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Apply code review comments; improve broadcast docs.

This commit is contained in:
Andreas Fackler 2018-06-28 21:46:51 +02:00
parent 824a23775d
commit 33eadc94ef
1 changed files with 11 additions and 9 deletions
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20
src/broadcast.rs
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@ -2,9 +2,10 @@
//!
//! The Reliable Broadcast Protocol assumes a network of `N` nodes that send signed messages to
//! each other, with at most `f` of them faulty, where `3 * f < N`. Handling the networking and
//! signing is the responsibility of this crate's user: only when a message has been verified to be
//! "from node i", it can be handed to the `Broadcast` instance. One of the nodes is the "proposer"
//! who sends a value. Under the above conditions, the protocol guarantees that either all or none
//! signing is the responsibility of this crate's user; a message is only handed to the Broadcast
//! instance after it has been verified to be "from node i". One of the nodes is the "proposer"
//! who sends a value. It needs to be determined beforehand, and all nodes need to know and agree
//! who it is. Under the above conditions, the protocol guarantees that either all or none
//! of the correct nodes output a value, and that if the proposer is correct, all correct nodes
//! output the proposed value.
//!
@ -19,15 +20,16 @@
//! contains the `i`-th share of my value."
//! * Every (correct) node that receives `Value(pi)` from the proposer sends it on to everyone else
//! as `Echo(pi)`. An `Echo` translates to: "I have received `pi` directly from the proposer." If
//! the proposer sends another `Value` message, that is ignored.
//! * So every node that has received at least `f + 1` `Echo` messages with the same root
//! hash will be able to decode a value.
//! the proposer sends another `Value` message it is ignored.
//! * So every node that receives at least `f + 1` `Echo` messages with the same root hash can
//! decode a value.
//! * Every node that has received `N - f` `Echo`s with the same root hash from different nodes
//! knows that at least `f + 1` _correct_ nodes have sent an `Echo` with that hash to everyone, and
//! therefore everyone will eventually receive at least `f + 1` of them. So upon receiving `N - f`
//! `Echo`s, they send a `Ready(h)` to everyone to indicate that. `Ready` translates to: "I know
//! that everyone will eventually be able to decode the value." Moreover, since every correct node
//! only ever sends one kind of `Echo` message, this cannot happen for two different root hashes.
//! `Echo`s, they send a `Ready(h)` to everyone. It translates to: "I know that everyone will
//! eventually be able to decode the value with root hash `h`." Moreover, since every correct node
//! only sends one kind of `Echo` message, there is no danger of receiving `N - f` `Echo`s with two
//! different root hashes.
//! * Even without enough `Echo` messages, if a node receives `f + 1` `Ready` messages, it knows
//! that at least one _correct_ node has sent `Ready`. It therefore also knows that everyone will
//! be able to decode eventually, and multicasts `Ready` itself.