error for leading zeros in integers

README.md

@@ -66,6 +66,11 @@ printf "3:ab" | cargo run
 Error: Unexpected end of input parsing string value
 ```
 
+```console
+echo "i00e" | cargo run
+Error: Leading zeros in integers are not allowed, for example b'i00e'
+```
+
 ## Library
 
 todo

src/parsers/error.rs

@@ -24,6 +24,9 @@ pub enum Error {
     #[error("Unexpected end of input parsing integer")]
     UnexpectedEndOfInputParsingInteger,
 
+    #[error("Leading zeros in integers are not allowed, for example b'i00e'")]
+    LeadingZerosInIntegersNotAllowed,
+
     // Strings
     #[error("Invalid string length byte, expected a digit, received byte: {0}, char: {1}")]
     InvalidStringLengthByte(u8, char),

src/parsers/integer.rs

@@ -33,6 +33,7 @@ pub fn parse<R: Read, W: Writer>(
     _initial_byte: u8,
 ) -> Result<(), Error> {
     let mut state = StateExpecting::DigitOrSign;
+    let mut first_digit_is_zero = false;
 
     loop {
         let byte = next_byte(reader)?;
@@ -43,6 +44,7 @@ pub fn parse<R: Read, W: Writer>(
             StateExpecting::DigitOrSign => {
                 if char.is_ascii_digit() {
                     writer.write_byte(byte)?;
+                    first_digit_is_zero = true;
                     StateExpecting::DigitOrEnd
                 } else if char == '-' {
                     writer.write_byte(byte)?;
@@ -61,6 +63,10 @@ pub fn parse<R: Read, W: Writer>(
             }
             StateExpecting::DigitOrEnd => {
                 if char.is_ascii_digit() {
+                    if char == '0' && first_digit_is_zero {
+                        return Err(Error::LeadingZerosInIntegersNotAllowed);
+                    }
+
                     writer.write_byte(byte)?;
                     StateExpecting::DigitOrEnd
                 } else if byte == BENCODE_END_INTEGER {
@@ -158,4 +164,18 @@ mod tests {
             Err(Error::UnexpectedByteParsingInteger(97, 'a'))
         ));
     }
+
+    #[test]
+    fn it_should_fail_when_it_finds_leading_zeros() {
+        // Leading zeros are not allowed.Only the zero integer can start with zero.
+
+        let int_with_invalid_byte = b"i00e";
+
+        let result = try_bencode_to_json(int_with_invalid_byte);
+
+        assert!(matches!(
+            result,
+            Err(Error::LeadingZerosInIntegersNotAllowed)
+        ));
+    }
 }