feat(cast): improve to/from rlp (#8454)

crates/cast/bin/opts.rs

@@ -259,18 +259,28 @@ pub enum CastSubcommand {
     },
 
     /// RLP encodes hex data, or an array of hex data.
+    ///
+    /// Accepts a hex-encoded string, or an array of hex-encoded strings.
+    /// Can be arbitrarily recursive.
+    ///
+    /// Examples:
+    /// - `cast to-rlp "[]"` -> `0xc0`
+    /// - `cast to-rlp "0x22"` -> `0x22`
+    /// - `cast to-rlp "[\"0x61\"]"` -> `0xc161`
+    /// - `cast to-rlp "[\"0xf1\", \"f2\"]"` -> `0xc481f181f2`
     #[command(visible_aliases = &["--to-rlp"])]
     ToRlp {
         /// The value to convert.
+        ///
+        /// This is a hex-encoded string, or an array of hex-encoded strings.
+        /// Can be arbitrarily recursive.
         value: Option<String>,
     },
 
-    /// Decodes RLP encoded data.
-    ///
-    /// Input must be hexadecimal.
+    /// Decodes RLP hex-encoded data.
     #[command(visible_aliases = &["--from-rlp"])]
     FromRlp {
-        /// The value to convert.
+        /// The RLP hex-encoded data.
         value: Option<String>,
     },
 

crates/cast/src/lib.rs

@@ -1355,7 +1355,7 @@ impl SimpleCast {
     /// assert_eq!(Cast::to_rlp("[]").unwrap(), "0xc0".to_string());
     /// assert_eq!(Cast::to_rlp("0x22").unwrap(), "0x22".to_string());
     /// assert_eq!(Cast::to_rlp("[\"0x61\"]",).unwrap(), "0xc161".to_string());
-    /// assert_eq!(Cast::to_rlp("[\"0xf1\",\"f2\"]").unwrap(), "0xc481f181f2".to_string());
+    /// assert_eq!(Cast::to_rlp("[\"0xf1\", \"f2\"]").unwrap(), "0xc481f181f2".to_string());
     /// # Ok::<_, eyre::Report>(())
     /// ```
     pub fn to_rlp(value: &str) -> Result<String> {

crates/cast/src/rlp_converter.rs

@@ -1,5 +1,6 @@
-use alloy_primitives::hex;
+use alloy_primitives::{hex, U256};
 use alloy_rlp::{Buf, Decodable, Encodable, Header};
+use eyre::Context;
 use serde_json::Value;
 use std::fmt;
 
@@ -49,11 +50,12 @@ impl Item {
         return match value {
             Value::Null => Ok(Self::Data(vec![])),
             Value::Bool(_) => {
-                eyre::bail!("RLP input should not contain booleans")
+                eyre::bail!("RLP input can not contain booleans")
             }
-            // If a value is passed without quotes we cast it to string
-            Value::Number(n) => Ok(Self::value_to_item(&Value::String(n.to_string()))?),
-            Value::String(s) => Ok(Self::Data(hex::decode(s).expect("Could not decode hex"))),
+            Value::Number(n) => {
+                Ok(Self::Data(n.to_string().parse::<U256>()?.to_be_bytes_trimmed_vec()))
+            }
+            Value::String(s) => Ok(Self::Data(hex::decode(s).wrap_err("Could not decode hex")?)),
             Value::Array(values) => values.iter().map(Self::value_to_item).collect(),
             Value::Object(_) => {
                 eyre::bail!("RLP input can not contain objects")