refactor: simplify string parser for length

src/parsers/string.rs

@@ -71,28 +71,11 @@ impl Length {
 
         self.bytes.push(byte);
 
-        Ok(())
-    }
+        let digit = (byte - b'0') as usize;
 
-    /// This function convert the current bytes representing the length to a
-    /// number.
-    ///
-    /// # Panics
-    ///
-    /// Will panic if the length bytes contain invalid UTF-8 chars or don't
-    /// represent a valid zero or positive integer.
-    fn convert_to_number(&mut self) -> usize {
-        // todo: maybe we should simply fail when we receive a byte that is not a digit (0..9).
-        // This error cannot be understood by users because we first convert into a UTF-8 string
-        // and later into a number.
-        let length_str =
-            str::from_utf8(&self.bytes).expect("invalid string length, non UTF-8 string length");
-
-        self.number = length_str
-            .parse::<usize>()
-            .expect("invalid string length, non zero or positive integer");
-
-        self.number
+        self.number = (self.number * 10) + digit;
+
+        Ok(())
     }
 }
 
@@ -149,8 +132,6 @@ impl StringParser {
         reader: &mut ByteReader<R>,
         initial_byte: u8,
     ) -> Result<(), Error> {
-        // code-review: length can be calculated on the fly as the original C implementation.
-
         self.length.add_byte(initial_byte)?;
 
         loop {
@@ -170,8 +151,6 @@ impl StringParser {
             match byte {
                 b':' => {
                     // End of string length
-                    self.process_end_of_string_length();
-                    self.length.convert_to_number();
                     break;
                 }
                 _ => {
@@ -206,12 +185,6 @@ impl StringParser {
         Ok(())
     }
 
-    /// This function is called when we receive the ':' byte which is the
-    /// delimiter for the end of bytes representing the string length.
-    fn process_end_of_string_length(&mut self) -> usize {
-        self.length.convert_to_number()
-    }
-
     fn utf8(&self) -> String {
         self.value.utf8()
     }