[RFC/PATCH 2/5] upload-pack: support out of band client capability requests

[Stefan Beller <sbeller@google.com>]

From: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>

The only difference from the original protocol client capabilities are
negotiated before initial refs advertisment.

Client capabilities are sent out of band (upload-pack receives it as
the second command line argument). The server sends one pkt-line back
advertising its capabilities.

Signed-off-by: Stefan Beller <sbeller@google.com>
---

Notes:
    v1:
    I am still undecided if the client should then accept/resend
    the capabilities to confirm them, which would make the client the
    ultimate decider which capabilities are used.
    
    My gut feeling is to rather let the server make the final decision
    for the capabilities, as it will use some requested capabilities
    already to not send out all the refs.

 Documentation/git-upload-pack.txt | 10 +++++++++-
 upload-pack.c                     | 42 +++++++++++++++++++++++++++------------
 2 files changed, 38 insertions(+), 14 deletions(-)

diff --git a/Documentation/git-upload-pack.txt b/Documentation/git-upload-pack.txt
index 0abc806..ad3a89d 100644
--- a/Documentation/git-upload-pack.txt
+++ b/Documentation/git-upload-pack.txt
@@ -9,7 +9,7 @@ git-upload-pack - Send objects packed back to git-fetch-pack
 SYNOPSIS
 --------
 [verse]
-'git-upload-pack' [--strict] [--timeout=<n>] <directory>
+'git-upload-pack' [--strict] [--timeout=<n>] <directory> [<capabilities>]
 
 DESCRIPTION
 -----------
@@ -34,6 +34,14 @@ OPTIONS
 <directory>::
 	The repository to sync from.
 
+capabilities::
+	Historically the capabilities were exchanged inside the protocol of
+	'git-upload-pack' talking to 'git-fetch-pack'. It turned out this was
+	too late as 'git-upload-pack' already did work, which may have been
+	avoided. This allows to pass in the capabilities the client wants to
+	use as one argument. The capabilites are separated by space.
+	See technical/protocol-capabilities.txt (TODO: how to make it a link?)
+
 SEE ALSO
 --------
 linkgit:gitnamespaces[7]
diff --git a/upload-pack.c b/upload-pack.c
index d9230ba..2e62c3f 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -31,6 +31,11 @@ static const char upload_pack_usage[] = "git upload-pack [--strict] [--timeout=<
 
 static unsigned long oldest_have;
 
+/**
+ * client capabilities presented as program arguments, dissallow further
+ * capabilities sent by client
+ */
+static int capabilities_first;
 static int multi_ack;
 static int no_done;
 static int use_thin_pack, use_ofs_delta, use_include_tag;
@@ -597,11 +602,14 @@ static void receive_needs(void)
 			die("git upload-pack: protocol error, "
 			    "expected to get sha, not '%s'", line);
 
-		if (first_want) {
-			parse_features(line + 45);
-			first_want = 0;
-		} else if (line[45])
-			die("garbage at the end of 'want' line %s", line + 45);
+		if (!capabilities_first) {
+			if (first_want) {
+				parse_features(line + 45);
+				first_want = 0;
+			} else if (line[45]) {
+				die("garbage at the end of 'want' line %s", line + 45);
+			}
+		}
 
 		o = parse_object(sha1_buf);
 		if (!o)
@@ -840,17 +848,25 @@ int main(int argc, char **argv)
 		}
 	}
 
-	if (i != argc-1)
-		usage(upload_pack_usage);
+	switch (argc - i) {
+		case 2:
+			capabilities_first = 1;
+			parse_features(argv[i + 1]);
+			/* fall through*/
+		case 1:
+			setup_path();
 
-	setup_path();
+			dir = argv[i];
 
-	dir = argv[i];
+			if (!enter_repo(dir, strict))
+				die("'%s' does not appear to be a git repository", dir);
 
-	if (!enter_repo(dir, strict))
-		die("'%s' does not appear to be a git repository", dir);
+			git_config(upload_pack_config, NULL);
+			upload_pack();
+			break;
+		default:
+			usage(upload_pack_usage);
+	}
 
-	git_config(upload_pack_config, NULL);
-	upload_pack();
 	return 0;
 }
-- 
2.3.0.81.gc37f363