improve: add to and from str for `Secret`

crates/cashu/src/secret.rs

@@ -2,6 +2,8 @@
 // Copyright (c) 2023 Clark Moody
 // https://github.com/clarkmoody/cashu-rs/blob/master/src/secret.rs
 
+use std::str::FromStr;
+
 use serde::{Deserialize, Serialize};
 
 /// The secret data that allows spending ecash
@@ -9,6 +11,11 @@ use serde::{Deserialize, Serialize};
 #[serde(transparent)]
 pub struct Secret(String);
 
+#[derive(Debug)]
+pub enum Error {
+    InvalidLength(u64),
+}
+
 impl Default for Secret {
     fn default() -> Self {
         Self::new()
@@ -17,7 +24,6 @@ impl Default for Secret {
 
 impl Secret {
     const BIT_LENGTH: usize = 128;
-
     /// Create secret value
     pub fn new() -> Self {
         use base64::{engine::general_purpose::URL_SAFE, Engine as _};
@@ -38,3 +44,39 @@ impl Secret {
         self.0.as_bytes()
     }
 }
+
+impl FromStr for Secret {
+    type Err = Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s.len().ne(&24) {
+            return Err(Error::InvalidLength(s.as_bytes().len() as u64));
+        }
+
+        Ok(Secret(s.to_string()))
+    }
+}
+
+impl ToString for Secret {
+    fn to_string(&self) -> String {
+        self.0.clone()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+
+    use super::*;
+
+    #[test]
+    fn test_secret_from_str() {
+        let secret = Secret::new();
+
+        let secret_str = secret.to_string();
+
+        let secret_n = Secret::from_str(&secret_str).unwrap();
+
+        assert_eq!(secret_n, secret)
+    }
+}