Summary

Note about releases

The 🍂Bronze Release🍂 is the first of 3 planned releases of the Balancer Protocol. Bronze emphasizes code clarity for audit and verification, and does not go to great lengths to optimize for gas.

The ❄️Silver Release❄️ will bring many gas optimizations and architecture changes that will reduce transaction overhead and enable more flexible usage patterns.

The ☀️Golden Release☀️ will introduce a few final features that will tie the whole system together.

Unless noted otherwise, this document describes the contract architecture for the 🍂Bronze Release🍂. We have attempted to make note of the functionality that will change for future releases, but it is possible for any aspect of the design to change in both very large and also very subtle ways.

Please take care when interacting with a Balancer pool to ensure you know which release it is associated with. Objects in the Balancer system provide getColor() returns (bytes32), which returns a left-padded ASCII representation of the all-caps color word, ie, bytes32("BRONZE").

Events

LOG_CALL is an anonymous event which uses the function signature as the event signature. It is fired by all stateful functions.

event LOG_CALL(
bytes4 indexed sig,
address indexed caller,
bytes data
) anonymous;

LOG_SWAP is fired (along with LOG_CALL) for all swap variants.

event LOG_SWAP(
address indexed caller,
address indexed tokenIn,
address indexed tokenOut,
uint256 tokenAmountIn,
uint256 tokenAmountOut
);

LOG_JOIN and LOG_EXIT are fired for each individual token join / exit

event LOG_JOIN(
address indexed caller,
address indexed tokenIn,
uint256 tokenAmountIn
);
event LOG_EXIT(
address indexed caller,
address indexed tokenOut,
uint256 tokenAmountOut
);

Mutex

All stateful functions use either a lock or viewlock function modifier. A mutex places a lock on contract state and prevents any sort of re-entrancy.

modifier _lock_() {
require(!_mutex, "ERR_REENTRY");
_mutex = true;
_;
_mutex = false;
}
modifier _viewlock_() {
require(!_mutex, "ERR_REENTRY");
_;
}