From b38e56f42ead2462615f4a984a24691a7ee89102 Mon Sep 17 00:00:00 2001
From: Marek <mail@marek.onl>
Date: Fri, 7 Mar 2025 14:13:44 +0100
Subject: [PATCH] Support negative heights in `HashOrHeight`

---
 zebra-rpc/src/methods.rs   | 10 +++++-----
 zebra-state/src/request.rs | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/zebra-rpc/src/methods.rs b/zebra-rpc/src/methods.rs
index 0a5e6e351f5..e487f01188f 100644
--- a/zebra-rpc/src/methods.rs
+++ b/zebra-rpc/src/methods.rs
@@ -839,11 +839,11 @@ where
             None
         };
 
-        let hash_or_height: HashOrHeight = hash_or_height
-            .parse()
-            // Reference for the legacy error code:
-            // <https://github.com/zcash/zcash/blob/99ad6fdc3a549ab510422820eea5e5ce9f60a5fd/src/rpc/blockchain.cpp#L629>
-            .map_error(server::error::LegacyCode::InvalidParameter)?;
+        let hash_or_height =
+            HashOrHeight::new(&hash_or_height, self.latest_chain_tip.best_tip_height())
+                // Reference for the legacy error code:
+                // <https://github.com/zcash/zcash/blob/99ad6fdc3a549ab510422820eea5e5ce9f60a5fd/src/rpc/blockchain.cpp#L629>
+                .map_error(server::error::LegacyCode::InvalidParameter)?;
 
         if verbosity == 0 {
             let request = zebra_state::ReadRequest::Block(hash_or_height);
diff --git a/zebra-state/src/request.rs b/zebra-state/src/request.rs
index 1535fa81c1f..7348041f43f 100644
--- a/zebra-state/src/request.rs
+++ b/zebra-state/src/request.rs
@@ -2,13 +2,13 @@
 
 use std::{
     collections::{HashMap, HashSet},
-    ops::{Deref, DerefMut, RangeInclusive},
+    ops::{Add, Deref, DerefMut, RangeInclusive},
     sync::Arc,
 };
 
 use zebra_chain::{
     amount::{Amount, NegativeAllowed, NonNegative},
-    block::{self, Block},
+    block::{self, Block, HeightDiff},
     history_tree::HistoryTree,
     orchard,
     parallel::tree::NoteCommitmentTrees,
@@ -133,6 +133,38 @@ impl HashOrHeight {
             None
         }
     }
+
+    /// Constructs a new [`HashOrHeight`] from a string containing a hash or a positive or negative
+    /// height.
+    ///
+    /// When the provided `hash_or_height` contains a negative height, the `tip_height` parameter
+    /// needs to be `Some` since height `-1` points to the tip.
+    pub fn new(hash_or_height: &str, tip_height: Option<block::Height>) -> Result<Self, String> {
+        hash_or_height
+            .parse()
+            .map(Self::Hash)
+            .or_else(|_| hash_or_height.parse().map(Self::Height))
+            .or_else(|_| {
+                hash_or_height
+                    .parse()
+                    .map_err(|_| "could not parse negative height")
+                    .and_then(|d: HeightDiff| {
+                        d.is_negative()
+                            .then(|| {
+                                Ok(HashOrHeight::Height(
+                                    tip_height
+                                        .ok_or("missing tip height")?
+                                        .add(d)
+                                        .ok_or("underflow when adding negative height to tip")?
+                                        .next()
+                                        .map_err(|_| "height -1 needs to point to tip")?,
+                                ))
+                            })
+                            .unwrap_or(Err("height was not negative"))
+                    })
+            })
+            .map_err(|e| format!("could not convert the input string to a hash or height: {e}"))
+    }
 }
 
 impl std::fmt::Display for HashOrHeight {