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Fixes to TCP wire format specification

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This commit is contained in:
Martin Lucina 2010-03-10 13:52:41 +01:00
parent 8f90ae8dfd
commit 5fef480aeb
1 changed files with 26 additions and 16 deletions
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42
doc/zmq_tcp.txt
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@ -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
--------