Use a byte buffer for the password

Introduces a "UnicodeError" to express improperly encoded
passwords.

src/error.rs

@@ -16,6 +16,8 @@ pub enum TerminalError {
     StdinError,
     /// Failed to parse number.
     ParseError,
+    /// Failed to read unicode encoded data.
+    UnicodeError
 }
 
 impl TerminalError {
@@ -27,6 +29,7 @@ impl TerminalError {
             TerminalError::StdoutError => "Failed to write to stdout.",
             TerminalError::StdinError => "Failed to read from stdin.",
             TerminalError::ParseError => "Failed to parse number.",
+            TerminalError::UnicodeError => "Failed to read unicode encoded data.",
         }
     }
 }

src/extra.rs

@@ -13,17 +13,19 @@ pub trait ReadExt {
 impl<R: Read> ReadExt for R {
     fn read_passwd<W: Write>(&mut self, writer: &mut W) -> Result<Option<String>, TerminalError> {
         let _raw = try!(writer.into_raw_mode());
-        let mut string = String::with_capacity(30);
+        let mut passbuf = Vec::with_capacity(30);
 
         for c in self.bytes() {
             match c {
                 Err(_) => return Err(TerminalError::StdinError),
                 Ok(0) | Ok(3) | Ok(4) => return Ok(None),
-                Ok(b'\n') | Ok(b'\r') => return Ok(Some(string)),
+                Ok(b'\n') | Ok(b'\r') => break,
-                Ok(c) => string.push(c as char),
+                Ok(c) => passbuf.push(c),
             }
         }
 
-        Ok(Some(string))
+        let passwd = try!(String::from_utf8(passbuf).map_err(|_| TerminalError::UnicodeError ));
+
+        Ok(Some(passwd))
     }
 }