0 1 2 3 4 5 6 7 8 9 a b c d e f 0 1 2 3 4 5 6 7 8 9 a b c d e f
+----------------------------------------------------------------+
| 0| LENGTH |
+----------------------------------------------------------------+
| 0| HEADER MAGIC | FLAGS |
+----------------------------------------------------------------+
| SEQUENCE NUMBER |
+----------------------------------------------------------------+
| 0| Header Size(/32) | ...
+---------------------------------
Header is of variable size:
(and starts at offset 14)
+----------------------------------------------------------------+
| PROTOCOL ID (varint) | NUM TRANSFORMS (varint) |
+----------------------------------------------------------------+
| TRANSFORM 0 ID (varint) | TRANSFORM 0 DATA ...
+----------------------------------------------------------------+
| ... ... |
+----------------------------------------------------------------+
| INFO 0 ID (varint) | INFO 0 DATA ...
+----------------------------------------------------------------+
| ... ... |
+----------------------------------------------------------------+
| |
| PAYLOAD |
| |
+----------------------------------------------------------------+
The LENGTH field is 32 bits, and counts the remaining bytes in the packet, NOT including the length field. The header size field is 16 bits, and defines the size of the header remaining NOT including the HEADER MAGIC, FLAGS, SEQUENCE NUMBER and header size fields. The Header size field is in bytes/4.
The transform ID‘s are varints. The data for each transform is defined by the transform ID in the code - no size is given in the header. If a transform ID is specified from a client and the server doesn’t know about the transform ID, an error MUST be returned as we don't know how to transform the data.
Conversely, data in the info headers is ignorable. This should only be things like timestamps, debugging tracing, etc. Using the header size you should be able to skip this data and read the payload safely if you don't know the info ID.
Info‘s should be oldest supported to newest supported order, so that if we read an info ID we don’t support, none of the remaining info ID's will be supported either, and we can safely skip to the payload.
Info ID‘s and transform ID’s should share the same ID space.
Header will be padded out to next 4-byte boundary with 0x00.
Max frame size is 0x3FFFFFFF, which is slightly less than HTTP_MAGIC. This allows us to distinguish between different (older) transports.
ZLIB_TRANSFORM 0x01 - No data for this. Use zlib to (de)compress the
data.
HMAC_TRANSFORM 0x02 - Variable amount of mac data. One byte to specify
size. Mac data is appended at the end of the packet.
SNAPPY_TRANSFORM 0x03 - No data for this. Use snappy to (de)compress the
data.
INFO_KEYVALUE 0x01 - varint32 number of headers.
- key/value pairs of varstrings (varint16 length plus
no-trailing-null string).