$$ \newcommand \PSfunction {\textbf{function }} \newcommand \PSreturn {\textbf{return }} \newcommand \PSendfunction {\textbf{end function}} \newcommand \PSswitch {\textbf{switch }} \newcommand \PScase {\textbf{case }} \newcommand \PSdefault {\textbf{default}} \newcommand \PSendswitch {\textbf{end switch}} \newcommand \PSfor {\textbf{for }} \newcommand \PSendfor {\textbf{end for}} \newcommand \PSwhile {\textbf{while }} \newcommand \PSendwhile {\textbf{end while}} \newcommand \PSdo {\textbf{ do}} \newcommand \PSif {\textbf{if }} \newcommand \PSelseif {\textbf{else if }} \newcommand \PSelse {\textbf{else}} \newcommand \PSthen {\textbf{ then}} \newcommand \PSendif {\textbf{end if}} \newcommand \PSnot {\textbf{not }} \newcommand \PScomment {\qquad \small \textsf} $$

$$ \newcommand \Resync {\mathrm{ResynchronizationAttempt}} \newcommand \BlockProposal {\mathrm{BlockProposal}} \newcommand \BlockAssembly {\mathrm{BlockAssembly}} \newcommand \Sortition {\mathrm{Sortition}} \newcommand \Broadcast {\mathrm{Broadcast}} \newcommand \RetrieveProposal {\mathrm{RetrieveProposal}} \newcommand \c {\mathit{credentials}} \newcommand \Proposal {\mathrm{Proposal}} \newcommand \Bundle {\mathrm{Bundle}} \newcommand \Vote {\mathrm{Vote}} \newcommand \prop {\mathit{proposal}} $$

Block Proposal

The following is an abstracted pseudocode of the \( \BlockProposal \) algorithm.

Algorithm

\( \textbf{Algorithm 3} \text{: Block Proposal} \)

$$ \begin{aligned} &\text{1: } \PSfunction \BlockProposal() \\ &\text{2: } \quad \PSif p \ne 0 \PSthen \\ &\text{3: } \quad \quad \Resync() \\ &\text{4: } \quad \PSendif \\ &\text{5: } \quad \PSfor a \in A \PSdo \\ &\text{6: } \quad \quad \c \gets \Sortition(a_I, r, p, \prop) \\ &\text{7: } \quad \quad \PSif \c_j > 0 \PSthen \\ &\text{8: } \quad \quad \quad \PSif p = 0 \lor \exists s’ \text{ such that } \Bundle(r, p-1, s’, \bot) \subset V \PSthen \\ &\text{9: } \quad \quad \quad \quad (e, y) \gets \BlockAssembly(a_I) \\ &\text{10:} \quad \quad \quad \quad \prop \gets \Proposal(e, y, p, a_I) \\ &\text{11:} \quad \quad \quad \quad v \gets \Proposal_\text{value}(\prop) \\ &\text{12:} \quad \quad \quad \quad \Broadcast(\Vote(a_I, r, p, \prop, v, \c)) \\ &\text{13:} \quad \quad \quad \quad \Broadcast(\prop) \\ &\text{14:} \quad \quad \quad \PSelse \\ &\text{15:} \quad \quad \quad \quad \Broadcast(\Vote(a_I, r, p, \prop, \bar{v}, \c)) \\ &\text{16:} \quad \quad \quad \quad \PSif \RetrieveProposal(\bar{v}) \ne \bot \PSthen \\ &\text{17:} \quad \quad \quad \quad \quad \Broadcast(\RetrieveProposal(\bar{v})) \\ &\text{18:} \quad \quad \quad \quad \PSendif \\ &\text{19:} \quad \quad \quad \PSendif \\ &\text{20:} \quad \quad \PSendif \\ &\text{21:} \quad \PSendfor \\ &\text{22: } \PSendfunction \end{aligned} $$

⚙️ IMPLEMENTATION

Block proposal reference implementation.

This algorithm is the first procedure executed when entering a new round, and upon starting any period where a reproposal is not possible.

Starting on Algorithm 3 - Line 2, the node attempts a resynchronization (described in the corresponding section), which has only effect on periods \( p > 0 \).

⚙️ IMPLEMENTATION

The reference implementation executes a resynchronization attempt when entering into a new period. Functionally, the behavior is the same, as resynchronization is performed before starting a new period, save for \( p = 0 \).

The algorithm loops over all the participating accounts (\( a \in A \)) registered on the node. This is a typical pattern in every main algorithm subroutine performing committee voting.

For each participating account, the sortition algorithm runs to check if said account is allowed to participate in the proposal.

If an account \( a \) is selected by sortition (because \( \c_j = \Sortition(a_I, r, p, \prop)_j > 0 \)) there are two options:

1. If this is a proposal step (\( p = 0 \)) or if the node has observed a bundle \( \Bundle(r, p-1, s’, \bot) \) (meaning there is no valid pinned value), then the node:

   • Assembles a block (see the Ledger non-normative section for details on this process),
   • Computes the proposal value for this block,
   • Broadcast a proposal vote by the account \( a \),
   • Broadcasts the full block in a \( \texttt{Proposal} \) type message.

2. Otherwise, a value \( \bar{v} \) has been pinned, supported by a bundle observed in period \( p - 1 \), and on Algorithm 3 - Line 15 the node:

   • Gets the pinned value,
   • Assembles a vote \( \Vote(a_I, r, p, \prop, \bar{v}, \c) \),
   • Broadcasts this vote,
   • Broadcast the proposal for the pinned vote if it has already been observed.

⚙️ IMPLEMENTATION

The reference implementation assembles a set of transactions and a block header independently of the proposer, in parallel with the proposer loop. This improves timing and guarantees the tight deadline constraints for the block proposal step.