http: support sending custom HTTP headers

We introduce a way to send custom HTTP headers with all requests.

This allows us, for example, to send an extra token from build agents
for temporary access to private repositories. (This is the use case that
triggered this patch.)

This feature can be used like this:

	git -c http.extraheader='Secret: sssh!' fetch $URL $REF

Note that `curl_easy_setopt(..., CURLOPT_HTTPHEADER, ...)` takes only
a single list, overriding any previous call. This means we have to
collect _all_ of the headers we want to use into a single list, and
feed it to cURL in one shot. Since we already unconditionally set a
"pragma" header when initializing the curl handles, we can add our new
headers to that list.

For callers which override the default header list (like probe_rpc),
we provide `http_copy_default_headers()` so they can do the same
trick.

Big thanks to Jeff King and Junio Hamano for their outstanding help and
patient reviews.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/http-push.c b/http-push.c
index bd60668707..ae2b7f19d2 100644
--- a/http-push.c
+++ b/http-push.c
@@ -211,7 +211,7 @@ static void curl_setup_http(CURL *curl, const char *url,
 static struct curl_slist *get_dav_token_headers(struct remote_lock *lock, enum dav_header_flag options)
 {
 	struct strbuf buf = STRBUF_INIT;
-	struct curl_slist *dav_headers = NULL;
+	struct curl_slist *dav_headers = http_copy_default_headers();
 
 	if (options & DAV_HEADER_IF) {
 		strbuf_addf(&buf, "If: (<%s>)", lock->token);
@@ -417,7 +417,7 @@ static void start_put(struct transfer_request *request)
 static void start_move(struct transfer_request *request)
 {
 	struct active_request_slot *slot;
-	struct curl_slist *dav_headers = NULL;
+	struct curl_slist *dav_headers = http_copy_default_headers();
 
 	slot = get_active_slot();
 	slot->callback_func = process_response;
@@ -845,7 +845,7 @@ static struct remote_lock *lock_remote(const char *path, long timeout)
 	char *ep;
 	char timeout_header[25];
 	struct remote_lock *lock = NULL;
-	struct curl_slist *dav_headers = NULL;
+	struct curl_slist *dav_headers = http_copy_default_headers();
 	struct xml_ctx ctx;
 	char *escaped;
 
@@ -1126,7 +1126,7 @@ static void remote_ls(const char *path, int flags,
 	struct slot_results results;
 	struct strbuf in_buffer = STRBUF_INIT;
 	struct buffer out_buffer = { STRBUF_INIT, 0 };
-	struct curl_slist *dav_headers = NULL;
+	struct curl_slist *dav_headers = http_copy_default_headers();
 	struct xml_ctx ctx;
 	struct remote_ls_ctx ls;
 
@@ -1204,7 +1204,7 @@ static int locking_available(void)
 	struct slot_results results;
 	struct strbuf in_buffer = STRBUF_INIT;
 	struct buffer out_buffer = { STRBUF_INIT, 0 };
-	struct curl_slist *dav_headers = NULL;
+	struct curl_slist *dav_headers = http_copy_default_headers();
 	struct xml_ctx ctx;
 	int lock_flags = 0;
 	char *escaped;