add(consensus): Add `slow_start_{interval/shift}` fields to `testnet::Parameters` (#8477)

* - Adds `slow_start_interval` field to `testnet::Parameters`
- Moves SLOW_START_INTERVAL/SLOW_START_SHIFT constants to zebra-chain

* Apply suggestions from code review

Co-authored-by: Marek <mail@marek.onl>

---------

Co-authored-by: Marek <mail@marek.onl>

zebra-chain/src/parameters.rs

@@ -12,6 +12,7 @@
 //! Typically, consensus parameters are accessed via a function that takes a
 //! `Network` and `block::Height`.
 
+pub mod constants;
 mod genesis;
 mod network;
 mod network_upgrade;

zebra-chain/src/parameters/constants.rs

@@ -0,0 +1,17 @@
+//! Definitions of Zebra chain constants, including:
+//! - slow start interval,
+//! - slow start shift
+
+use crate::block::Height;
+
+/// An initial period from Genesis to this Height where the block subsidy is gradually incremented. [What is slow-start mining][slow-mining]
+///
+/// [slow-mining]: https://z.cash/support/faq/#what-is-slow-start-mining
+pub const SLOW_START_INTERVAL: Height = Height(20_000);
+
+/// `SlowStartShift()` as described in [protocol specification §7.8][7.8]
+///
+/// [7.8]: https://zips.z.cash/protocol/protocol.pdf#subsidies
+///
+/// This calculation is exact, because `SLOW_START_INTERVAL` is divisible by 2.
+pub const SLOW_START_SHIFT: Height = Height(SLOW_START_INTERVAL.0 / 2);

zebra-chain/src/parameters/network.rs

@@ -189,14 +189,6 @@ impl Network {
         }
     }
 
-    /// Returns true if proof-of-work validation should be disabled for this network
-    pub fn disable_pow(&self) -> bool {
-        if let Self::Testnet(params) = self {
-            params.disable_pow()
-        } else {
-            false
-        }
-    }
     /// Returns the [`NetworkKind`] for this network.
     pub fn kind(&self) -> NetworkKind {
         match self {

zebra-chain/src/parameters/network/testnet.rs

@@ -6,8 +6,9 @@ use zcash_primitives::constants as zp_constants;
 use crate::{
     block::{self, Height},
     parameters::{
-        network_upgrade::TESTNET_ACTIVATION_HEIGHTS, Network, NetworkUpgrade,
-        NETWORK_UPGRADES_IN_ORDER,
+        constants::{SLOW_START_INTERVAL, SLOW_START_SHIFT},
+        network_upgrade::TESTNET_ACTIVATION_HEIGHTS,
+        Network, NetworkUpgrade, NETWORK_UPGRADES_IN_ORDER,
     },
 };
 
@@ -76,6 +77,8 @@ pub struct ParametersBuilder {
     hrp_sapling_extended_full_viewing_key: String,
     /// Sapling payment address human-readable prefix for this network
     hrp_sapling_payment_address: String,
+    /// Slow start interval for this network
+    slow_start_interval: Height,
     /// A flag for disabling proof-of-work checks when Zebra is validating blocks
     disable_pow: bool,
 }
@@ -98,6 +101,7 @@ impl Default for ParametersBuilder {
             genesis_hash: TESTNET_GENESIS_HASH
                 .parse()
                 .expect("hard-coded hash parses"),
+            slow_start_interval: SLOW_START_INTERVAL,
             disable_pow: false,
         }
     }
@@ -237,6 +241,12 @@ impl ParametersBuilder {
         self
     }
 
+    /// Sets the slow start interval to be used in the [`Parameters`] being built.
+    pub fn with_slow_start_interval(mut self, slow_start_interval: Height) -> Self {
+        self.slow_start_interval = slow_start_interval;
+        self
+    }
+
     /// Sets the `disable_pow` flag to be used in the [`Parameters`] being built.
     pub fn with_disable_pow(mut self, disable_pow: bool) -> Self {
         self.disable_pow = disable_pow;
@@ -252,6 +262,7 @@ impl ParametersBuilder {
             hrp_sapling_extended_spending_key,
             hrp_sapling_extended_full_viewing_key,
             hrp_sapling_payment_address,
+            slow_start_interval,
             disable_pow,
         } = self;
         Parameters {
@@ -261,6 +272,8 @@ impl ParametersBuilder {
             hrp_sapling_extended_spending_key,
             hrp_sapling_extended_full_viewing_key,
             hrp_sapling_payment_address,
+            slow_start_interval,
+            slow_start_shift: Height(slow_start_interval.0 / 2),
             disable_pow,
         }
     }
@@ -290,6 +303,10 @@ pub struct Parameters {
     hrp_sapling_extended_full_viewing_key: String,
     /// Sapling payment address human-readable prefix for this network
     hrp_sapling_payment_address: String,
+    /// Slow start interval for this network
+    slow_start_interval: Height,
+    /// Slow start shift for this network, always half the slow start interval
+    slow_start_shift: Height,
     /// A flag for disabling proof-of-work checks when Zebra is validating blocks
     disable_pow: bool,
 }
@@ -322,6 +339,7 @@ impl Parameters {
             ..Self::build()
                 .with_genesis_hash(REGTEST_GENESIS_HASH)
                 .with_disable_pow(true)
+                .with_slow_start_interval(Height::MIN)
                 .with_sapling_hrps(
                     zp_constants::regtest::HRP_SAPLING_EXTENDED_SPENDING_KEY,
                     zp_constants::regtest::HRP_SAPLING_EXTENDED_FULL_VIEWING_KEY,
@@ -353,6 +371,8 @@ impl Parameters {
             hrp_sapling_extended_spending_key,
             hrp_sapling_extended_full_viewing_key,
             hrp_sapling_payment_address,
+            slow_start_interval,
+            slow_start_shift,
             disable_pow,
         } = Self::new_regtest(None);
 
@@ -361,6 +381,8 @@ impl Parameters {
             && self.hrp_sapling_extended_spending_key == hrp_sapling_extended_spending_key
             && self.hrp_sapling_extended_full_viewing_key == hrp_sapling_extended_full_viewing_key
             && self.hrp_sapling_payment_address == hrp_sapling_payment_address
+            && self.slow_start_interval == slow_start_interval
+            && self.slow_start_shift == slow_start_shift
             && self.disable_pow == disable_pow
     }
 
@@ -394,8 +416,47 @@ impl Parameters {
         &self.hrp_sapling_payment_address
     }
 
+    /// Returns slow start interval for this network
+    pub fn slow_start_interval(&self) -> Height {
+        self.slow_start_interval
+    }
+
+    /// Returns slow start shift for this network
+    pub fn slow_start_shift(&self) -> Height {
+        self.slow_start_shift
+    }
+
     /// Returns true if proof-of-work validation should be disabled for this network
     pub fn disable_pow(&self) -> bool {
         self.disable_pow
     }
 }
+
+impl Network {
+    /// Returns true if proof-of-work validation should be disabled for this network
+    pub fn disable_pow(&self) -> bool {
+        if let Self::Testnet(params) = self {
+            params.disable_pow()
+        } else {
+            false
+        }
+    }
+
+    /// Returns slow start interval for this network
+    pub fn slow_start_interval(&self) -> Height {
+        if let Self::Testnet(params) = self {
+            params.slow_start_interval()
+        } else {
+            SLOW_START_INTERVAL
+        }
+    }
+
+    /// Returns slow start shift for this network
+    pub fn slow_start_shift(&self) -> Height {
+        if let Self::Testnet(params) = self {
+            params.slow_start_shift()
+        } else {
+            SLOW_START_SHIFT
+        }
+    }
+}

zebra-consensus/src/block/check.rs

@@ -15,7 +15,7 @@ use zebra_chain::{
     },
 };
 
-use crate::{error::*, parameters::SLOW_START_INTERVAL};
+use crate::error::*;
 
 use super::subsidy;
 
@@ -162,7 +162,7 @@ pub fn subsidy_is_valid(block: &Block, network: &Network) -> Result<(), BlockErr
     let slow_start_interval = if network.disable_pow() {
         Height(0)
     } else {
-        SLOW_START_INTERVAL
+        network.slow_start_interval()
     };
 
     if height < slow_start_interval {

zebra-consensus/src/block/subsidy/general.rs

@@ -25,20 +25,13 @@ pub fn halving_divisor(height: Height, network: &Network) -> Option<u64> {
         .activation_height(network)
         .expect("blossom activation height should be available");
 
-    // TODO: Add this as a field on `testnet::Parameters` instead of checking `disable_pow()`, this is 0 for Regtest in zcashd,
-    //       see <https://github.com/zcash/zcash/blob/master/src/chainparams.cpp#L640>
-    let slow_start_shift = if network.disable_pow() {
-        Height(0)
-    } else {
-        SLOW_START_SHIFT
-    };
-
-    if height < slow_start_shift {
-        unreachable!(
-            "unsupported block height {height:?}: checkpoints should handle blocks below {slow_start_shift:?}",
+    if height < network.slow_start_shift() {
+        panic!(
+            "unsupported block height {height:?}: checkpoints should handle blocks below {:?}",
+            network.slow_start_shift()
         )
     } else if height < blossom_height {
-        let pre_blossom_height = height - slow_start_shift;
+        let pre_blossom_height = height - network.slow_start_shift();
         let halving_shift = pre_blossom_height / PRE_BLOSSOM_HALVING_INTERVAL;
 
         let halving_div = 1u64
@@ -51,7 +44,7 @@ pub fn halving_divisor(height: Height, network: &Network) -> Option<u64> {
 
         Some(halving_div)
     } else {
-        let pre_blossom_height = blossom_height - slow_start_shift;
+        let pre_blossom_height = blossom_height - network.slow_start_shift();
         let scaled_pre_blossom_height =
             pre_blossom_height * HeightDiff::from(BLOSSOM_POW_TARGET_SPACING_RATIO);
 
@@ -87,9 +80,10 @@ pub fn block_subsidy(height: Height, network: &Network) -> Result<Amount<NonNega
 
     // TODO: Add this as a field on `testnet::Parameters` instead of checking `disable_pow()`, this is 0 for Regtest in zcashd,
     //       see <https://github.com/zcash/zcash/blob/master/src/chainparams.cpp#L640>
-    if height < SLOW_START_INTERVAL && !network.disable_pow() {
+    if height < network.slow_start_interval() && !network.disable_pow() {
         unreachable!(
-            "unsupported block height {height:?}: callers should handle blocks below {SLOW_START_INTERVAL:?}",
+            "unsupported block height {height:?}: callers should handle blocks below {:?}",
+            network.slow_start_interval()
         )
     } else if height < blossom_height {
         // this calculation is exact, because the halving divisor is 1 here
@@ -145,7 +139,7 @@ mod test {
 
         assert_eq!(
             1,
-            halving_divisor((SLOW_START_INTERVAL + 1).unwrap(), network).unwrap()
+            halving_divisor((network.slow_start_interval() + 1).unwrap(), network).unwrap()
         );
         assert_eq!(
             1,
@@ -274,7 +268,7 @@ mod test {
         // https://z.cash/support/faq/#what-is-slow-start-mining
         assert_eq!(
             Amount::try_from(1_250_000_000),
-            block_subsidy((SLOW_START_INTERVAL + 1).unwrap(), network)
+            block_subsidy((network.slow_start_interval() + 1).unwrap(), network)
         );
         assert_eq!(
             Amount::try_from(1_250_000_000),

zebra-consensus/src/block/tests.rs

@@ -20,7 +20,7 @@ use zebra_chain::{
 use zebra_script::CachedFfiTransaction;
 use zebra_test::transcript::{ExpectedTranscriptError, Transcript};
 
-use crate::{parameters::SLOW_START_SHIFT, transaction};
+use crate::transaction;
 
 use super::*;
 
@@ -470,7 +470,7 @@ fn miner_fees_validation_for_network(network: Network) -> Result<(), Report> {
     let block_iter = network.block_iter();
 
     for (&height, block) in block_iter {
-        if Height(height) > SLOW_START_SHIFT {
+        if Height(height) > network.slow_start_shift() {
             let block = Block::zcash_deserialize(&block[..]).expect("block should deserialize");
 
             // fake the miner fee to a big amount

zebra-consensus/src/parameters/subsidy.rs

@@ -10,18 +10,6 @@ use zebra_chain::{
     parameters::{Network, NetworkKind, NetworkUpgrade},
 };
 
-/// An initial period from Genesis to this Height where the block subsidy is gradually incremented. [What is slow-start mining][slow-mining]
-///
-/// [slow-mining]: https://z.cash/support/faq/#what-is-slow-start-mining
-pub const SLOW_START_INTERVAL: Height = Height(20_000);
-
-/// `SlowStartShift()` as described in [protocol specification §7.8][7.8]
-///
-/// [7.8]: https://zips.z.cash/protocol/protocol.pdf#subsidies
-///
-/// This calculation is exact, because `SLOW_START_INTERVAL` is divisible by 2.
-pub const SLOW_START_SHIFT: Height = Height(SLOW_START_INTERVAL.0 / 2);
-
 /// The largest block subsidy, used before the first halving.
 ///
 /// We use `25 / 2` instead of `12.5`, so that we can calculate the correct value without using floating-point.