cosmrs: match upstream Cosmos SDK's Denom validation logic (cosmos#470)

Implements the same checks as the upstream Cosmos SDK's `MatchDenom`:

https://github.com/cosmos/cosmos-sdk/blob/6a07568/types/coin.go#L885-L906

cosmrs/src/base/denom.rs

@@ -6,6 +6,14 @@ use std::{fmt, str::FromStr};
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Denom(String);
 
+impl Denom {
+    /// Minimum length of a [`Denom`].
+    pub const MIN_LENGTH: usize = 3;
+
+    /// Maximum length of a [`Denom`].
+    pub const MAX_LENGTH: usize = 128;
+}
+
 impl AsRef<str> for Denom {
     fn as_ref(&self) -> &str {
         self.0.as_ref()
@@ -21,15 +29,18 @@ impl fmt::Display for Denom {
 impl FromStr for Denom {
     type Err = ErrorReport;
 
+    /// NOTE: implements the same checks as the `MatchDenom` function from the upstream Cosmos SDK.
+    /// <https://github.com/cosmos/cosmos-sdk/blob/6a07568/types/coin.go#L885-L906>
     fn from_str(s: &str) -> Result<Self> {
-        // TODO(tarcieri): ensure this is the proper validation for a denom name
-        if s.chars()
-            .all(|c| matches!(c, 'A'..='Z' | 'a'..='z' | '0'..='9' | '/' | ':' | '.' | '_' | '-'))
-        {
-            Ok(Denom(s.to_owned()))
-        } else {
-            Err(Error::Denom { name: s.to_owned() }.into())
+        if s.len() < Self::MIN_LENGTH || s.len() > Self::MAX_LENGTH {
+            return Err(Error::Denom { name: s.to_owned() }.into());
+        }
+
+        if !s.chars().all(is_valid_denom_char) {
+            return Err(Error::Denom { name: s.to_owned() }.into());
         }
+
+        Ok(Denom(s.to_owned()))
     }
 }
 
@@ -47,6 +58,15 @@ impl Serialize for Denom {
     }
 }
 
+/// Check if a given character is allowed in a `Denom` name.
+///
+/// NOTE: implements the same checks as the `isValidRune` function from the upstream Cosmos SDK.
+/// <https://github.com/cosmos/cosmos-sdk/blob/6a07568/types/coin.go#L879-L883>
+#[inline]
+fn is_valid_denom_char(c: char) -> bool {
+    matches!(c, 'A'..='Z' | 'a'..='z' | '0'..='9' | '/' | ':' | '.' | '_' | '-')
+}
+
 #[cfg(test)]
 mod tests {
     use super::Denom;