HTSMSG Binary Format
Message Structure
A message can be of either map or list type. In a map each field has a name, in a list the members do not have names, but the order should be preserved.
The field types are:
Map
1
Sub message of type map
S64
2
Signed 64bit integer
Str
3
UTF-8 encoded string
Bin
4
Binary blob
List
5
Sub message of type list
Dbl
6
Double precision floating point
Bool
7
Boolean
UUID
8
64 bit UUID in binary format
All in all the message structure is quite similar to JSON but most notably; no boolean nor null type exist and HTSMSG supports binary objects.
HTSMSG Binary Format
The binary format is designed to for back-to-back transmission of messages over a network (TCP) connection.
The root message must always be of type map.
Root body
Length
4 byte integer
Total length of message (not including this length field itself)
Body
HTSMSG-Field * N
Fields in the root body
HTSMSG-Field
Type
1 byte integer
Type of field (see field type IDs above)
Namelength
1 byte integer
Length of name of field. If a field is part of a list message this must be 0
Datalength
4 byte integer
Length of field data
Name
N bytes
Field name, length as specified by Namelength
Data
N bytes
Field payload, for details see below
Field encoding for type: map and list
The data is repeated HTSMSG-Fields exactly as the root body. Note the subtle difference in that for the root-message the length includes the 4 bytes of length field itself whereas in the field encoding the length written includes just the actual payload.
Field encoding for type: s64
Integers are encoded using a very simple variable length encoding. All leading bytes that are 0 is discarded. So to encode the value 100, datalength should be 1 and the data itself should be just one byte [0x64]. To encode 1337; datalength=2, data=[0x39 0x05].
Note that there is no sign extension in this encoding scheme so if you need to encode -1 you need to set datalength=8 and data = [0xff 0xff 0xff 0xff 0xff 0xff 0xff 0xff]. This can certainly be thought of as a bug, but it is the way it is.
Field encoding for type: str
Datalength should be the length of the string (NOT including the null terminating character). Thus the null terminator should not be present in data either.
Field encoding for type: bin
Datalength should be the length of the binary object. Data is the binary object itself.
Last updated