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

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

Suggested-by: Jeff King <redacted>
Signed-off-by: Alex Riesen <redacted>
---

Jeff King, Tue, Sep 15, 2020 15:05:06 +0200:

On Tue, Sep 15, 2020 at 01:50:25PM +0200, Alex Riesen wrote:

quoted

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