Add chunked mempool txids endpoint

src/new_index/mempool.rs

@@ -1,3 +1,4 @@
+use bitcoin::hashes::Hash;
 use bounded_vec_deque::BoundedVecDeque;
 use itertools::Itertools;
 
@@ -288,6 +289,30 @@ impl Mempool {
         self.txstore.keys().collect()
     }
 
+    // Get all txids in the mempool with the given prefix
+    pub fn txids_by_prefix(&self, prefix: &str) -> Result<Vec<&Txid>> {
+        let _timer = self
+            .latency
+            .with_label_values(&["txids_by_prefix"])
+            .start_timer();
+
+        // get Txid range bounds for the given prefix
+        let start_bytes =
+            hex::decode(format!("{:0<64}", prefix)).chain_err(|| "invalid hash prefix")?;
+        let end_bytes =
+            hex::decode(format!("{:f<64}", prefix)).chain_err(|| "invalid hash prefix")?;
+        let start_txid =
+            Txid::from_hash(Hash::from_slice(&start_bytes).chain_err(|| "invalid hash prefix")?);
+        let end_txid =
+            Txid::from_hash(Hash::from_slice(&end_bytes).chain_err(|| "invalid hash prefix")?);
+
+        Ok(self
+            .txstore
+            .range(start_txid..=end_txid)
+            .map(|(k, _v)| k)
+            .collect())
+    }
+
     // Get all txs in the mempool
     pub fn txs(&self) -> Vec<Transaction> {
         let _timer = self.latency.with_label_values(&["txs"]).start_timer();

src/rest.rs

@@ -1256,6 +1256,12 @@ fn handle_request(
         (&Method::GET, Some(&"mempool"), Some(&"txids"), None, None, None) => {
             json_response(query.mempool().txids(), TTL_SHORT)
         }
+        (&Method::GET, Some(&"mempool"), Some(&"txids"), Some(prefix), None, None) => {
+            match query.mempool().txids_by_prefix(prefix) {
+                Ok(txids) => json_response(txids, TTL_SHORT),
+                Err(err) => http_message(StatusCode::BAD_REQUEST, err.to_string(), 0),
+            }
+        }
         (
             &Method::GET,
             Some(&INTERNAL_PREFIX),