[PATCH uhttpd] ubus: support GET method with CORS requests

[Rafał Miłecki]

From: Rafał Miłecki <rafal at milecki.pl>

Complex GET requests (e.g. those with custom headers) require browsers
to send preflight OPTIONS request with:
Access-Control-Request-Method: GET

It's important to reply to such requests with all relevant
Access-Control-Allow-* headers to allow CORS requests.

Adding GET to the Access-Control-Allow-Methods is cosmetical as
according to the Fetch standard:

> If request’s method is not in methods, request’s method is not a
> CORS-safelisted method, and request’s credentials mode is "include" or
> methods does not contain `*`, then return a network error.

It basically means that Access-Control-Allow-Methods value is ignored
for GET, HEAD and POST methods.

Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 ubus.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ubus.c b/ubus.c
index 1cf5c5f..39b38b2 100644
--- a/ubus.c
+++ b/ubus.c
@@ -164,7 +164,7 @@ static void uh_ubus_add_cors_headers(struct client *cl)
 	{
 		char *hdr = (char *) blobmsg_data(tb[HDR_ACCESS_CONTROL_REQUEST_METHOD]);
 
-		if (strcmp(hdr, "POST") && strcmp(hdr, "OPTIONS"))
+		if (strcmp(hdr, "GET") && strcmp(hdr, "POST") && strcmp(hdr, "OPTIONS"))
 			return;
 	}
 
@@ -175,7 +175,7 @@ static void uh_ubus_add_cors_headers(struct client *cl)
 		ustream_printf(cl->us, "Access-Control-Allow-Headers: %s\r\n",
 		               blobmsg_get_string(tb[HDR_ACCESS_CONTROL_REQUEST_HEADERS]));
 
-	ustream_printf(cl->us, "Access-Control-Allow-Methods: POST, OPTIONS\r\n");
+	ustream_printf(cl->us, "Access-Control-Allow-Methods: GET, POST, OPTIONS\r\n");
 	ustream_printf(cl->us, "Access-Control-Allow-Credentials: true\r\n");
 }
 
-- 
2.27.0