From bf7f95b0e96402d65b7d5974bfbbbfb95ae21aef Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Thu, 23 Apr 2020 21:38:54 -0600
Subject: [PATCH] TZE consensus context and program sets

Co-authored-by: Kris Nuttycombe <kris.nuttycombe@gmail.com>
---
 zcash_primitives/src/consensus.rs             |   4 +-
 zcash_primitives/src/consensus/extensions.rs  |   3 +
 .../src/consensus/extensions/transparent.rs   | 109 ++++++++++++++++++
 3 files changed, 115 insertions(+), 1 deletion(-)
 create mode 100644 zcash_primitives/src/consensus/extensions.rs
 create mode 100644 zcash_primitives/src/consensus/extensions/transparent.rs

diff --git a/zcash_primitives/src/consensus.rs b/zcash_primitives/src/consensus.rs
index 4cc67f49b..952c14aa3 100644
--- a/zcash_primitives/src/consensus.rs
+++ b/zcash_primitives/src/consensus.rs
@@ -1,8 +1,10 @@
-//! Consensus parameters.
+//! Consensus logic and parameters.
 
 use std::convert::TryFrom;
 use std::fmt;
 
+pub mod extensions;
+
 /// Zcash consensus parameters.
 pub trait Parameters {
     fn activation_height(nu: NetworkUpgrade) -> Option<u32>;
diff --git a/zcash_primitives/src/consensus/extensions.rs b/zcash_primitives/src/consensus/extensions.rs
new file mode 100644
index 000000000..6210d3fcd
--- /dev/null
+++ b/zcash_primitives/src/consensus/extensions.rs
@@ -0,0 +1,3 @@
+//! Consensus logic for Zcash extensions.
+
+pub mod transparent;
diff --git a/zcash_primitives/src/consensus/extensions/transparent.rs b/zcash_primitives/src/consensus/extensions/transparent.rs
new file mode 100644
index 000000000..2c3e21745
--- /dev/null
+++ b/zcash_primitives/src/consensus/extensions/transparent.rs
@@ -0,0 +1,109 @@
+//! Consensus logic for Transparent Zcash Extensions.
+
+use std::convert::TryFrom;
+use zcash_extensions_api::transparent::{Error, Extension, Precondition, Witness};
+
+use crate::extensions::transparent::demo;
+use crate::transaction::components::TzeOut;
+use crate::transaction::Transaction;
+
+/// The set of programs that have assigned type IDs within the Zcash consensus rules.
+#[derive(Debug, Clone, Copy)]
+pub enum ExtensionId {
+    Demo,
+}
+
+pub struct InvalidExtId(usize);
+
+impl TryFrom<usize> for ExtensionId {
+    type Error = InvalidExtId;
+
+    fn try_from(t: usize) -> Result<Self, Self::Error> {
+        match t {
+            0 => Ok(ExtensionId::Demo),
+            n => Err(InvalidExtId(n)),
+        }
+    }
+}
+
+impl From<ExtensionId> for usize {
+    fn from(type_id: ExtensionId) -> usize {
+        match type_id {
+            ExtensionId::Demo => 0,
+        }
+    }
+}
+
+/// The complete set of context data that is available to any extension having
+/// an assigned extension type ID.
+pub struct Context<'a> {
+    pub height: i32,
+    pub tx: &'a Transaction,
+}
+
+impl<'a> Context<'a> {
+    pub fn new(height: i32, tx: &'a Transaction) -> Self {
+        Context { height, tx }
+    }
+}
+
+pub trait Epoch {
+    type Error;
+
+    fn verify<'a>(
+        &self,
+        precondition: &Precondition,
+        witness: &Witness,
+        ctx: &Context<'a>,
+    ) -> Result<(), Error<Self::Error>>;
+}
+
+/// Implementation of required operations for the demo extension, as satisfied
+/// by the context.
+impl<'a> demo::Context for Context<'a> {
+    fn is_tze_only(&self) -> bool {
+        self.tx.vin.is_empty()
+            && self.tx.vout.is_empty()
+            && self.tx.shielded_spends.is_empty()
+            && self.tx.shielded_outputs.is_empty()
+            && self.tx.joinsplits.is_empty()
+    }
+
+    fn tx_tze_outputs(&self) -> &[TzeOut] {
+        &self.tx.tze_outputs
+    }
+}
+
+/// Wire identifier for the dummy network upgrade epoch.
+pub const V1_EPOCH_ID: u32 = 0x7473_6554;
+
+/// A set of demo TZEs associated with the dummy network upgrade.
+struct EpochV1;
+
+impl Epoch for EpochV1 {
+    type Error = String;
+
+    fn verify<'a>(
+        &self,
+        precondition: &Precondition,
+        witness: &Witness,
+        ctx: &Context<'a>,
+    ) -> Result<(), Error<Self::Error>> {
+        // This epoch contains the following set of programs:
+        let ext_id = ExtensionId::try_from(precondition.extension_id)
+            .map_err(|InvalidExtId(id)| Error::InvalidExtensionId(id))?;
+        match ext_id {
+            ExtensionId::Demo => demo::Program
+                .verify(precondition, witness, ctx)
+                .map_err(|e| Error::ProgramError(format!("Epoch v1 program error: {}", e))),
+        }
+    }
+}
+
+pub fn epoch_for_branch(consensus_branch_id: u32) -> Option<Box<dyn Epoch<Error = String>>> {
+    // Map from consensus branch IDs to epochs.
+    match consensus_branch_id {
+        V1_EPOCH_ID => Some(Box::new(EpochV1)),
+        _ => None,
+    }
+}