Add the max_uint subcommand to cast and cli

cast/src/lib.rs

@@ -340,6 +340,21 @@ impl SimpleCast {
         Ok(U256::from_str(hex)?)
     }
 
+    /// Returns maximum U256 value
+    ///
+    /// ```
+    /// use cast::SimpleCast as Cast;
+    /// use ethers_core::types::U256;
+    ///
+    /// fn main() -> eyre::Result<()> {
+    ///     assert_eq!(U256::MAX, Cast::max_uint()?);
+    ///
+    ///     Ok(())
+    /// }
+    pub fn max_uint() -> Result<U256> {
+        Ok(U256::MAX)
+    }
+
     /// Converts integers with specified decimals into fixed point numbers
     ///
     /// ```

cli/src/cast.rs

@@ -18,6 +18,9 @@ async fn main() -> eyre::Result<()> {
 
     let opts = Opts::from_args();
     match opts.sub {
+        Subcommands::MaxUint { } => {
+            println!("{}", SimpleCast::max_uint()?);
+        }
         Subcommands::FromUtf8 { text } => {
             let val = unwrap_or_stdin(text)?;
             println!("{}", SimpleCast::from_utf8(&val));

cli/src/cast_opts.rs

@@ -12,6 +12,9 @@ use structopt::StructOpt;
 #[derive(Debug, StructOpt)]
 #[structopt(about = "Perform Ethereum RPC calls from the comfort of your command line.")]
 pub enum Subcommands {
+    #[structopt(name = "--max-uint")]
+    #[structopt(about = "maximum u256 value")]
+    MaxUint { },
     #[structopt(aliases = &["--from-ascii"])]
     #[structopt(name = "--from-utf8")]
     #[structopt(about = "convert text data into hexdata")]