Feature-guard backward verification behind "unstable" flag

informalsystems · Jan 21, 2021 · 2474ed9 · 2474ed9
1 parent 15c7f22
commit 2474ed9
Show file tree

Hide file tree

Showing 2 changed files with 28 additions and 11 deletions.
diff --git a/light-client/Cargo.toml b/light-client/Cargo.toml
@@ -33,6 +33,7 @@ default = ["rpc-client", "lightstore-sled"]
 rpc-client = ["tokio", "tendermint-rpc/http-client"]
 secp256k1 = ["tendermint/secp256k1", "tendermint-rpc/secp256k1"]
 lightstore-sled = ["sled"]
+unstable = []
 
 [dependencies]
 tendermint = { version = "0.17.1", path = "../tendermint" }
@@ -50,6 +51,7 @@ sled = { version = "0.34.3", optional = true }
 static_assertions = "1.1.0"
 thiserror = "1.0.15"
 tokio = { version = "1.0", features = ["rt"], optional = true }
+cfg-if = "1.0.0"
 
 [dev-dependencies]
 tendermint-testgen = { path = "../testgen"}

diff --git a/light-client/src/light_client.rs b/light-client/src/light_client.rs
@@ -2,26 +2,24 @@
 //!
 //! [1]: https://github.com/informalsystems/tendermint-rs/blob/master/docs/spec/lightclient/verification/verification.md
 
+use std::{fmt, time::Duration};
+
+use cfg_if::cfg_if;
 use contracts::*;
 use derive_more::Display;
 use serde::{Deserialize, Serialize};
-use std::{convert::TryFrom, fmt, time::Duration};
 
-use crate::contracts::*;
 use crate::{
     bail,
+    components::{clock::Clock, io::*, scheduler::*, verifier::*},
+    contracts::*,
     errors::{Error, ErrorKind},
+    operations::Hasher,
     state::State,
     types::{Height, LightBlock, PeerId, Status, TrustThreshold},
 };
-use crate::{
-    components::{clock::Clock, io::*, scheduler::*, verifier::*},
-    operations::Hasher,
-};
 
 /// Verification parameters
-///
-/// TODO: Find a better name than `Options`
 #[derive(Copy, Clone, Debug, PartialEq, Display, Serialize, Deserialize)]
 #[display(fmt = "{:?}", self)]
 pub struct Options {
@@ -56,11 +54,15 @@ pub struct LightClient {
     pub peer: PeerId,
     /// Options for this light client
     pub options: Options,
+
     clock: Box<dyn Clock>,
     scheduler: Box<dyn Scheduler>,
     verifier: Box<dyn Verifier>,
-    hasher: Box<dyn Hasher>,
     io: Box<dyn Io>,
+
+    // Only used in verify_backwards when "unstable" feature is enabled
+    #[allow(dead_code)]
+    hasher: Box<dyn Hasher>,
 }
 
 impl fmt::Debug for LightClient {
@@ -182,8 +184,18 @@ impl LightClient {
             // Perform forward verification with bisection
             self.verify_bisection(target_height, state)
         } else {
-            // Perform sequential backward verification
-            self.verify_backwards(target_height, state)
+            cfg_if! {
+                if #[cfg(feature = "unstable")] {
+                    // Perform sequential backward verification
+                    self.verify_backwards(target_height, state)
+                } else {
+                    Err(ErrorKind::TargetLowerThanTrustedState {
+                        target_height,
+                        trusted_height: highest.height(),
+                    }
+                    .into())
+            }
+            }
         }
     }
 
@@ -269,11 +281,14 @@ impl LightClient {
     }
 
     /// Perform sequential backward verification
+    #[cfg(feature = "unstable")]
     fn verify_backwards(
         &self,
         target_height: Height,
         state: &mut State,
     ) -> Result<LightBlock, Error> {
+        use std::convert::TryFrom;
+
         let root = state
             .light_store
             .latest_trusted_or_verified()