Remove duplicated code and make base64 error handling better

src/bytes_base64.rs

@@ -55,7 +55,7 @@ impl BytesBase64 {
         Bytes(v.chunks(4).map(|c| to_bytes(c)).flatten().collect())
     }
 
-    pub fn from_base64(s: &str) -> BytesBase64 {
+    pub fn from_base64(s: &str) -> Result<BytesBase64, String> {
         let mut r: Vec<u8> = Vec::with_capacity(s.len());
         for c in s.chars() {
             match c {
@@ -64,10 +64,15 @@ impl BytesBase64 {
                 '0'..='9' => r.push((c as u8) - ('0' as u8) + 52),
                 '+' => r.push(62),
                 '/' => r.push(63),
-                _ => (),
+                '\n' => (),
+                '=' => (),
+                ' ' => (),
+                _ => {
+                    return Err(format!("Unexpected character '{}'", c));
+                }
             }
         }
-        BytesBase64(r)
+        Ok(BytesBase64(r))
     }
 
     pub fn to_string(&self) -> String {