Re: [PATCH v2] http: support sending custom HTTP headers

[Jeff King <peff@peff.net>]

On Tue, Apr 26, 2016 at 10:03:14AM -0700, Junio C Hamano wrote:

> > +http.extraHeader::
> > +	Pass an additional HTTP header when communicating with a server.  If
> > +	more than one such entry exists, all of them are added as extra headers.
> > +	This feature is useful e.g. to increase security, or to allow
> > +	time-limited access based on expiring tokens.
> > +
> 
> I think one-time/short-lived use case does not want to have this in
> a configuration file, and instead want to do the command line thing
> you illustrated in the proposed log message.  I however wonder if
> there are other use cases where having this in $GIT_DIR/config for
> repeated use is useful.  If there is, not being able to override a
> configured value per invocation would become a problem.
> 
> Peff, what do you think?  I vaguely recollect that you did a hack to
> one variable that declares "an empty value means discard accumulated
> values so far" or something like that, and this variable deserves a
> mechanism like that, too.

Yes, it was for credential.helper. I think the _implementation_ is a
hack (because each callback has to handle it individually), but the
user-facing part is reasonably elegant, given the constraint of not
introducing new syntax.

In this case it would be something like:

diff --git a/http.c b/http.c
index 3d662bb..a7a4be5 100644
--- a/http.c
+++ b/http.c
@@ -325,8 +325,13 @@ static int http_options(const char *var, const char *value, void *cb)
 	}
 
 	if (!strcmp("http.extraheader", var)) {
-		extra_http_headers =
-			curl_slist_append(extra_http_headers, value);
+		if (*value)
+			extra_http_headers =
+				curl_slist_append(extra_http_headers, value);
+		else {
+			curl_slist_free_all(extra_http_headers);
+			extra_http_headers = NULL;
+		}
 		return 0;
 	}
 

But I think this block (even before my patch) also needs to handle the
case where "value" is NULL (presumably by complaining with
config_error_nonbool).

-Peff