add initial support for Git protocol v2

Implement Git protocol version negotiation and use Git protocol v2 for fetches if supported. For now, the observable behaviour of Dulwich is equivalent regardless of protocol version, except that two new features may be used if the server supports Git protocol v2. The first feature is a reference prefix list which may be used to filter refs server-side. This can be used to reduce the size of the initial reference listing announced by the server. Reducing the size of this announcement was a major design goal for protocol v2 to avoid sending of very large announcements when a repository contains a lot of references. This feature is intended as an optimization which servers are free to ignore depending on available server-side resources. Therefore, users of Dulwich should still be prepared to filter redundant refs manually (this limitation also applies to Git itself). A new --refspec porcelain option is provided in order to test this feature on the command line. The second feature is an object filter specification, which corresponds to the --filter option of 'git clone'. This can be used to omit objects while cloning repositories. For instance, the following command will clone a given repsitory without fetching any blob objects: dulwich clone --filter blob:none --bare REPO_URL (In this example the --bare option is used because creation of a work tree would fail without any blobs present.) The test suite now enables protocol v2 and keeps passing for me.
jelmer · jelmer · Jun 28, 2024 · Jun 25, 2024 · Jun 25, 2024 · Jun 25, 2024
commit 2b975ec7e49caf98c1c4d0b1eea848d0dd86ae77
@@ -263,6 +263,19 @@ def run(self, args):
             type=str,
             help=("Check out branch instead of branch pointed to by remote " "HEAD"),
         )
+        parser.add_option(
+            "--refspec",
+            dest="refspec",
+            type=str,
+            help="References to fetch",
+            action="append",
+        )
+        parser.add_option(
+            "--filter",
+            dest="filter_spec",
+            type=str,
+            help="git-rev-list-style object filter",
+        )
         options, args = parser.parse_args(args)
 
         if args == []:
@@ -282,6 +295,8 @@ def run(self, args):
                 bare=options.bare,
                 depth=options.depth,
                 branch=options.branch,
+                refspec=options.refspec,
+                filter_spec=options.filter_spec,
             )
         except GitProtocolError as e:
             print(f"{e}")
@@ -586,13 +601,17 @@ def run(self, args):
 
 class cmd_pull(Command):
     def run(self, args):
-        parser = optparse.OptionParser()
-        options, args = parser.parse_args(args)
-        try:
-            from_location = args[0]
-        except IndexError:
-            from_location = None
-        porcelain.pull(".", from_location)
+        parser = argparse.ArgumentParser()
+        parser.add_argument("--from_location", type=str)
+        parser.add_argument("--refspec", type=str, nargs="*")
+        parser.add_argument("--filter", type=str, nargs=1)
+        args = parser.parse_args(args)
+        porcelain.pull(
+            ".",
+            args.from_location or None,
+            args.refspec or None,
+            filter_spec=args.filter,
+        )
 
 
 class cmd_push(Command):