[electrs] Feature Request: Add endpoint for querying txs by op_return

[daniel-savu]

It would be great to be able to have an endpoint such as GET /opreturn/:hash256 that returns all transactions whose op_return output matches the :hash256 parameter. Adding this feature would probably require either:

1. iterating through all transactions, or
2. storing an additional RocksDB object for transactions, indexed by the op_return

[shesek]

You can represent the OP_RETURN as a scripthash (SHA256(scriptPubKey)) and use the existing GET /scripthash/:scripthash/txs endpoint to get what you want.

Edit: Oops, sorry, no - you cannot do this. Provably unspendable outputs are explicitly ignored and not added to the index, so they cannot be queried.

[shesek]

Modifying the source code to make it index provably unspendable outputs is pretty straightforward though - you'll just need to remove the is_spendable check in schema.rs:1075 and mempool.rs:386, like so:

diff --git a/src/new_index/mempool.rs b/src/new_index/mempool.rs
index 16a771c..3acef9c 100644
--- a/src/new_index/mempool.rs
+++ b/src/new_index/mempool.rs
@@ -383,7 +383,6 @@ impl Mempool {
                 .output
                 .iter()
                 .enumerate()
-                .filter(|(_, txo)| is_spendable(txo))
                 .map(|(index, txo)| {
                     (
                         compute_script_hash(&txo.script_pubkey),
diff --git a/src/new_index/schema.rs b/src/new_index/schema.rs
index facc9f3..9014889 100644
--- a/src/new_index/schema.rs
+++ b/src/new_index/schema.rs
@@ -1072,7 +1072,7 @@ fn index_transaction(
     //      S{funding-txid:vout}{spending-txid:vin} → ""
     let txid = full_hash(&tx.txid()[..]);
     for (txo_index, txo) in tx.output.iter().enumerate() {
-        if is_spendable(txo) {
+        if true {
             let history = TxHistoryRow::new(
                 &txo.script_pubkey,
                 confirmed_height,

[daniel-savu]

Thanks for your quick reply @shesek!

If I opened a PR for this feature would you be willing to merge it? This way I wouldn't have to deploy my own esplora service

[shesek]

If you make it configurable via a new CLI flag, something like --index-unspendables, I could consider merging it. But it probably wouldn't be enabled on the blockstream.info live production servers, because its somewhat of an exotic use-case that users don't typically need.