Don't try to do a base58 checksum if an address is excessively long

src/util/address.rs

@@ -259,6 +259,10 @@ impl FromStr for Address {
             });
         }
 
+        if s.len() > 50 {
+            return Err(Error::Base58(base58::Error::InvalidLength(s.len() * 11 / 15)));
+        }
+
         // Base 58
         let data = try!(base58::from_check(s));
 

src/util/base58.rs

@@ -27,6 +27,8 @@ pub enum Error {
     /// Checksum was not correct (expected, actual)
     BadChecksum(u32, u32),
     /// The length (in bytes) of the object was not correct
+    /// Note that if the length is excessively long the provided length may be
+    /// an estimate (and the checksum step may be skipped).
     InvalidLength(usize),
     /// Version byte(s) were not recognized
     InvalidVersion(Vec<u8>),