TTHeader

Referring to the Thrift THeader protocol, we designed the TTheader protocol.

Header Format

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        | ...
+---------------------------------

                  Header is of variable size:

                   (and starts at offset 14)

+----------------------------------------------------------------+
| PROTOCOL ID  |NUM TRANSFORMS . |TRANSFORM 0 ID (uint8)|
+----------------------------------------------------------------+
|  TRANSFORM 0 DATA ...
+----------------------------------------------------------------+
|         ...                              ...                   |
+----------------------------------------------------------------+
| INFO 0 ID (uint8)|       INFO 0  DATA ...
+----------------------------------------------------------------+
|         ...                              ...                   |
+----------------------------------------------------------------+
|                                                                |
|                              PAYLOAD                           |
|                                                                |
+----------------------------------------------------------------+

• LENGTH: 32bits, including the byte size of the remaining part of the data packet, but does not include itself
• HEADER MAGIC: 16bits, value: 0x1000, it’s used to identify TTHeaderTransport
• FLAGS: 16bits, it’s a reserved field, not used yet, default value is 0x0000
• SEQUENCE NUMBER: 32bits, it’s the seqId of the message packet, can be used for multiplexing, and ensure it is incremented within a single connection
• HEADER SIZE: 16bits, it’s equal to the number of bytes divided by 4 of the head length. The header length calculation starts from the 14th byte and continues until before PAYLOAD (Notice: The maximum length of the header is 64K)
• PROTOCOL ID: uint8 encoding, the values are:
  • ProtocolIDBinary = 0
  • ProtocolIDCompact = 2
• NUM TRANSFORMS: uint8 encoding, the number of TRANSFORM
• TRANSFORM ID: uint8 encoding, refer the instructions below
• INFO ID: uint8 encoding, refer the instructions below
• PAYLOAD: message content

PADDING

Header will be padded out to next 4-byte boundary with 0x00.

Transform IDs

Transform IDs represents the compression way, which is a reserved field and is not supported currently. The values are:

• ZLIB_TRANSFORM = 0x01: the corresponding data is empty, indicating that the data is compressed with zlib
• SNAPPY_TRANSFORM = 0x03: the corresponding data is empty, indicating that the data is compressed with snappy

Info IDs

Info IDs is used to transmit some key/value pair information, the values are:

• INFO_KEYVALUE = 0x01: the corresponding data is a key/value pair, key and value are each composed of the length of uint16 plus no-training-null string, which is generally used to transmit some common meta information, such as tracingId
• INFO_INTKEYVALUE = 0x10: the corresponding data is a key/value pair, the key is uint16, the value is composed of the length of uint16 plus the no-trading-null string, which is generally used to transmit some internally customized meta information, some keys are required as request:
  • TRANSPORT_TYPE = 1 (value: framed/unframed)
  • LOG_ID = 2
  • FROM_SERVICE = 3
  • FROM_CLUSTER = 4 (default)
  • FROM_IDC = 5
  • TO_SERVICE = 6
  • TO_METHOD = 9
• ACL_TOKEN_KEYVALUE = 0x11: the corresponding data is a key/value pair, key and value are each composed of the length of uint16 plus no-trading-null string, used to transmit ACL Token