Add dropaware Sender new type

[mattsse]

Describe the feature

the way the rpc cache works is a single loop over actions:

reth/crates/rpc/rpc-eth-types/src/cache/mod.rs

Line 345 in 3af2afe

match ready!(this.action_rx.poll_next_unpin(cx)) {

disk lookups also reuse that single channel and send actions back to that sender:

reth/crates/rpc/rpc-eth-types/src/cache/mod.rs

Line 360 in 3af2afe

let action_tx = this.action_tx.clone();

in the meantime the oneshot response senders wait for that action:

reth/crates/rpc/rpc-eth-types/src/cache/mod.rs

Lines 222 to 225 in 3af2afe

	/// The LRU cache for full blocks grouped by their hash.
	full_block_cache: BlockLruCache<Provider::Block, LimitBlocks>,
	/// The LRU cache for full blocks grouped by their hash.
	receipts_cache: ReceiptsLruCache<Provider::Receipt, LimitReceipts>,

these response channels remain in the lru until the action arrives in the mainloop.

This is problematic if the spawned task panics because then nothing is emitted back to the mainloop.
for example if this operation panics

reth/crates/rpc/rpc-eth-types/src/cache/mod.rs

Lines 365 to 372 in 3af2afe

	// Only look in the database to prevent situations where we
	// looking up the tree is blocking
	let block_sender = provider
	.sealed_block_with_senders(
	BlockHashOrNumber::Hash(block_hash),
	TransactionVariant::WithHash,
	)
	.map(|maybe_block| maybe_block.map(Arc::new));

no action is generated by that task.

we can solve this by introducing a drop aware sender wrapper that sends an action on drop, if not consumed:

like:

reth/crates/rpc/rpc-eth-types/src/cache/mod.rs

Lines 373 to 376 in 3af2afe

	let _ = action_tx.send(CacheAction::BlockWithSendersResult {
	block_hash,
	res: block_sender,
	});

struct ActionSender {
  blockhash: B256,
  tx: Option<UnboundedSender<...>
}

impl ActionSender {
  fn send_block(self,...)
}

impl Drop for ActionSender {
  if let Some(tx)
   ... send error
}

Additional context

No response

[coxmars]

Hi @mattsse I would like to help you in this one. I will open a PR asap 🫡

[mattsse]

ty, assigned

[ABD-AZE]

Hey @mattsse,
Can I work on this issue?