Add lcli tool for checking deposit data (#940)

* Add check-deposit-data tool

* Update help text

* Update function name

lcli/src/check_deposit_data.rs

@@ -0,0 +1,31 @@
+use crate::helpers::{parse_hex_bytes, parse_u64};
+use clap::ArgMatches;
+use deposit_contract::{decode_eth1_tx_data, DEPOSIT_DATA_LEN};
+use tree_hash::TreeHash;
+use types::EthSpec;
+
+pub fn run<T: EthSpec>(matches: &ArgMatches) -> Result<(), String> {
+    let rlp_bytes = parse_hex_bytes(matches, "deposit-data")?;
+    let amount = parse_u64(matches, "deposit-amount")?;
+
+    if rlp_bytes.len() != DEPOSIT_DATA_LEN {
+        return Err(format!(
+            "The given deposit-data is {} bytes, expected {}",
+            rlp_bytes.len(),
+            DEPOSIT_DATA_LEN
+        ));
+    }
+
+    let (deposit_data, root) = decode_eth1_tx_data(&rlp_bytes, amount)
+        .map_err(|e| format!("Invalid deposit data bytes: {:?}", e))?;
+
+    let expected_root = deposit_data.tree_hash_root();
+    if root != expected_root {
+        return Err(format!(
+            "Deposit data root is invalid. Expected {:?}, but got {:?}. Perhaps the amount is incorrect?",
+            expected_root, root
+        ));
+    }
+
+    Ok(())
+}