Add ability to iterate over N map storage keys

examples/examples/storage_query.rs

@@ -0,0 +1,165 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is part of subxt.
+//
+// subxt is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// subxt is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+//! To run this example, a local polkadot node should be running. Example verified against polkadot 0.9.18-4542a603cc-aarch64-macos.
+//!
+//! E.g.
+//! ```bash
+//! curl "https://github.com/paritytech/polkadot/releases/download/v0.9.18/polkadot" --output /usr/local/bin/polkadot --location
+//! polkadot --dev --tmp
+//! ```
+
+use codec::Decode;
+use subxt::{
+    rpc::Rpc,
+    storage::{
+        StorageClient,
+        StorageKeyPrefix,
+    },
+    ClientBuilder,
+    DefaultConfig,
+    PolkadotExtrinsicParams,
+    StorageEntryKey,
+    StorageMapKey,
+};
+
+#[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata.scale")]
+pub mod polkadot {}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    tracing_subscriber::fmt::init();
+
+    let api = ClientBuilder::new()
+        .build()
+        .await?
+        .to_runtime_api::<polkadot::RuntimeApi<DefaultConfig, PolkadotExtrinsicParams<DefaultConfig>>>();
+
+    // Obtain the storage client wrapper from the API.
+    let storage: StorageClient<_> = api.client.storage();
+
+    // The VersionNotifiers type of the XcmPallet is defined as:
+    //
+    // ```
+    //  All locations that we have requested version notifications from.
+    // 	#[pallet::storage]
+    // 	pub(super) type VersionNotifiers<T: Config> = StorageDoubleMap<
+    // 		_,
+    // 		Twox64Concat,
+    // 		XcmVersion,
+    // 		Blake2_128Concat,
+    // 		VersionedMultiLocation,
+    // 		QueryId,
+    // 		OptionQuery,
+    // 	>;
+    // ```
+
+    // Example 1. Iterate over fetched keys manually.
+    {
+        // Fetch at most 10 keys from below the prefix XcmPallet' VersionNotifiers.
+        let keys = storage
+            .fetch_keys::<polkadot::xcm_pallet::storage::VersionNotifiers>(10, None, None)
+            .await?;
+
+        println!("Example 1. Obtained keys:");
+        for key in keys.iter() {
+            println!("Key: 0x{}", hex::encode(&key));
+
+            if let Some(storage_data) = storage.fetch_raw(key.clone(), None).await? {
+                // We know the return value to be `QueryId` (`u64`) from inspecting either:
+                // - polkadot code
+                // - polkadot.rs generated file under `version_notifiers()` fn
+                // - metadata in json format
+                let value = u64::decode(&mut &storage_data.0[..])?;
+                println!("  Value: {}", value);
+            }
+        }
+    }
+
+    // Example 2. Iterate over (keys, value) using the storage client.
+    {
+        let mut iter = storage
+            .iter::<polkadot::xcm_pallet::storage::VersionNotifiers>(None)
+            .await?;
+
+        println!("\nExample 2. Obtained keys:");
+        while let Some((key, value)) = iter.next().await? {
+            println!("Key: 0x{}", hex::encode(&key));
+            println!("  Value: {}", value);
+        }
+    }
+
+    // Example 3. Iterate over (keys, value) using the polkadot API.
+    {
+        let mut iter = api
+            .storage()
+            .xcm_pallet()
+            .version_notifiers_iter(None)
+            .await?;
+
+        println!("\nExample 3. Obtained keys:");
+        while let Some((key, value)) = iter.next().await? {
+            println!("Key: 0x{}", hex::encode(&key));
+            println!("  Value: {}", value);
+        }
+    }
+
+    // Example 4. Custom iteration over double maps.
+    {
+        // Obtain the inner RPC from the API.
+        let rpc: &Rpc<_> = api.client.rpc();
+
+        // Obtain the prefixed `twox_128("XcmPallet") ++ twox_128("VersionNotifiers")`
+        let prefix =
+            StorageKeyPrefix::new::<polkadot::xcm_pallet::storage::VersionNotifiers>();
+        // From the VersionNotifiers definition above, the first key is represented by
+        // ```
+        // 		Twox64Concat,
+        // 		XcmVersion,
+        // ```
+        // while `XcmVersion` is `u32`.
+        // Pass `2` as `XcmVersion` and concatenate the key to the prefix.
+        let entry_key = StorageEntryKey::Map(vec![StorageMapKey::new(
+            &2u32,
+            ::subxt::StorageHasher::Twox64Concat,
+        )]);
+
+        // The final query key is:
+        // `twox_128("XcmPallet") ++ twox_128("VersionNotifiers") ++ twox_64(2u32) ++ 2u32`
+        let query_key = entry_key.final_key(prefix);
+        println!("\nExample 4\nQuery key: 0x{}", hex::encode(&query_key));
+
+        let keys = rpc
+            .storage_keys_paged(Some(query_key), 10, None, None)
+            .await?;
+
+        println!("Obtained keys:");
+        for key in keys.iter() {
+            println!("Key: 0x{}", hex::encode(&key));
+
+            if let Some(storage_data) = storage.fetch_raw(key.clone(), None).await? {
+                // We know the return value to be `QueryId` (`u64`) from inspecting either:
+                // - polkadot code
+                // - polkadot.rs generated file under `version_notifiers()` fn
+                // - metadata in json format
+                let value = u64::decode(&mut &storage_data.0[..])?;
+                println!("  Value: {}", value);
+            }
+        }
+    }
+
+    Ok(())
+}

subxt/src/rpc.rs

@@ -28,7 +28,6 @@ use std::{
 
 use crate::{
     error::BasicError,
-    storage::StorageKeyPrefix,
     Config,
     Metadata,
     PhantomDataSendSync,
@@ -277,13 +276,12 @@ impl<T: Config> Rpc<T> {
     /// If `start_key` is passed, return next keys in storage in lexicographic order.
     pub async fn storage_keys_paged(
         &self,
-        prefix: Option<StorageKeyPrefix>,
+        key: Option<StorageKey>,
         count: u32,
         start_key: Option<StorageKey>,
         hash: Option<T::Hash>,
     ) -> Result<Vec<StorageKey>, BasicError> {
-        let prefix = prefix.map(|p| p.to_storage_key());
-        let params = rpc_params![prefix, count, start_key, hash];
+        let params = rpc_params![key, count, start_key, hash];
         let data = self.client.request("state_getKeysPaged", params).await?;
         Ok(data)
     }

subxt/src/storage.rs

@@ -235,10 +235,10 @@ impl<'a, T: Config> StorageClient<'a, T> {
         start_key: Option<StorageKey>,
         hash: Option<T::Hash>,
     ) -> Result<Vec<StorageKey>, BasicError> {
-        let prefix = StorageKeyPrefix::new::<F>();
+        let key = StorageKeyPrefix::new::<F>().to_storage_key();
         let keys = self
             .rpc
-            .storage_keys_paged(Some(prefix), count, start_key, hash)
+            .storage_keys_paged(Some(key), count, start_key, hash)
             .await?;
         Ok(keys)
     }