EIP-712 Structs

A python interface for simple EIP-712 struct construction.

In this module, a "struct" is structured data as defined in the standard. It is not the same as the Python Standard Library's struct (e.g., import struct).

Read the proposal:
https://github.com/ethereum/EIPs/blob/master/EIPS/eip-712.md

Supported Python Versions

• 3.6
• 3.7

Install

pip install eip712-structs

Usage

See API.md for a succinct summary of available methods.

Examples/Details below.

Quickstart

Say we want to represent the following struct, convert it to a message and sign it:

struct MyStruct {
    string some_string;
    uint256 some_number;
}

With this module, that would look like:

# Make a unique domain
from eip712_structs import make_domain
domain = make_domain(name='Some name', version='1.0.0')  # Make a Domain Separator

# Define your struct type
from eip712_structs import EIP712Struct, String, Uint
class MyStruct(EIP712Struct):
    some_string = String()
    some_number = Uint(256)

# Create an instance with some data
mine = MyStruct(some_string='hello world', some_number=1234)

# Into a message dict (serializable to JSON) - domain required
my_msg = mine.to_message(domain)

# Into signable bytes - domain required
my_bytes = mine.signable_bytes(domain)

See Member Types for more information on supported types.

Dynamic construction

Attributes may be added dynamically as well. This may be necessary if you want to use a reserved keyword like from.

from eip712_structs import EIP712Struct, Address
class Message(EIP712Struct):
    pass

Message.to = Address()
setattr(Message, 'from', Address())

The domain separator

EIP-712 specifies a domain struct, to differentiate between identical structs that may be unrelated. A helper method exists for this purpose. All values to the make_domain() function are optional - but at least one must be defined. If omitted, the resulting domain struct's definition leaves out the parameter entirely.

The full signature:
make_domain(name: string, version: string, chainId: uint256, verifyingContract: address, salt: bytes32)

Setting a default domain

Constantly providing the same domain can be cumbersome. You can optionally set a default, and then forget it. It is automatically used by .to_message() and .signable_bytes()

import eip712_structs

foo = SomeStruct()

my_domain = eip712_structs.make_domain(name='hello world')
eip712_structs.default_domain = my_domain

assert foo.to_message() == foo.to_message(my_domain)
assert foo.signable_bytes() == foo.signable_bytes(my_domain)

Member Types

Basic types

EIP712's basic types map directly to solidity types.

from eip712_structs import Address, Boolean, Bytes, Int, String, Uint

Address()  # Solidity's 'address'
Boolean()  # 'bool'
Bytes()    # 'bytes'
Bytes(N)   # 'bytesN' - N must be an int from 1 through 32
Int(N)     # 'intN' - N must be a multiple of 8, from 8 to 256
String()   # 'string'
Uint(N)    # 'uintN' - N must be a multiple of 8, from 8 to 256

Use like:

from eip712_structs import EIP712Struct, Address, Bytes

class Foo(EIP712Struct):
    member_name_0 = Address()
    member_name_1 = Bytes(5)
    # ...etc

Struct references

In addition to holding basic types, EIP712 structs may also hold other structs! Usage is almost the same - the difference is you don't "instantiate" the class.

Example:

from eip712_structs import EIP712Struct, String

class Dog(EIP712Struct):
    name = String()
    breed = String()

class Person(EIP712Struct):
    name = String()
    dog = Dog  # Take note - no parentheses!

# Dog "stands alone"
Dog.encode_type()     # Dog(string name,string breed)

# But Person knows how to include Dog
Person.encode_type()  # Person(string name,Dog dog)Dog(string name,string breed)

Instantiating the structs with nested values may be done a couple different ways:

# Method one: set it to a struct
dog = Dog(name='Mochi', breed='Corgi')
person = Person(name='E.M.', dog=dog)

# Method two: set it to a dict - the underlying struct is built for you
person = Person(
    name='E.M.',
    dog={
        'name': 'Mochi',
        'breed': 'Corgi',
    }
)

Arrays

Arrays are also supported for the standard.

array_member = Array(<item_type>[, <optional_length>])

• <item_type> - The basic type or struct that will live in the array
• <optional_length> - If given, the array is set to that length.

For example:

dynamic_array = Array(String())      # String[] dynamic_array
static_array  = Array(String(), 10)  # String[10] static_array
struct_array = Array(MyStruct, 10)   # MyStruct[10] - again, don't instantiate structs like the basic types

Development

Contributions always welcome.

Install dependencies:

• pip install -r requirements.txt

Run tests:

• python setup.py test
• Some tests expect an active local ganache chain on http://localhost:8545. Docker will compile the contracts and start the chain for you.
• Docker is optional, but useful to test the whole suite. If no chain is detected, chain tests are skipped.
• Usage:
  • docker-compose up -d (Starts containers in the background)
  • Note: Contracts are compiled when you run up, but won't be deployed until the test is run.
  • Cleanup containers when you're done: docker-compose down

Deploying a new version:

• Bump the version number in setup.py, commit it into master.
• Make a release tag on the master branch in Github. Travis should handle the rest.

Shameless Plug

Written by ConsenSys for ourselves and the community! ❤️