tendermint/docs/specs/wire-protocol.md

Wire Protocol

The Tendermint wire protocol encodes data in c-style binary and JSON form.

Supported types

• Primitive types
  • uint8 (aka byte), uint16, uint32, uint64
  • int8, int16, int32, int64
  • uint, int: variable length (un)signed integers
  • string, []byte
  • time
• Derived types
  • structs
  • var-length arrays of a particular type
  • fixed-length arrays of a particular type
  • interfaces: registered union types preceded by a type byte
  • pointers

Binary

Fixed-length primitive types are encoded with 1,2,3, or 4 big-endian bytes.

• uint8 (aka byte), uint16, uint32, uint64: takes 1,2,3, and 4 bytes respectively
• int8, int16, int32, int64: takes 1,2,3, and 4 bytes respectively
• time: int64 representation of nanoseconds since epoch

Variable-length integers are encoded with a single leading byte representing the length of the following big-endian bytes. For signed negative integers, the most significant bit of the leading byte is a 1.

• uint: 1-byte length prefixed variable-size (0 ~ 255 bytes) unsigned integers
• int: 1-byte length prefixed variable-size (0 ~ 127 bytes) signed integers

NOTE: While the number 0 (zero) is encoded with a single byte x00, the number 1 (one) takes two bytes to represent: x0101. This isn't the most efficient representation, but the rules are easier to remember.

number	binary uint	binary int
0	x00	x00
1	x0101	x0101
2	x0102	x0102
256	x020100	x020100
2^(127*8)-1	x7FFFFF...	x7FFFFF...
2^(127*8)	x800100...	overflow
2^(255*8)-1	xFFFFFF...	overflow
-1	n/a	x8101
-2	n/a	x8102
-256	n/a	x820100

Structures are encoded by encoding the field values in order of declaration.

type Foo struct {
    MyString string
    MyUint32 uint32
}
var foo = Foo{"626172", math.MaxUint32}

/* The binary representation of foo:
 0103626172FFFFFFFF
 0103:               `int` encoded length of string, here 3
     626172:         3 bytes of string "bar"
           FFFFFFFF: 4 bytes of uint32 MaxUint32
*/

Variable-length arrays are encoded with a leading int denoting the length of the array followed by the binary representation of the items. Fixed-length arrays are similar but aren't preceded by the leading int.

foos := []Foo{foo, foo}

/* The binary representation of foos:
 01020103626172FFFFFFFF0103626172FFFFFFFF
 0102:                                     `int` encoded length of array, here 2
     0103626172FFFFFFFF:                   the first `foo`
                       0103626172FFFFFFFF: the second `foo`
*/

foos := [2]Foo{foo, foo} // fixed-length array

/* The binary representation of foos:
 0103626172FFFFFFFF0103626172FFFFFFFF
 0103626172FFFFFFFF:                   the first `foo`
                   0103626172FFFFFFFF: the second `foo`
*/

Interfaces can represent one of any number of concrete types. The concrete types of an interface must first be declared with their corresponding type byte. An interface is then encoded with the leading type byte, then the binary encoding of the underlying concrete type.

NOTE: The byte x00 is reserved for the nil interface value and nil pointer values.

type Animal interface{}
type Dog uint32
type Cat string

RegisterInterface(
    struct{ Animal }{},          // Convenience for referencing the 'Animal' interface
    ConcreteType{Dog(0),  0x01}, // Register the byte 0x01 to denote a Dog
    ConcreteType{Cat(""), 0x02}, // Register the byte 0x02 to denote a Cat
)

var animal Animal = Dog(02)

/* The binary representation of animal:
 010102
 01:     the type byte for a `Dog`
   0102: the bytes of Dog(02)
*/

Pointers are encoded with a single leading byte x00 for nil pointers, otherwise encoded with a leading byte x01 followed by the binary encoding of the value pointed to.

NOTE: It's easy to convert pointer types into interface types, since the type byte x00 is always nil.

JSON

The JSON codec is compatible with the binary codec, and is fairly intuitive if you're already familiar with golang's JSON encoding. Some quirks are noted below:

• variable-length and fixed-length bytes are encoded as uppercase hexadecimal strings
• interface values are encoded as an array of two items: [type_byte, concrete_value]
• times are encoded as rfc2822 strings