Add a method to return the block header at a given block

subxt/src/client.rs

@@ -4,6 +4,7 @@ mod online_client;
 use crate::config::{Config, HashFor};
 use crate::constants::ConstantsClient;
 use crate::custom_values::CustomValuesClient;
+use crate::error::BlockError;
 use crate::events::EventsClient;
 use crate::extrinsics::ExtrinsicsClient;
 use crate::runtime_apis::RuntimeApisClient;
@@ -105,4 +106,22 @@ where
     pub fn block_hash(&self) -> HashFor<T> {
         self.client.block_hash()
     }
+
+    /// The header for this block.
+    pub async fn block_header(&self) -> Result<T::Header, BlockError> {
+        let block_hash = self.block_hash();
+        let header = self
+            .client
+            .backend()
+            .block_header(block_hash)
+            .await
+            .map_err(|e| BlockError::CouldNotDownloadBlockHeader {
+                block_hash: block_hash.into(),
+                reason: e,
+            })?
+            .ok_or_else(|| BlockError::BlockNotFound {
+                block_hash: block_hash.into(),
+            })?;
+        Ok(header)
+    }
 }

subxt/src/error.rs

@@ -40,6 +40,8 @@ pub enum Error {
     #[error(transparent)]
     ExtrinsicDecodeErrorAt(#[from] ExtrinsicDecodeErrorAt),
     #[error(transparent)]
+    BlockError(#[from] BlockError),
+    #[error(transparent)]
     ConstantError(#[from] ConstantError),
     #[error(transparent)]
     CustomValueError(#[from] CustomValueError),
@@ -147,6 +149,7 @@ impl Error {
             Error::OnlineClientError(e) => e.backend_error(),
             Error::RuntimeApiError(e) => e.backend_error(),
             Error::EventsError(e) => e.backend_error(),
+            Error::BlockError(e) => e.backend_error(),
             Error::ExtrinsicError(e) => e.backend_error(),
             Error::ViewFunctionError(e) => e.backend_error(),
             Error::TransactionProgressError(e) => e.backend_error(),
@@ -384,6 +387,28 @@ impl OnlineClientAtBlockError {
     }
 }
 
+#[derive(Debug, thiserror::Error)]
+#[non_exhaustive]
+#[allow(missing_docs)]
+pub enum BlockError {
+    #[error("Could not find the block with hash {block_hash}")]
+    BlockNotFound { block_hash: Hex },
+    #[error("Could not download the block header with hash {block_hash}: {reason}")]
+    CouldNotDownloadBlockHeader {
+        block_hash: Hex,
+        reason: BackendError,
+    },
+}
+
+impl BlockError {
+    fn backend_error(&self) -> Option<&BackendError> {
+        match self {
+            BlockError::CouldNotDownloadBlockHeader { reason, .. } => Some(reason),
+            _ => None,
+        }
+    }
+}
+
 #[derive(Debug, thiserror::Error)]
 #[non_exhaustive]
 #[allow(missing_docs)]