers:
+        return list(entries)
+
+    prefers = [p.split('=', 1) for p in prefers]
+
+    # Our sort function.
+    def compareentry(a, b):
+        for prefkey, prefvalue in prefers:
+            avalue = a.get(prefkey)
+            bvalue = b.get(prefkey)
+
+            # Special case for b missing attribute and a matches exactly.
+            if avalue is not None and bvalue is None and avalue == prefvalue:
+                return -1
+
+            # Special case for a missing attribute and b matches exactly.
+            if bvalue is not None and avalue is None and bvalue == prefvalue:
+                return 1
+
+            # We can't compare unless attribute present on both.
+            if avalue is None or bvalue is None:
+                continue
+
+            # Same values should fall back to next attribute.
+            if avalue == bvalue:
+                continue
+
+            # Exact matches come first.
+            if avalue == prefvalue:
+                return -1
+            if bvalue == prefvalue:
+                return 1
+
+            # Fall back to next attribute.
+            continue
+
+        # If we got here we couldn't sort by attributes and prefers. Fall
+        # back to index order.
+        return 0
+
+    return sorted(entries, cmp=compareentry)
+
 def trypullbundlefromurl(ui, repo, url):
     """Attempt to apply a bundle from a URL."""
     lock = repo.lock()