From 955ac2d58f26646181be64f2432f1a3f7e8cccc7 Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Wed, 20 Mar 2024 11:51:03 +0100
Subject: [PATCH] abi decoding of custom error fails on trailing bytes

---
 ethers/errors.nim                |  2 ++
 testmodule/testErrorDecoding.nim | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/ethers/errors.nim b/ethers/errors.nim
index 00b6ccc..fa2c3bb 100644
--- a/ethers/errors.nim
+++ b/ethers/errors.nim
@@ -29,6 +29,8 @@ func decode*[E: SolidityError](_: type E, data: seq[byte]): ?!(ref E) =
       return failure "unable to decode " & $E & ": " & error.msg
     success (ref E)(arguments: arguments)
   else:
+    if data.len > 4:
+      return failure "unable to decode " & $E & ": unread trailing bytes found"
     success (ref E)()
 
 func encode*[E: SolidityError](_: type AbiEncoder, error: ref E): seq[byte] =
diff --git a/testmodule/testErrorDecoding.nim b/testmodule/testErrorDecoding.nim
index 6112d28..a843e76 100644
--- a/testmodule/testErrorDecoding.nim
+++ b/testmodule/testErrorDecoding.nim
@@ -34,6 +34,18 @@ suite "Decoding of custom errors":
     let decoded = SimpleError.decode(invalid)
     check decoded.isFailure
 
+  test "returns failure when there are trailing bytes":
+    let invalid = @[0xc2'u8, 0xbb, 0x94, 0x7c, 0x0] # one byte too many
+    let decoded = SimpleError.decode(invalid)
+    check decoded.isFailure
+
+  test "returns failure when there are trailing bytes after arguments":
+    let error = (ref ErrorWithArguments)(arguments: (1.u256, true))
+    let encoded = AbiEncoder.encode(error)
+    let invalid = encoded & @[0x0'u8] # one byte too many
+    let decoded = ErrorWithArguments.decode(invalid)
+    check decoded.isFailure
+
   test "decoding only works for SolidityErrors":
     type InvalidError = ref object of CatchableError
     const works = compiles: