内容简介：Simple binary data exchange format that is based onErnie is fun over the original BERT name, from the Sesame Street Bert & Ernie couple.No, this document will not define RPC syntax because of 2 reasons:
Ernie
Simple binary data exchange format that is based on External Term Format in Erlang. This is update on BERT which is a little bit outdated right now.
Name
Ernie is fun over the original BERT name, from the Sesame Street Bert & Ernie couple.
RPC
No, this document will not define RPC syntax because of 2 reasons:
- This is out of scope of this document. It is meant to define only data encoding format, not services one will use it for.
- Authors of this document believes that RPC are bad, and you should not use them. Instead use message passing between your services.
Schema/structured data
This is meant to encode free-form data, if you want to encode structured data with schema then we highly suggest you to take look into other formats like:
- ASN.1 and any of it's encodings
- ProtoBuffers
- Apache Thrift
- FlatBuffers
- Cap'n'Proto
Specification
Introduction
- The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 .
Types
-
Integer
Binary representation of integers.
Implementation MUST support at least 8-bit unsigned and 32-bit signed integers with full precision.
-
64-bit Float
IEEE 754 double precision floats.
Implementation MUST support all non-NaN, non-infinite, non-subnormal values described in IEEE 754 binary64 spec. Implementations SHOULD NOT encode these values.
-
Tuple
Fixed length sequence of values.
-
List
Dynamic length sequence of values.
-
Binary
Representation of bytes with arbitrary length. If used to store human-readable strings it MUST be encoded as correct UTF-8 string.
-
Map
List of key-value pairs in arbitrary order. Keys MUST NOT appear twice in the same map.
Encoding
-
Top level
Binary encoded data MUST start with magic byte of decimal value of
131followed by single byteTagvalue followed by arbitrary length data:0 1 2 +--------+-------+-------+------- | 131 | Tag | Data ... +--------+-------+-------+-------
-
Integer
Integer can be encoded in 3 different forms:
-
Values in range 0..255 (aka byte)
0 1 2 +-------+--------+ | 97 | Data | +-------+--------+
Where
Datais unsigned byte representation of value. -
Values in range -4 294 967 295..4 294 967 294 (signed 32-bit value)
0 1 2 3 4 5 +-------+-------+------+------+------+ | 98 | Data | +-------+-------+------+------+------+
Where
Datais signed 32-bit representation of integer in U2 big-endian encoding. -
"Short" arbitrary long signed integers (up to 2040-bit)
0 1 2 3 ... N+3 +-------+-------+-------+------+------+ | 110 | N | Sign | Data | +-------+-------+-------+------+------+
Nis big-endian 16-bit unsigned integer.Datarepresents little-endian encodedNbyte long integer.Signis0for positive integer and1for negative one. -
"Long" arbitrary long signed integers (from 2041 to 524 288-bit long)
0 1 2 3 4 ... N+4 +-------+-------+-------+-------+------+------+ | 111 | N | Sign | Data | +-------+-------+-------+-------+------+------+
Nis big-endian 16-bit unsigned integer.Datarepresents little-endian encodedNbyte long integer.Signis0for positive integer and1for negative one.
-
-
Float
0 1 2 3 4 5 6 7 8 9 +-------+-------+--------+-------+-------+-------+-------+-------+-------+ | 70 | Data | +-------+-------+--------+-------+-------+-------+-------+-------+-------+
Where
Datais IEEE 754 double precision floating-point number encoded as big-endian. -
Tuple
-
Tuples up to 255 elements
0 1 2 ... N+2 +-------+-------+--------+--------+ | 104 | Arity | Data ... | +-------+-------+--------+--------+
-
Tuples up to 4 294 967 295 elements
0 1 2 3 4 5 ... N+5 +-------+-------+--------+--------+--------+--------+--------+ | 105 | Arity | Data ... | +-------+-------+--------+--------+--------+--------+--------+
Where
Arityis big-endian unsigned integer declaring amount of elements inData. -
-
List
-
Byte list
0 1 2 3 ... N+3 +-------+-------+-------+-------+-------+ | 107 | N | Data ... | +-------+-------+-------+-------+-------+
This is optimisation for lists that contains only values in range 0..255, inclusive.
-
General list
0 1 2 3 4 5 ... N+5 N+6 +-------+-------+-------+-------+-------+-------+-------+-------+ | 108 | Arity | Data ... | 106 | +-------+-------+-------+-------+-------+-------+-------+-------+
Where
Arityis big-endian unsigned 32-bit integer declaring amount of elements inData. -
Empty list
0 1 +-------+ | 106 | +-------+
-
-
Binary
0 1 2 3 4 5 ... N+5 +-------+-------+-------+-------+-------+-------+-------+ | 109 | N | Data ... | +-------+-------+-------+-------+-------+-------+-------+
-
Map
0 1 2 3 4 5 ... N+5 +-------+-------+-------+-------+-------+-------+-------+ | 116 | Arity | Data ... | +-------+-------+-------+-------+-------+-------+-------+
The
Arityfield is an unsigned 32-bit integer in big-endian format that determines the number of key-value pairs in the map. Key and value pairs (Ki => Vi) are encoded in sectionDatain the following order:K1, V1, K2, V2,..., Kn, Vn.
Open questions
- Should we support atoms?
- Should we allow defining improper lists?
License
This document is released on Creative Commons Attribution-ShareAlike 4.0 International License .
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