dry-run mode for init bridge command (#1690)

* `dry-run` mode for init bridge command

* fix clippy

bridges/relays/bin-substrate/src/cli/init_bridge.rs

@@ -15,6 +15,7 @@
 // along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
 
 use async_trait::async_trait;
+use codec::Encode;
 
 use crate::{
 	chains::{
@@ -46,6 +47,9 @@ pub struct InitBridge {
 	target: TargetConnectionParams,
 	#[structopt(flatten)]
 	target_sign: TargetSigningParams,
+	/// Generates all required data, but does not submit extrinsic
+	#[structopt(long)]
+	dry_run: bool,
 }
 
 #[derive(Debug, EnumString, EnumVariantNames)]
@@ -77,6 +81,7 @@ where
 		let source_client = data.source.into_client::<Self::Source>().await?;
 		let target_client = data.target.into_client::<Self::Target>().await?;
 		let target_sign = data.target_sign.to_keypair::<Self::Target>()?;
+		let dry_run = data.dry_run;
 
 		let (spec_version, transaction_version) = target_client.simple_runtime_version().await?;
 		substrate_relay_helper::finality::initialize::initialize::<Self::Engine, _, _, _>(
@@ -90,11 +95,15 @@ where
 				signer: target_sign,
 			},
 			move |transaction_nonce, initialization_data| {
-				Ok(UnsignedTransaction::new(
-					Self::encode_init_bridge(initialization_data).into(),
-					transaction_nonce,
-				))
+				let call = Self::encode_init_bridge(initialization_data);
+				log::info!(
+					target: "bridge",
+					"Initialize bridge call encoded as hex string: {:?}",
+					format!("0x{}", hex::encode(call.encode()))
+				);
+				Ok(UnsignedTransaction::new(call.into(), transaction_nonce))
 			},
+			dry_run,
 		)
 		.await;