From e6a8630b350cd61b41843139faacbcd0cec97321 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Wed, 27 Nov 2019 13:12:28 +0000
Subject: [PATCH] impl TryFrom<u32> for BranchId

---
 zcash_primitives/src/consensus.rs | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/zcash_primitives/src/consensus.rs b/zcash_primitives/src/consensus.rs
index f7cf480d2..8a7385c7e 100644
--- a/zcash_primitives/src/consensus.rs
+++ b/zcash_primitives/src/consensus.rs
@@ -1,5 +1,6 @@
 //! Consensus parameters.
 
+use std::convert::TryFrom;
 use std::fmt;
 
 /// Zcash consensus parameters.
@@ -128,6 +129,21 @@ pub enum BranchId {
     Heartwood,
 }
 
+impl TryFrom<u32> for BranchId {
+    type Error = &'static str;
+
+    fn try_from(value: u32) -> Result<Self, Self::Error> {
+        match value {
+            0 => Ok(BranchId::Sprout),
+            0x5ba8_1b19 => Ok(BranchId::Overwinter),
+            0x76b8_09bb => Ok(BranchId::Sapling),
+            0x2bb4_0e60 => Ok(BranchId::Blossom),
+            0xf5b9_230b => Ok(BranchId::Heartwood),
+            _ => Err("Unknown consensus branch ID"),
+        }
+    }
+}
+
 impl From<BranchId> for u32 {
     fn from(consensus_branch_id: BranchId) -> u32 {
         match consensus_branch_id {
@@ -159,7 +175,9 @@ impl BranchId {
 
 #[cfg(test)]
 mod tests {
-    use super::{BranchId, Parameters, MainNetwork, NetworkUpgrade, UPGRADES_IN_ORDER};
+    use std::convert::TryFrom;
+
+    use super::{BranchId, MainNetwork, NetworkUpgrade, Parameters, UPGRADES_IN_ORDER};
 
     #[test]
     fn nu_ordering() {
@@ -194,6 +212,12 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn branch_id_from_u32() {
+        assert_eq!(BranchId::try_from(0), Ok(BranchId::Sprout));
+        assert!(BranchId::try_from(1).is_err());
+    }
+
     #[test]
     fn branch_id_for_height() {
         assert_eq!(BranchId::for_height::<MainNetwork>(0), BranchId::Sprout,);