diff options
| -rw-r--r-- | doc/zmq_tcp.txt | 42 |
1 files changed, 26 insertions, 16 deletions
diff --git a/doc/zmq_tcp.txt b/doc/zmq_tcp.txt index 3f21352..4819256 100644 --- a/doc/zmq_tcp.txt +++ b/doc/zmq_tcp.txt @@ -53,12 +53,25 @@ A 'peer address' may be specified by either of the following: WIRE FORMAT ----------- -0MQ messages are transmitted over TCP in frames consisting of the message -length followed by flags byte and the message data. The length MUST correspond -to the length of the remaining part of the frame. +0MQ messages are transmitted over TCP in frames consisting of an encoded +'payload length', followed by a 'flags' field and the message body. The 'payload +length' is defined as the combined length in octets of the message body and the +'flags' field. -. A single 'frame' can be defined by the -following ABNF grammar: +For frames with a 'payload length' not exceeding 254 octets, the 'payload +length' shall be encoded as a single octet. The minimum valid 'payload length' +of a frame is 1 octet, thus a 'payload length' of 0 octets is invalid and such +frames SHOULD be ignored. + +For frames with a 'payload length' exceeding 254 octets, the 'payload length' +shall be encoded as a single octet with the value `255` followed by the +'payload length' represented as a 64-bit unsigned integer in network byte +order. + +The 'flags' field consists of a single octet reserved for future expansion and +MUST be set to `0`. + +The following ABNF grammar represents a single 'frame': .... frame = (length flags data) @@ -68,39 +81,36 @@ following ABNF grammar: data = *OCTET .... - -For messages of 0 to 253 octets in length, the message length is represented by -a single octet: +The following diagram illustrates the layout of a frame with a 'payload length' +not exceeding 254 octets: .... 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -| Message size | Flags | Message body ... | +| Payload length| Flags | Message body ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message body ... +-+-+-+-+-+-+- ... .... -For messages of 254 or more octets in length, the message length is represented -by a single octet with the value `255` followed by the message length -represented as a 64-bit unsigned integer in network byte order: +The following diagram illustrates the layout of a frame with a 'payload length' +exceeding 254 octets: .... 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -| 0xff | Message size ... | +| 0xff | Payload length ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -| Message size ... | +| Payload length ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -| Message size | Flags | Message body ... | +| Payload length| Flags | Message body ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message body ... +-+-+-+-+-+-+-+ ... .... -The flags field is reserved and MUST be set to 0. EXAMPLES -------- |