The uwsgi Protocol

The uwsgi (lowercase!) protocol is the native protocol used by the uWSGI server.

It is a binary protocol that can carry any type of data. The first 4 bytes of a uwsgi packet describe the type of the data contained by the packet.

Every uwsgi request generates a response in the uwsgi format.

Even the web server handlers obey this rule, as an HTTP response is a valid uwsgi packet (look at the modifier1 = 72).

The protocol works mainly via TCP but the master process can bind to a UDP Unicast/Multicast for The embedded SNMP server or cluster management/messaging requests.

SCTP support is being worked on.

uwsgi packet header

struct uwsgi_packet_header {
    uint8_t modifier1;
    uint16_t datasize;
    uint8_t modifier2;
};

Unless otherwise specified the datasize value contains the size (16-bit little endian) of the packet body.

Packet descriptions

modifier1	datasize	modifier2	packet type
0	size of WSGI block vars (HTTP request body excluded)	0	Standard WSGI request followed by the HTTP request body
1	reserved for UNBIT
2	reserved for UNBIT
3	reserved for UNBIT
5	size of PSGI block vars (HTTP request body excluded)	0	Standard PSGI request followed by the HTTP request body
6	size of LUA WSAPI block vars (HTTP request body excluded)	0	Standard LUA/WSAPI request followed by the HTTP request body
7	size of RACK block vars (HTTP request body excluded)	0	Standard RACK request followed by the HTTP request body
8	size of JWSGI/Ring block vars (HTTP request body excluded)	0	Standard JVM request for The JWSGI interface and The Clojure/Ring JVM request handler followed by the HTTP request body
9	size of CGI block vars (HTTP request body excluded)	0	Standard Running CGI scripts on uWSGI request followed by the HTTP request body
10	size of block vars	0- 255	Management interface request: setup flag specified by modifier2. For a list of management flag look at ManagementFlag
14	size of CGI block vars (HTTP request body excluded)	0	Standard Running PHP scripts in uWSGI request followed by the HTTP request body
15	size of Mono ASP.NET block vars (HTTP request body excluded)	0	Standard The Mono ASP.NET plugin request followed by the HTTP request body
17	size of Spooler block vars	0- 255	The uWSGI Spooler request, the block vars is converted to a dictionary/hash/table and passed to the spooler callable. The second modifier is currently ignored.
18	size of CGI block vars	0-255	direct call to c-like symbols
22	size of code string	0- 255	Raw Code evaluation. The interpreter is chosen by the modifier2. 0 is Python, 5 is Perl. It does not return a valid uwsgi response, but a raw string (that may be an HTTP response)
23	size of CGI vars	0- 255	invoke the The XSLT plugin
24	size of CGI vars	0- 255	invoke the uWSGI V8 support
25	size of CGI vars	0- 255	invoke the The GridFS plugin
26	size of CGI vars	0- 255	invoke the The GlusterFS plugin
27	0	0- 255	call the FastFuncs specified by the modifier2 field
28	0	0- 255	invoke the The RADOS plugin
30	size of WSGI block vars (HTTP request body excluded)	0 (if defined the size of the block vars is 24bit le, for now none of the webserver handlers support this feature)	Standard WSGI request followed by the HTTP request body. The PATH_INFO is automatically modified, removing the SCRIPT_NAME from it
31	size of block vars	0- 255	Generic message passing (reserved)
32	size of char array	0- 255	array of char passing (reserved)
33	size of marshal object	0- 255	marshalled/serialzed object passing (reserved)
48	snmp specific	snmp specific	identify a SNMP request/response (mainly via UDP)
72	chr(TT)	chr(P)	Corresponds to the ‘HTTP’ string and signals that this is a raw HTTP response.
73	announce message size (for sanity check)	announce type (0 = hostname)	announce message
74	multicast message size (for sanity check)	0	array of chars; a custom multicast message managed by uwsgi.multicast_manager
95	cluster membership dict size	action	add/remove/enable/disable node from a cluster. Action may be 0 = add, 1 = remove, 2 = enable, 3 = disable. Add action requires a dict of at least 3 keys: hostname, address and workers
96	log message size	0	Remote logging (clustering/multicast/unicast)
97	0	0, 1	brutal reload request (0 request - 1 confirmation)
98	0	0, 1	graceful reload request (0 request - 1 confirmation)
99	size of options dictionary (if response)	0, 1	request configuration data from a uwsgi node (even via multicast)
100	0	0, 1	PING- PONG if modifier2 is 0 it is a PING request otherwise it is a PONG (a response). Useful for cluster health- check
101	size of packet	0	ECHO service
109	size of clean payload	0 to 255	legion msg (UDP, the body is encrypted)
110	size of payload	0 to 255	uwsgi_signal framework (payload is optional), modifier2 is the signal num
111	size of packet	0, 1, 2, 3	Cache operations. 0: read, 1: write, 2: delete, 3: dict_based
123	size of packet		special modifier for signaling corerouters about special conditions
173	size of packet	0, 1	RPC. The packet is an uwsgi array where the first item is the name of the function and the following are the args (if modifier2 is 1 the RPC will be ‘raw’ and all of the response will be returned to the app, uwsgi header included, if available.
200	0	0	Close mark for persistent connections
224	size of packet	0	Subscription packet. see SubscriptionServer
255	0	0- 255	Generic response. Request dependent. For example a spooler response set 0 for a failed spool or 1 for a successful one

The uwsgi vars

The uwsgi block vars represent a dictionary/hash. Every key-value is encoded in this way:

struct uwsgi_var {
    uint16_t key_size;
    uint8_t key[key_size];
    uint16_t val_size;
    uint8_t val[val_size];
}