update source to Ceph Pacific 16.2.2

[ceph.git] / ceph / src / jaegertracing / thrift / doc / specs / HeaderFormat.md

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+
+Header format for the THeader.h
+===============================
+
+      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, debuging 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.
+
+### PADDING:
+
+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 distingush between different (older) transports.
+
+### Transform IDs:
+
+    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 IDs:
+
+    INFO_KEYVALUE 0x01 - varint32 number of headers.
+                       - key/value pairs of varstrings (varint16 length plus
+                         no-trailing-null string).
+