Wrap and export BlockNumber (paritytech#87)

* Add fetch example and wrap BlockNumber impl

* Fmt

Author: ascjones

examples/fetch_remote.rs

@@ -0,0 +1,45 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of substrate-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 substrate-subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+use substrate_subxt::{
+    system::System,
+    Error,
+    KusamaRuntime,
+};
+
+fn main() {
+    async_std::task::block_on(async move {
+        env_logger::init();
+
+        let block_hash = fetch_block_hash(1).await;
+        match block_hash {
+            Ok(Some(hash)) => println!("Block hash for block number 1: {}", hash),
+            Ok(None) => println!("Block number 1 not found."),
+            Err(_) => eprintln!("Failed to fetch block hash"),
+        }
+    });
+}
+
+async fn fetch_block_hash(
+    block_number: u32,
+) -> Result<Option<<KusamaRuntime as System>::Hash>, Error> {
+    substrate_subxt::ClientBuilder::<KusamaRuntime>::new()
+        .set_url("wss://kusama-rpc.polkadot.io")
+        .build()
+        .await?
+        .block_hash(Some(block_number.into()))
+        .await
+}

src/lib.rs

@@ -85,7 +85,10 @@ pub use self::{
     events::RawEvent,
     extrinsic::*,
     frame::*,
-    rpc::ExtrinsicSuccess,
+    rpc::{
+        BlockNumber,
+        ExtrinsicSuccess,
+    },
     runtimes::*,
 };
 use self::{
@@ -104,7 +107,6 @@ use self::{
     },
     metadata::Metadata,
     rpc::{
-        BlockNumber,
         ChainBlock,
         Rpc,
     },

src/rpc.rs

@@ -38,6 +38,7 @@ use jsonrpsee::{
 use num_traits::bounds::Bounded;
 
 use frame_metadata::RuntimeMetadataPrefixed;
+use serde::Serialize;
 use sp_core::{
     storage::{
         StorageChangeSet,
@@ -82,7 +83,30 @@ use crate::{
 
 pub type ChainBlock<T> =
     SignedBlock<Block<<T as System>::Header, <T as System>::Extrinsic>>;
-pub type BlockNumber<T> = NumberOrHex<<T as System>::BlockNumber>;
+
+/// Wrapper for NumberOrHex to allow custom From impls
+#[derive(Serialize)]
+#[serde(bound = "<T as System>::BlockNumber: Serialize")]
+pub struct BlockNumber<T: System>(NumberOrHex<<T as System>::BlockNumber>);
+
+impl<T> From<NumberOrHex<<T as System>::BlockNumber>> for BlockNumber<T>
+where
+    T: System,
+{
+    fn from(x: NumberOrHex<<T as System>::BlockNumber>) -> Self {
+        BlockNumber(x)
+    }
+}
+
+impl<T> From<u32> for BlockNumber<T>
+where
+    T: System,
+    <T as System>::BlockNumber: From<u32>,
+{
+    fn from(x: u32) -> Self {
+        NumberOrHex::Number(x.into()).into()
+    }
+}
 
 /// Client for substrate rpc interfaces
 #[derive(Clone)]