Ignore importdescriptor error

The importdescriptor call will throw a `Resource temporarily unavialble`
error only in the first initial sync, where the wallet
has to rescan from genesis.

The sync process carries on as usual after the error, so this patch
makes it ignore only that particular error and carry on the with sync.
All other errors are captured as usual.

src/blockchain/rpc.rs

@@ -678,20 +678,43 @@ where
             })
             .collect(),
     );
-    for v in client.call::<Vec<Value>>("importdescriptors", &[requests])? {
-        match v["success"].as_bool() {
-            Some(true) => continue,
-            Some(false) => {
-                return Err(Error::Generic(
-                    v["error"]["message"]
-                        .as_str()
-                        .map_or("unknown error".into(), ToString::to_string),
-                ))
-            }
-            _ => return Err(Error::Generic("Unexpected response form Core".to_string())),
-        }
-    }
-    Ok(())
+
+    client
+        .call::<Vec<Value>>("importdescriptors", &[requests])
+        .map_or_else(
+            |e| {
+                // While rescaning a new wallet from genesis, core rpc sometimes throw "Resource Temporarily Unavailable" Transport error.
+                // This doesn't stop the sync, so it's safe to ignore.
+                // See: https://github.com/bitcoindevkit/bdk/issues/859
+                if let bitcoincore_rpc::Error::JsonRpc(
+                    bitcoincore_rpc::jsonrpc::Error::Transport(_),
+                ) = e
+                {
+                    debug!("Resource Temporarily Unavailable, carrying on!!");
+                    Ok(())
+                } else {
+                    return Err(e.into());
+                }
+            },
+            |result| {
+                for v in result {
+                    match v["success"].as_bool() {
+                        Some(true) => continue,
+                        Some(false) => {
+                            return Err(Error::Generic(
+                                v["error"]["message"]
+                                    .as_str()
+                                    .map_or("unknown error".into(), ToString::to_string),
+                            ))
+                        }
+                        _ => {
+                            return Err(Error::Generic("Unexpected response form Core".to_string()))
+                        }
+                    }
+                }
+                Ok(())
+            },
+        )
 }
 
 fn import_multi<'a, S>(client: &Client, start_epoch: u64, scripts_iter: S) -> Result<(), Error>