[PATCH] config: option transfer.ipversion to set transport protocol version for network fetches

[Alex Riesen <alexander.riesen@cetitec.com>]

Affecting the transfers caused by git-fetch, the
option allows to control network operations similar
to --ipv4 and --ipv6 options.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Alex Riesen <alexander.riesen@cetitec.com>
---

Jeff King, Tue, Sep 15, 2020 15:05:06 +0200:
> On Tue, Sep 15, 2020 at 01:50:25PM +0200, Alex Riesen wrote:
> > Sure! Thinking about it, I actually would have preferred to have both: a
> > config option and a command-line option. So that I can set --ipv4 in, say,
> > ~/.config/git/config file, but still have the option to try --ipv6 from time
> > to time to check if the network setup magically fixed itself.
> > 
> > What would the preferred name for that config option be? fetch.ipv?
> 
> It looks like we've got similar options for clone/pull (which are really
> fetch under the hood of course) and push. We have the "transfer.*"
> namespace which applies to both already. So maybe "transfer.ipversion"
> or something?

Something like this?

 Documentation/config/transfer.txt |  7 +++++++
 builtin/fetch.c                   | 11 +++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/config/transfer.txt b/Documentation/config/transfer.txt
index f5b6245270..cc0e97fbb1 100644
--- a/Documentation/config/transfer.txt
+++ b/Documentation/config/transfer.txt
@@ -69,3 +69,10 @@ transfer.unpackLimit::
 	When `fetch.unpackLimit` or `receive.unpackLimit` are
 	not set, the value of this variable is used instead.
 	The default value is 100.
+
+transfer.ipversion::
+	Limit the network operations to the specified version of the transport
+	protocol. Can be specified as `4` to allow IPv4 only, `6` for IPv6, or
+	`all` to allow all protocols.
+	See also linkgit:git-fetch[1] options `--ipv4` and `--ipv6`.
+	The default value is `all` to allow all protocols.
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 447d28ac29..da01c8f7b3 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -118,6 +118,17 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "transfer.ipversion")) {
+		if (!strcmp(v, "all"))
+			;
+		else if (!strcmp(v, "4"))
+			family = TRANSPORT_FAMILY_IPV4;
+		else if (!strcmp(v, "6"))
+			family = TRANSPORT_FAMILY_IPV6;
+		else
+			die(_("transfer.ipversion can be only 4, 6, or any"));
+		return 0;
+	}
 	return git_default_config(k, v, cb);
 }
 
-- 
2.28.0.21.g178b32a6fd.dirty