Make it clearer which extrinsic failed to decode (#1835)

* Add an extrinsic index to decode errors so that we know which extrinsic failed

* Fix subxt::BlockError to align with subxt_core::BlockError

---------

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

core/src/blocks/extrinsics.rs

@@ -32,7 +32,8 @@ impl<T: Config> Extrinsics<T> {
     pub fn decode_from(extrinsics: Vec<Vec<u8>>, metadata: Metadata) -> Result<Self, Error> {
         let extrinsics = extrinsics
             .into_iter()
-            .map(|bytes| {
+            .enumerate()
+            .map(|(extrinsic_index, bytes)| {
                 let cursor = &mut &*bytes;
 
                 // Try to decode the extrinsic.
@@ -41,12 +42,19 @@ impl<T: Config> Extrinsics<T> {
                     metadata.deref(),
                     metadata.types(),
                 )
-                .map_err(BlockError::ExtrinsicDecodeError)?
+                .map_err(|error| BlockError::ExtrinsicDecodeError {
+                    extrinsic_index,
+                    error,
+                })?
                 .into_owned();
 
                 // We didn't consume all bytes, so decoding probably failed.
                 if !cursor.is_empty() {
-                    return Err(BlockError::LeftoverBytes(cursor.len()).into());
+                    return Err(BlockError::LeftoverBytes {
+                        extrinsic_index,
+                        num_leftover_bytes: cursor.len(),
+                    }
+                    .into());
                 }
 
                 Ok(Arc::new((decoded_info, bytes)))
@@ -493,7 +501,10 @@ mod tests {
         assert_matches!(
             result.err(),
             Some(crate::Error::Block(
-                crate::error::BlockError::ExtrinsicDecodeError(_)
+                crate::error::BlockError::ExtrinsicDecodeError {
+                    extrinsic_index: 0,
+                    error: _
+                }
             ))
         );
     }
@@ -510,9 +521,10 @@ mod tests {
         assert_matches!(
             result.err(),
             Some(crate::Error::Block(
-                crate::error::BlockError::ExtrinsicDecodeError(
-                    ExtrinsicDecodeError::VersionNotSupported(3)
-                )
+                crate::error::BlockError::ExtrinsicDecodeError {
+                    extrinsic_index: 0,
+                    error: ExtrinsicDecodeError::VersionNotSupported(3),
+                }
             ))
         );
     }

core/src/error.rs

@@ -59,21 +59,40 @@ impl_from!(codec::Error => Error::Codec);
 #[derive(Debug)]
 pub enum BlockError {
     /// Leftover bytes found after decoding the extrinsic.
-    LeftoverBytes(usize),
+    LeftoverBytes {
+        /// Index of the extrinsic that failed to decode.
+        extrinsic_index: usize,
+        /// Number of bytes leftover after decoding the extrinsic.
+        num_leftover_bytes: usize,
+    },
     /// Something went wrong decoding the extrinsic.
-    ExtrinsicDecodeError(ExtrinsicDecodeError),
+    ExtrinsicDecodeError {
+        /// Index of the extrinsic that failed to decode.
+        extrinsic_index: usize,
+        /// The decode error.
+        error: ExtrinsicDecodeError,
+    },
 }
 impl Display for BlockError {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
-            BlockError::LeftoverBytes(n) => {
+            BlockError::LeftoverBytes {
+                extrinsic_index,
+                num_leftover_bytes,
+            } => {
                 write!(
                     f,
-                    "After decoding, {n} bytes were left, suggesting that decoding may have failed"
+                    "After decoding the extrinsic at index {extrinsic_index}, {num_leftover_bytes} bytes were left, suggesting that decoding may have failed"
                 )
             }
-            BlockError::ExtrinsicDecodeError(e) => {
-                write!(f, "{e}")
+            BlockError::ExtrinsicDecodeError {
+                extrinsic_index,
+                error,
+            } => {
+                write!(
+                    f,
+                    "Failed to decode extrinsic at index {extrinsic_index}: {error}"
+                )
             }
         }
     }