fix(mqtt-proxy): client id can be empty (#5816)

apisix/stream/plugins/mqtt-proxy.lua

@@ -111,7 +111,13 @@ local function parse_mqtt(data)
         return res
     end
 
-    res.client_id = str_sub(data, parsed_pos + 1, parsed_pos + client_id_len)
+    if client_id_len == 0 then
+        -- A Server MAY allow a Client to supply a ClientID that has a length of zero bytes
+        res.client_id = ""
+    else
+        res.client_id = str_sub(data, parsed_pos + 1, parsed_pos + client_id_len)
+    end
+
     parsed_pos = parsed_pos + client_id_len
 
     res.expect_len = parsed_pos
@@ -120,10 +126,10 @@ end
 
 
 function _M.preread(conf, ctx)
-    core.log.warn("plugin rewrite phase, conf: ", core.json.encode(conf))
-    -- core.log.warn(" ctx: ", core.json.encode(ctx, true))
     local sock = ngx.req.socket()
-    local data, err = sock:peek(16)
+    -- the header format of MQTT CONNECT can be found in
+    -- https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901033
+    local data, err = sock:peek(14)
     if not data then
         core.log.error("failed to read first 16 bytes: ", err)
         return 503

t/stream-plugin/mqtt-proxy.t

@@ -316,5 +316,23 @@ passed
 "\x10\x0f\x00\x04\x4d\x51\x54\x54\x04\x02\x00\x3c\x00\x03\x66\x6f\x6f"
 --- stream_response
 hello world
+--- grep_error_log eval
+qr/mqtt client id: \w+/
+--- grep_error_log_out
+mqtt client id: foo
+--- no_error_log
+[error]
+
+
+
+=== TEST 13: hit route with empty client id
+--- stream_enable
+--- stream_request eval
+"\x10\x0f\x00\x04\x4d\x51\x54\x54\x04\x02\x00\x3c\x00\x00"
+--- stream_response
+hello world
+--- grep_error_log eval
+qr/mqtt client id: \w+/
+--- grep_error_log_out
 --- no_error_log
 [error]