Explain proof-of-history in the readme
Also: * Hash userdata so that verification works as the readme describes. * Drop itertools package. Found a way to use std::iter instead. Fixes #8
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@ -24,7 +24,6 @@ asm = ["sha2-asm"]
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[dependencies]
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rayon = "1.0.0"
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itertools = "0.7.6"
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sha2 = "0.7.0"
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sha2-asm = {version="0.3", optional=true}
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digest = "0.7.2"
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18
README.md
18
README.md
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@ -35,7 +35,7 @@ use std::sync::mpsc::SendError;
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fn create_log(hist: &Historian) -> Result<(), SendError<Event>> {
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hist.sender.send(Event::Tick)?;
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thread::sleep(time::Duration::new(0, 100_000));
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hist.sender.send(Event::UserDataKey(0xdeadbeef))?;
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hist.sender.send(Event::UserDataKey(Sha256Hash::default()))?;
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thread::sleep(time::Duration::new(0, 100_000));
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hist.sender.send(Event::Tick)?;
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Ok(())
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@ -50,6 +50,9 @@ fn main() {
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for entry in &entries {
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println!("{:?}", entry);
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}
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// Proof-of-History: Verify the historian learned about the events
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// in the same order they appear in the vector.
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assert!(verify_slice(&entries, &seed));
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}
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```
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@ -62,6 +65,19 @@ Entry { num_hashes: 6, end_hash: [67, ...], event: UserDataKey(3735928559) }
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Entry { num_hashes: 5, end_hash: [123, ...], event: Tick }
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```
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Proof-of-History
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---
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Take note of the last line:
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```rust
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assert!(verify_slice(&entries, &seed));
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```
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[It's a proof!](https://en.wikipedia.org/wiki/Curry–Howard_correspondence) For each entry returned by the
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historian, we can verify that `end_hash` is the result of applying a sha256 hash to the previous `end_hash`
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exactly `num_hashes` times, and then hashing then event data on top of that. Because the event data is
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included in the hash, the events cannot be reordered without regenerating all the hashes.
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# Developing
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@ -8,7 +8,7 @@ use std::sync::mpsc::SendError;
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fn create_log(hist: &Historian) -> Result<(), SendError<Event>> {
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hist.sender.send(Event::Tick)?;
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thread::sleep(time::Duration::new(0, 100_000));
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hist.sender.send(Event::UserDataKey(0xdeadbeef))?;
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hist.sender.send(Event::UserDataKey(Sha256Hash::default()))?;
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thread::sleep(time::Duration::new(0, 100_000));
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hist.sender.send(Event::Tick)?;
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Ok(())
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@ -7,7 +7,7 @@
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use std::thread::JoinHandle;
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use std::sync::mpsc::{Receiver, Sender};
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use log::{hash, Entry, Event, Sha256Hash};
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use log::{extend_and_hash, hash, Entry, Event, Sha256Hash};
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pub struct Historian {
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pub sender: Sender<Event>,
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@ -24,31 +24,33 @@ pub enum ExitReason {
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fn log_events(
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receiver: &Receiver<Event>,
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sender: &Sender<Entry>,
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num_hashes: u64,
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end_hash: Sha256Hash,
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) -> Result<u64, (Entry, ExitReason)> {
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num_hashes: &mut u64,
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end_hash: &mut Sha256Hash,
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) -> Result<(), (Entry, ExitReason)> {
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use std::sync::mpsc::TryRecvError;
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let mut num_hashes = num_hashes;
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loop {
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match receiver.try_recv() {
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Ok(event) => {
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if let Event::UserDataKey(key) = event {
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*end_hash = extend_and_hash(end_hash, &key);
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}
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let entry = Entry {
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end_hash,
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num_hashes,
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end_hash: *end_hash,
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num_hashes: *num_hashes,
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event,
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};
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if let Err(_) = sender.send(entry.clone()) {
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return Err((entry, ExitReason::SendDisconnected));
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}
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num_hashes = 0;
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*num_hashes = 0;
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}
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Err(TryRecvError::Empty) => {
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return Ok(num_hashes);
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return Ok(());
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}
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Err(TryRecvError::Disconnected) => {
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let entry = Entry {
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end_hash,
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num_hashes,
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end_hash: *end_hash,
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num_hashes: *num_hashes,
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event: Event::Tick,
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};
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return Err((entry, ExitReason::RecvDisconnected));
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@ -69,9 +71,8 @@ pub fn create_logger(
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let mut end_hash = start_hash;
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let mut num_hashes = 0;
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loop {
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match log_events(&receiver, &sender, num_hashes, end_hash) {
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Ok(n) => num_hashes = n,
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Err(err) => return err,
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if let Err(err) = log_events(&receiver, &sender, &mut num_hashes, &mut end_hash) {
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return err;
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}
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end_hash = hash(&end_hash);
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num_hashes += 1;
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@ -108,7 +109,7 @@ mod tests {
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hist.sender.send(Event::Tick).unwrap();
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sleep(Duration::new(0, 1_000_000));
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hist.sender.send(Event::UserDataKey(0xdeadbeef)).unwrap();
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hist.sender.send(Event::UserDataKey(zero)).unwrap();
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sleep(Duration::new(0, 1_000_000));
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hist.sender.send(Event::Tick).unwrap();
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@ -2,6 +2,5 @@
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pub mod log;
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pub mod historian;
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extern crate digest;
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extern crate itertools;
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extern crate rayon;
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extern crate sha2;
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54
src/log.rs
54
src/log.rs
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@ -32,24 +32,24 @@ pub struct Entry {
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#[derive(Debug, PartialEq, Eq, Clone)]
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pub enum Event {
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Tick,
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UserDataKey(u64),
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UserDataKey(Sha256Hash),
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}
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impl Entry {
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/// Creates a Entry from the number of hashes 'num_hashes' since the previous event
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/// and that resulting 'end_hash'.
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pub fn new_tick(num_hashes: u64, end_hash: &Sha256Hash) -> Self {
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let event = Event::Tick;
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Entry {
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num_hashes,
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end_hash: *end_hash,
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event,
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event: Event::Tick,
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}
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}
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/// Verifies self.end_hash is the result of hashing a 'start_hash' 'self.num_hashes' times.
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/// If the event is a UserDataKey, then hash that as well.
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pub fn verify(self: &Self, start_hash: &Sha256Hash) -> bool {
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self.end_hash == next_tick(start_hash, self.num_hashes).end_hash
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self.end_hash == next_hash(start_hash, self.num_hashes, &self.event)
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}
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}
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@ -60,13 +60,36 @@ pub fn hash(val: &[u8]) -> Sha256Hash {
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hasher.result()
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}
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/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
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pub fn next_tick(start_hash: &Sha256Hash, num_hashes: u64) -> Entry {
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/// Return the hash of the given hash extended with the given value.
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pub fn extend_and_hash(end_hash: &Sha256Hash, val: &[u8]) -> Sha256Hash {
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let mut hash_data = end_hash.to_vec();
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hash_data.extend_from_slice(val);
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hash(&hash_data)
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}
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pub fn next_hash(start_hash: &Sha256Hash, num_hashes: u64, event: &Event) -> Sha256Hash {
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let mut end_hash = *start_hash;
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for _ in 0..num_hashes {
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end_hash = hash(&end_hash);
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}
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Entry::new_tick(num_hashes, &end_hash)
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if let Event::UserDataKey(key) = *event {
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return extend_and_hash(&end_hash, &key);
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}
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end_hash
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}
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/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
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pub fn next_entry(start_hash: &Sha256Hash, num_hashes: u64, event: Event) -> Entry {
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Entry {
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num_hashes,
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end_hash: next_hash(start_hash, num_hashes, &event),
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event,
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}
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}
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/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
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pub fn next_tick(start_hash: &Sha256Hash, num_hashes: u64) -> Entry {
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next_entry(start_hash, num_hashes, Event::Tick)
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}
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/// Verifies the hashes and counts of a slice of events are all consistent.
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@ -86,13 +109,16 @@ pub fn verify_slice_seq(events: &[Entry], start_hash: &Sha256Hash) -> bool {
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/// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
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pub fn create_ticks(start_hash: &Sha256Hash, num_hashes: u64, len: usize) -> Vec<Entry> {
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use itertools::unfold;
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let mut events = unfold(*start_hash, |state| {
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let event = next_tick(state, num_hashes);
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*state = event.end_hash;
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return Some(event);
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});
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events.by_ref().take(len).collect()
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use std::iter;
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let mut end_hash = *start_hash;
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iter::repeat(Event::Tick)
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.take(len)
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.map(|event| {
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let entry = next_entry(&end_hash, num_hashes, event);
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end_hash = entry.end_hash;
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entry
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})
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.collect()
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}
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#[cfg(test)]
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