daemon/http: expose HTTP headers to kr_request

(Currently rebased on top of !1164 (merged))

Add HTTP headers to an optional kr_request.qsource.headers structure. Headers are stored as name, value string pairs.

In the configuration, headers to be exposed can be selected with net.doh_headers() that takes either a string or a table of strings. These string are the names of headers that should be copied into kr_request.qsource.headers. Comparison is case-insensitive and pseudo-headers are supported as well.

net.doh_headers({'accept', ':method'})

The following snippet can be used to access the headers in lua modules:

for i = 1, tonumber(req.qsource.headers.len) do
	local name = ffi.string(req.qsource.headers.at[i - 1].name)
	local value = ffi.string(req.qsource.headers.at[i - 1].value)
	print(name, value)
end

Fixes #616 (closed)

TODO:

• configuration interface to select which headers should be exposed
• expose only selected headers
• documentation
• config test

daemon/bindings/net.c

@@ -435,6 +435,55 @@ static int net_tls(lua_State *L)
 	return 1;
 }
 
+/** Configure HTTP headers for DoH requests. */
+static int net_doh_headers(lua_State *L)
+{
+	doh_headerlist_t *headers = &the_worker->doh_qry_headers;
+	int i;
+	const char *name;
+
+	/* Only return current configuration. */
+	if (lua_gettop(L) == 0) {
+		lua_newtable(L);
+		for (i = 0; i < headers->len; i++) {
+			lua_pushinteger(L, i + 1);
+			name = headers->at[i];
+			lua_pushlstring(L, name, strlen(name));
+			lua_settable(L, -3);
+		}
+		return 1;
+	}
+
+	if (lua_gettop(L) != 1)
+		lua_error_p(L, "net.doh_headers() takes one parameter (string or table)");
+
+	if (!lua_istable(L, 1) && !lua_isstring(L, 1))
+		lua_error_p(L, "net.doh_headers() argument must be string or table");
+
+	/* Clear existing headers. */
+	for (i = 0; i < headers->len; i++)
+		free((void *)headers->at[i]);
+	array_clear(*headers);
+
+	if (lua_istable(L, 1)) {
+		for (i = 1; !lua_isnil(L, -1); i++) {
+			lua_pushinteger(L, i);
+			lua_gettable(L, 1);
+			if (lua_isnil(L, -1))  /* missing value - end iteration */
+				break;
+			if (!lua_isstring(L, -1))
+				lua_error_p(L, "net.doh_headers() argument table can only contain strings");
+			name = lua_tostring(L, -1);
+			array_push(*headers, strdup(name));
+		}
+	} else if (lua_isstring(L, 1)) {
+		name = lua_tostring(L, 1);
+		array_push(*headers, strdup(name));
+	}
+
+	return 0;
+}
+
 /** Return a lua table with TLS authentication parameters.
  * The format is the same as passed to policy.TLS_FORWARD();
  * more precisely, it's in a compatible canonical form. */
@@ -1083,6 +1132,7 @@ int kr_bindings_net(lua_State *L)
 		{ "bpf_set",      net_bpf_set },
 		{ "bpf_clear",    net_bpf_clear },
 		{ "register_endpoint_kind", net_register_endpoint_kind },
+		{ "doh_headers", net_doh_headers },
 		{ NULL, NULL }
 	};
 	luaL_register(L, "net", lib);